# Patent

## Title
Maize variety inbred PH18K6

## Abstract

A novel maize variety designated PH18K6 and seed, plants and plant parts thereof. Methods for producing a maize plant that comprise crossing maize variety PH18K6 with another maize plant. Methods for producing a maize plant containing in its genetic material one or more traits introgressed into PH18K6 through backcross conversion and/or transformation, and to the maize seed, plant and plant part produced thereby. Hybrid maize seed, plant or plant part produced by crossing the variety PH18K6 or a locus conversion of PH18K6 with another maize variety.

## Background
FIELD OF THE INVENTION
This invention relates generally to the field of maize breeding, specifically relating to an inbred maize variety designated PH18K6.
BACKGROUND OF THE INVENTION
The goal of plant breeding is to combine, in a single variety or hybrid, various desirable traits. For field crops, these traits may include resistance to diseases and insects, resistance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination, stand establishment, growth rate, maturity, plant height and ear height, is important. Traditional plant breeding is an important tool in developing new and improved commercial crops.
SUMMARY OF THE INVENTION
According to the invention, there is provided a novel maize variety, designated PH18K6 and processes for making PH18K6. This invention relates to seed of maize variety PH18K6, to the plants of maize variety PH18K6, to plant parts of maize variety PH18K6, and to processes for making a maize plant that comprise crossing maize variety PH18K6 with another maize plant. This invention also relates to processes for making a maize plant containing in its genetic material one or more traits introgressed into PH18K6 through backcross conversion and/or transformation, and to the maize seed, plant and plant parts produced thereby. This invention further relates to a hybrid maize seed, plant or plant part produced by crossing the variety PH18K6 or a locus conversion of PH18K6 with another maize variety.
DEFINITIONS
Certain definitions used in the specification are provided below. Also in the examples that follow, a number of terms are used herein. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided. NOTE: ABS is in absolute terms and % MN is percent of the mean for the experiments in which the inbred or hybrid was grown. PCT designates that the trait is calculated as a percentage. % NOT designates the percentage of plants that did not exhibit a trait. For example, STKLDG % NOT is the percentage of plants in a plot that were not stalk lodged. These designators will follow the descriptors to denote how the values are to be interpreted. Below are the descriptors used in the data tables included herein.
ABIOTIC STRESS TOLERANCE: resistance to non-biological sources of stress conferred by traits such as nitrogen utilization efficiency, altered nitrogen responsiveness, drought resistance, cold, and salt resistance
ABTSTK=ARTIFICIAL BRITTLE STALK: A count of the number of “snapped” plants per plot following machine snapping. A snapped plant has its stalk completely snapped at a node between the base of the plant and the node above the ear. Expressed as percent of plants that did not snap.
ALLELE: Any of one or more alternative forms of a genetic sequence. In a diploid cell or organism, the two alleles of a given sequence typically occupy corresponding loci on a pair of homologous chromosomes.
ALTER: The utilization of up-regulation, down-regulation, or gene silencing.
ANTHESIS: The time of a flower's opening.
ANTIOXIDANT: A chemical compound or substance that inhibits oxidation, including but not limited to tocopherol or tocotrienols.
ANT ROT=ANTHRACNOSE STALK ROT (Colletotrichum graminicola): A 1 to 9 visual rating indicating the resistance to Anthracnose Stalk Rot. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
BACKCROSSING: Process in which a breeder crosses a hybrid progeny variety back to one of the parental genotypes one or more times.
BACKCROSS PROGENY: Progeny plants produced by crossing PH18K6 with plants of another maize line that comprise a desired trait or locus, selecting F1 progeny plants that comprise the desired trait or locus, and crossing the selected F1 progeny plants with the PH18K6 plants 1 or more times to produce backcross progeny plants that comprise said trait or locus.
BARPLT=BARREN PLANTS: The percent of plants per plot that were not barren (lack ears).
BLUP=BEST LINEAR UNBIASED PREDICTION. The BLUP values are determined from a mixed model analysis of hybrid performance observations at various locations and replications. BLUP values for inbred maize plants, breeding values, are estimated from the same analysis using pedigree information.
BORBMN=ARTIFICIAL BRITTLE STALK MEAN: The mean percent of plants not “snapped” in a plot following artificial selection pressure. A snapped plant has its stalk completely snapped at a node between the base of the plant and the node above the ear. Expressed as percent of plants that did not snap. A high number is good and indicates tolerance to brittle snapping.
BRENGMN=BRITTLE STALK ENERGY MEAN: The mean amount of energy per unit area needed to artificially brittle snap a corn stalk. A high number is good and indicates tolerance to brittle snapping.
BREEDING: The genetic manipulation of living organisms.
BREEDING CROSS: A cross to introduce new genetic material into a plant for the development of a new variety. For example, one could cross plant A with plant B, wherein plant B would be genetically different from plant A. After the breeding cross, the resulting F1 plants could then be selfed or sibbed for one, two, three or more times (F1, F2, F3, etc.) until a new inbred variety is developed.
BREEDING VALUE: A relative value determined by evaluating the progeny of the parent. For corn the progeny is often the F1 generation and the parent is often an inbred variety.
BRLPNE=ARTIFICIAL ROOT LODGING EARLY SEASON: The percent of plants not root lodged in a plot following artificial selection pressure applied prior to flowering. A plant is considered root lodged if it leans from the vertical axis at an approximately 30 degree angle or greater. Expressed as percent of plants that did not root lodge. A high number is good and indicates tolerance to root lodging.
BRLPNL=ARTIFICIAL ROOT LODGING LATE SEASON: The percent of plants not root lodged in a plot following artificial selection pressure during grain fill. A plant is considered root lodged if it leans from the vertical axis at an approximately 30 degree angle or greater. Expressed as percent of plants that did not root lodge. A high number is good and indicates tolerance to root lodging.
BRTSTK=BRITTLE STALKS: This is a measure of the stalk breakage near the time of pollination, and is an indication of whether a hybrid or inbred would snap or break near the time of flowering under severe winds. Data are presented as percentage of plants that did not snap. Data are collected only when sufficient selection pressure exists in the experiment measured.
BRTPCN=BRITTLE STALKS: This is an estimate of the stalk breakage near the time of pollination, and is an indication of whether a hybrid or inbred would snap or break near the time of flowering under severe winds. Data are presented as percentage of plants that did not snap. Data are collected only when sufficient selection pressure exists in the experiment measured.
CARBOHYDRATE: Organic compounds comprising carbon, oxygen and hydrogen, including sugars, starches and cellulose.
CELL: Cell as used herein includes a plant cell, whether isolated, in tissue culture or incorporated in a plant or plant part.
CLDTST=COLD TEST: The percent of plants that germinate under cold test conditions.
CLN═CORN LETHAL NECROSIS: Synergistic interaction of maize chlorotic mottle virus (MCMV) in combination with either maize dwarf mosaic virus (MDMV-A or MDMV-B) or wheat streak mosaic virus (WSMV). A 1 to 9 visual rating indicating the resistance to Corn Lethal Necrosis. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
CMSMT=COMMON SMUT: This is the percentage of plants not infected with Common Smut. Data are collected only when sufficient selection pressure exists in the experiment measured.
COMRST=COMMON RUST (Puccinia sorghi): A 1 to 9 visual rating indicating the resistance to Common Rust. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
CROSS POLLINATION: Fertilization by the union of two gametes from different plants.
CROSSING: The combination of genetic material by traditional methods such as a breeding cross or backcross, but also including protoplast fusion and other molecular biology methods of combining genetic material from two sources.
D and D1-Dn: represents the generation of doubled haploid.
D/D=DRYDOWN: This represents the relative rate at which a hybrid will reach acceptable harvest moisture compared to other hybrids on a 1 to 9 rating scale. A high score indicates a hybrid that dries relatively fast while a low score indicates a hybrid that dries slowly.
DIGENG=DIGESTIBLE ENERGY: Near-infrared transmission spectroscopy, NIT, prediction of digestible energy.
DIPERS=DIPLODIA EAR MOLD SCORES (Diplodia maydis and Diplodia macrospora): A 1 to 9 visual rating indicating the resistance to Diplodia Ear Mold. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
DIPLOID PLANT PART: Refers to a plant part or cell that has the same diploid genotype as PH18K6.
DIPROT=DIPLODIA STALK ROT SCORE: Score of stalk rot severity due to Diplodia (Diplodia maydis). Expressed as a 1 to 9 score with 9 being highly resistant. Data are collected only when sufficient selection pressure exists in the experiment measured.
DRPEAR=DROPPED EARS: A measure of the number of dropped ears per plot and represents the percentage of plants that did not drop ears prior to harvest. Data are collected only when sufficient selection pressure exists in the experiment measured.
D/T=DROUGHT TOLERANCE: This represents a 1 to 9 rating for drought tolerance, and is based on data obtained under stress conditions. A high score indicates good drought tolerance and a low score indicates poor drought tolerance. Data are collected only when sufficient selection pressure exists in the experiment measured.
EARHT=EAR HEIGHT: The ear height is a measure from the ground to the highest placed developed ear node attachment and is measured in inches.
EARMLD=GENERAL EAR MOLD: Visual rating (1 to 9 score) where a 1 is very susceptible and a 9 is very resistant. This is based on overall rating for ear mold of mature ears without determining the specific mold organism, and may not be predictive for a specific ear mold. Data are collected only when sufficient selection pressure exists in the experiment measured.
EARSZ=EAR SIZE: A 1 to 9 visual rating of ear size. The higher the rating the larger the ear size.
EBTSTK=EARLY BRITTLE STALK: A count of the number of “snapped” plants per plot following severe winds when the corn plant is experiencing very rapid vegetative growth in the V5-V8 stage. Expressed as percent of plants that did not snap. Data are collected only when sufficient selection pressure exists in the experiment measured.
ECB1LF=EUROPEAN CORN BORER FIRST GENERATION LEAF FEEDING (Ostrinia nubilalis): A 1 to 9 visual rating indicating the resistance to preflowering leaf feeding by first generation European Corn Borer. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
ECB21T=EUROPEAN CORN BORER SECOND GENERATION INCHES OF TUNNELING (Ostrinia nubilalis): Average inches of tunneling per plant in the stalk. Data are collected only when sufficient selection pressure exists in the experiment measured.
ECB2SC=EUROPEAN CORN BORER SECOND GENERATION (Ostrinia nubilalis): A 1 to 9 visual rating indicating post flowering degree of stalk breakage and other evidence of feeding by second generation European Corn Borer. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
ECBDPE=EUROPEAN CORN BORER DROPPED EARS (Ostrinia nubilalis): Dropped ears due to European Corn Borer. Percentage of plants that did not drop ears under second generation European Corn Borer infestation. Data are collected only when sufficient selection pressure exists in the experiment measured.
ECBLSI=EUROPEAN CORN BORER LATE SEASON INTACT (Ostrinia nubilalis): A 1 to 9 visual rating indicating late season intactness of the corn plant given damage (stalk breakage above and below the top ear) caused primarily by 2nd and/or 3rd generation ECB larval feeding before harvest. A higher score is good and indicates more intact plants. Data are collected only when sufficient selection pressure exists in the experiment measured.
EGRWTH=EARLY GROWTH: This is a measure of the relative height and size of a corn seedling at the 2-4 leaf stage of growth. This is a visual rating (1 to 9), with 1 being weak or slow growth, 5 being average growth and 9 being strong growth. Taller plants, wider leaves, more green mass and darker color constitute higher score. Data are collected only when sufficient selection pressure exists in the experiment measured.
ERTLDG=EARLY ROOT LODGING: The percentage of plants that do not root lodge prior to or around anthesis; plants that lean from the vertical axis at an approximately 30 degree angle or greater would be counted as root lodged. Data are collected only when sufficient selection pressure exists in the experiment measured.
ERTLPN=EARLY ROOT LODGING: An estimate of the percentage of plants that do not root lodge prior to or around anthesis; plants that lean from the vertical axis at an approximately 30 degree angle or greater would be considered as root lodged. Data are collected only when sufficient selection pressure exists in the experiment measured.
ERTLSC=EARLY ROOT LODGING SCORE: Score for severity of plants that lean from a vertical axis at an approximate 30 degree angle or greater which typically results from strong winds prior to or around flowering recorded within 2 weeks of a wind event. Expressed as a 1 to 9 score with 9 being no lodging. Data are collected only when sufficient selection pressure exists in the experiment measured.
ESSENTIAL AMINO ACIDS: Amino acids that cannot be synthesized de novo by an organism and therefore must be supplied in the diet.
ESTCNT=EARLY STAND COUNT: This is a measure of the stand establishment in the spring and represents the number of plants that emerge on per plot basis for the inbred or hybrid.
EXPRESSING: Having the genetic potential such that under the right conditions, the phenotypic trait is present.
EXTSTR=EXTRACTABLE STARCH: Near-infrared transmission spectroscopy, NIT, prediction of extractable starch.
EYESPT=EYE SPOT (Kabatiella zeae or Aureobasidium zeae): A 1 to 9 visual rating indicating the resistance to Eye Spot. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
FATTY ACID: A carboxylic acid (or organic acid), often with a long aliphatic tail (long chains), either saturated or unsaturated.
F1 PROGENY: A progeny plant produced by crossing a plant of maize variety PH18K6 with a plant of another maize line.
FUSERS=FUSARIUM EAR ROT SCORE (Fusarium moniliforme or Fusarium subglutinans): A 1 to 9 visual rating indicating the resistance to Fusarium Ear Rot. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
GDU=GROWING DEGREE UNITS: Using the Barger Heat Unit Theory, which assumes that maize growth occurs in the temperature range 50 degrees F.-86 degrees F. and that temperatures outside this range slow down growth; the maximum daily heat unit accumulation is 36 and the minimum daily heat unit accumulation is 0. The seasonal accumulation of GDU is a major factor in determining maturity zones.
GDUSHD=GDU TO SHED: The number of growing degree units (GDUs) or heat units required for an inbred variety or hybrid to have approximately 50 percent of the plants shedding pollen and is measured from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hour period are:




