bluuebunny/crossref_metadata_2025 huggingface dataset:
Grazing Termination Date Influence on Annual Ryegrass Seed Production and Reseeding in the Southeastern USA
Authors: Evers Gerald W. , Nelson Lloyd R.
Published: July 2010

Production costs could be reduced if annual ryegrass (Lolium multiflorum Lam.) could be managed for reseeding. Spring grazing termination dates (GTD) of 31 March, 14 April, 28 April, and 12 May were evaluated on seven cultivars for two growing seasons to study spring seed production and volunteer reseeding the following autumn in northeast Texas. There were year × GTD × cultivar interactions for spike density, seed yield, seed weight per spike, and volunteer seedling density and a year × GTD interaction for 1000‐seed weight. Moisture conditions were good during the 1994‐1995 growing season followed by a dry summer. Spike density was high (1256 ± 59 spikes m−2), seed yields were low (48.7 ± 3.2 g m−2), but seed weight was high with a 1000‐seed weight of 3.12 ± 0.03 mg. All cultivars exceeded the 500 seedlings m−2 target in 1995 when grazed through 28 April. In the 1996‐1997 growing season, May was very dry followed by high June rainfall. Spike density was lower but seed yields were higher than in 1995. However, 1000‐seed weight was only 1.37 mg. Only `Surrey' exceeded 500 seedlings m−2 through 28 April GTD, `TAM 90' through 14 April GTD, and `Rio', `Gulf', and `Jackson' at only one of the two early GTDs. The superior reseeding ability of Surrey is probably due to its selection for a high level of high temperature dormancy. In normal rainfall years in the southeastern USA, most cultivars of annual ryegrass can be grazed until late April and still produce satisfactory volunteer stands the following autumn.
Genetic Base of Japanese Soybean Cultivars Released during 1950 to 1988
Authors: Zhou Xingliang , Carter Thomas E. , Cui Zhanglin , Miyazaki Shoji , Burton Joseph W.
Published: July 2010

Plant breeding success is dependent, in part, upon the genetic diversity found within applied breeding programs. To characterize genetic diversity in applied breeding, plant breeders have invoked the concept of genetic base, which can be defined as the ancestral pool from which breeding is derived. The genetic base of modern Japanese soybean [Glycine max (L.) Merr.] cultivars is not well characterized. The objective of this study was to quantify the genetic base of Japanese soybean cultivars by coefficient of parentage (CP) analysis, to compare the genetic bases of major growing regions and release eras in Japan, and to compare the Japanese base with that of other countries. Seventy‐four ancestors were identified in the pedigrees of 86 public Japanese cultivars registered from 1950 to 1988. Ancestors originating from Japan contributed 76% of the genes to the Japanese breeding, while exotic ancestors from the USA and Canada (US‐CAN), China, and Korea contributed 2, 5, and 2%, respectively. The remaining portion of the base was of unknown, but presumed Japanese origin. Three major growing regions of Japan displayed very distinct genetic bases with at least 50% of the ancestral contribution unique to each region. Comparisons revealed that the Japanese base was more diverse than that of the US‐CAN. The more diverse genetic base was exemplified by (i) more ancestors accounting for 50 and 80% of the genes in Japanese breeding; (ii) a continual expansion of the genetic base since 1950, while the US‐CAN base remained relatively static; and (iii) a higher ratio of ancestors employed to cultivars released. The number of ancestors contributing to breeding in Japan was much smaller than that for China in terms of number of ancestors, even though both genetic bases expanded with time. The long history of soybean breeding in Japan, its diverse genetic base and its relative isolation from US‐CAN and China suggest that Japanese, Chinese, and North American breeding pools may serve as important reservoirs of diversity for each other. Twelve Japanese cultivars released from 1950 through 1988 derived at least 25% of their pedigree from improved U.S. or Chinese breeding materials.
Antioxidant Activity and Phenolic Content of Oat as Affected by Cultivar and Location
Authors: Emmons Cheryld L. , Peterson David M.
Published: July 2010

Phenolic compounds in oat (Avena sativa L.) may have health‐promoting effects on humans due to their antioxidant or other properties. The objective of this study was to determine the effects of cultivar and location on phenolic contents and antioxidant activities of alcohol‐soluble extracts from oat groats. Antioxidant activities (AOA) and concentrations of eight phenolic compounds having AOA were measured in three cultivars grown at seven locations in Wisconsin during 1998. There were significant differences among cultivars for AOA, concentrations of all of the phenolic compounds measured except p‐coumaric and ferulic acids, and for total free phenolic contents (FPC). Location significantly affected the concentrations of five of the phenolics and total FPC, but did not affect AOA. There were significant cultivar × location interactions for the concentrations of avenanthramides and for total FPC. The unexpectedly high concentrations of avenanthramides from the Sturgeon Bay location were confirmed by analysis of groats from 1999 and 2000. It should be possible to improve the AOA and phenolic concentrations of oat as quantitative traits in a cultivar development program, but significant location effects may attenuate rapid progress.
Ear Temperature and Pollination Timing Effects on Maize Kernel Set
Authors: Cárcova Jorgelina , Otegui María E.
Published: July 2010

