Patent Publication Number: US-6040507-A

Title: Inbred corn line HX622

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a new and distinctive corn inbred line, designated HX622. There are numerous steps in the development of any novel, desirable plant germplasm. Plant breeding begins with the analysis and definition of problems and weaknesses of the current germplasm, the establishment of program goals, and the definition of specific breeding objectives. The next step is selection of germplasm that possess the traits to meet the program goals. The goal is to combine in a single variety or hybrid an improved combination of desirable traits from the parental germplasm. These important traits may include higher yield, resistance to diseases and insects, better stalks and roots, tolerance to drought and heat, and better agronomic quality. 
     Choice of breeding or selection methods depends on the mode of plant reproduction, the heritability of the trait(s) being improved, and the type of cultivar used commercially (e.g., F 1  hybrid cultivar, pureline cultivar, etc.). For highly heritable traits, a choice of superior individual plants evaluated at a single location will be effective, whereas for traits with low heritability, selection should be based on mean values obtained from replicated evaluations of families of related plants. Popular selection methods commonly include pedigree selection, modified pedigree selection, mass selection, and recurrent selection. 
     The complexity of inheritance influences choice of the breeding method. Backcross breeding is used to transfer one or a few favorable genes for a highly heritable trait into a desirable cultivar. This approach has been used extensively for breeding disease-resistant cultivars. Various recurrent selection techniques are used to improve quantitatively inherited traits controlled by numerous genes. The use of recurrent selection in self-pollinating crops depends on the ease of pollination, the frequency of successful hybrids from each pollination, and the number of hybrid offspring from each successful cross. 
     Each breeding program should include a periodic, objective evaluation of the efficiency of the breeding procedure. Evaluation criteria vary depending on the goal and objectives, but should include gain from selection per year based on comparisons to an appropriate standard, overall value of the advanced breeding lines, and number of successful cultivars produced per unit of input (e.g., per year, per dollar expended, etc.). 
     Promising advanced breeding lines are thoroughly tested and compared to appropriate standards in environments representative of the commercial target area(s) for three years at least. The best lines are candidates for new commercial cultivars; those still deficient in a few traits are used as parents to produce new populations for further selection. 
     These processes, which lead to the final step of marketing and distribution, usually take from eight to 12 years from the time the first cross is made. Therefore, development of new cultivars is a time-consuming process that requires precise forward planning, efficient use of resources, and a minimum of changes in direction. 
     A most difficult task is the identification of individuals that are genetically superior, because for most traits the true genotypic value is masked by other confounding plant traits or environmental factors. One method of identifying a superior plant is to observe its performance relative to other experimental plants and to a widely grown standard cultivar. If a single observation is inconclusive, replicated observations provide a better estimate of its genetic worth. 
     The goal of plant breeding is to develop new, unique and superior corn inbred lines and hybrids. The breeder initially selects and crosses two or more parental lines, followed by repeated selfing and selection, producing many new genetic combinations. The breeder can theoretically generate billions of different genetic combinations via crossing, selfing and mutations. The breeder has no direct control at the cellular level. Therefore, two breeders will never develop the same line, or even very similar lines, having the same corn traits. 
     Each year, the plant breeder selects the germplasm to advance to the next generation. This germplasm is grown under unique and different geographical, climatic and soil conditions, and further selections are then made, during and at the end of the growing season. The inbred lines which are developed are unpredictable. This unpredictability is because the breeder&#39;s selection occurs in unique environments, with no control at the DNA level (using conventional breeding procedures), and with millions of different possible genetic combinations being generated. A breeder of ordinary skill in the art cannot predict the final resulting lines he develops, except possibly in a very gross and general fashion. The same breeder cannot produce the same line twice by using the exact same original parents and the same selection techniques. This unpredictability results in the expenditure of large research monies to develop a superior new corn inbred line. 
     The development of commercial corn hybrids requires the development of homozygous inbred lines, the crossing of these lines, and the evaluation of the crosses. Pedigree breeding and recurrent selection breeding methods are used to develop inbred lines from breeding populations. Breeding programs combine desirable traits from two or more inbred lines or various broad-based sources into breeding pools from which inbred lines are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred lines and the hybrids from these crosses are evaluated to determine which have commercial potential. 