  
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The units determined by the Barger Method are then divided by 10. The highest maximum temperature used is 86 degrees F. and the lowest minimum temperature used is 50 degrees F. For each inbred or hybrid it takes a certain number of GDUs to reach various stages of plant development.
GDUSLK=GDU TO SILK: The number of growing degree units required for an inbred variety or hybrid to have approximately 50 percent of the plants with silk emergence from time of planting. Growing degree units are calculated by the Barger Method as given in GDU SHD definition and then divided by 10.
GENE SILENCING: The interruption or suppression of the expression of a gene at the level of transcription or translation.
GENOTYPE: Refers to the genetic mark-up or profile of a cell or organism.
GIBERS=GIBBERELLA EAR ROT (PINK MOLD) (Gibberella zeae): A 1 to 9 visual rating indicating the resistance to Gibberella Ear Rot. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
GIBROT=GIBBERELLA STALK ROT SCORE: Score of stalk rot severity due to Gibberella (Gibberella zeae). Expressed as a 1 to 9 score with 9 being highly resistant. Data are collected only when sufficient selection pressure exists in the experiment measured.
GLFSPT=GRAY LEAF SPOT (Cercospora zeae-maydis): A 1 to 9 visual rating indicating the resistance to Gray Leaf Spot. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
GOSWLT=GOSS' WILT (Corynebacterium nebraskense): A 1 to 9 visual rating indicating the resistance to Goss' Wilt. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
GRNAPP=GRAIN APPEARANCE: This is a 1 to 9 rating for the general appearance of the shelled grain as it is harvested based on such factors as the color of harvested grain, any mold on the grain, and any cracked grain. High scores indicate good grain visual quality.
HAPLOID PLANT PART: Refers to a plant part or cell that has the same haploid genotype as PH18K6.
H and H1: Refers to the haploid generation.
HCBLT=HELMINTHOSPORIUM CARBONUM LEAF BLIGHT (Helminthosporium carbonum): A 1 to 9 visual rating indicating the resistance to Helminthosporium infection. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
HD SMT=HEAD SMUT (Sphacelotheca reiliana): This indicates the percentage of plants not infected. Data are collected only when sufficient selection pressure exists in the experiment measured.
HSKCVR=HUSK COVER: A 1 to 9 score based on performance relative to key checks, with a score of 1 indicating very short husks, tip of ear and kernels showing; 5 is intermediate coverage of the ear under most conditions, sometimes with thin husk; and a 9 has husks extending and closed beyond the tip of the ear. Scoring can best be done near physiological maturity stage or any time during dry down until harvested.
HTFRM=Near-infrared transmission spectroscopy, NIT, prediction of fermentables.
HYBRID VARIETY: A substantially heterozygous hybrid line and minor genetic modifications thereof that retain the overall genetics of the hybrid line including but not limited to a locus conversion, a mutation, or a somoclonal variant.
INBRED: A variety developed through inbreeding or doubled haploidy that preferably comprises homozygous alleles at about 95% or more of its loci.
INC D/A=GROSS INCOME (DOLLARS PER ACRE): Relative income per acre assuming drying costs of two cents per point above 15.5 percent harvest moisture and current market price per bushel.
INCOME/ACRE: Income advantage of hybrid to be patented over other hybrid on per acre basis.
INC ADV=GROSS INCOME ADVANTAGE: Gross income advantage of variety #1 over variety #2.
INTROGRESSION: The process of transferring genetic material from one genotype to another.
KERUNT=KERNELS PER UNIT AREA (Acres or Hectares).
KERPOP=KERNEL POP SCORE: The visual 1-9 rating of the amount of rupturing of the kernel pericarp at an early stage in grain fill. A higher score is good and indicates no popped (ruptured) kernels.
KER_WT=KERNEL NUMBER PER UNIT WEIGHT (Pounds or Kilograms): The number of kernels in a specific measured weight; determined after removal of extremely small and large kernels.
KSZDCD=KERNEL SIZE DISCARD: The percent of discard seed; calculated as the sum of discarded tip kernels and extra large kernels.
LINKAGE: Refers to a phenomenon wherein alleles on the same chromosome tend to segregate together more often than expected by chance if their transmission was independent.
LINKAGE DISEQUILIBRIUM: Refers to a phenomenon wherein alleles tend to remain together in linkage groups when segregating from parents to offspring, with a greater frequency than expected from their individual frequencies.
LOCUS: A specific location on a chromosome.
LOCUS CONVERSION: (Also called a TRAIT CONVERNSION) A locus conversion refers to plants within a variety that have been modified in a manner that retains the overall genetics of the variety and further comprises one or more loci with a specific desired trait, such as male sterility, insect control, disease control or herbicide tolerance. Examples of single locus conversions include mutant genes, transgenes and native traits finely mapped to a single locus. One or more locus conversion traits may be introduced into a single corn variety.
L/POP=YIELD AT LOW DENSITY: Yield ability at relatively low plant densities on a 1 to 9 relative system with a higher number indicating the hybrid responds well to low plant densities for yield relative to other hybrids. A 1, 5, and 9 would represent very poor, average, and very good yield response, respectively, to low plant density.
LRTLDG=LATE ROOT LODGING: The percentage of plants that do not root lodge after anthesis through harvest; plants that lean from the vertical axis at an approximately 30 degree angle or greater would be counted as root lodged. Data are collected only when sufficient selection pressure exists in the experiment measured.
LRTLPN=LATE ROOT LODGING: An estimate of the percentage of plants that do not root lodge after anthesis through harvest; plants that lean from the vertical axis at an approximately 30 degree angle or greater would be considered as root lodged. Data are collected only when sufficient selection pressure exists in the experiment measured.
LRTLSC=LATE ROOT LODGING SCORE: Score for severity of plants that lean from a vertical axis at an approximate 30 degree angle or greater which typically results from strong winds after flowering. Recorded prior to harvest when a root-lodging event has occurred. This lodging results in plants that are leaned or “lodged” over at the base of the plant and do not straighten or “goose-neck” back to a vertical position. Expressed as a 1 to 9 score with 9 being no lodging. Data are collected only when sufficient selection pressure exists in the experiment measured.
MALE STERILITY: A male sterile plant is one which produces no viable pollen no (pollen that is able to fertilize the egg to produce a viable seed). Male sterility prevents self pollination. These male sterile plants are therefore useful in hybrid plant production.
MDMCPX=MAIZE DWARF MOSAIC COMPLEX (MDMV=Maize Dwarf Mosaic Virus and MCDV=Maize Chlorotic Dwarf Virus). A 1 to 9 visual rating indicating the resistance to Maize Dwarf Mosaic Complex. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
MILKLN=percent milk in mature grain.
MST=HARVEST MOISTURE: The moisture is the actual percentage moisture of the grain at harvest.
MSTADV=MOISTURE ADVANTAGE: The moisture advantage of variety #1 over variety #2 as calculated by: MOISTURE of variety #2—MOISTURE of variety #1=MOISTURE ADVANTAGE of variety #1.
NEI DISTANCE: A quantitative measure of percent similarity between two varieties. Nei's distance between varieties A and B can be defined as 1-(2*number alleles in common/(number alleles in A+number alleles in B). For example, if varieties A and B are the same for 95 out of 100 alleles, the Nei distance would be 0.05. If varieties A and B are the same for 98 out of 100 alleles, the Nei distance would be 0.02. Free software for calculating Nei distance is available on the internet at multiple locations such as, for example, at: evolution.genetics.washington.edu/phylip.html. See Nei, Proc Natl Acad Sci, 76:5269-5273 (1979) which is incorporated by reference for this purpose.
NLFBLT=NORTHERN LEAF BLIGHT (Helminthosporium turcicum or Exserohilum turcicum): A 1 to 9 visual rating indicating the resistance to Northern Leaf Blight. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
NUCLEIC ACID: An acidic, chainlike biological macromolecule consisting of multiple repeat units of phosphoric acid, sugar and purine and pyrimidine bases.
OILT=GRAIN OIL: Absolute value of oil content of the kernel as predicted by Near-Infrared Transmittance and expressed as a percent of dry matter.
PERCENT IDENTITY: Percent identity as used herein refers to the comparison of the alleles present in two varieties. For example, when comparing two inbred plants to each other, each inbred plant will have the same allele (and therefore be homozygous) at almost all of their loci. Percent identity is determined by comparing a statistically significant number of the homozygous alleles of two varieties. For example, a percent identity of 90% between PH18K6 and other variety means that the two varieties have the same homozygous alleles at 90% of their loci.
PLANT: As used herein, the term “plant” includes reference to an immature or mature whole plant, including a plant that has been detasseled or from which seed or grain has been removed. Seed or embryo that will produce the plant is also considered to be the plant.
PLANT PART: As used herein, the term “plant part” includes leaves, stems, roots, seed, grain, embryo, pollen, ovules, flowers, ears, cobs, husks, stalks, root tips, anthers, pericarp, silk, tissue, cells and the like.
PLATFORM indicates the variety with the base genetics and the variety with the base genetics comprising locus conversion(s). There can be a platform for the inbred maize variety and the hybrid maize variety.
PLTHT=PLANT HEIGHT: This is a measure of the height of the plant from the ground to the tip of the tassel in inches.
POLPRD=POLLEN PRODUCTION SCORE: The estimated total amount of pollen produced by tassels based on the number of tassel branches and the density of the spikelets.
POLSC=POLLEN SCORE: A 1 to 9 visual rating indicating the amount of pollen shed. The higher the score the more pollen shed.
POLWT=POLLEN WEIGHT: This is calculated by dry weight of tassels collected as shedding commences minus dry weight from similar tassels harvested after shedding is complete.
POP K/A=PLANT POPULATIONS: Measured as 1000's per acre.
POP ADV=PLANT POPULATION ADVANTAGE: The plant population advantage of variety #1 over variety #2 as calculated by PLANT POPULATION of variety #2—PLANT POPULATION of variety #1=PLANT POPULATION ADVANTAGE of variety #1.
PRM=PREDICTED RELATIVE MATURITY: This trait, predicted relative maturity, is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes standard linear regression analyses and is also referred to as the Comparative Relative Maturity Rating System that is similar to the Minnesota Relative Maturity Rating System.
PRMSHD: A relative measure of the growing degree units (GDU) required to reach 50% pollen shed. Relative values are predicted values from the linear regression of observed GDU's on relative maturity of commercial checks.
PROT=GRAIN PROTEIN: Absolute value of protein content of the kernel as predicted by Near-Infrared Transmittance and expressed as a percent of dry matter.
RESISTANCE: Synonymous with tolerance. The ability of a plant to withstand exposure to an insect, disease, herbicide or other condition. A resistant plant variety will have a level of resistance higher than a comparable wild-type variety.
RTLDG=ROOT LODGING: Root lodging is the percentage of plants that do not root lodge; plants that lean from the vertical axis at an approximately 30 degree angle or greater would be counted as root lodged. Data are collected only when sufficient selection pressure exists in the experiment measured.
RTLADV=ROOT LODGING ADVANTAGE: The root lodging advantage of variety #1 over variety #2. Data are collected only when sufficient selection pressure exists in the experiment measured.
SCTGRN=SCATTER GRAIN: A 1 to 9 visual rating indicating the amount of scatter grain (lack of pollination or kernel abortion) on the ear. The higher the score the less scatter grain.
SDGVGR=SEEDLING VIGOR: This is the visual rating (1 to 9) of the amount of vegetative growth after emergence at the seedling stage (approximately five leaves). A higher score indicates better vigor.
SEED: Fertilized and ripened ovule, consisting of the plant embryo, varying amounts of stored food material, and a protective outer seed coat. Synonymous with grain.
SEFIELD: Percent stress emergence in field.
SELAB: Average % stress emergence in lab tests.
SEL IND=SELECTION INDEX: The selection index gives a single measure of the hybrid's worth based on information for multiple traits. A maize breeder may utilize his or her own set of traits for the selection index. One of the traits that is almost always included is yield. The selection index data presented in the tables represent the mean value averaged across testing stations.
SELF POLLINATION: A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant.
SIB POLLINATION: A plant is sib-pollinated when individuals within the same family or variety are used for pollination.
SITE SPECIFIC INTEGRATION: Genes that create a site for site specific DNA integration. This includes the introduction of FRT sites that may be used in the FLP/FRT system and/or Lox sites that may be used in the Cre/Loxp system. For example, see Lyznik, et al., Site-Specific Recombination for Genetic Engineering in Plants, Plant Cell Rep (2003) 21:925-932 and WO 99/25821.
SLFBLT=SOUTHERN LEAF BLIGHT (Helminthosporium maydis or Bipolaris maydis): A 1 to 9 visual rating indicating the resistance to Southern Leaf Blight. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
SOURST=SOUTHERN RUST (Puccinia polysora): A 1 to 9 visual rating indicating the resistance to Southern Rust. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
SPKDSC=SPIKELET DENSITY SCORE: The visual 1-9 rating of how dense spikelets are on the middle tassel branches. A higher score indicates higher spikelet density.
STAGRN=STAY GREEN: Stay green is the measure of plant health near the time of black layer formation (physiological maturity). A high score indicates better late-season plant health.
STDADV=STALK STANDING ADVANTAGE: The advantage of variety #1 over variety #2 for the trait STKCNT.
STKCNT=NUMBER OF PLANTS: This is the final stand or number of plants per plot.
STKCTE: This is the early stand count of plants per plot.
STKLDG=STALK LODGING REGULAR: This is the percentage of plants that did not stalk lodge (stalk breakage) at regular harvest (when grain moisture is between about 20% and 30%) as measured by either natural lodging or pushing the stalks and determining the percentage of plants that break below the ear. Data are collected only when sufficient selection pressure exists in the experiment measured.
STKLDS=STALK LODGING SCORE: A plant is considered as stalk lodged if the stalk is broken or crimped between the ear and the ground. This can be caused by any or a combination of the following: strong winds late in the season, disease pressure within the stalks, ECB damage or genetically weak stalks. This trait should be taken just prior to or at harvest. Expressed on a 1 to 9 scale with 9 being no lodging. Data are collected only when sufficient selection pressure exists in the experiment measured.
STLLPN=LATE STALK LODGING: This is the percent of plants that did not stalk lodge (stalk breakage or crimping) at or around late season harvest (when grain moisture is below 20%) as measured by either natural lodging or pushing the stalks and determining the percentage of plants that break or crimp below the ear. Data are collected only when sufficient selection pressure exists in the experiment measured.
STLPCN=STALK LODGING REGULAR: This is an estimate of the percentage of plants that did not stalk lodge (stalk breakage) at regular harvest (when grain moisture is between about 20% and 30%) as measured by either natural lodging or pushing the stalks and determining the percentage of plants that break below the ear. Data are collected only when sufficient selection pressure exists in the experiment measured.
STLTIP=STERILE TIPS SCORE: The visual 1 to 9 rating of the relative lack of glumes on the tassel central spike and branches. A higher score indicates less incidence of sterile tips or lack of glumes on the tassel.
STRT=GRAIN STARCH: Absolute value of starch content of the kernel as predicted by Near-Infrared Transmittance and expressed as a percent of dry matter.
STWWLT=Stewart's Wilt (Erwinia stewartii): A 1 to 9 visual rating indicating the resistance to Stewart's Wilt. A higher score indicates a higher resistance. Data are collected only when sufficient selection pressure exists in the experiment measured.
SSRs: Genetic markers based on polymorphisms in repeated nucleotide sequences, such as microsatellites. A marker system based on SSRs can be highly informative in linkage analysis relative to other marker systems in that multiple alleles may be present.
TASBLS=TASSEL BLAST: A 1 to 9 visual rating was used to measure the degree of blasting (necrosis due to heat stress) of the tassel at the time of flowering. A 1 would indicate a very high level of blasting at time of flowering, while a 9 would have no tassel blasting. Data are collected only when sufficient selection pressure exists in the experiment measured.
TASBRN=TASSEL BRANCH NUMBER: The number of tassel branches, with anthers originating from the central spike.
TASSZ=TASSEL SIZE: A 1 to 9 visual rating was used to indicate the relative size of the tassel. The higher the rating the larger the tassel.
TAS WT=TASSEL WEIGHT: This is the average weight of a tassel (grams) just prior to pollen shed.
TEXEAR=EAR TEXTURE: A 1 to 9 visual rating was used to indicate the relative hardness (smoothness of crown) of mature grain. A 1 would be very soft (extreme dent) while a 9 would be very hard (flinty or very smooth crown).
TILLER=TILLERS: A count of the number of tillers per plot that could possibly shed pollen was taken. Data are given as a percentage of tillers: number of tillers per plot divided by number of plants per plot. A tiller is defined as a secondary shoot that has developed as a tassel capable of shedding pollen.
TSTWTN=TEST WEIGHT (ADJUSTED): The measure of the weight of the grain (in pounds) for a given volume (bushel), adjusted for MST less than or equal to 22%.
TSTWTN=TEST WEIGHT (UNADJUSTED): The measure of the weight of the grain in pounds for a given volume (bushel).
TSWADV=TEST WEIGHT ADVANTAGE: The test weight advantage of variety #1 over variety #2.
VARIETY: A maize line and minor genetic modifications thereof that retain the overall genetics of the line including but not limited to a locus conversion, a mutation, or a somoclonal variant.
WIN M %=PERCENT MOISTURE WINS.
WIN Y %=PERCENT YIELD WINS.
YIELD BU/A=YIELD (BUSHELS/ACRE): Yield of the grain at harvest by weight or volume (bushels) per unit area (acre) adjusted to 15% moisture.
YLDADV=YIELD ADVANTAGE: The yield advantage of variety #1 over variety #2 as calculated by: YIELD of variety #1−YIELD variety #2=YIELD ADVANTAGE of variety #1.
YIELDMST=YIELD/MOISTURE RATIO.
YLDSC=YIELD SCORE: A 1 to 9 visual rating was used to give a relative rating for yield based on plot ear piles. The higher the rating the greater visual yield appearance.