Maize (Zea mays L.) kernel set can be improved through synchronous pollination within and between ears. Reductions in kernel set could be expected because of asynchronous pollination between early‐ and late‐appearing silks. We analyzed the effect of (i) selective ear heating around the time of silking, and (ii) different time gaps between early‐ and late‐pollinated silks in an attempt to modify kernel set. Tip ear heating was expected to minimize the advantage of early silking ovaries. Lateral heating and pollination gaps were expected to exaggerate this advantage. Three pollination gaps (2, 4, and 6 d) were tested for two plant populations (3 and 9 plants m−2). Ear temperature in the heated zone averaged 4.5°C above air temperature. Temperature in the nonheated side closely followed air temperature. Treatments promoted greater differences in maize kernel number (KN) per ear (73% variation) than in the number of silks exposed 5 d after silking (6% variation). Lateral ear heating reduced KN per ear in comparison with the nonheated control, but tip ear heating did not modify KN per ear. At 9 plants m−2, synchronous pollination resulted in ∼15% increase in KN per plant. Pollination gaps of 2 and 4 d reduced KN per plant drastically (up to 51%), but the reduction was smaller for the 6‐d gap. This study (i) gives evidence of the negative impact of delayed pollination timing among silks on kernel set, which was not related to reduced silk receptivity, and (ii) defines the time gap for maximum interference of early‐ on late‐pollinated ovaries, a period shorter than 4 d.
Seed Germination and Dormancy in Eastern Gamagrass
Authors: Springer T. L. , Dewald C. L. , Aiken G. E.
Published: July 2010

Eastern gamagrass [Tripsacum dactyloides (L.) L.] is an important native rangeland species and could be a more widely used perennial pasture grass. Stand establishment, however, is slow, and it can take 3 yr before a full stand is attained. Our objectives were to determine the caryopsis weight distribution, the relationship between caryopsis weight and percentage germination, the role of the cupulate fruit case in seed dormancy, and the force required to open the cupulate fruit case. Caryopses of ‘Iuka’ and ‘Pete’ eastern gamagrass were extracted from the cupulate fruit case by hand, individually weighed, separated into five weight classes, and germinated in a germination chamber. Differences in percentage observed germination and total potential germination at 7 and 14 d were attributed to caryopsis weight (P > 0.05). No caryopsis weight × cultivar interaction occurred, suggesting homogeneity of slopes for cultivars (P > 0.25). An artificial fruit case (band) was fashioned from an extruded plastic tube and a caryopsis placed inside to examine the role of the fruit case in germination. Germination of unbanded caryopses (44.8%) was significantly greater than banded caryopses (6.3%, P ≤ 0.01). A lever and fulcrum were used to find the force required to open the fruit case. We concluded that seed dormancy was likely mechanical for these cultivars. Under natural conditions, the integrity of the fruit case must be reduced before germination will proceed normally. Light, alternating temperatures, freezing and thawing, fire, rodents, and soil microorganisms, to name a few, may be involved in the decay of the fruit case.
A Retrospective DNA Marker Assessment of the Development of Insect Resistant Soybean
Authors: Narvel James M. , Walker David R. , Rector Brian G. , All John N. , Parrott Wayne A. , Boerma H. Roger
Published: July 2010

There has been limited success over the past 30 yr in the development of superior soybean cultivars [Glycine max (L.) Merr] with insect resistance. Success may be hampered by the quantitative nature of resistance and by linkage drag from resistant plant introduction (PI) donor parents. Soybean insect resistance quantitative trait loci (SIR QTLs) have been identified from PI 229358 and PI 171451 by restriction fragment length polymorphism (RFLP) analysis. The objective of this study was to tag the SIR QTLs from PI 229358 with simple sequence repeat (SSR) markers and to determine the extent to which the SIR QTLs have been introgressed in registered cultivars, germplasm releases, or breeding lines that have resistance derived from this PI or from PI 171451. Marker analysis defined intervals by 5 centimorgans (cM) or less for a SIR QTL on linkage group D1b (SIR‐D1b), and for SIR‐G, SIR‐H, and SIR‐M. SIR QTLs were tracked through pedigrees by evaluating the inheritance of PI alleles at marker loci tightly linked to the QTLs during the phenotypic selection for insect resistance. It was inferred that at least 13 of the 15 SIR genotypes studied had introgressed SIR‐M. PI genome introgression around SIR‐M was measured to assess linkage drag. Some genotypes exhibited a dramatic reduction in the amount of linked PI genome, which likely occurred in response to phenotypic selection for agronomic performance as a means of reducing linkage drag. Only a few genotypes were inferred to possess SIR‐G or SIR‐H, and no genotypes possessed SIR‐D1b. The results of this study indicate that marker‐assisted selection for SIR QTLs is needed to introgress these loci into elite genetic backgrounds.
Genetic Diversity and Population Structure of Wild Lentil Tare
Authors: Huh Man Kyu , Huh Hong Wook
Published: July 2010

Genetic diversity has been studied extensively in the cultivated faba bean (Vicia faba L.). Compared with other ecologically and economically significant herbaceous species, population structure of lentil tare, Vicia tetrasperma (L.) Schreber (Leguminosae), has not been studied. The objectives of this study were to estimate the level of genetic diversity in the species and to describe how its genetic variation is distributed within and among its populations. The percentage of polymorphic loci was 50.0%. Genetic diversity was high at both the species and population levels , whereas the extent of the population divergence was relatively low In the hierarchical analysis, a great amount of variance was exhibited among populations with respect to regions and a large component of the value was explained by variance among regions with respect to the total The results were consistent with the strong geographic effect indicated by unweighted pairwise groups method using arithmetic average (UPGMA) and Mantel's test. The correlation between genetic distance and geographic distance by Mantel's test was high and significant Fis, a measure of the deviation from random mating within populations, was 0.503, indicating that V. tetrasperma is an inbreeding species. An indirect estimate of the number of migrants per generation indicated that gene flow was high among populations. Nearly 88.4% of the total genetic diversity in V. tetrasperma was apportioned within populations. The wide geographic ranges, wild condition of the species, and high fecundity are proposed as possible factors contributing to high genetic diversity.
A Description and Interpretation of the NPGS Birdsfoot Trefoil Core Subset Collection
Authors: Steiner J. J. , Beuselinck P. R. , Greene S. L. , Kamm J. A. , Kirkbride J. H. , Roberts C. A.
Published: July 2010