     Pedigree breeding is used commonly for the improvement of self-pollinating crops or inbred lines of cross-pollinating crops. Two parents which possess favorable, complementary traits are crossed to produce an F 1 . An F 2  population is produced by selfing one or several F 1  &#39;s or by intercrossing two F 1  &#39;s (sib mating). Selection of the best individuals is usually begun in the F 2  population; then, beginning in the F 3 , the best individuals in the best families are selected. Replicated testing of families, or hybrid combinations involving individuals of these families, often follows in the F 4  generation to improve the effectiveness of selection for traits with low heritability. At an advanced stage of inbreeding (i.e., F 6  and F 7 ), the best lines or mixtures of phenotypically similar lines are tested for potential release as new cultivars. 
     Mass and recurrent selections can be used to improve populations of either self- or cross-pollinating crops. A genetically variable population of heterozygous individuals is either identified or created by intercrossing several different parents. The best plants are selected based on individual superiority, outstanding progeny, or excellent combining ability. The selected plants are intercrossed to produce a new population in which further cycles of selection are continued. 
     Backcross breeding has been used to transfer genes for a simply inherited, highly heritable trait into a desirable homozygous cultivar or inbred line which is the recurrent parent. The source of the trait to be transferred is called the donor parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. After the initial cross, individuals possessing the phenotype of the donor parent are selected and repeatedly crossed (backcrossed) to the recurrent parent. The resulting plant is expected to have the attributes of the recurrent parent (e.g., cultivar) and the desirable trait transferred from the donor parent. 
     Descriptions of other breeding methods that are commonly used for different traits and crops can be found in one of several reference books (e.g., Allard, 1960; Simmonds, 1979; Sneep et al., 1979; Fehr, 1987). 
     Proper testing should detect any major faults and establish the level of superiority or improvement over current cultivars. In addition to showing superior performance, there must be a demand for a new cultivar that is compatible with industry standards or which creates a new market. The introduction of a new cultivar will incur additional costs to the seed producer, the grower, processor and consumer; for special advertising and marketing, altered seed and commercial production practices, and new product utilization. The testing preceding release of a new cultivar should take into consideration research and development costs as well as technical superiority of the final cultivar. For seed-propagated cultivars, it must be feasible to produce seed easily and economically. 
     Once the inbreds that give the best hybrid performance have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parent is maintained. A single-cross hybrid is produced when two inbred lines are crossed to produce the F 1  progeny. A double-cross hybrid is produced from four inbred lines crossed in pairs (A×B and C×D) and then the two F 1  hybrids are crossed again (A×B)×(C×D). Much of the hybrid vigor exhibited by F 1  hybrids is lost in the next generation (F 2 ). Consequently, seed from hybrid varieties is not used for planting stock. 
     Corn is an important and valuable field crop. Thus, a continuing goal of plant breeders is to develop stable, high yielding corn hybrids that are agronomically sound. The reasons for this goal are obviously to maximize the amount of grain produced on the land used and to supply food for both animals and humans. To accomplish this goal, the corn breeder must select and develop corn plants that have the traits that result in superior parental lines for producing hybrids. 
     SUMMARY OF THE INVENTION 
     According to the invention, there is provided a novel inbred corn line, designated HX622. This invention thus relates to the seeds of inbred corn line HX622, to the plants of inbred corn line HX622 and to methods for producing a corn plant produced by crossing the inbred line HX622 with itself or another corn line. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line HX622 with another corn line. 
     The inbred corn plant of the invention may further comprise or have a cytoplasmic factor that is capable of conferring male sterility. Parts of the corn plant of the present invention are also provided, such as e.g., pollen obtained from an inbred plant and an ovule of the inbred plant. 
     In another aspect, the present invention provides for single gene converted plants of HX622. The single transferred gene may preferably be a dominant or recessive allele. Preferably, the single transferred gene will confer such traits as male sterility, herbicide resistance, insect resistance, resistance for bacterial, fungal or viral disease, male fertility, enhanced nutritional quality and industrial usage. The single gene may be a naturally occurring maize gene or a transgene introduced through genetic engineering techniques. 