DETAILED DESCRIPTION OF THE INVENTION AND FURTHER EMBODIMENTS
All tables discussed in the Detailed Description of the Invention and Further Embodiments section can found at the end of the section.
Breeding History of PH18K6
Inbred Maize variety PH18K6 was developed by the following method. A cross was made between inbred line PHE3D and inbred line PHE4N. Inbred PH18K6 was developed by selfing the F1 plants, selfing and bulking the F2, selfing and using ear-to-row (pedigree) selection from the F3 to F8 generation, and bulking the F9 seed.
Maize variety PH18K6, being substantially homozygous, can be reproduced by planting seeds of the variety, growing the resulting maize plants under self-pollinating or sib-pollinating conditions with adequate isolation, and harvesting the resulting seed using techniques familiar to the agricultural arts.
Phenotypic Characteristics of PH18K6
Inbred maize variety PH18K6 may be used as a male or female in the production of the first generation F1 hybrid. Inbred maize variety PH18K6 has a relative maturity of approximately 105 based on the Comparative Relative Maturity Rating System for harvest moisture of grain. The variety has shown uniformity and stability within the limits of environmental influence for all the traits as described in the Variety Description Information (Table 1, found at the end of the section). The variety has been self-pollinated and ear-rowed a sufficient number of generations with careful attention paid to uniformity of plant type to ensure the homozygosity and phenotypic stability necessary for use in commercial hybrid seed production. The variety has been increased both by hand and in isolated fields with continued observation for uniformity. No variant traits have been observed or are expected in PH18K6.
Genotypic Characteristics of PH18K6
In addition to phenotypic observations, a plant can also be identified by its genotype. The genotype of a plant can be characterized through a genetic marker profile.
As a result of inbreeding, PH18K6 is substantially homozygous. This homozygosity can be characterized at the loci shown in a marker profile. An F1 hybrid made with PH18K6 would substantially comprise the marker profile of PH18K6. This is because an F1 hybrid is the sum of its inbred parents, e.g., if one inbred parent is homozygous for allele x at a particular locus, and the other inbred parent is homozygous for allele y at that locus, the F1 hybrid will be x.y (heterozygous) at that locus. A genetic marker profile can therefore be used to identify hybrids comprising PH18K6 as a parent, since such hybrids will comprise two sets of alleles, one set of which will be from PH18K6. The determination of the male set of alleles and the female set of alleles may be made by profiling the hybrid and the pericarp of the hybrid seed, which is composed of maternal parent cells. One way to obtain the paternal parent profile is to subtract the pericarp profile from the hybrid profile.
Subsequent generations of progeny produced by selection and breeding are expected to be of genotype xx (homozygous), yy (homozygous), or xy (heterozygous) for these locus positions. When the F1 plant is used to produce an inbred, the resulting inbred should be either x or y for that allele.
Therefore, in accordance with the above, an embodiment of this invention is a PH18K6 progeny maize plant or plant part that is a first generation (F1) hybrid maize plant comprising two sets of alleles, wherein one set of the alleles is the same as PH18K6 at substantially all loci. A maize cell wherein one set of the alleles is the same as PH18K6 at substantially all loci is also an embodiment of the invention. This maize cell may be a part of a hybrid seed, plant or plant part produced by crossing PH18K6 with another maize plant.
Genetic marker profiles can be obtained by techniques such as Restriction Fragment Length Polymorphisms (RFLPs), Randomly Amplified Polymorphic DNAs (RAPDs), Arbitrarily Primed Polymerase Chain Reaction (AP-PCR), DNA Amplification Fingerprinting (DAF), Sequence Characterized Amplified Regions (SCARs), Amplified Fragment Length Polymorphisms (AFLPs), Simple Sequence Repeats (SSRs) which are also referred to as Microsatellites, and Single Nucleotide Polymorphisms (SNPs). For example, see Berry, Don et al., “Assessing Probability of Ancestry Using Simple Sequence Repeat Profiles: Applications to Maize Hybrids and Inbreds”, Genetics, 2002, 161:813-824, and Berry, Don et al., “Assessing Probability of Ancestry Using Simple Sequence Repeat Profiles: Applications to Maize Inbred Lines and Soybean Varieties”, Genetics, 2003, 165: 331-342.
Particular markers used for these purposes are not limited to the set of markers disclosed herein, but may include any type of marker and marker profile which provides a means of distinguishing varieties. In addition to being used for identification of maize variety PH18K6, a hybrid produced through the use of PH18K6, and the identification or verification of pedigree for progeny plants produced through the use of PH18K6, a genetic marker profile is also useful in developing a locus conversion of PH18K6.
Means of performing genetic marker profiles using SSR polymorphisms are well known in the art. SSRs are genetic markers based on polymorphisms in repeated nucleotide sequences, such as microsatellites. A marker system based on SSRs can be highly informative in linkage analysis relative to other marker systems in that multiple alleles may be present. Another advantage of this type of marker is that, through use of flanking primers, detection of SSRs can be achieved, for example, by the polymerase chain reaction (PCR), thereby eliminating the need for labor-intensive Southern hybridization. The PCR detection is done by use of two oligonucleotide primers flanking the polymorphic segment of repetitive DNA. Repeated cycles of heat denaturation of the DNA followed by annealing of the primers to their complementary sequences at low temperatures, and extension of the annealed primers with DNA polymerase, comprise the major part of the methodology.
Following amplification, markers can be scored by electrophoresis of the amplification products. Scoring of marker genotype is based on the size of the amplified fragment, which may be measured by the number of base pairs of the fragment. While variation in the primer used or in laboratory procedures can affect the reported fragment size, relative values should remain constant regardless of the specific primer or laboratory used. When comparing plants it is preferable if all SSR profiles are performed in the same lab. An SSR service is available to the public on a contractual basis by DNA Landmarks in Saint-Jean-sur-Richelieu, Quebec, Canada.
Primers used to perform SSRs are publicly available and may be found in the Maize GDB on the World Wide Web at maizegdb.org (sponsored by the USDA Agricultural Research Service), in Sharopova et al. (Plant Mol. Biol. 48(5-6):463-481), Lee et al. (Plant Mol. Biol. 48(5-6); 453-461). Primers may be constructed from publicly available sequence information. Some marker information may also be available from DNA Landmarks.
PH18K6 and its plant parts can be identified through a molecular marker profile. Such plant parts may be either diploid or haploid. Also encompassed within the scope of the invention are plants and plant parts substantially benefiting from the use of PH18K6 in their development, such as PH18K6 comprising a locus conversion.
Comparing PH18K6 to Other Inbreds
A breeder uses various methods to help determine which plants should be selected from segregating populations and ultimately which inbred varieties will be used to develop hybrids for commercialization. In addition to knowledge of the germplasm and plant genetics, a part of the selection process is dependent on experimental design coupled with the use of statistical analysis. Experimental design and statistical analysis are used to help determine which plants, which family of plants, and finally which inbred varieties and hybrid combinations are significantly better or different for one or more traits of interest. Experimental design methods are used to assess error so that differences between two inbred varieties or two hybrid varieties can be more accurately evaluated. Statistical analysis includes the calculation of mean values, determination of the statistical significance of the sources of variation, and the calculation of the appropriate variance components. Either a five or a one percent significance level is customarily used to determine whether a difference that occurs for a given trait is real or due to the environment or experimental error. One of ordinary skill in the art of plant breeding would know how to evaluate the traits of two plant varieties to determine if there is a significant difference between the two traits expressed by those varieties. For example, see Fehr, Walt, Principles of Cultivar Development, p. 261-286 (1987). Mean trait values may be used to determine whether trait differences are significant. Trait values should preferably be measured on plants grown under the same environmental conditions, and environmental conditions should be appropriate for the traits or traits being evaluated. Sufficient selection pressure should be present for optimum measurement of traits of interest such as herbicide tolerance, insect or disease resistance. A locus conversion of PH18K6 for herbicide tolerance should be compared with an isogenic counterpart in the absence of the converted trait. In addition, a locus conversion for insect or disease resistance should be compared to the isogenic counterpart, in the absence of disease pressure or insect pressure.
Development of Maize Hybrids Using PH18K6
A single cross maize hybrid results from the cross of two inbred varieties, each of which has a genotype that complements the genotype of the other. A hybrid progeny of the first generation is designated F1. In the development of commercial hybrids in a maize plant breeding program, only the F1 hybrid plants are sought. F1 hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, can be manifested in many polygenic traits, including increased vegetative growth and increased yield.
PH18K6 may be used to produce hybrid maize. One such embodiment is the method of crossing maize variety PH18K6 with another maize plant, such as a different maize variety, to form a first generation F1 hybrid seed. The first generation F1 hybrid seed, plant and plant part produced by this method is an embodiment of the invention. The first generation F1 seed, plant and plant part will comprise an essentially complete set of the alleles of variety PH18K6. One of ordinary skill in the art can utilize molecular methods to identify a particular F1 hybrid plant produced using variety PH18K6. Further, one of ordinary skill in the art may also produce F1 hybrids with transgenic, male sterile and/or locus conversions of variety PH18K6.
The development of a maize hybrid in a maize plant breeding program involves three steps: (1) the selection of plants from various germplasm pools for initial breeding crosses; (2) the selfing of the selected plants from the breeding crosses for several generations to produce a series of varieties, such as PH18K6, which, although different from each other, breed true and are highly uniform; and (3) crossing the selected varieties with different varieties to produce the hybrids. During the inbreeding process in maize, the vigor of the varieties decreases, and so one would not be likely to use PH18K6 directly to produce grain. However, vigor is restored when PH18K6 is crossed to a different inbred variety to produce a commercial F1 hybrid. An important consequence of the homozygosity and homogeneity of the inbred variety is that the hybrid between a defined pair of inbreds may be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained.
PH18K6 may be used to produce a single cross hybrid, a double cross hybrid, or a three-way hybrid. A single cross hybrid is produced when two inbred varieties are crossed to produce the F1 progeny. A double cross hybrid is produced from four inbred varieties crossed in pairs (A×B and C×D) and then the two F1 hybrids are crossed again (A×B)×(C×D). A three-way cross hybrid is produced from three inbred varieties where two of the inbred varieties are crossed (A×B) and then the resulting F1 hybrid is crossed with the third inbred (A×B)×C. In each case, pericarp tissue from the female parent will be a part of and protect the hybrid seed.
Combining Ability of PH18K6
Combining ability of a variety, as well as the performance of the variety per se, is a factor in the selection of improved maize inbreds. Combining ability refers to a variety's contribution as a parent when crossed with other varieties to form hybrids. The hybrids formed for the purpose of selecting superior varieties may be referred to as test crosses, and include comparisons to other hybrid varieties grown in the same environment (same cross, location and time of planting). One way of measuring combining ability is by using values based in part on the overall mean of a number of test crosses weighted by number of experiment and location combinations in which the hybrid combinations occurs. The mean may be adjusted to remove environmental effects and known genetic relationships among the varieties.
General combining ability provides an overall score for the inbred over a large number of test crosses. Specific combining ability provides information on hybrid combinations formed by PH18K6 and a specific inbred parent. A variety such as PH18K6 which exhibits good general combining ability may be used in a large number of hybrid combinations.
A general combining ability report for PH18K6 is provided in Table 2. In Table 2, found at the end of this section, BLUP, Best Linear Unbiased Prediction, values are reported for the breeding value of the maize inbred PH18K6 platform. The BLUP values are reported for numerous traits of hybrids that have inbred PH18K6 or a locus conversion of PH18K6 as a parent. The inbred PH18K6 and various locus conversions of PH18K6 are together considered a platform. The values reported indicate a BLUP value averaged for all members of the platform weighted by the inverse of the Standard Errors.
Hybrid Comparisons
These hybrid comparisons represent specific hybrid crosses with PH18K6 and a comparison of these specific hybrids with other hybrids with favorable characteristics. These comparisons illustrate the good specific combining ability of PH18K6.
The results in Table 3 compare a specific hybrid for which PH18K6 is a parent with other hybrids. The data in Table 3 shows that numerous species of the genus of F1 hybrids created with PH18K6 have been reduced to practice. These comparisons illustrate the good specific combining ability of PH18K6. In Table 3, found at the end of this section, BLUP values are reported for different hybrids wherein one parent is the maize variety PH18K6 or PH18K6 comprising locus conversions. The BLUP values and Standard Errors, SE, are reported for numerous traits.
Data are presented for these hybrids are based on replicated field trials.
Locus Conversions of PH18K6
PH18K6 represents a new base genetic variety into which a new locus may be introgressed. Direct transformation and backcrossing represent two important methods that can be used to accomplish such an introgression. The term locus conversion is used to designate the product of such an introgression.
A locus conversion of PH18K6 will retain the genetic integrity of PH18K6. A locus conversion of PH18K6 will comprise at least 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or 99% of the genetic identity of PH18K6 as determined by using SSR markers or SNP markers. For example, a locus conversion of PH18K6 can be developed when DNA sequences are introduced through backcrossing (Hallauer et al. in Corn and Corn Improvement, Sprague and Dudley, Third Ed. 1998), with PH18K6 utilized as the recurrent parent. Both naturally occurring and transgenic DNA sequences may be introduced through backcrossing techniques. A backcross conversion may produce a plant with a trait or locus conversion in at least one or more backcrosses, including at least 2 crosses, at least 3 crosses, at least 4 crosses, at least 5 crosses and the like. Molecular marker assisted breeding or selection may be utilized to reduce the number of backcrosses necessary to achieve the backcross conversion. For example, see Openshaw, S. J. et al., Marker-assisted Selection in Backcross Breeding, In: Proceedings Symposium of the Analysis of Molecular Data, August 1994, Crop Science Society of America, Corvallis, Oreg., where it is demonstrated that a locus conversion can be made in as few as two backcrosses.