Systematic evaluations for a range of traits from accessions in National Plant Germplasm System (NPGS) core subset collections should assist collection management and enhance germplasm utilization. The objectives of this research were to: (i) evaluate the 48‐accession NPGS birdsfoot trefoil (Lotus corniculatus L.) core subset collection by means of a variety of biochemical, morphological, and agronomic characters; (ii) determine how these characters were distributed among the core subset accessions and associations among plant and ecogeographic characters; (iii) define genetic diversity pools on the basis of descriptor interpretive groups; and (iv) develop a method to utilize the core subset as a reference collection to evaluate newly acquired accessions for their similarity or novelty. Geographic information system (GIS) databases were used to estimate the ecogeography of accession origins. Interpretive groups were constructed to describe the range of core subset descriptor variation by cluster analysis and verified by discriminant analysis. Associations among plant descriptors and with ecogeographic characteristics were determined by Pearson's correlation coefficients or the Mantel Z statistic. The accessions were classified into four distinct genetic diversity pools that were described by plant traits and ecogeographic origins. The core subset used as a reference collection successfully classified three unique accessions not originally included in the core subset. This approach identified germplasm that was different from that present in most North American cultivars and can be used to evaluate future acquisitions. The concepts of interpretive groups, genetic diversity pools, and reference collection comparisons should be applicable for assessing and managing other core subset collections.
Analysis of Resource Allocation in Final Stage Sugarcane Clonal Selection
Authors: Brown J.Steven , Glaz Barry
Published: July 2010

Superior genotypes of sugarcane (interspecific hybrids of Saccharum spp.) must continue to be developed with current resources as selection criteria evolve and expand. Developing future cultivars of sugarcane for the Everglades Agricultural Area (EAA) of South Florida with high water table tolerance and increased P‐uptake efficiency could be an integral part of Everglades restoration. The objective of this study was to assess the current allocation of resources in the final selection phase of cultivar (clonal) development of the Canal Point, FL, sugarcane breeding program. Variance component analyses were conducted on elite genotypes from 7 yr of trials. Variance components were used to compare relative magnitudes of sources of variation and to explore more efficient use of resources. Variation attributable to crop × location interaction was nearly always the largest relative source of variation next to the residual term. The contributions to variance due to genotype × crop and genotype × location interactions were low, though these interactions cannot be discounted in cultivar release decisions. Variance due to replications was extremely low. Four statistics were used as metrics of experimental precision when reducing the number of replications. Reducing replications from eight to four did not compromise experimental precision. Removing the second‐year planting sequence compromised little, if any, useful information for effective cultivar release decisions. Better allocation of resources could be achieved by alternative experimental design scenarios. Testing for high water table tolerance or P‐uptake efficiency could also be included, improving ecological compatibility of agriculture in the EAA.
Gas Exchange and Water Relations in Diploid and Tetraploid Russian Wildrye
Authors: Frank A.B. , Berdahl J.D.
Published: July 2010

Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski] is a drought tolerant, cool‐season forage grass used in seeded pastures in the Northern Great Plains where water often limits production. Seedling vigor is generally poor in diploid cultivars, but tetraploid germplasm has improved seedling vigor. Objectives of this study were to determine the relationships between water‐use efficiency (WUE), carbon isotope discrimination (CID), and gas exchange rates for a diploid cultivar (Vinall) and a tetraploid entry over 3 yr, two water treatments (50 and 150% of mean monthly precipitation), and two fertilizer rates (10 and 134 kg N ha−1) in a rain shelter. The tetraploid entry exhibited higher carbon exchange rate (CER), stomatal conductance (gs), and transpiration (T) than the diploid entry at the 50% but not the 150% water treatment. Leaf water potentials (LWP) were 0.6 and 0.3 MPa less negative for the tetraploid entry than diploid entry at the 50 and 150% water treatment, respectively. Values of CER averaged 12.4 and 14.2 μmol m−2 s−1, T averaged 5.2 and 6.0 mmol m−2 s−1, and gs averaged 0.21 and 0.28 mol m−2 s−1 for the diploid and tetraploid entry, respectively. The diploid entry had a significantly greater CID, averaging 20.37‰ compared with 19.65‰ for the tetraploid entry and CID was negatively associated with WUE. The more favorable plant water relations, gas exchange, and dry matter production under limited soil water suggests tetraploid populations of Russian wildrye should be emphasized in future breeding and management programs.
CMS‐D8 Restoration in Cotton Is Conditioned by One Dominant Gene
Authors: Zhang J.F. , Stewart J.McD.
Published: July 2010