     In another aspect, the present invention provides regenerable cells for use in tissue culture of inbred corn plant HX622. The tissue culture will preferably be capable of regenerating plants having the physiological and morphological characteristics of the foregoing inbred corn plant and of regenerating plants having substantially the same genotype as the foregoing inbred corn plant. Preferably, the regenerable cells in such tissue cultures will be embryos, protoplasts, meristematic cells, callis, pollen, leaves, anthers, roots, root tips, silk flowers, kernels, ears, cobs, husks or stalks. Still further, the present invention provides corn plants regenerated from the tissue cultures of the invention. 
     DEFINITIONS 
     In the description and tables which follow, a number of terms are used. 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: 
     Predicted RM. This trait for a hybrid, predicted relative maturity (RM), is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes conventional maturity systems such as the Minnesota Relative Maturity Rating System. 
     MN RM. This represents the Minnesota Relative Maturity Rating (MN RM) for the hybrid and is based on the harvest moisture of the grain relative to a standard set of checks of previously determined MN RM rating. Regression analysis is used to compute this rating. 
     Yield (Bushels/Acre). The yield in bushels/acre is the actual yield of the grain at harvest adjusted to 15.5% moisture. 
     Moisture. The moisture is the actual percentage moisture of the grain at harvest. 
     GDU Silk. The GDU silk (=heat unit silk) is the number of growing degree units (GDU) or heat units required for an inbred line or hybrid to reach silk emergence from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hour period are: ##EQU1## The highest maximum used is 86° F. and the lowest minimum used is 50° F. For each hybrid, it takes a certain number of GDUs to reach various stages of plant development. GDUs are a way of measuring plant maturity. 
     Stalk Lodging. This is the percentage of plants that stalk lodge, i.e., stalk breakage, as measured by either natural lodging or pushing the stalks determining the percentage of plants that break off below the ear. This is a relative rating of a hybrid to other hybrids for standability. 
     Root Lodging. The root lodging is the percentage of plants that root lodge; i.e., those that lean from the vertical axis at an approximate 30° angle or greater would be counted as root lodged. 
     Plant Height. This is a measure of the height of the hybrid from the ground to the tip of the tassel and is measured in centimeters. 
     Ear Height. The ear height is a measure from the ground to the ear node attachment and is measured in centimeters. 
     Dropped Ears. This is a measure of the number of dropped ears per plot, and represents the percentage of plants that dropped an ear prior to harvest. 
     Allele. The allele is any of one or more alternative forms of a gene, all of which alleles relate to one trait or characteristic. In a diploid cell or organism, the two alleles of a given gene occupy corresponding loci on a pair of homologous chromosomes. 
     Backcrossing. This is a process in which a breeder repeatedly crosses hybrid progeny back to one of the parents, for example, a first generation hybrid F 1  with one of the parental genotypes of the F 1  hybrid. 
     Essentially all the physiological and morphological characteristics. A plant having essentially all the physiological and morphological characteristics means a plant having all the physiological and morphological traits, except for also having the trait derived from the converted gene. 
     Quantitative Trait Loci (QTL). Quantitative Trait Loci (QTL) refer to genetic loci that control, to some degree, numerically representable traits that are usually continuously distributed. 
     Regeneration. Regeneration refers to the development of a plant from tissue culture. 
     Single Gene Converted. Single gene converted or conversion plant refers to plants which are developed by a plant breeding technique called backcrossing wherein essentially all of the desired morphological and physiological characteristics of an inbred are recovered in addition to the single gene transferred into the inbred via the backcrossing technique. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Inbred corn line HX622 is a yellow dent corn with superior characteristics, and provides an excellent parental line in crosses for producing first generation (F 1 ) hybrid corn. 
     HX622 is a corn inbred line developed from the cross of LH109×LH51 which was then selfed and the pedigree system of plant breeding was used in the development of HX622. Yield, stalk quality, root quality, disease tolerance, late plant greenness, late plant intactness, ear retention, pollen shedding ability, silking ability and corn borer tolerance were the criteria used to determine the rows from which ears were selected. 