The complexity of the backcross conversion method depends on the type of trait being transferred (single genes or closely linked genes as vs. unlinked genes), the level of expression of the trait, the type of inheritance (cytoplasmic or nuclear) and the types of parents included in the cross. It is understood by those of ordinary skill in the art that for single locus traits that are relatively easy to classify, the backcross method is effective and relatively easy to manage. (See Hallauer et al. in Corn and Corn Improvement, Sprague and Dudley, Third Ed. 1998). Desired traits that may be transferred through locus conversion include, but are not limited to, waxy starch, sterility (nuclear and cytoplasmic), fertility restoration, grain color (white), nutritional enhancements, drought resistance, enhanced nitrogen utilization efficiency, altered nitrogen responsiveness, altered fatty acid profile, increased digestibility, low phytate, industrial enhancements, disease resistance (bacterial, fungal or viral), insect resistance, herbicide tolerance and yield enhancements. A locus conversion, also called a trait conversion, can be a native trait or a transgenic trait. In addition, an introgression site itself, such as an FRT site, Lox site or other site specific integration site, may be inserted by backcrossing and utilized for direct insertion of one or more genes of interest into a specific plant variety. The seed industry commonly markets “triple stacks” of base genetics; which can be varieties comprising a locus conversion of at least 3 loci. Similarly, “quadruple stacks” would comprise the base genetics and could comprise a locus conversion of at least 4 loci. A single locus may contain several transgenes, such as a transgene for disease resistance that, in the same expression vector, also contains a transgene for herbicide tolerance. As used herein, the phrase ‘comprising a’ transgene, transgenic event or locus conversion means one or more transgenes, transgenic events or locus conversions. The gene for herbicide tolerance may be used as a selectable marker and/or as a phenotypic trait. A locus conversion of a site specific integration system allows for the integration of multiple genes at the converted loci. Further, SSI and FRT technologies known to those of skill in the art in the art may result in multiple gene introgressions at a single locus.
The locus conversion may result from either the transfer of a dominant allele or a recessive allele. Selection of progeny containing the trait of interest is accomplished by direct selection for a trait associated with a dominant allele. Transgenes transferred via backcrossing typically function as a dominant single gene trait and are relatively easy to classify. Selection of progeny for a trait that is transferred via a recessive allele, such as the waxy starch characteristic, requires growing and selfing the first backcross generation to determine which plants carry the recessive alleles. Recessive traits may require additional progeny testing in successive backcross generations to determine the presence of the locus of interest. The last backcross generation is usually selfed to give pure breeding progeny for the gene(s) being transferred, although a backcross conversion with a stably introgressed trait may also be maintained by further backcrossing to the recurrent parent with selection for the converted trait.
Along with selection for the trait of interest, progeny are selected for the phenotype and/or genotype of the recurrent parent. While occasionally additional polynucleotide sequences or genes may be transferred along with the backcross conversion, the backcross conversion variety “fits into the same hybrid combination as the recurrent parent inbred variety and contributes the effect of the additional locus added through the backcross.” ((Poehlman et al (1995) Breeding Field Crop, 4th Ed., Iowa State University Press, Ames, Iowa., pp. 132-155 and 321-344)). When one or more traits are introgressed into the variety a difference in quantitative agronomic traits, such as yield or dry down, between the variety and an introgressed version of the variety in some environments may occur. For example, the introgressed version may provide a net yield increase in environments where the trait provides a benefit, such as when a variety with an introgressed trait for insect resistance is grown in an environment where insect pressure exists, or when a variety with herbicide tolerance is grown in an environment where herbicide is used.
One process for adding or modifying a trait or locus in maize variety PH18K6 comprises crossing PH18K6 plants grown from PH18K6 seed with plants of another maize variety that comprise the desired trait or locus, selecting F1 progeny plants that comprise the desired trait or locus to produce selected F1 progeny plants, crossing the selected progeny plants with the PH18K6 plants to produce backcross progeny plants, selecting for backcross progeny plants that have the desired trait or locus and the phenotypic characteristics of maize variety PH18K6 to produce selected backcross progeny plants; and backcrossing to PH18K6 one or more times in succession to produce backcross progeny plants that comprise said trait or locus. The modified PH18K6 may be further characterized as having essentially the same phenotypic characteristics of maize variety PH18K6 listed in Table 1 and/or may be characterized by percent identity to PH18K6 as determined by molecular markers, such as SSR markers or SNPs.
In addition, the above process and other similar processes described herein may be used to produce F1 hybrid maize seed by adding a step at the end of the process that comprises crossing PH18K6 with the locus conversion with a different maize plant and harvesting the resultant F1 hybrid maize seed.
Traits are also used by those of ordinary skill in the art to characterize progeny. Traits are commonly evaluated at a significance level, such as a 1%, 5% or 10% significance level, when measured in plants grown in the same environmental conditions.
Male Sterility and Hybrid Seed Production
Hybrid seed production requires elimination or inactivation of pollen produced by the female inbred parent. Incomplete removal or inactivation of the pollen provides the potential for self-pollination. A reliable method of controlling male fertility in plants offers the opportunity for improved seed production.
PH18K6 can be produced in a male-sterile form. There are several ways in which a maize plant can be manipulated so that it is male sterile. These include use of manual or mechanical emasculation (or detasseling), use of one or more genetic factors that confer male sterility, including cytoplasmic genetic and/or nuclear genetic male sterility, use of gametocides and the like. A male sterile designated PH18K6 may include one or more genetic factors, which result in cytoplasmic genetic and/or nuclear genetic male sterility. All of such embodiments are within the scope of the present claims. The male sterility may be either partial or complete male sterility.
Hybrid maize seed is often produced by a male sterility system incorporating manual or mechanical detasseling. Alternate strips of two maize inbreds are planted in a field, and the pollen-bearing tassels are removed from one of the inbreds (female). Provided that there is sufficient isolation from sources of foreign maize pollen, the ears of the detasseled inbred will be fertilized only from the other inbred (male), and the resulting seed is therefore hybrid and will form hybrid plants.
The laborious detasseling process can be avoided by using cytoplasmic male-sterile (CMS) inbreds. Plants of a CMS inbred are male sterile as a result of genetic factors in the cytoplasm, as opposed to the nucleus, and so nuclear linked genes are not transferred during backcrossing. Thus, this characteristic is inherited exclusively through the female parent in maize plants, since only the female provides cytoplasm to the fertilized seed. CMS plants are fertilized with pollen from another inbred that is not male-sterile. Pollen from the second inbred may or may not contribute genes that make the hybrid plants male-fertile, and either option may be preferred depending on the intended use of the hybrid. The same hybrid seed, a portion produced from detasseled fertile maize and a portion produced using the CMS system, can be blended to insure that adequate pollen loads are available for fertilization when the hybrid plants are grown. CMS systems have been successfully used since the 1950's, and the male sterility trait is routinely backcrossed into inbred varieties. See Wych, Robert D. (1988) “Production of Hybrid Seed”, Corn and Corn Improvement, Ch. 9, pp. 565-607.
There are several methods of conferring genetic male sterility available, such as multiple mutant genes at separate locations within the genome that confer male sterility, as disclosed in U.S. Pat. Nos. 4,654,465 and 4,727,219 to Brar et al. and chromosomal translocations as described by Patterson in U.S. Pat. Nos. 3,861,709 and 3,710,511. In addition to these methods, Albertsen et al., U.S. Pat. No. 5,432,068, describes a system of nuclear male sterility which includes: identifying a gene which is critical to male fertility; silencing this native gene which is critical to male fertility; removing the native promoter from the essential male fertility gene and replacing it with an inducible promoter; inserting this genetically engineered gene back into the plant; and thus creating a plant that is male sterile because the inducible promoter is not “on” resulting in the male fertility gene not being transcribed. Fertility is restored by inducing, or turning “on”, the promoter, which in turn allows the gene that confers male fertility to be transcribed.
These, and the other methods of conferring genetic male sterility in the art, each possess their own benefits and drawbacks. Some other methods use a variety of approaches such as delivering into the plant a gene encoding a cytotoxic substance associated with a male tissue specific promoter or an antisense system in which a gene critical to fertility is identified and an antisense to that gene is inserted in the plant (see Fabinjanski, et al. EPO 89/3010153.8 publication no. 329,308 and PCT application PCT/CA90/00037 published as WO 90/08828).
Another system for controlling male sterility makes use of gametocides. Gametocides are not a genetic system, but rather a topical application of chemicals. These chemicals affect cells that are critical to male fertility. The application of these chemicals affects fertility in the plants only for the growing season in which the gametocide is applied (see Carlson, Glenn R., and U.S. Pat. No. 4,936,904). Application of the gametocide, timing of the application and genotype specificity often limit the usefulness of the approach and it is not appropriate in all situations.
Incomplete control over male fertility may result in self-pollinated seed being unintentionally harvested and packaged with hybrid seed. This would typically be only female parent seed, because the male plant is grown in rows that are typically destroyed prior to seed development. Once the seed from the hybrid bag is planted, it is possible to identify and select these self-pollinated plants. These self-pollinated plants will be one of the inbred varieties used to produce the hybrid. Though the possibility of PH18K6 being included in a hybrid seed bag exists, the occurrence is very low because much care is taken by seed companies to avoid such inclusions. It is worth noting that hybrid seed is sold to growers for the production of grain or forage and not for breeding or seed production. These self-pollinated plants can be identified and selected by one skilled in the art due to their less vigorous appearance for vegetative and/or reproductive characteristics, including shorter plant height, small ear size, ear and kernel shape, or other characteristics.
Identification of these self-pollinated varieties can also be accomplished through molecular marker analyses. See, “The Identification of Female Selfs in Hybrid Maize: A Comparison Using Electrophoresis and Morphology”, Smith, J. S. C. and Wych, R. D., Seed Science and Technology 14, 1-8 (1995), the disclosure of which is expressly incorporated herein by reference. Through these technologies, the homozygosity of the self pollinated variety can be verified by analyzing allelic composition at various loci along the genome. Those methods allow for rapid identification of the invention disclosed herein. See also, “Identification of Atypical Plants in Hybrid Maize Seed by Postcontrol and Electrophoresis” Sarca, V. et al., Probleme de Genetica Teoritica si Aplicata Vol. 20 (1) p. 29-42.
Transformation
The advent of new molecular biological techniques has allowed the isolation and characterization of genetic elements with specific functions, such as encoding specific protein products. Scientists in the field of plant biology developed a strong interest in engineering the genome of plants to contain and express foreign genetic elements, or additional, or modified versions of native or endogenous genetic elements in order to alter the traits of a plant in a specific manner. Any DNA sequences, whether from a different species or from the same species, which are stably inserted into the cell using transformation are referred to herein collectively as “transgenes” and/or “transgenic events”. In some embodiments of the invention, a transformed variant of PH18K6 may comprise at least one transgene but could contain at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and/or no more than 15, 14, 13, 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, or 2. Over the last fifteen to twenty years several methods for producing transgenic plants have been developed, and the present invention also relates to transformed versions of the claimed maize variety PH18K6 as well as hybrid combinations thereof.
Numerous methods for plant transformation have been developed, including biological and physical plant transformation protocols. See, for example, Miki et al., “Procedures for Introducing Foreign DNA into Plants” in Methods in Plant Molecular Biology and Biotechnology, Glick, B. R. and Thompson, J. E. Eds. (CRC Press, Inc., Boca Raton, 1993) pages 67-88 and Armstrong, “The First Decade of Maize Transformation: A Review and Future Perspective” (Maydica 44:101-109, 1999). In addition, expression vectors and in vitro culture methods for plant cell or tissue transformation and regeneration of plants are available. See, for example, Gruber et al., “Vectors for Plant Transformation” in Methods in Plant Molecular Biology and Biotechnology, Glick, B. R. and Thompson, J. E. Eds. (CRC Press, Inc., Boca Raton, 1993) pages 89-119.
The most prevalent types of plant transformation involve the construction of an expression vector. Such a vector comprises a DNA sequence that contains a gene under the control of or operatively linked to a regulatory element, for example a promoter. The vector may contain one or more genes and one or more regulatory elements.
A transgenic event which has been stably engineered into the germ cell line of a particular maize plant using transformation techniques, could be moved into the germ cell line of another variety using traditional breeding techniques that are well known in the plant breeding arts. For example, a backcrossing approach is commonly used to move a transgenic event from a transformed maize plant to another variety, and the resulting progeny would then comprise the transgenic event(s). Also, if an inbred variety was used for the transformation then the transgenic plants could be crossed to a different inbred in order to produce a transgenic hybrid maize plant.
Various genetic elements can be introduced into the plant genome using transformation. These elements include, but are not limited to genes; coding sequences; inducible, constitutive, and tissue specific promoters; enhancing sequences; and signal and targeting sequences. For example, see the traits, genes and transformation methods listed in U.S. Pat. Nos. 6,118,055 and 6,284,953, which are herein incorporated by reference. In addition, transformability of a variety can be increased by introgressing the trait of high transformability from another variety known to have high transformability, such as Hi-II. See U.S. Patent Application Publication US200410016030 (2004).
With transgenic plants according to the present invention, a foreign protein can be produced in commercial quantities. Thus, techniques for the selection and propagation of transformed plants, which are well understood in the art, yield a plurality of transgenic plants that are harvested in a conventional manner, and a foreign protein then can be extracted from a tissue of interest or from total biomass. Protein extraction from plant biomass can be accomplished by known methods which are discussed, for example, by Heney and Orr, Anal. Biochem. 114: 92-6 (1981).
Transgenic events can be mapped by one of ordinary skill in the art and such techniques are well known to those of ordinary skill in the art. For exemplary methodologies in this regard, see for example, Glick and Thompson, Methods in Plant Molecular Biology and Biotechnology 269-284 (CRC Press, Boca Raton, 1993).