Cytoplasmic male sterile (CMS‐D8) and fertile restorer lines (D8R) of cotton (Gossypium hirsutum L.) (AD1) were developed by transferring the cytoplasm and nuclear gene(s) from G. trilobum (DC.) Skovst. (D8) into the cotton nuclear background. Understanding the genetics of fertility restoration in this CMS system is essential for its use in a hybrid breeding system. The objective of this investigation was to determine the mode of inheritance of D8R restoration to CMS‐D8. The experimental approach involved a series of crossing schemes involving nuclear permutations among the AD1 and D8 alloplasms. Eighteen normal genotypes did not restore fertility to the CMS‐D8 (A line) and could be used as maintainer (B) lines. D8R crossed as female with B lines yielded F1 and F2 populations with all fertile plants. F1 pollen also produced all fertile progeny in crosses on A lines. Thus, the D8 restorer functions at the gametophytic level. When heterozygous restored plants were pollinated with B lines, or when reciprocal F1's with normal cytoplasm were crossed as male with the A line, the progeny ratio was one fertile to one sterile. A 3:1 ratio was obtained when restored F1 plants with D8 cytoplasm were pollinated by their reciprocal F1's with normal cytoplasm. Accordingly, restoration of CMS‐D8 by the D8R restorer is conditioned by a single dominant gene (Rf2). The genotypes for A, B, and D8R lines in the CMS‐D8 system are designated S (rf2rf2), N (rf2rf2), and S (Rf2Rf2), respectively. This gametophytic restoration system is potentially useful for utilizing F2 heterosis in cotton.
Family and Line Selection for Seed Yield of Soybean
Authors: Streit Leon G. , Fehr Walter R. , Welke Grace A.
Published: July 2010

Plant‐row‐yield tests (PRYT) are used by soybean [Glycine max (L.) Merr.] breeders for the initial evaluation of experimental lines. The highest yielding lines in the PRYT are advanced for additional testing in replicated tests. The objective of this study was to determine the reliability of selection for seed yield in unreplicated plots by the family and line methods of selection. Four F3‐derived lines from each of 21 F2 families from four populations were grown in a PRYT during 1995 and in replicated tests at four environments in 1996. For the family method, the mean seed yield of the four F3‐derived lines of each F2 family was used to identify superior families from which to select individual lines. For the line method, lines were selected without regard to the family structure. The seed yield of the selected and unselected lines on the basis of data from the PRYT was compared with their mean seed yield in the 1996 environments. The total number of lines selected by the family method was less than for the line method in all populations. The percentage of selected lines that were correctly classified was similar for both methods. There was a greater percentage of lines incorrectly rejected by the family method than by the line method. The use of replication at an individual location did not improve the selection of lines by the family or line methods of selection. For the selection of lines for seed yield in unreplicated plots, breeding methods that rely on family performance would not be more effective or efficient than methods that ignore family structure. To obtain lines for yield tests at multiple locations, selection of lines by the line method on the basis of their performance in a PRYT would be better than the use of random lines.
Diurnal Fluctuations of Nitrate Uptake and In Vivo Nitrate Reductase Activity in Pima and Acala Cotton
Authors: Aslam M. , Travis R.L. , Rains D.W.
Published: July 2010

This study was conducted to determine whether diurnal fluctuations of nitrate reductase activity in two cotton species, Pima (Gossypium barbadense L.) and Acala (Gossypium hirsutum L.), are regulated by NO−3 uptake or leaf NO−3 concentration. The two species differ greatly in their N use efficiency. The seedlings were grown for 25 d in nutrient solutions containing 0.05, 0.10 or 1.0 mM NO−3 under a 14‐h light/10‐h dark cycle at 30°C/20°C. Uptake rates were measured by following NO−3 depletion from the uptake solutions at 20°C or 30°C. Nitrate reductase activity (NRA) in fully expanded first true leaves was determined by an anaerobic method in vivo. Upon illumination uptake rates for both species, measured at 30°C, increased until they plateaued in about 5 h and were maintained at that level for the remainder of the light period and the following dark cycle. When measured at 20°C in the dark, however, the uptake rates decreased 25 to 30% for the first 3 h and then remained constant. Leaf NRA increased rapidly during the first hour of illumination, reached a plateau and then decreased after 4 to 6 h of illumination. The decline was more rapid when NRA was assayed in the absence of NO−3 In darkness, NRA levels were low and did not fluctuate. Upon illumination, leaf NO−3 concentration also increased for about 7 h and then decreased gradually. The results indicate that (i) the diurnal rhythm of NO−3 uptake is modulated by temperature rather than by light/dark transitions, and (ii) while the increase in NRA upon illumination may be regulated by NO−3 flux from roots to shoots, the decrease in NRA under prolonged illumination is independent of that flux.
Carbon Dioxide and Temperature Effects on Forage Dry Matter Production
Authors: Newman Y.C. , Sollenberger L.E. , Boote K.J. , Allen L.H. , Littell R.C.
Published: July 2010

Atmospheric CO2 and temperature may significantly modify plant production. Grasslands occupy in excess of 25% of the Earth's land area, but grassland species have received limited attention from researchers studying climate change. A 3‐yr study was conducted to determine the effects of elevated atmospheric CO2 and temperature on dry matter (DM) harvested from the C3 legume ‘Florigraze’ rhizoma peanut (RP, Arachis glabrata Benth.) and the C4 grass ‘Pensacola’ bahiagrass (BG, Paspalum notatum Flügge). Both species were field grown in Millhopper fine sand (loamy siliceous Grossarenic Paleudult) in temperature‐gradient greenhouses under different CO2 (360 and 700 μmol mol−1) and temperature conditions (baseline [B], B+1.5, B+3.0, and B+4.5°C, where B equaled ambient temperature). Plots (2 by 5 m) were harvested three times in 1996 and four times each in 1997 and 1998. Analyzed across years, yield increased 25% for RP (P = 0.02) and tended to increase for BG (15%; P = 0.18) with the near doubling of CO2, but there was species by CO2 interaction (P = 0.06) as a result of the greater response to CO2 by the C3 legume. There was a positive effect of increasing temperature on yield of both species. Averaged across species, yield increased 11% in 1996, 12% in 1997, and 26% in 1998 as temperature increased from B to B+4.5°C. Under well‐watered conditions in this experiment, elevated CO2 increased DM harvested of a C3 legume and tended to increase that of a C4 grass, while the yield response to increasing temperature was positive for both species.
Wheat Grain and Forage Yields are Affected by Planting and Harvest Dates in the Central Great Plains
Authors: Lyon Drew J. , Baltensperger David D. , Siles Melicio
Published: July 2010