     Inbred corn line HX622 has the following morphologic and other characteristics (based primarily on data collected at Hooper, Nebr.). 
     Variety Description Information 
     1. TYPE: Dent 
     2. REGION WHERE DEVELOPED: Northcentral U.S. 
     3. MATURITY: 
     
         ______________________________________                                    
                         Days   Heat Units                                
From emergence to 50% of plants in silk:                                  
                         69     1440                                      
From 50% silk to harvest at 25% kernel moisture:                          
                         44     1080                                      
Heat Units: =                                                             
           [Max. Temp. (≦86° F.) +                          
           Min. Temp. (≧50° F.)] - 50                       
           2                                                              
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     4. PLANT: 
     Plant Height (to tassel tip): 190 cm. 
     Ear Height (to base of top ear): 71 cm. 
     Average Number of Tillers: 0 
     Average Number of Ears per Stalk: 1 
     Cytoplasm Type: Normal 
     5. LEAF: 
     Width of Ear Node Leaf (at widest point): 10 cm. 
     Length of Ear Node Leaf: 71 cm. 
     Number of leaves per mature plant: 16 
     Angle from Stalk (Upper half): &lt;30° 
     Leaf Color: Medium Green 
     Leaf Sheath Pubescence: Light 
     Marginal Waves: Few 
     Longitudinal Creases: Absent 
     6. TASSEL: 
     Number of Lateral Branches: 6 
     Branch Angle from Central Spike: 30°-40° 
     Peduncle Length (from top leaf to basal branches): 9 cm. 
     Pollen Shed: Heavy 
     Anther Color: Yellow 
     Glume Color: Green 
     7. EAR: (Husked Ear Data) 
     Ear Length: 18 cm 
     Number of Kernel Rows: 16 
     Kernel Rows: Distinct 
     Row Alignment: Slightly curved 
     Silk Color: Green 
     Husk Color: 
     Fresh: Light Green 
     Dry: Buff 
     Husk Extension: Medium (Barely covering ear) 
     Husk Leaf: Medium 
     Shank Position at Dry Husk Stage: Upright 
     Taper: Average 
     8. KERNEL: (Dried) 
     Aleurone Color Pattern: Homozygous 
     Aleurone Color: White 
     Hard Endosperm Color: Pale Yellow 
     Endosperm Type: Normal Starch 
     9. COB: 
     Cob Strength: Strong 
     Cob Color: Red 
     10. DISEASE RESISTANCE: 
     Rating [1=(susceptible); 2=(resistant)] 
     Stalk Rot (Diplodia): 2 
     Stalk Rot (Fusarium): 2 
     Stalk Rot (Gibberella): 2 
     Northern Leaf Blight: 2 
     Southern Leaf Blight: 2 
     Smut: 2 
     Southern Rust: 2 
     Corn Smut: 2 
     Maize Dwarf Mosaic: 1 
     This invention is also directed to methods for producing a corn plant by crossing a first parent corn plant with a second parent corn plant, wherein the first or second corn plant is the inbred corn plant from the line HX622. Further, both first and second parent corn plants may be from the inbred line HX622. Therefore, any methods using the inbred corn line HX622 are part of this invention: selfing, backcrosses, hybrid breeding and crosses to populations. Any plants produced using inbred corn line HX622 as a parent are within the scope of this invention. Advantageously, the inbred corn line is used in crosses with other corn varieties to produce first generation (F 1 ) corn hybrid seed and plants with superior characteristics. 
     As used herein, the term &#34;plant&#34; includes plant cells, plant protoplasts, plant cell of tissue culture from which corn plants can be regenerated, plant calli, plant clumps, and plant cells that are intact in plants or parts of plants, such as pollen, flowers, kernels, ears, cobs, leaves, husks, stalks, and the like. 
     The present invention contemplates a corn plant regenerated from a tissue culture of an inbred (e.g. HX622) or hybrid plant of the present invention. As is well known in the art, tissue culture of corn can be used for the in vitro regeneration of a corn plant. By way of example, a process of tissue culturing and regeneration of corn is described in European Patent Application, publication 160,390, the disclosure of which is incorporated by reference. Corn tissue culture procedures are also described in Green &amp; Rhodes (1982) and Duncan et al., (1985). The study by Duncan et al. (1985) indicates that 97 percent of cultured plants produced calli capable of regenerating plants. Subsequent studies have shown that both inbreds and hybrids produced 91 percent regenerable calli that produced plants. 