Likewise, by means of the present invention, plants can be genetically engineered to express various phenotypes of agronomic interest. Through the transformation of maize the expression of genes can be altered to enhance disease resistance, insect resistance, herbicide tolerance, agronomic traits, grain quality and other traits. Transformation can also be used to insert DNA sequences which control or help control male-sterility. DNA sequences native to maize as well as non-native DNA sequences can be transformed into maize and used to alter levels of native or non-native proteins. Various promoters, targeting sequences, enhancing sequences, and other DNA sequences can be inserted into the maize genome for the purpose of altering the expression of proteins. Reduction of the activity of specific genes (also known as gene silencing, or gene suppression) is desirable for several aspects of genetic engineering in plants.
Many techniques for gene silencing are well known to one of skill in the art, including but not limited to knock-outs (such as by insertion of a transposable element such as mu (Vicki Chandler, The Maize Handbook Ch. 118 (Springer-Verlag 1994) or other genetic elements such as a FRT, Lox or other site specific integration site, antisense technology (see, e.g., Sheehy et al. (1988) PNAS USA 85:8805-8809; and U.S. Pat. Nos. 5,107,065; 5,453,566; and 5,759,829); co-suppression (e.g., Taylor (1997) Plant Cell 9:1245; Jorgensen (1990) Trends Biotech. 8(12):340-344; Flavell (1994) PNAS USA 91:3490-3496; Finnegan et al. (1994) Bio/Technology 12: 883-888; and Neuhuber et al. (1994) Mol. Gen. Genet. 244:230-241); RNA interference (Napoli et al. (1990) Plant Cell 2:279-289; U.S. Pat. No. 5,034,323; Sharp (1999) Genes Dev. 13:139-141; Zamore et al. (2000) Cell 101:25-33; and Montgomery et al. (1998) PNAS USA 95:15502-15507), virus-induced gene silencing (Burton, et al. (2000) Plant Cell 12:691-705; and Baulcombe (1999) Curr. Op. Plant Bio. 2:109-113); target-RNA-specific ribozymes (Haseloff et al. (1988) Nature 334: 585-591); hairpin structures (Smith et al. (2000) Nature 407:319-320; WO 99/53050; and WO 98/53083); MicroRNA (Aukerman & Sakai (2003) Plant Cell 15:2730-2741); ribozymes (Steinecke et al. (1992) EMBO J. 11:1525; and Perriman et al. (1993) Antisense Res. Dev. 3:253); oligonucleotide mediated targeted modification (e.g., WO 03/076574 and WO 99/25853); Zn-finger targeted molecules (e.g., WO 01/52620; WO 03/048345; and WO 00/42219); and other methods or combinations of the above methods known to those of skill in the art.
Exemplary nucleotide sequences that may be altered by genetic engineering include, but are not limited to, those categorized below.
1. Transgenes that Confer Resistance to Insects or Disease and that Encode:
(A) Plant disease resistance genes. Plant defenses are often activated by specific interaction between the product of a disease resistance gene (R) in the plant and the product of a corresponding avirulence (Avr) gene in the pathogen. A plant variety can be transformed with cloned resistance gene to engineer plants that are resistant to specific pathogen strains. See, for example Jones et al., Science 266: 789 (1994) (cloning of the tomato Cf-9 gene for resistance to Cladosporium fulvum); Martin et al., Science 262: 1432 (1993) (tomato Pto gene for resistance to Pseudomonas syringae pv. tomato encodes a protein kinase); Mindrinos et al., Cell 78: 1089 (1994) (Arabidopsis RSP2 gene for resistance to Pseudomonas syringae), McDowell & Woffenden, (2003) Trends Biotechnol. 21(4): 178-83 and Toyoda et al., (2002) Transgenic Res. 11(6):567-82. A plant resistant to a disease is one that is more resistant to a pathogen as compared to the wild type plant.
(B) A Bacillus thuringiensis protein, a derivative thereof or a synthetic polypeptide modeled thereon. See, for example, Geiser et al., Gene 48: 109 (1986), who disclose the cloning and nucleotide sequence of a Bt delta-endotoxin gene. Moreover, DNA molecules encoding delta-endotoxin genes can be purchased from American Type Culture Collection (Rockville, Md.), for example, under ATCC Accession Nos. 40098, 67136, 31995 and 31998. Other non-limiting examples of Bacillus thuringiensis transgenes being genetically engineered are given in the following patents and patent applications and hereby are incorporated by reference for this purpose: U.S. Pat. Nos. 5,188,960; 5,689,052; 5,880,275; 5,986,177; 7,105,332; 7,208,474; WO 91/14778; WO 99/31248; WO 01/12731; WO 99/24581; WO 97/40162 and U.S. application Ser. Nos. 10/032,717; 10/414,637; 11/018,615; 11/404,297; 11/404,638; 11/471,878; 11/780,501; 11/780,511; 11/780,503; 11/953,648; 11/953,648; and 11/957,893.
(C) An insect-specific hormone or pheromone such as an ecdysteroid and juvenile hormone, a variant thereof, a mimetic based thereon, or an antagonist or agonist thereof. See, for example, the disclosure by Hammock et al., Nature 344: 458 (1990), of baculovirus expression of cloned juvenile hormone esterase, an inactivator of juvenile hormone.
(D) An insect-specific peptide which, upon expression, disrupts the physiology of the affected pest. For example, see the disclosures of Regan, J. Biol. Chem. 269: 9 (1994) (expression cloning yields DNA coding for insect diuretic hormone receptor); Pratt et al., Biochem. Biophys. Res. Comm. 163: 1243 (1989) (an allostatin is identified in Diploptera puntata); Chattopadhyay et al. (2004) Critical Reviews in Microbiology 30 (1): 33-54 2004; Zjawiony (2004) J Nat Prod 67 (2): 300-310; Carlini & Grossi-de-Sa (2002) Toxicon, 40 (11): 1515-1539; Ussuf et al. (2001) Curr Sci. 80 (7): 847-853; and Vasconcelos & Oliveira (2004) Toxicon 44 (4): 385-403. See also U.S. Pat. No. 5,266,317 to Tomalski et al., who disclose genes encoding insect-specific toxins.
(E) An enzyme responsible for a hyperaccumulation of a monterpene, a sesquiterpene, a steroid, hydroxamic acid, a phenylpropanoid derivative or another non-protein molecule with insecticidal activity.
(F) An enzyme involved in the modification, including the post-translational modification, of a biologically active molecule; for example, a glycolytic enzyme, a proteolytic enzyme, a lipolytic enzyme, a nuclease, a cyclase, a transaminase, an esterase, a hydrolase, a phosphatase, a kinase, a phosphorylase, a polymerase, an elastase, a chitinase and a glucanase, whether natural or synthetic. See PCT application WO 93/02197 in the name of Scott et al., which discloses the nucleotide sequence of a callase gene. DNA molecules which contain chitinase-encoding sequences can be obtained, for example, from the ATCC under Accession Nos. 39637 and 67152. See also Kramer et al., Insect Biochem. Molec. Biol. 23: 691 (1993), who teach the nucleotide sequence of a cDNA encoding tobacco hookworm chitinase, and Kawalleck et al., Plant Molec. Biol. 21: 673 (1993), who provide the nucleotide sequence of the parsley ubi4-2 polyubiquitin gene, and U.S. Pat. Nos. 6,563,020; 7,145,060 and 7,087,810.
(G) A molecule that stimulates signal transduction. For example, see the disclosure by Botella et al., Plant Molec. Biol. 24: 757 (1994), of nucleotide sequences for mung bean calmodulin cDNA clones, and Griess et al., Plant Physiol. 104: 1467 (1994), who provide the nucleotide sequence of a maize calmodulin cDNA clone.
(H) A hydrophobic moment peptide. See PCT application WO 95/16776 and U.S. Pat. No. 5,580,852 disclosure of peptide derivatives of Tachyplesin which inhibit fungal plant pathogens) and PCT application WO 95/18855 and U.S. Pat. No. 5,607,914 (teaches synthetic antimicrobial peptides that confer disease resistance).
(I) A membrane permease, a channel former or a channel blocker. For example, see the disclosure by Jaynes et al., Plant Sci. 89: 43 (1993), of heterologous expression of a cecropin-beta lytic peptide analog to render transgenic tobacco plants resistant to Pseudomonas solanacearum. 
(J) A viral-invasive protein or a complex toxin derived therefrom. For example, the accumulation of viral coat proteins in transformed plant cells imparts resistance to viral infection and/or disease development effected by the virus from which the coat protein gene is derived, as well as by related viruses. See Beachy et al., Ann. Rev. Phytopathol. 28: 451 (1990). Coat protein-mediated resistance has been conferred upon transformed plants against alfalfa mosaic virus, cucumber mosaic virus, tobacco streak virus, potato virus X, potato virus Y, tobacco etch virus, tobacco rattle virus and tobacco mosaic virus. Id.
(K) An insect-specific antibody or an immunotoxin derived therefrom. Thus, an antibody targeted to a critical metabolic function in the insect gut would inactivate an affected enzyme, killing the insect. Cf. Taylor et al., Abstract #497, SEVENTH INT'L SYMPOSIUM ON MOLECULAR PLANT-MICROBE INTERACTIONS (Edinburgh, Scotland, 1994) (enzymatic inactivation in transgenic tobacco via production of single-chain antibody fragments).
(L) A virus-specific antibody. See, for example, Tavladoraki et al., Nature 366: 469 (1993), which shows that transgenic plants expressing recombinant antibody genes are protected from virus attack.
(M) A developmental-arrestive protein produced in nature by a pathogen or a parasite. Thus, fungal endo alpha-1,4-D-polygalacturonases facilitate fungal colonization and plant nutrient release by solubilizing plant cell wall homo-alpha-1,4-D-galacturonase. See Lamb et al., Bio/Technology 10: 1436 (1992). The cloning and characterization of a gene which encodes a bean endopolygalacturonase-inhibiting protein is described by Toubart et al., Plant J. 2: 367 (1992).
(N) A developmental-arrestive protein produced in nature by a plant. For example, Logemann et al., Bio/Technology 10: 305 (1992), have shown that transgenic plants expressing the barley ribosome-inactivating gene have an increased resistance to fungal disease.
(O) Genes involved in the Systemic Acquired Resistance (SAR) Response and/or the pathogenesis related genes. Briggs, S., Current Biology, 5(2) (1995), Pieterse & Van Loon (2004) Curr. Opin. Plant Bio. 7(4):456-64 and Somssich (2003) Cell 113(7):815-6.
(P) Antifungal genes (Cornelissen and Melchers, Pl. Physiol. 101:709-712, (1993) and Parijs et al., Planta 183:258-264, (1991) and Bushnell et al., Can. J. of Plant Path. 20(2):137-149 (1998). Also see U.S. application Ser. Nos. 09/950,933; 11/619,645; 11/657,710; 11/748,994; 11/774,121 and U.S. Pat. Nos. 6,891,085 and 7,306,946.
(Q) Detoxification genes, such as for fumonisin, beauvericin, moniliformin and zearalenone and their structurally related derivatives. For example, see U.S. Pat. Nos. 5,716,820; 5,792,931; 5,798,255; 5,846,812; 6,083,736; 6,538,177; 6,388,171 and 6,812,380.
(R) Cystatin and cysteine proteinase inhibitors. See U.S. Pat. No. 7,205,453.
(S) Defensin genes. See WO03000863 and U.S. Pat. Nos. 6,911,577; 6,855,865; 6,777,592 and 7,238,781.
(T) Genes conferring resistance to nematodes. See e.g. PCT Application WO96/30517; PCT Application WO93/19181, WO 03/033651 and Urwin et al., Planta 204:472-479 (1998), Williamson (1999) Curr Opin Plant Bio. 2(4):327-31; and U.S. Pat. Nos. 6,284,948 and 7,301,069.
(U) Genes that confer resistance to Phytophthora Root Rot, such as the Rps 1, Rps 1-a, Rps 1-b, Rps 1-c, Rps 1-d, Rps 1-e, Rps 1-k, Rps 2, Rps 3-a, Rps 3-b, Rps 3-c, Rps 4, Rps 5, Rps 6, Rps 7 and other Rps genes. See, for example, Shoemaker et al, Phytophthora Root Rot Resistance Gene Mapping in Soybean, Plant Genome IV Conference, San Diego, Calif. (1995).
(V) Genes that confer resistance to Brown Stem Rot, such as described in U.S. Pat. No. 5,689,035 and incorporated by reference for this purpose.
(W) Genes that confer resistance to Colletotrichum, such as described in US Patent publication US20090035765 and incorporated by reference for this purpose. This includes the Rcg locus that may be utilized as a single locus conversion.
2. Transgenes that Confer Tolerance to a Herbicide, for Example:
(A) A herbicide that inhibits the growing point or meristem, such as an imidazolinone or a sulfonylurea. Exemplary genes in this category code for mutant ALS and AHAS enzyme as described, for example, by Lee et al., EMBO J. 7: 1241 (1988), and Miki et al., Theor. Appl. Genet. 80: 449 (1990), respectively. See also, U.S. Pat. Nos. 5,605,011; 5,013,659; 5,141,870; 5,767,361; 5,731,180; 5,304,732; 4,761,373; 5,331,107; 5,928,937; and 5,378,824; U.S. application Ser. No. 11/683,737, and international publication WO 96/33270.
(B) Glyphosate (tolerance imparted by mutant 5-enolpyruvl-3-phosphikimate synthase (EPSP) and aroA genes, respectively) and other phosphono compounds such as glufosinate (phosphinothricin acetyl transferase (PAT) and Streptomyces hygroscopicus phosphinothricin acetyl transferase (bar) genes), and pyridinoxy or phenoxy proprionic acids and cyclohexones (ACCase inhibitor-encoding genes). See, for example, U.S. Pat. No. 4,940,835 to Shah et al., which discloses the nucleotide sequence of a form of EPSPS which can confer glyphosate tolerance. U.S. Pat. No. 5,627,061 to Barry et al. also describes genes encoding EPSPS enzymes. See also U.S. Pat. Nos. 6,566,587; 6,338,961; 6,248,876 B1; 6,040,497; 5,804,425; 5,633,435; 5,145,783; 4,971,908; 5,312,910; 5,188,642; 4,940,835; 5,866,775; 6,225,114 B1; 6,130,366; 5,310,667; 4,535,060; 4,769,061; 5,633,448; 5,510,471; Re. 36,449; RE 37,287 E; and 5,491,288; and international publications EP1173580; WO 01/66704; EP1173581 and EP1173582, which are incorporated herein by reference for this purpose. Glyphosate tolerance is also imparted to plants that express a gene that encodes a glyphosate oxido-reductase enzyme as described more fully in U.S. Pat. Nos. 5,776,760 and 5,463,175, which are incorporated herein by reference for this purpose. In addition glyphosate tolerance can be imparted to plants by the over expression of genes encoding glyphosate N-acetyltransferase. See, for example, U.S. application Ser. Nos. 10/427,692; 10/835,615 and 11/507,751. A DNA molecule encoding a mutant aroA gene can be obtained under ATCC accession No. 39256, and the nucleotide sequence of the mutant gene is disclosed in U.S. Pat. No. 4,769,061 to Comai. European Patent Application No. 0 333 033 to Kumada et al. and U.S. Pat. No. 4,975,374 to Goodman et al. disclose nucleotide sequences of glutamine synthetase genes which confer tolerance to herbicides such as L-phosphinothricin. The nucleotide sequence of a phosphinothricin-acetyl-transferase gene is provided in European Patent No. 0 242 246 and 0 242 236 to Leemans et al. De Greef et al., Bio/Technology 7: 61 (1989), describe the production of transgenic plants that express chimeric bar genes coding for phosphinothricin acetyl transferase activity. See also, U.S. Pat. Nos. 5,969,213; 5,489,520; 5,550,318; 5,874,265; 5,919,675; 5,561,236; 5,648,477; 5,646,024; 6,177,616 B1; and 5,879,903, which are incorporated herein by reference for this purpose. Exemplary genes conferring resistance to phenoxy proprionic acids and cyclohexones, such as sethoxydim and haloxyfop, are the Acc1-S1, Acc1-S2 and Acc1-S3 genes described by Marshall et al., Theor. Appl. Genet. 83: 435 (1992).
(C) A herbicide that inhibits photosynthesis, such as a triazine (psbA and gs+ genes) and a benzonitrile (nitrilase gene). Przibilla et al., Plant Cell 3: 169 (1991), describe the transformation of Chlamydomonas with plasmids encoding mutant psbA genes. Nucleotide sequences for nitrilase genes are disclosed in U.S. Pat. No. 4,810,648 to Stalker, and DNA molecules containing these genes are available under ATCC Accession Nos. 53435, 67441 and 67442. Cloning and expression of DNA coding for a glutathione S-transferase is described by Hayes et al., Biochem. J. 285: 173 (1992).
(D) Acetohydroxy acid synthase, which has been found to make plants that express this enzyme resistant to multiple types of herbicides, has been introduced into a variety of plants (see, e.g., Hattori et al. (1995) Mol Gen Genet. 246:419). Other genes that confer tolerance to herbicides include: a gene encoding a chimeric protein of rat cytochrome P4507A1 and yeast NADPH-cytochrome P450 oxidoreductase (Shiota et al. (1994) Plant Physiol 106:17), genes for glutathione reductase and superoxide dismutase (Aono et al. (1995) Plant Cell Physiol 36:1687, and genes for various phosphotransferases (Datta et al. (1992) Plant Mol Biol 20:619).
(E) Protoporphyrinogen oxidase (protox) is necessary for the production of chlorophyll, which is necessary for all plant survival. The protox enzyme serves as the target for a variety of herbicidal compounds. These herbicides also inhibit growth of all the different species of plants present, causing their total destruction. The development of plants containing altered protox activity which are tolerant to these herbicides are described in U.S. Pat. Nos. 6,288,306 B1; 6,282,837 B1; and 5,767,373; and international publication WO 01/12825.
3. Transgenes that Confer or Contribute to an Altered Grain Characteristic, Such As:
(A) Altered fatty acids, for example, by