Although grazing of winter wheat (Triticum aestivum L.) is a common practice in the southern Great Plains, little is known about the efficacy of wheat as a dual‐purpose crop in the Nebraska Panhandle. The objective of this study was to evaluate the effects of establishment and harvest times on forage and grain production of wheat cultivars adapted to the region. Six cultivars were planted at four dates (very early, recommended early, recommended late, and very late) in each of 3 yr. Forage samples were taken from a previously nonharvested area late in the fall, at jointing, and at the boot stage. Grain yield at maturity was measured from each forage harvest treatment and from a full‐season unharvested control. In 2 of 3 yr, grain yield was reduced an average of 25% compared with the full‐season check when plants were harvested for forage at the joint stage. No grain was produced when forage was removed at the boot stage. Forage removal during the fall averaged 1300 kg ha−1 dry matter and resulted in insignificant losses in grain yield. While most of the fall growth was too low to the ground for clipping, it could provide high‐value supplemental grazing on account of the high crude protein (310 g kg−1) and in vitro organic matter digestibility (800 g kg−1) levels. Spring grazing in this region is limited to the time prior to jointing if market conditions favor grain production.
Population Diallel of Elite Medium‐ and Long‐Duration Pearl Millet Composites: I. Populations and Their F1 Crosses
Authors: Ali Adam Mohamed , Hash C.Tom , Ibrahim Abu Elhassan S. , Raj A.G.Bhasker
Published: July 2010

Pearl millet [Pennisetum glaucum (L.) R. Br.] varieties grown in semiarid Africa and Asia have low grain yields. Information on heterosis and combining ability of diverse open‐pollinated cultivars, breeding populations, and genepools is needed for efficient choice of breeding methods and parental materials to use in developing productive base populations for this crop. Data for grain and biomass yield, growth rate, time to flowering, plant height, panicle length, and productive tillers were collected from an 11‐parent variety cross diallel of diverse pearl millet populations evaluated in five field environments in peninsular India. Data were summarized using the Gardner–Eberhart Analysis II. When genotype × environment interactions were significant, ranks of parental general combining abilities (GCA) were used to identify particular environments and parents contributing most to these interactions. Parental population effects were significant for all characters, as were differences in GCA. Populations NWC C2, AfPop 88, and LHGP consistently had the poorest ranks for general combining ability for grain yield across test environments. Populations ICMV 91059, SenPop, ICMP 91751, and ICMP 92951 constitute a genetically diverse subset of the parents that consistently had the best ranks for grain yield GCA across test environments. With ICMV 155 (crosses of which performed poorly in only one of five test environments), this latter group is a good source of more broad‐based breeding populations for dual‐purpose pearl millet improvement targeting peninsular India.
Grain Yield and Yield Components of Doublecropped Winter Wheat as Affected by Wheat and Previous Soybean Production Practices
Authors: Frederick James R. , Bauer Philip J. , Busscher Warren J.
Published: July 2010

Development and grain yield of doublecropped winter wheat (Triticum aestivum L.) are influenced by the production practices used to produce the wheat crop and potentially by those used to produce the previous crop. This 2‐yr field study was conducted on a Goldsboro loamy sand (fine‐loamy, siliceous, thermic Aquic Kandiudult) to determine whether production practices used in the spring to produce the previous soybean [Glycine max (L.) Merr.] crop affect wheat grain yield and yield component responses to fall production practices. Treatments were deep tillage the previous spring prior to planting soybean using row widths of 19 or 76 cm, deep tillage in the fall prior to wheat planting, deep tillage in both the spring and fall, and no deep tillage for wheat planted with and without surface tillage. Fall deep tillage was the only treatment that consistently increased grain yield and all of the yield components; increasing grain yield, fertile head number per square meter, kernel number per head, and individual kernel weight by an average of 27, 11, 10, and 3%, respectively, over all other treatments. Grain yield and kernel number per square meter responses to fall deep tillage were greatest with no spring deep tillage, with no surface tillage, or when the previous soybean was grown using 76‐cm‐row widths. Grain yield, fertile head number per square meter, and kernel weight were all higher without surface tillage than with surface tillage. Results from this study show that production practices used to produce the previous soybean crop, such as row width and spring deep tillage, can have a significant effect on the grain yield and yield component responses of wheat to fall production practices.
Breeding Behavior of the Cytogenetically Engineered Wheat‐Rye Translocation Chromosomes 1RS.1BL
Authors: Lukaszewski Adam J.
Published: July 2010