     Other studies indicate that non-traditional tissues are capable of producing somatic embryogenesis and plant regeneration. See, e.g., Songstad et al. (1988); Rao et al. (1986); and Conger et al. (1987), the disclosures of which are incorporated herein by reference. Regenerable cultures may be initiated from immature embryos as described in PCT publication WO 95/06128, the disclosure of which is incorporated herein by reference. Thus, another aspect of this invention is to provide for cells which upon growth and differentiation produce the inbred line HX622. 
     LH109 and LH51, the progenitors of HX622, are both proprietary field corn inbred lines of Holden&#39;s Foundation Seeds, Inc. of Williamsburg, Iowa. 
     HX622 is similar to MO17, however, there are numerous differences. HX622 is earlier to flower than MO17 and silks at or before pollen shed. HX622 contains 16-18 rows of kernels whereas MO17 contains 12-14 rows of kernels. HX622 also has lower ears, better stalks and a higher yield than MO17. 
     HX622 is an early season field corn inbred line that has good late-season plant health. Hybrids containing HX622 are very stable and have good stress tolerance. 
     Some of the criteria used to select ears in various generations include: yield, stalk quality, root quality, disease tolerance, late plant greenness, late season plant intactness, ear retention, pollen shedding ability, silking ability, and corn borer tolerance. During the development of the line, crosses were made to inbred testers for the purpose of estimating the line&#39;s general and specific combining ability, and evaluations were run by the Hooper, Nebr. Research Station. The inbred was evaluated further as a line and in numerous crosses by other research stations across the Corn Belt. The inbred has proven to have a very wide, general combining ability with stiff stalk-type lines in hybrid combinations. 
     The inbred has shown uniformity and stability for the traits. It has been self-pollinated and ear-rowed a sufficient number of generations, with careful attention to uniformity of plant type. The line has been increased both by hand and sibbed in isolated fields with continued observations for uniformity. 
     Tables 
     In the table that follows, the traits and characteristics of inbred corn line HX622 are given in hybrid combination. The data collected on inbred corn line HX622 is presented for the key characteristics and traits. The table presents yield test information about HX622. HX622 was tested in several hybrid combinations at numerous locations, with two or three replications per location. 
     In column 1, the first genotype listed is the hybrid containing HX622 and the remaining genotypes listed are other hybrids. Columns 2 and 3 show the bushels/acre and percent moisture for each genotype. In columns 4, 5, 6 and 7 show information for each genotype including: percent root lodging (% RTLG), percent dropped ears (% DE), plant height (PL. HT.) and ear height (EAR HT.). 
     
                       TABLE 1                                                     
______________________________________                                    
OVER 16 LOCATIONS                                                         
               %       %       %    PL.  EAR                              
          BU/A MST     RTLG    DE   HT.  HT.                              
______________________________________                                    
HC33xHX622  196.1  20.0    0.9   0.1  114.0                               
                                           43.0                           
Pioneer35N05                                                              
            191.8  18.8    1.0   0.2  113.0                               
                                           46.0                           
Pioneer3489 191.3  19.8    0.6   0.1  112.0                               
                                           38.0                           
LH198xSG1787                                                              
            181.5  19.7    1.9   0.1  110.0                               
                                           44.0                           
LH198xMBS4681                                                             
            176.9  19.4    2.6   0.2  108.0                               
                                           40.0                           
LH168xSGI808                                                              
            173.0  19.2    1.8   0.2   97.0                               
                                           40.0                           
______________________________________                                    
 
    
     When the term inbred corn plant is used in the context of the present invention, this also includes any single gene conversions of that inbred. The term single gene converted plant as used herein refers to those corn plants which are developed by a plant breeding technique called backcrossing wherein essentially all of the desired morphological and physiological characteristics of an inbred are recovered in addition to the single gene transferred into the inbred via the backcrossing technique. Backcrossing methods can be used with the present invention to improve or introduce a characteristic into the inbred. The term backcrossing as used herein refers to the repeated crossing of a hybrid progeny back to one of the parental corn plants for that inbred. The parental corn plant which contributes the gene for the desired characteristic is termed the nonrecurrent or donor parent. This terminology refers to the fact that the nonrecurrent parent is used one time in the backcross protocol and therefore does not recur. The parental corn plant to which the gene or genes from the nonrecurrent parent are transferred is known as the recurrent parent as it is used for several rounds in the backcrossing protocol (Poehlman &amp; Sleper, 1994; Fehr. 1978). In a typical backcross protocol, the original inbred of interest (recurrent parent) is crossed to a second inbred (nonrecurrent parent) that carries the single gene of interest to be transferred. The resulting progeny from this cross are then crossed again to the recurrent parent and the process is repeated until a corn plant is obtained wherein essentially all of the desired morphological and physiological characteristics of the recurrent parent are recovered in the converted plant, in addition to the single transferred gene from the nonrecurrent plant. 