    
    
        (1) Down-regulation of stearoyl-ACP desaturase to increase stearic acid content of the plant. See Knultzon et al., Proc. Natl. Acad. Sci. USA 89: 2624 (1992) and WO99/64579 (Genes for Desaturases to Alter Lipid Profiles in Corn),
        (2) Elevating oleic acid via FAD-2 gene modification and/or decreasing linolenic acid via FAD-3 gene modification (see U.S. Pat. Nos. 6,063,947; 6,323,392; 6,372,965 and WO 93/11245),
        (3) Altering conjugated linolenic or linoleic acid content, such as in WO 01/12800,
        (4) Altering LEC1, AGP, Dek1, Superal1, mi1 ps, various Ipa genes such as Ipa1, Ipa3, hpt or hggt. For example, see WO 02/42424, WO 98/22604, WO 03/011015, WO02/057439, WO03/011015, U.S. Pat. Nos. 6,423,886, 6,197,561, 6,825,397, and U.S. Application Serial Nos. US2003/0079247, US2003/0204870, and Rivera-Madrid, R. et al. Proc. Natl. Acad. Sci. 92:5620-5624 (1995).
    
    


B) Altered phosphorus content, for example, by the
(1) Introduction of a phytase-encoding gene would enhance breakdown of phytate, adding more free phosphate to the transformed plant. For example, see Van Hartingsveldt et al., Gene 127: 87 (1993), for a disclosure of the nucleotide sequence of an Aspergillus niger phytase gene.
(2) Modulating a gene that reduces phytate content. In maize, this, for example, could be accomplished, by cloning and then re-introducing DNA associated with one or more of the alleles, such as the LPA alleles, identified in maize mutants characterized by low levels of phytic acid, such as in WO 05/113778 and/or by altering inositol kinase activity as in WO 02/059324, US2003/0009011, WO 03/027243, US2003/0079247, WO 99/05298, U.S. Pat. No. 6,197,561, U.S. Pat. No. 6,291,224, U.S. Pat. No. 6,391,348, WO2002/059324, US2003/0079247, Wo98/45448, WO99/55882, WO01/04147.
(C) Altered carbohydrates affected, for example, by altering a gene for an enzyme that affects the branching pattern of starch or, a gene altering thioredoxin such as NTR and/or TRX (see. (See U.S. Pat. No. 6,531,648 which is incorporated by reference for this purpose) and/or a gamma zein knock out or mutant such as cs27 or TUSC27 or en27 (See U.S. Pat. No. 6,858,778 and US2005/0160488, US2005/0204418; which are incorporated by reference for this purpose). See Shiroza et al., J. Bacteriol. 170: 810 (1988) (nucleotide sequence of Streptococcus mutans fructosyltransferase gene), Steinmetz et al., Mol. Gen. Genet. 200: 220 (1985) (nucleotide sequence of Bacillus subtilis levansucrase gene), Pen et al., Bio/Technology 10: 292 (1992) (production of transgenic plants that express Bacillus lichenifonnis alpha-amylase), Elliot et al., Plant Molec. Biol. 21: 515 (1993) (nucleotide sequences of tomato invertase genes), Søgaard et al., J. Biol. Chem. 268: 22480 (1993) (site-directed mutagenesis of barley alpha-amylase gene), and Fisher et al., Plant Physiol. 102: 1045 (1993) (maize endosperm starch branching enzyme II), WO 99/10498 (improved digestibility and/or starch extraction through modification of UDP-D-xylose 4-epimerase, Fragile 1 and 2, Ref1, HCHL, C4H), U.S. Pat. No. 6,232,529 (method of producing high oil seed by modification of starch levels (AGP)). The fatty acid modification genes mentioned herein may also be used to affect starch content and/or composition through the interrelationship of the starch and oil pathways.
(D) Altered antioxidant content or composition, such as alteration of tocopherol or tocotrienols. For example, see U.S. Pat. No. 6,787,683, US2004/0034886 and WO 00/68393 involving the manipulation of antioxidant levels, and WO 03/082899 through alteration of a homogentisate geranyl geranyl transferase (hggt).
(E) Altered essential seed amino acids. For example, see U.S. Pat. No. 6,127,600 (method of increasing accumulation of essential amino acids in seeds), U.S. Pat. No. 6,080,913 (binary methods of increasing accumulation of essential amino acids in seeds), U.S. Pat. No. 5,990,389 (high lysine), WO99/40209 (alteration of amino acid compositions in seeds), WO99/29882 (methods for altering amino acid content of proteins), U.S. Pat. No. 5,850,016 (alteration of amino acid compositions in seeds), WO98/20133 (proteins with enhanced levels of essential amino acids), U.S. Pat. No. 5,885,802 (high methionine), U.S. Pat. No. 5,885,801 (high threonine), U.S. Pat. No. 6,664,445 (plant amino acid biosynthetic enzymes), U.S. Pat. No. 6,459,019 (increased lysine and threonine), U.S. Pat. No. 6,441,274 (plant tryptophan synthase beta subunit), U.S. Pat. No. 6,346,403 (methionine metabolic enzymes), U.S. Pat. No. 5,939,599 (high sulfur), U.S. Pat. No. 5,912,414 (increased methionine), WO98/56935 (plant amino acid biosynthetic enzymes), WO98/45458 (engineered seed protein having higher percentage of essential amino acids), WO98/42831 (increased lysine), U.S. Pat. No. 5,633,436 (increasing sulfur amino acid content), U.S. Pat. No. 5,559,223 (synthetic storage proteins with defined structure containing programmable levels of essential amino acids for improvement of the nutritional value of plants), WO96/01905 (increased threonine), WO95/15392 (increased lysine), US2003/0163838, US2003/0150014, US2004/0068767, U.S. Pat. No. 6,803,498, WO01/79516.
4. Genes that Control Male-Sterility:
There are several methods of conferring genetic male sterility available, such as multiple mutant genes at separate locations within the genome that confer male sterility, as disclosed in U.S. Pat. Nos. 4,654,465 and 4,727,219 to Brar et al. and chromosomal translocations as described by Patterson in U.S. Pat. Nos. 3,861,709 and 3,710,511. In addition to these methods, Albertsen et al., U.S. Pat. No. 5,432,068, describe a system of nuclear male sterility which includes: identifying a gene which is critical to male fertility; silencing this native gene which is critical to male fertility; removing the native promoter from the essential male fertility gene and replacing it with an inducible promoter; inserting this genetically engineered gene back into the plant; and thus creating a plant that is male sterile because the inducible promoter is not “on” resulting in the male fertility gene not being transcribed. Fertility is restored by inducing, or turning “on”, the promoter, which in turn allows the gene that confers male fertility to be transcribed.
(A) Introduction of a deacetylase gene under the control of a tapetum-specific promoter and with the application of the chemical N-Ac-PPT (WO 01/29237).
(B) Introduction of various stamen-specific promoters (WO 92/13956, WO 92/13957).
(C) Introduction of the barnase and the barstar gene (Paul et al. Plant Mol. Biol. 19:611-622, 1992).
For additional examples of nuclear male and female sterility systems and genes, see also, U.S. Pat. Nos. 5,859,341; 6,297,426; 5,478,369; 5,824,524; 5,850,014; and 6,265,640; all of which are hereby incorporated by reference.
5. Genes that create a site for site specific DNA integration. This includes the introduction of FRT sites that may be used in the FLP/FRT system and/or Lox sites that may be used in the Cre/Loxp system. For example, see Lyznik, et al., Site-Specific Recombination for Genetic Engineering in Plants, Plant Cell Rep (2003) 21:925-932 and WO 99/25821 which are hereby incorporated by reference. Other systems that may be used include the Gin recombinase of phage Mu (Maeser et al., 1991; Vicki Chandler, The Maize Handbook Ch. 118 (Springer-Verlag 1994), the Pin recombinase of E. coli (Enomoto et al., 1983), and the R/RS system of the pSRi plasmid (Araki et al., 1992).

6. Genes that affect abiotic stress resistance (including but not limited to flowering, ear and seed development, enhancement of nitrogen utilization efficiency, altered nitrogen responsiveness, drought resistance or tolerance, cold resistance or tolerance, and salt resistance or tolerance) and increased yield under stress. For example, see: WO 00/73475 where water use efficiency is altered through alteration of malate; U.S. Pat. Nos. 5,892,009; 5,965,705; 5,929,305; 5,891,859; 6,417,428; 6,664,446; 6,706,866; 6,717,034; 6,801,104; WO2000060089; WO2001026459; WO2001035725; WO2001034726; WO2001035727; WO2001036444; WO2001036597; WO2001036598; WO2002015675; WO2002017430; WO2002077185; WO2002079403; WO2003013227; WO2003013228; WO2003014327; WO2004031349; WO2004076638; WO9809521; and WO9938977 describing genes, including CBF genes and transcription factors effective in mitigating the negative effects of freezing, high salinity, and drought on plants, as well as conferring other positive effects on plant phenotype; US2004/0148654 and WO01/36596 where abscisic acid is altered in plants resulting in improved plant phenotype such as increased yield and/or increased tolerance to abiotic stress; WO2000/006341, WO04/090143, U.S. application Ser. Nos. 10/817,483 and 09/545,334 where cytokinin expression is modified resulting in plants with increased stress tolerance, such as drought tolerance, and/or increased yield. Also see WO0202776, WO2003052063, JP2002281975, U.S. Pat. No. 6,084,153, WO0164898, U.S. Pat. No. 6,177,275, and U.S. Pat. No. 6,107,547 (enhancement of nitrogen utilization and altered nitrogen responsiveness). For ethylene alteration, see US20040128719, US20030166197 and WO200032761. For plant transcription factors or transcriptional regulators of abiotic stress, see e.g. US20040098764 or US20040078852.