The rye (Secale cereale L.) chromosome arm in the wheat‐rye centric translocation 1RS.1BL in wheat (Triticum aestivum L.) had been engineered by induced homoeologous recombination to remove the associated breadmaking quality defect. From a range of primary wheat‐rye recombinant chromosomes, two classes of multipoint translocated chromosomes were assembled, MA and Te, that contain Gli‐B1 and Glu‐B3 loci of wheat and are missing the Sec‐1 locus of rye. Their disassembly rates by recombination with normal 1BS and 1RS and the segregation ratios from heterozygotes were studied in populations involving the original, unmodified translocation 1RS.1BL and chromosomes 1B from several wheat cultivars. Overall, the four‐point translocation chromosomes MA recombined with 1BS with 4.4% frequency; their intercalary rye segment recombined with 1RS with 3.2% frequency. The overall recombination frequency of the three‐point translocation chromosome Te1 with 1BS was 18.1% but only 5.4% resulted in the disassembly of the chromosome. The remaining 12.7% recombination was in the terminal wheat segment and in most cases it introduced new alleles at the wheat storage protein loci. The male transmission rate of all engineered chromosomes was similar to that of the original 1RS.1BL translocation. In competition with 1B, it was reduced to about 22 to 37%. As a result of the disassembly and reduced transmission, the probability of selection of homozygotes for unaltered engineered chromosomes among the progenies of heterozygotes with 1B was about 15 to 16%.
DNA Endoreduplication in Maize Endosperm Cells is Reduced by High Temperature During the Mitotic Phase
Authors: Engelen‐Eigles G. , Jones R. J. , Phillips R. L.
Published: July 2010

DNA endoreduplication is the replication of nuclear DNA without subsequent mitosis and cell division, and is believed to be important in maize (Zea mays L.) kernel development. DNA endoreduplication has been shown to be negatively affected by high temperature treatments (HTTs) imposed during early kernel development in maize; however, the specific period of endosperm development at which the process is most sensitive to HTT has not been determined. To address this issue, HTTs (4 and 6 d at 35°C) were applied to in vitro‐grown maize kernels starting at 4, 6, 8, 10, or 12 d after pollination (DAP). Our approach was to isolate endosperms to determine the effect of elevated temperature on endosperm fresh weight (FW), number of endosperm cells, mitotic index, and DNA endoreduplication. The 4‐ and 6‐d HTTs imposed during the mitotic phase of the endosperm cell cycle (4, 6, and 8 DAP) reduced nuclei number and kernel FW, delayed cell division, decreased average DNA content, and reduced the percentage of nuclei in the 24, 48, and 96 C classes (C is the DNA content of a haploid nucleus in maize). In contrast, delaying the imposition of the 4‐ or 6‐d HTTs until 10 or 12 DAP (during the endoreduplication phase of the endosperm cell cycle) did not affect nuclei number, average DNA content, and DNA endoreduplication compared to the control. Thus, HTTs are most deleterious to DNA endoreduplication, endosperm FW, and nuclei number when applied during the mitotic phase of the endosperm cell cycle. These data further show that 4 to 10 DAP is the period during maize endosperm development that is most sensitive to high temperature, and that prolonged exposure restricts entry of mitotic cells into the endoreduplication phase of the cell cycle.
Inhibition of Net Nitrate Uptake by Ammonium in Pima and Acala Cotton Roots
Authors: Aslam Muhammad , Travis Robert L. , Rains Donald W.
Published: July 2010

This study was conducted to determine whether the inhibition of net NO−3 uptake by NH+
4 in cotton roots is due to inhibition of NO−
3 influx per se, and/or enhancement of efflux. Two cotton species, Pima (Gossypium barbadense L.) and Acala (G. hirsutum L.), which differ in NO−
3 influx and efflux, were used. Seedlings were grown hydroponically for 10 to 11 d and then induced for NO−
3 uptake with 0.01, 0.10, or 1.0 mM NO−
3 Net uptake was determined by following NO−
3 depletion from uptake solutions, containing 0.1 mM NO−
3, in the presence or absence of 10 mM NH+
4 Roots induced with 0.01 mM NO−
3 contained only 5 to 6 μmol NO−
3 g−1 fresh weight (FW) after the induction treatment. In these roots, net NO−
3 uptake was equivalent to influx, and was not inhibited by NH+
4 Roots induced with 0.1 mM NO−
3 contained 36 to 38 μmol NO−
3 g−1 FW, and NH+
4 inhibited net NO−
3 uptake albeit after a lag of ≈12 min. In contrast, roots induced with 1.0 mM NO−
3 contained 65 μmol NO−
3 g−1 FW, and NH+
4 immediately inhibited net uptake. Exposure to NH+
4 increased NO−
3 efflux by both species. At similar root NO−
3 concentrations, NH+
4 inhibited net NO−
3 uptake and stimulated efflux more in Pima than in Acala cotton. These results indicate that the response of both cotton species to NH+
4 is dependent upon root NO−
3 concentration, and supports the argument that NH+
4 has little effect on NO−
3 influx, but inhibits net uptake by stimulating efflux.
Molecular Analysis of White Clover Population Structure in Grazed Swards during Two Growing Seasons
Authors: Gustine David L. , Sanderson Matt A.
Published: July 2010