     The selection of a suitable recurrent parent is an important step for a successful backcrossing procedure. The goal of a backcross protocol is to alter or substitute a single trait or characteristic in the original inbred. To accomplish this, a single gene of the recurrent inbred is modified or substituted with the desired gene from the nonrecurrent parent while retaining essentially all of the rest of the desired genetic, and therefore the desired physiological and morphological, constitution of the original inbred. The choice of the particular nonrecurrent parent will depend on the purpose of the backcross, one of the major purposes is to add some commercially desirable agronomically important trait to the plant. The exact backcrossing protocol will depend on the characteristic or trait being altered to determine an appropriate testing protocol. Although backcrossing methods are simplified when the characteristic being transferred is a dominant allele, a recessive allele may also be transferred. In this instance, it may be necessary to introduce a test of the progeny to determine if the desired characteristic has been successfully transferred. 
     Many single gene traits have been identified that are not regularly selected in the development of a new inbred but that can be improved by backcrossing techniques. Single gene traits may or may not be transgenic. Examples of these traits include, but are not limited to, male sterility, waxy starch, herbicide resistance, resistance for bacterial, fungal, or viral disease, insect resistance, male fertility, enhanced nutritional quality, industrial usage, yield stability and yield enhancement. These genes are generally inherited through the nucleus. Some known exceptions to this are the genes for male sterility, some of which are inherited cytoplasmically, but still act as single gene traits. Several of these single gene traits are described in U.S. Pat. No. 5,777,196, the disclosure of which is specifically hereby incorporated by reference. 
     A further aspect of the invention relates to tissue culture of corn plants designated HX622. As used herein, the term &#34;tissue culture&#34; indicates a composition comprising isolated cells of the same or a different type or a collection of such cells organized into parts of a plant. Exemplary types of tissue cultures are protoplasts, calli, plant clumps and plant cells that can generate tissue culture that are intact in plants or parts of plants, such as embryos, pollen, flowers, kernels, ears, cobs, leaves, husks, stalks, roots, root tips, anthers, silk and the like. In a preferred embodiment, tissue culture is embryos, protoplast, meristematic cells, pollen, leaves or anthers. Means for preparing and maintaining plant tissue culture are well known in the art. By way of example, a tissue culture comprising organs such as tassels or anthers, has been used to produce regenerated plants (See, U.S. Pat. No. 5,445,961 and U.S. Pat. No. 5,322,789, issued Jun. 21, 1994, the disclosures of which are incorporated herein by reference). 
     Deposit Information 
     A deposit of the corn seed of this invention is maintained by Hoegemeyer Hybrids, Route 2, Hooper, Nebr. 68031. Access to this deposit will be available during the pendency of this application to persons determined by the Commissioner of Patents and Trademarks to be entitled thereto under 37 CFR 1.14 and 35 USC 122. Upon allowance of any claims in this application, all restrictions on the availability to the public of the variety will be irrevocably removed by affording access to a deposit of at least 2,500 seeds of the same variety with the American Type Culture Collection, Manassas, Va. 
     Although the foregoing invention has been described in some detail by way of illustration and example for purposes of clarity and understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the invention, as limited only by the scope of the appended claims.