Other genes and transcription factors that affect plant growth and agronomic traits such as yield, flowering, plant growth and/or plant structure, can be introduced or introgressed into plants, see e.g. WO97/49811 (LHY), WO98/56918 (ESD4), WO97/10339 and U.S. Pat. No. 6,573,430 (TFL), U.S. Pat. No. 6,713,663 (FT), WO96/14414 (CON), WO96/38560, WO01/21822 (VRN1), WO00/44918 (VRN2), WO99/49064 (GI), WO00/46358 (FRI), WO97/29123, U.S. Pat. No. 6,794,560, U.S. Pat. No. 6,307,126 (GAI), WO99/09174 (D8 and Rht), WO2004076638 and WO2004031349 (transcription factors).
Using PH18K6 to Develop Another Maize Plant
Maize varieties such as PH18K6 are typically developed for use in the production of hybrid maize varieties. However, varieties such as PH18K6 also provide a source of breeding material that may be used to develop new maize inbred varieties. Plant breeding techniques known in the art and used in a maize plant breeding program include, but are not limited to, recurrent selection, mass selection, bulk selection, mass selection, backcrossing, pedigree breeding, open pollination breeding, restriction fragment length polymorphism enhanced selection, genetic marker enhanced selection, making double haploids, and transformation. Often combinations of these techniques are used. The development of maize hybrids in a maize plant breeding program requires, in general, the development of homozygous inbred varieties, the crossing of these varieties, and the evaluation of the crosses. There are many analytical methods available to evaluate the result of a cross. The oldest and most traditional method of analysis is the observation of phenotypic traits but genotypic analysis may also be used.
This invention is also directed to methods for producing a maize plant by crossing a first parent maize plant with a second parent maize plant wherein either the first or second parent maize plant is a maize plant of the variety PH18K6. The other parent may be any other maize plant, such as another inbred variety or a plant that is part of a synthetic or natural population. Any such methods using the maize variety PH18K6 are part of this invention: selfing, sibbing, backcrosses, mass selection, pedigree breeding, bulk selection, hybrid production, crosses to populations, and the like. These methods are well known in the art and some of the more commonly used breeding methods are described below. Descriptions of breeding methods can also be found in one of several reference books (e.g., Allard, Principles of Plant Breeding, 1960; Simmonds, Principles of Crop Improvement, 1979; Fehr, “Breeding Methods for Cultivar Development”, Production and Uses, 2nd ed., Wilcox editor, 1987 the disclosure of which is incorporated herein by reference).
Pedigree Breeding
Pedigree breeding starts with the crossing of two genotypes, such as PH18K6 and one other inbred variety having one or more desirable characteristics that is lacking or which complements PH18K6. If the two original parents do not provide all the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive filial generations. In the succeeding filial generations the heterozygous condition gives way to homogeneous varieties as a result of self-pollination and selection. Typically in the pedigree method of breeding, five or more successive filial generations of selfing and selection is practiced: F1→F2; F2→F3; F3→F4; F4→F5, etc. After a sufficient amount of inbreeding, successive filial generations will serve to increase seed of the developed inbred. Preferably, the inbred variety comprises homozygous alleles at about 95% or more of its loci.
Recurrent Selection and Mass Selection
Recurrent selection is a method used in a plant breeding program to improve a population of plants. PH18K6 is suitable for use in a recurrent selection program. The method entails individual plants cross pollinating with each other to form progeny. The progeny are grown and the superior progeny selected by any number of selection methods, which include individual plant, half-sib progeny, full-sib progeny, selfed progeny and toperossing. The selected progeny are cross pollinated with each other to form progeny for another population. This population is planted and again superior plants are selected to cross pollinate with each other. Recurrent selection is a cyclical process and therefore can be repeated as many times as desired. The objective of recurrent selection is to improve the traits of a population. The improved population can then be used as a source of breeding material to obtain inbred varieties to be used in hybrids or used as parents for a synthetic cultivar. A synthetic cultivar is the resultant progeny formed by the intercrossing of several selected inbreds.
PH18K6 is suitable for use in mass selection. Mass selection is a useful technique when used in conjunction with molecular marker enhanced selection. In mass selection seeds from individuals are selected based on phenotype and/or genotype. These selected seeds are then bulked and used to grow the next generation. Bulk selection requires growing a population of plants in a bulk plot, allowing the plants to self-pollinate, harvesting the seed in bulk and then using a sample of the seed harvested in bulk to plant the next generation. Instead of self pollination, directed pollination could be used as part of the breeding program.
Mutation Breeding
Mutation breeding is one of many methods that could be used to introduce new traits into PH18K6. PH18K6 is suitable for use in a mutation breeding program. Mutations that occur spontaneously or are artificially induced can be useful sources of variability for a plant breeder. The goal of artificial mutagenesis is to increase the rate of mutation for a desired characteristic. Mutation rates can be increased by many different means including temperature, long-term seed storage, tissue culture conditions, radiation; such as X-rays, Gamma rays (e.g. cobalt 60 or cesium 137), neutrons, (product of nuclear fission by uranium 235 in an atomic reactor), Beta radiation (emitted from radioisotopes such as phosphorus 32 or carbon 14), or ultraviolet radiation (preferably from 2500 to 2900 nm), or chemical mutagens (such as base analogues (5-bromo-uracil), related compounds (8-ethoxy caffeine), antibiotics (streptonigrin), alkylating agents (sulfur mustards, nitrogen mustards, epoxides, ethylenamines, sulfates, sulfonates, sulfones, lactones), azide, hydroxylamine, nitrous acid, or acridines. Once a desired trait is observed through mutagenesis the trait may then be incorporated into existing germplasm by traditional breeding techniques, such as backcrossing. Details of mutation breeding can be found in “Principles of Cultivar Development” Fehr, 1993 Macmillan Publishing Company, the disclosure of which is incorporated herein by reference. In addition, mutations created in other varieties may be used to produce a backcross conversion of PH18K6 that comprises such mutation.
Production of Double Haploids
The production of double haploids can also be used for the development of inbreds in the breeding program. For example, an F1 hybrid for which PH18K6 is a parent can be used to produce double haploid plants. Double haploids are produced by the doubling of a set of chromosomes (1N) from a heterozygous plant to produce a completely homozygous individual. For example, see Wan et al., “Efficient Production of Doubled Haploid Plants Through Colchicine Treatment of Anther-Derived Maize Callus”, Theoretical and Applied Genetics, 77:889-892, 1989 and US2003/0005479. This can be advantageous because the process omits the generations of selfing needed to obtain a homozygous plant from a heterozygous source.
Haploid induction systems have been developed for various plants to produce haploid tissues, plants and seeds. The haploid induction system can produce haploid plants from any genotype by crossing a selected variety (as female) with an inducer variety. Such inducer varieties for maize include Stock 6 (Coe, 1959, Am. Nat. 93:381-382; Sharkar and Coe, 1966, Genetics 54:453-464) RWS (see world wide web site www.uni-hohenheim.de/%7Eipspwww/350b/indexe.html#Project3), KEMS (Deimling, Roeber, and Geiger, 1997, Vortr. Pflanzenzuchtg 38:203-224), KMS and ZMS (Chalyk, Bylich & Chebotar, 1994, MNL 68:47; Chalyk & Chebotar, 2000, Plant Breeding 119:363-364), and indeterminate gametophyte (ig) mutation (Kermicle 1969 Science 166:1422-1424). The disclosures of which are incorporated herein by reference.
Methods for obtaining haploid plants are also disclosed in Kobayashi, M. et al., Journ. of Heredity 71(1):9-14, 1980, Pollacsek, M., Agronomie (Paris) 12(3):247-251, 1992; Cho-Un-Haing et al., Journ. of Plant Biol., 1996, 39(3):185-188; Verdoodt, L., et al., February 1998, 96(2):294-300; Genetic Manipulation in Plant Breeding, Proceedings International Symposium Organized by EUCARPIA, Sep. 8-13, 1985, Berlin, Germany; Chalyk et al., 1994, Maize Genet Coop. Newsletter 68:47; Chalyk, S. T., 1999, Maize Genet. Coop. Newsletter 73:53-54; Coe, R. H., 1959, Am. Nat. 93:381-382; Deimling, S. et al., 1997, Vortr. Pflanzenzuchtg 38:203-204; Kato, A., 1999, J. Hered. 90:276-280; Lashermes, P. et al., 1988, Theor. Appl. Genet. 76:570-572 and 76:405-410; Tyrnov, V. S. et al., 1984, Dokl. Akad. Nauk. SSSR 276:735-738; Zabirova, E. R. et al., 1996, Kukuruza I Sorgo N4, 17-19; Aman, M. A., 1978, Indian J. Genet Plant Breed 38:452-457; Chalyk S. T., 1994, Euphytica 79:13-18; Chase, S. S., 1952, Agron. J. 44:263-267; Coe, E. H., 1959, Am. Nat. 93:381-382; Coe, E. H., and Sarkar, K. R., 1964 J. Hered. 55:231-233; Greenblatt, I. M. and Bock, M., 1967, J. Hered. 58:9-13; Kato, A., 1990, Maize Genet. Coop. Newsletter 65:109-110; Kato, A., 1997, Sex. Plant Reprod. 10:96-100; Nanda, D. K. and Chase, S. S., 1966, Crop Sci. 6:213-215; Sarkar, K. R. and Coe, E. H., 1966, Genetics 54:453-464; Sarkar, K. R. and Coe, E. H., 1971, Crop Sci. 11:543-544; Sarkar, K. R. and Sachan J. K. S., 1972, Indian J. Agric. Sci. 42:781-786; Kermicle J. L., 1969, Mehta Yeshwant, M. R., Genetics and Molecular Biology, September 2000, 23(3):617-622; Tahir, M. S. et al. Pakistan Journal of Scientific and Industrial Research, August 2000, 43(4):258-261; Knox, R. E. et al. Plant Breeding, August 2000, 119(4):289-298; U.S. Pat. No. 5,639,951 and U.S. patent application Ser. No. 10/121,200, the disclosures of which are incorporated herein by reference.
Thus, an embodiment of this invention is a process for making a homozygous PH18K6 progeny plant substantially similar to PH18K6 by producing or obtaining a seed from the cross of PH18K6 and another maize plant and applying double haploid methods to the F1 seed or F1 plant or to any successive filial generation. Such methods decrease the number of generations required to produce an inbred with similar genetics or characteristics to PH18K6. See Bernardo, R. and Kahler, A. L., Theor. Appl. Genet. 102:986-992, 2001.
In particular, a process of making seed substantially retaining the molecular marker profile of maize variety PH18K6 is contemplated, such process comprising obtaining or producing F1 hybrid seed for which maize variety PH18K6 is a parent, inducing double haploids to create progeny without the occurrence of meiotic segregation, obtaining the molecular marker profile of maize variety PH18K6, and selecting progeny that retain the molecular marker profile of PH18K6.
Use of PH18K6 in Tissue Culture
This invention is also directed to the use of PH18K6 in tissue culture. As used herein, the term “tissue culture” includes plant protoplasts, plant cell tissue culture, cultured microspores, plant calli, plant clumps, and the like. As used herein, phrases such as “growing the seed” or “grown from the seed” include embryo rescue, isolation of cells from seed for use in tissue culture, as well as traditional growing methods.
Duncan, Williams, Zehr, and Widholm, Planta (1985) 165:322-332 reflects that 97% of the plants cultured that produced callus were capable of plant regeneration. Subsequent experiments with both inbreds and hybrids produced 91% regenerable callus that produced plants. In a further study in 1988, Songstad, Duncan & Widholm in Plant Cell Reports (1988), 7:262-265 reports several media additions that enhance regenerability of callus of two inbred varieties. Other published reports also indicated that “nontraditional” tissues are capable of producing somatic embryogenesis and plant regeneration. K. P. Rao, et al., Maize Genetics Cooperation Newsletter, 60:64-65 (1986), refers to somatic embryogenesis from glume callus cultures and B. V. Conger, et al., Plant Cell Reports, 6:345-347 (1987) indicates somatic embryogenesis from the tissue cultures of maize leaf segments. Thus, it is clear from the literature that the state of the art is such that these methods of obtaining plants are, and were, “conventional” in the sense that they are routinely used and have a very high rate of success.
Tissue culture of maize, including tassel/anther culture, is described in U.S. 2002/0062506A1 and European Patent Application, publication EP0160,390, each of which are incorporated herein by reference for this purpose. Maize tissue culture procedures are also described in Green and Rhodes, “Plant Regeneration in Tissue Culture of Maize,” Maize for Biological Research (Plant Molecular Biology Association, Charlottesville, Va. 1982, at 367-372) and in Duncan, et al., “The Production of Callus Capable of Plant Regeneration from Immature Embryos of Numerous Zea Mays Genotypes,” 165 Planta 322-332 (1985). Thus, another aspect of this invention is to provide cells which upon growth and differentiation produce maize plants having the genotype and/or phenotypic characteristics of variety PH18K6.
INDUSTRIAL APPLICABILITY
Maize is used as human food, livestock feed, and as raw material in industry. The food uses of maize, in addition to human consumption of maize kernels, include both products of dry- and wet-milling industries. The principal products of maize dry milling are grits, meal and flour. The maize wet-milling industry can provide maize starch, maize syrups, and dextrose for food use. Maize oil is recovered from maize germ, which is a by-product of both dry- and wet-milling industries.
Maize, including both grain and non-grain portions of the plant, is also used extensively as livestock feed, primarily for beef cattle, dairy cattle, hogs, and poultry.
Industrial uses of maize include production of ethanol, maize starch in the wet-milling industry and maize flour in the dry-milling industry. The industrial applications of maize starch and flour are based on functional properties, such as viscosity, film formation, adhesive properties, and ability to suspend particles. The maize starch and flour have application in the paper and textile industries. Other industrial uses include applications in adhesives, building materials, foundry binders, laundry starches, explosives, oil-well muds, and other mining applications.
Plant parts other than the grain of maize are also used in industry: for example, stalks and husks are made into paper and wallboard and cobs are used for fuel and to make charcoal.
The seed of maize variety PH18K6, the plant produced from the seed, the hybrid maize plant produced from the crossing of the variety, hybrid seed, and various parts of the hybrid maize plant and transgenic versions of the foregoing, can be utilized for human food, livestock feed, and as a raw material in industry.