White clover (Trifolium repens L.) populations persist for years in grazing lands primarily through clonal growth, yet retain high genetic variability. This study was conducted to determine how clone structure dynamics affected intraspecific genetic variation of white clover at three pasture sites. Up to 37 trifoliate leaf samples were taken monthly by resampling specific points in four 1.2 x 1.2 m area quadrats from April to September for 2 yr; random amplified polymorphic DNA (RAPD) profiles of 1160 and 973 samples, in 1997 and 1998, respectively, were analyzed. Significantly more clones were sampled in 1997 (162) than in 1998 (58) (P < 0.0001). The majority of clones were not detected more than once during each year. The soil water content was significantly lower in 1998 than in 1997 (P < 0.0001). The number of sampled clonal members in quadrats ranged from 0.5 to 12.8 across both years on the three pastures. Within‐population analysis of molecular variances (AMOVA) by date for the three pastures ranged from 15 to 74% and 46 to 80% in 1997 and 1998, respectively, indicating low to medium genetic diversity in the populations. The fraction of clonal samples relative to the total number of samples ranged from 0.03 to 0.78 in 1997 and 0.04 to 0.33 in 1998. Higher numbers of clonal members appeared to reduce genetic diversity; however, this was offset by rapid turnover of clones. We conclude that genetic variability of white clover is dynamic at the local scale, which contributes to its long‐term persistence in grazing lands.
Osmotic Adjustment and Root Growth Associated with Drought Preconditioning‐Enhanced Heat Tolerance in Kentucky Bluegrass
Authors: Jiang Yiwei , Huang Bingru
Published: July 2010

Prior exposure to drought stress (drought preconditioning) affects turfgrass tolerance to subsequent heat stress. The study was designed to examine whether these effects for Kentucky bluegrass (Poa pratensis L.) are associated with osmotic adjustment and root growth. Plants were subjected to two cycles of drying and rewatering, and turf quality was then allowed to recover to the well watered control level before being exposed to 21 d of heat stress (35°C/30°C) in growth chambers. Compared with nonpreconditioned plants, drought‐preconditioned plants had 13 and 21% higher turf quality, 6 and 10% higher leaf relative water content, and 17 and 48% higher osmotic adjustment at 14 and 21 d of heat stress, respectively. Total ion (K+, Ca2+, Na+, Ma2+, Cl−, and P) concentration of cell sap increased during heat stress and was 11 to 16% higher in drought‐preconditioned plants than nonpreconditioned plants. The concentration of K+ accounted for 59 to 65% of total ion solutes in both groups of plants during heat stress. Soluble carbohydrate content (WSC) of leaves increased during heat stress and was about 21 and 44% higher in drought‐preconditioned plants than nonpreconditioned plants at 14 and 21 d, respectively. Heat stress decreased root dry weight (DW) and WSC, but significant higher DW and WSC content of roots in the 40–60 cm soil layer were observed for preconditioned plants than nonpreconditioned plants before and after heat stress. The results demonstrated that drought preconditioning enhanced heat tolerance in Kentucky bluegrass, which could be related to the maintenance of higher osmotic adjustment associated with accumulation of ion solutes and water soluble carbohydrates and development of extensive roots deeper in the soil profile.
Biomass Partitioning, Forage Nutritive Value, and Yield of Contrasting Genotypes of Timothy
Authors: Brégard A. , Bélanger G. , Michaud R. , Tremblay G. F.
Published: July 2010

Forage nutritive value and dry matter (DM) yield are negatively related. Hence, the improvement of both DM yield and nutritive value requires the identification of genotypes that deviate from that negative relationship. Our objectives were to evaluate the potential of simultaneously selecting for high forage yield and high nutritive value in timothy (Phleum pratense L.), and to study the relationship between DM yield, nutritive value, and biomass partitioning. Nine genotypes, and a reference cultivar, Champ, were studied in a growth room, with limiting and nonlimiting N rates. At both N rates, some genotypes differed significantly in forage (FDM) and total biomass (TBDM) DM yield, leaf weight ratio (LWR), and root weight ratio, but did not differ in forage (FNC) and total biomass (TBNC) N concentration. Genotypes differed in neutral detergent fiber concentration, in vitro true digestibility, and in vitro cell wall digestibility under limiting N only. Significant interaction (P < 0.05) was found between genotype and N rate for DM yield and for most of the other measured parameters. Principal component analysis indicated that, for most genotypes, the differences in FDM resulted from differences in TBDM and not only from changes in biomass partitioning between shoots and roots. Also, variability in the relationship between FDM and LWR indicated the possibility of selecting genotypes having high yield with high LWR. Consequently, it is possible to break the linkage between high DM yield and declining nutritive value parameters and select for high‐ yielding genotypes with superior forage nutritive value.
Mapping of QTL for Resistance to White Mold Disease in Common Bean
Authors: Park Soon O. , Coyne Dermot P. , Steadman James R. , Skroch Paul W.
Published: July 2010

White mold (WM), incited by Sclerotinia sclerotiorum (Lib.) de Bary, is a serious disease of common bean (Phaseolus vulgaris L.). However, plant breeders have had very limited success in developing resistant (R) cultivars. Molecular markers linked to genes for R to WM may improve selection for R. The objective was to identify random amplified polymorphic DNA (RAPD) markers linked to quantitative trait loci (QTL) for partial physiological resistance (PPR), partial field resistance (PFR), porosity over the furrow (POF), and plant height (PH) in a linkage map by means of recombinant inbred lines (RILs) from the cross ‘PC‐50’ (R) × XAN‐159 (susceptible). The parents and RILs were inoculated in two separate greenhouse experiments for each isolate and were also infected naturally in the field. Significant correlations (0.39, 0.47) were found for the WM reactions in the greenhouse and field. Nine candidate QTL were found affecting PPR isolate 152 (comparison‐wise P < 0.05) with strong evidence (genome‐wise P < 0.01) for three QTL on linkage groups (LGs) 4, 7, and 8, based on composite interval mapping analysis. Candidate QTL affecting PPR to isolate 279 were found on LGs 2, 3, 4, 7, and 8 with very strong evidence (genome‐wise P < 0.001) for a QTL linked to the C locus for seedcoat pattern. Seven candidate QTL for PFR were observed on LGs 4, 7, 8, and 11. Six of the seven candidate QTL for PFR were found in the same locations as QTL for PPR. However, two of the seven genomic regions were associated with PFR and POF that may contribute to disease avoidance.
AFLP Variation in Agamospermous and Dioecious Bluegrasses of Western North America
Authors: Larson S. R. , Waldron B. L. , Monsen S. B. , St. John L. , Palazzo A. J. , McCracken C. L. , Harrison R. D.
Published: July 2010