TABLE 1





VARIETY DESCRIPTION INFORMATION - PH18K6



















1.
TYPE: (Describe intermediate types in comments section)






1 = Sweet, 2 = Dent, 3 = Flint, 4 = Flour, 5 = Pop and 6 = Ornamental.


3



Comments: Flint Like













2.
MATURITY: 
Days
Heat Units



Emergence to 50% of plants in silk
51.0
1300



Emergence to 50% of plants in pollen shed
51.0
1300



10% to 90% pollen shed
0.5
12











3.
PLANT 
Value
StDev
Number



Plant Height (to tassel tip) (cm)
80.0
3.63
18



Ear Height (to base of top ear node)
24.0
2.22
18



Length of Top Ear Internode (cm)
16.0
1.08
18


**
Average Number of Tillers per Plant
0.0
0.00
2


**
Average Number of Ears per Stalk
0.9
0.00
2



Anthocyanin of Brace Roots: 1 = Absent, 2 = Faint,
4





3 = Moderate, 4 = Dark





4.
LEAF: 






Width of Ear Node Leaf (cm)
8.7
0.57
18



Length of Ear Node Leaf (cm)
78.8
3.60
18



Number of Leaves above Top Ear
6.3
0.67
18



Leaf Angle: (at anthesis, 2nd leaf above ear to
22.5
3.93
18



stalk above leaf) (Degrees)
















Leaf Color: 
V. Dark Green 





*
Munsell: 
5GY36















Leaf Sheath Pubescence: 1 = none to 9 = like peach fuzz
4




5. 
TASSEL: 






Number of Primary Lateral Branches
5.2
1.63
18



Branch Angle from Central Spike (Degrees)
23.9
7.78
18



Tassel Length: (from peduncle node to tassel tip) (cm)
52.2
2.65
18



Peduncle Length: (From top leaf node to lower branch)(cm)
21.3
2.30
18



Pollen Shed: 0 = male sterile, 9 = heavy shed
6





Bar Glumes (glume bands): 1 = absent, 2 = present
1















Anther Color: 
Pink Orange





*
Munsell: 
2.5YR48






Glume Color: 
Red





*
Munsell: 
10RP38














6a.
EAR (Unhusked ear)
















Silk color: (3 days after silk emergence)
Light Red 





*
Munsell: 
10RP58






Fresh husk color: 
Med. Green 





*
Munsell: 
2.5GY66






Dry husk color: (65 days after 50% silking)
Buff 





*
Munsell: 
10RP38















Ear position at dry husk stage: 1 = Upright, 2 = Horizontal,
2





3 = Pendant






Husk Tightness: (1 = very loose, 9 = very tight)
7





Husk Extension (at harvest): 1 = short(ears exposed),
2





2 = medium (<8 cm), 3 = long (8-10 cm), 4 = v. long (>10 cm)





6b.
EAR (Husked ear data)






Shank Length (cm): 
7.4
2.64
18



Ear Length (cm): 
14.1
1.08
18



Ear Diameter at mid-point (mm)
36.3
1.19
18



Ear Weight (gm): 
97.0
11.54
18



Number of Kernel Rows: 
13.1
1.23
18



Kernel Rows: 1 = indistinct, 2 = distinct
2





Row Alignment: 1 = straight, 2 = slightly curved, 3 = spiral
2





Ear Taper: 1 = slight cylind., 2 = average, 3 = extreme conic.
2




7.
KERNEL (Dried): 






Kernel Length (mm): 
10.3
0.75
18



Kernel Width (mm):
7.7
0.57
18



Kernel Thickness (mm): 
4.2
0.43
18


**
Weight per 100 Kernels (unsized sample) (gm): 
23.0
0.00
2


**
Round Kernels (shape grade) (%)
28.6
5.78
2



Aleurone Color Pattern: 1 = homozygous, 2 = segregating
1





Endosperm Type:






1 = sweet (su1), 2 = extra sweet (sh2), 3 = normal starch,
3





4 = high amylose starch, 5 = waxy starch, 6 = high protein,






7 = high lysine, 8 = super sweet (se), 9 = high oil, 10 = other
















Aleurone Color: 
Yellow 





*
Munsell: 
10YR714






Hard Endosperm Color: 
Yellow 





*
Munsell: 
10YR714














8.
COB: 






Cob Diameter at mid-point (mm): 
19.7
1.13
18













Cob Color: 
White





*
Munsell: 
5Y91





Number is the number of individual plants that were scored.


Value is an average if more than one plant or plot is scored.


* Munsell Glossy Book of color, (A standard color reference). Kollmorgen Inst. Corp. New Windsor, NY.


**Sample number reflects the number of plots where the trait(s) was observed and not the number of individual plants scored.













TABLE 2







Inbred PH18K6 platform BLUP breeding values











Weighted



Trait
BLUP value














ANTROT
5.0



BORBMN
55.7



BRLPNE
64.4



BRLPNL
92.3



BRTSTK
96.0



DIGENG
1812.7



EARHT
44.5



ERTLPN
86.1



EXTSTR
66.7



FUSERS
3.8



GDUSHD
125.5



GDUSLK
123.5



GIBERS
7.8



GLFSPT
4.7



GOSWLT
6.5



HDSMT
94.2



HSKCVR
5.3



HTFRM
38.3



LRTLPN
78.2



MILKLN
41.8



MST
19.2



NLFBLT
6.0



PLTHT
114.6



STAGRN
4.0



STKCTE
92.5



STLLPN
78.9



STLPCN
94.1



TSTWT
57.9



TSTWTN
57.5



YIELD
192.3

















TABLE 3





Inbred PH18K6 as parent in hybrid





















BRLPNE
BRLPNL
BRTSTK















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)




95.1
1.7


Hybrid2
(a,b)
60.0
6.5
80.4
4.9
95.4
1.7


Hybrid3
(a)
59.8
5.6
82.9
3.7
96.0
1.5


Hybrid4
(a,b)




96.6
1.5
















DIGENG
EARHT
ERTLPN















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)


47.8
0.5
88.8 
2.9


Hybrid2
(a,b) 
1810.6
4.7
47.9
0.5
87.1
2.8


Hybrid3
(a)
1811.5
4.1
47.7
0.7
84.7
2.9


Hybrid4
(a,b)


49.3
0.7
84.3
2.9
















EXTSTR
GDUSHD
GDUSLK















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)


128.2
0.8
126.1
0.6


Hybrid2
(a,b)
66.2
0.3
127.0
0.8
125.0
0.6


Hybrid3
(a)
67.3
0.2
131.3
0.8
130.1
0.8


Hybrid4
(a,b)


131.0
0.8
129.6
0.8
















GLFSPT
GOSWLT
HDSMT















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)








Hybrid2
(a,b)
5.0
0.3
6.5
0.4
93.4
3.5


Hybrid3
(a)
4.5
0.2
6.7
0.3
94.3
4.3


Hybrid4
(a,b)
4.8
0.3
















HTFRM
LRTLPN
MILKLN















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)


79.6
4.2
40.8
2.8


Hybrid2
(a,b)
38.2
0.1
85.8
4.0
40.3
2.8


Hybrid3
(a)
38.4
0.1
85.2
5.2




Hybrid4
(a,b)


84.9 
5.3
















MST
NLFBLT
PLTHT















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)
19.4
0.1
5.8
0.4
118.0
0.7


Hybrid2
(a,b)
18.9
0.1
5.3
0.3
116.1
0.7


Hybrid3
(a)
18.8
0.1
6.3
0.3
118.9
0.9


Hybrid4
(a,b)
19.1
0.1
6.1
0.3
119.0
0.9
















STAGRN
STKCTE
STLLPN















ftnote
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)
4.6
0.3
91.6
0.6




Hybrid2
(a,b)
4.3
0.4
90.8
0.5
88.8
5.0


Hybrid3
(a)
4.2
0.2
87.5
0.6
78.7
4.2


Hybrid4
(a,b)
4.8
0.3
87.4
0.6
















STLPCN
TSTWT
TSTWTN















ftnote 
BLUP
SE
BLUP
SE
BLUP
SE





Hybrid1
(a,b)
90.8
2.9
57.6
0.1
57.0
0.1


Hybrid2
(a,b)
90.8
2.8
57.2
0.1
56.6
0.1


Hybrid3
(a)
87.1
3.0
57.3
0.1
57.0
0.1


Hybrid4
(a,b)
84.6
3.0
57.3
0.1
56.9
0.1














YIELD











ftnote
BLUP
SE





Hybrid1
(a,b)
197.8
1.5


Hybrid2
(a,b)
191.7
1.5


Hybrid3
(a)
194.0
1.6


Hybrid4
(a,b)
196.1
1.6





a wherein inbred comprises a trait conversion conferring insect control


b wherein inbred comprises a trait conversion conferring herbicide tolerance


c wherein inbred comprises a trait conversion conferring disease control






DEPOSITS
Applicant has made a deposit of at least 2500 seeds of Maize Variety PH18K6 with the American Type Culture Collection (ATCC), 10801 University Boulevard, Manassas, Va. 20110-2209, USA, with ATCC Deposit No. PTA-120185. The seeds deposited with the ATCC on Apr. 12, 2013 were obtained from the seed of the variety maintained by Pioneer Hi-Bred International, Inc., 7250 NW 62nd Avenue, Johnston, Iowa, 50131 since prior to the filing date of this application. Access to this seed will be available during the pendency of the application to the Commissioner of Patents and Trademarks and persons determined by the Commissioner to be entitled thereto upon request. Upon allowance of any claims in the application, the Applicant will make the deposit available to the public pursuant to 37 C.F.R. §1.808. This deposit of the Maize Variety PH18K6 will be maintained in the ATCC depository, which is a public depository, for a period of 30 years, or 5 years after the most recent request, or for the enforceable life of the patent, whichever is longer, and will be replaced if it becomes nonviable during that period. Additionally, Applicant has or will satisfy all of the requirements of 37 C.F.R. §§1.801-1.809, including providing an indication of the viability of the sample upon deposit. Applicant has no authority to waive any restrictions imposed by law on the transfer of biological material or its transportation in commerce. Applicant does not waive any infringement of rights granted under this patent or under the Plant Variety Protection Act (7 USC 2321 et seq.).

## Claims

1. A seed of inbred maize variety PH18K6, representative seed of said variety having been deposited under ATCC accession number PTA-120185.

2. A method of collecting molecular data comprising isolating nucleic acids contained in the seed of claim 1, analyzing said nucleic acids, and recording data based on the nucleic acids.

3. A plant, plant part, or cell produced by growing the seed of inbred maize variety of claim 1.

4. A method of collecting molecular data comprising isolating nucleic acids contained in the plant, plant part, or cell of claim 3, analyzing said nucleic acids, and recording data based on the nucleic acids.

5. A maize seed produced by crossing the plant or plant part of claim 3 with a different maize plant.

6. A maize plant produced by growing the maize seed of claim 5.

7. A method for producing a second maize plant comprising applying plant breeding techniques to a first maize plant, or parts thereof, wherein said first maize plant is the maize plant of claim 6, and wherein application of said techniques results in the production of said second maize plant.

8. The method of claim 7, further defined as producing a maize plant derived from the inbred maize variety PH18K6, the method comprising the steps of:
(a) crossing said first maize plant with itself or another maize plant to produce seed of a subsequent generation;
(b) harvesting and planting the seed of the subsequent generation to produce at least one plant of the subsequent generation; and
(c) repeating steps (a) and (b) for an additional 2-10 generations to produce a maize plant derived from maize variety PH18K6.

9. An inbred maize plant derived from the inbred maize variety PH18K6 produced by the method of claim 8, wherein said inbred maize plant has essentially the same morphological and physiological characteristics as inbred maize variety PH18K6 when grown under the same environmental conditions.

10. The method of claim 7, further defined as producing an inbred maize plant derived from maize variety PH18K6, the method comprising the steps of:
(a) crossing said first maize plant with an inducer variety to produce haploid seed; and
(b) doubling the haploid seed to produce an inbred maize plant derived from maize variety PH18K6.

11. The inbred maize plant derived from the inbred maize variety PH18K6 produced by the method of claim 10, wherein said inbred maize plant has essentially the same morphological and physiological characteristics as inbred maize variety PH18K6 when grown under the same environmental conditions.

12. A converted seed of inbred maize variety PH18K6, representative seed of said variety having been deposited under ATCC accession number PTA-120185; wherein said converted seed comprises a locus conversion; and wherein said converted seed grows into a plant having essentially the same morphological and physiological characteristics as maize variety PH18K6 when grown under the same environmental conditions.

13. The converted seed of claim 12, wherein the locus conversion confers a trait selected from the group consisting of male sterility, site-specific recombination, abiotic stress tolerance, altered phosphorus, altered antioxidants, altered fatty acids, altered essential amino acids, altered carbohydrates, herbicide tolerance, insect resistance and disease resistance.

14. A method of collecting molecular data comprising isolating nucleic acids contained in the converted seed of claim 12, analyzing said nucleic acids, and recording data based on the nucleic acids.

15. A plant or plant part produced by growing the converted seed of the inbred maize variety PH18K6 of claim 12.

16. A method of collecting molecular data comprising isolating nucleic acids contained in the plant, plant part, or cell of claim 15, analyzing said nucleic acids, and recording data based on the nucleic acids.

17. A maize seed produced by crossing the plant or plant part of claim 15 with a different maize plant.

18. A maize plant produced by growing the seed of claim 17.

19. A method for producing a second maize plant comprising applying plant breeding techniques to a first maize plant, or parts thereof, wherein said first maize plant is the maize plant of claim 18, and wherein application of said techniques results in the production of said second maize plant.

20. The method of claim 19, further defined as producing a maize plant, the method comprising the steps of:
(a) crossing said first maize plant with itself or another maize plant to produce seed of a subsequent generation;
(b) harvesting and planting the seed of the subsequent generation to produce at least one plant of the subsequent generation; and
(c) repeating steps (a) and (b) for an additional 2-10 generations to produce a maize plant.

21. An inbred maize plant derived from the inbred maize variety PH18K6 produced by the method of claim 20, wherein said inbred maize plant has essentially the same morphological and physiological characteristics as inbred maize variety PH18K6 when grown under the same environmental conditions.

22. The method of claim 19, further defined as producing a maize plant, the method comprising the steps of:
(a) crossing said first maize plant with an inducer variety to produce haploid seed; and
(b) doubling the haploid seed to produce an inbred maize plant.

23. The inbred maize plant derived from the inbred maize variety PH18K6 produced by the method of claim 22, wherein said inbred maize plant has essentially the same morphological and physiological characteristics as inbred maize variety PH18K6 when grown under the same environmental conditions.