Native perennial bluegrasses are common and persistent in the understory steppe vegetation of western North America. The agamospermous Poa secunda Presl. complex circumscribes a number of commonly recognized forms including big bluegrass (P. ampla Merr.), canby bluegrass (P. canbyi Scribn.), and sandberg bluegrass (P. sandbergii Vasey). Poa fendleriana (Steudel) Vasey is a dioecious, morphologically distinct bluegrass species that is also native to western North America. The amplified fragment length polymorphism (AFLP) method was used to analyze genetic variation within and among cv. Canbar canby bluegrass, cv. Sherman big bluegrass, two allopatric natural populations of sandberg bluegrass, and one natural germplasm source of P. fendleriana Results indicate that Sherman and Canbar are comprised of one or several fixed genotypes, respectively, that are related to sandberg bluegrass. Although several fixed genotypes were also detected within the two natural sandberg bluegrass populations, high levels of genetic diversity were present in the agamospermous sandberg populations and dioecious P. fendleriana population. Patterns of AFLP variation in P. secunda are consistent with facultative apomixis and outcrossing mode of reproduction. Moreover, population differentiation between the two highly diverse natural sandberg bluegrass populations, collected from sites nearly 600 km apart, is very low (GS = 0.14) and reflect a high degree of gene flow. However, the AFLP profiles of Canbar canby bluegrass and Sherman big bluegrass were distinct from sandberg bluegrass. The P. secunda complex, as a group, was clearly distinguishable from P. fendleriana Thus, DNA fingerprinting was used to characterize naturally diverse bluegrass germplasm sources that may be used for large‐scale revegetation efforts across the western USA.
Parent‐Progeny Relationships and Genotype × Environment Effects for Factors Associated with Grass Tetany and Forage Quality in Russian Wildrye
Authors: Asay Kay H. , Mayland Henry F. , Jefferson Paul G. , Berdahl John D. , Karn James F. , Waldron Blair L.
Published: July 2010

Grass tetany (hypomagnesemia) has caused severe economic losses in ruminant animals grazing cool‐season grasses, including Russian wildrye [Psathyrostachys juncea (Fisch.) Nevski]. The malady has been associated with deficiencies in Mg, Ca, and carbohydrates, and high levels of K. The K/(Ca + Mg) ratio (KRAT), expressed as moles of charge, is often used to express the grass tetany potential of forage. Development and use of new cultivars with an improved balance of the associated minerals would be an economical approach to reduce the incidence of grass tetany. Objectives of this study were to characterize the genetic variability, genotype by environment interactions, and intercharacter relationships for P, K, Ca, Mg, KRAT, crude protein (CP), neutral detergent fiber (NDF), and in vitro dry matter digestibility (IVDMD), among 21 clonal lines of Russian wildrye and their polycross progenies. Evaluations were made for 2 yr at three diverse locations in the USA and Canada. The clonal lines were derived from cultivars and plant introductions. Although the clone × location interaction was usually significant, differences among the clonal lines were significant for K, Ca, Mg, and KRAT, and three forage quality estimates of CP, NDF, and true IVDMD. Although the magnitude of the genetic variability among the progenies was substantially less than that found among the clonal lines, we conclude that the grass tetany potential, CP, NDF, IVDMD, and P concentration of this breeding population can be altered through breeding. Opportunities for genetic improvement in forage quality were particularly favorable for CP. Genetic correlations among the clonal lines suggested that selection for higher levels of CP would be accompanied by increased K, Ca, Mg, and IVDMD and reduced KRAT and NDF.
Marker‐Assisted Backcrossing for Introgression of a Recessive Gene
Authors: Frisch Matthias , Melchinger Albrecht E.
Published: July 2010

Molecular markers are used to trace the presence of target genes (foreground selection) and accelerate recovery of the recurrent parent genome (background selection) in backcross programs. In this study, we present an approach for introgression of a recessive target gene from a donor into the genetic background of a recipient line by foreground selection combined with background selection for reducing the donor chromosome segment around the target gene. The goal of the proposed breeding plan is to generate with a given probability, q2, up to the second backcross generation (BC2) at least k ≥ 1 individuals, which carry the target gene and are homozygous for the recurrent parent alleles at flanking markers, by means of a minimum number of individuals. We provide formulas for calculation of (i) the population size required in generation BC1 and (ii) the probability of success q2 of the breeding program in generation BC2 The latter depends on the number and genotype of the BC1 individuals selected for further backcrossing and the size of their BC2 families. The optimum allocation of individuals to generations BC1 and BC2 was determined by computer simulations for various map distances between the target gene and the flanking markers. Our approach is demonstrated by a numerical example and can assist breeders in the optimum design of breeding programs for marker‐assisted introgression of a recessive gene.