Synthetic Corn Hybrid P55

This invention is in the field of plant breeding. Specifically, this invention relates to a novel synthetic corn hybrid having the designation P55 and useful in the proprietary TopCross.RTM. grain production system described in U.S. patent applications Ser. Nos. 07/615,839 and 08/464,249 by Bergquist, et al.

Uses Of Corn

Corn (Zea mays L.) is an important crop used as a human food source, animal feed, and as a raw material in industry. The food uses of corn, in addition to the human consumption of corn kernels, include products of both the dry milling and wet milling industries. The principal products of dry milling include grits, meal and flour. The principal products of wet milling include starch, syrups, and dextrose. A by product of both dry and wet milling is corn oil, which is recovered from corn germ. As animal feed, corn is used primarily as a feedstock for beef cattle, dairy cattle, swine, poultry, and fish.

Industrial uses of corn mainly consist of the use of corn starch produced by wet milling and corn flour produced by dry milling and the whole kernel fermentation for production of food-grade and industrial use ethanol. The industrial applications of corn starch and flour are based on their functional properties, such as viscosity, film formation ability, adhesiveness, absorbent properties and ability to suspend particles. Corn starch and flour are used in the paper and textile industries, and as components in adhesives, building materials, foundry binders, laundry starches, sanitary diapers, seed treatments, explosives, and oil-well muds. Plant parts other than the corn kernels are also used in industry. For example, stalks and husks can be made into paper and wallboard, and corn cobs can be used for fuel and to make charcoal and a source of furfural.

Principles of conventional plant breeding

Virtually all of the commercial corn produced in the United States is produced from hybrid seed. The production of hybrid seed first requires the development of elite corn inbred lines that possess good combining ability to produce agronomically superior hybrids. The majority of hybrid seed produced in the United States is of the single cross type, wherein two inbred lines are intermated, or crossed, to produce what is termed an F.sub.1 single cross hybrid. The resulting kernels from this intermating are then sold as seed to commercial growers who plant the seed and harvest the second generation, or F.sub.2 grain, for use on farm or for commercial sale.

The production of a conventional single cross hybrid seed involves controlling the direction of pollination from one inbred to the other to assure the production of predominantly hybrid (cross pollinated) seed. Typically directed pollination is accomplished by interplanting separate rows of female corn plantswith male corn plants. The female corn plants that are male sterile may be produced by genetic mechanisms which render the corn tassel nonfunctional or by detasseling the plants in the field.

The development of corn hybrids requires the development of homozygous inbred lines or uniform synthetic populations of unique heterotic background, the crossing of these lines or synthetic populations, and evaluation of test crosses. Pedigree breeding and recurrent selection breeding programs are used to develop inbred lines and synthetic populations from breeding populations. Breeding various broad-based sources into breeding pools from which new inbred lines or synthetic populations are developed by inbreeding or random mating and selection of desired phenotypes. The new inbreds and/or synthetic lines are crossed with other inbred lines and/or synthetic populations and the hybrids from these crosses are evaluated to determine which have commercial value and agronomic usefulness.

Pedigree breeding starts with the crossing of two genotypes, each of which may have one or more desirable characteristics that is lacking in the other or which complements the other. If the two original genotypes do not provide all of the desired characteristics, other sources can be included during the breeding. In the pedigree breeding method, superior plants are selfed or random mated and the resulting seed selected in successive generations. Pedigree records of ancestry are carefully maintained for each family and ear row selection through succeeding generations. In the succeeding generations, the heterozygous condition of the corn germplasm gives way to homozygous true breeding lines as a result of inbreeding and selection. Typically in the pedigree method of breeding, five or more generations of inbreeding and selection is practiced: F.sub.1 to F.sub.2 ; F.sub.2 to F.sub.3 ; F.sub.3 to F.sub.4 ; F.sub.4 to F.sub.5, etc.

Backcrossing can be used to improve an inbred line by transferring a specific desirable trait from one inbred or source to another inbred that lacks that trait. This can be accomplished, for example, by first crossing a superior inbred (recurrent parent) to a donor inbred (nonrecurrent parent). The donor inbred carries (donates) the appropriate gene(s) for the desired trait to the next generation. After five or more backcross generations with selection for the desired trait, the inbred will be heterozygous for loci controlling the characteristic being transferred, but will be like the superior parent for most or almost all other genes. The last backcross generation can be selfed to produce a pure breeding progeny for the gene(s) being transferred.

An important consequence of the homozygosity and homogeneity of the inbred lines is that the hybrid between any two inbreds will always be the same. Once the inbreds or synthetics that give the best hybrid have been identified, the hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred or synthetic parents is maintained.

A synthetic hybrid consists of an array of similar genotypes that were identified from intercross tests and bulked into a random mating population having a desired phenotype. The intercrosses between two different heterotic groups results in the continuous production of a specific synthetic hybrid of desired phenotype.

As previously noted, a single cross hybrid is produced when two unrelated inbred or synthetic lines are crossed to produce the F.sub.1 progeny. A three-way cross hybrid is produced from three inbred lines (or synthetics) where two of the inbred lines (or synthetics) are crossed (A.times.B) and then the resulting F.sub.1 hybrid is crossed with the third inbred (or synthetics) (A.times.B).times.C. A double cross hybrid is produced from four inbred lines (or synthetics) by crossing pairs (A.times.B) and (C.times.D) and then crossing the two F.sub.1 hybrids (A.times.B).times.(C.times.D).

Much of the hybrid vigor exhibited by F.sub.1 hybrids is lost in the next generation (F.sub.2) Consequently, seed (grain) from hybrid varieties is not used for planting stock.

The objective of typical plant breeding is to combine in a single variety/hybrid the desirable traits of the parental lines. For field crops such as corn, these desirable traits may include resistance to diseases, insects, herbicide tolerance, and tolerance to heat and drought, reducing time to crop maturity, and improved agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination time and stand establishment, growth rate, and fruit/seed size are also desirable.

The problem with conventional breeding techniques is that there are several grain quality traits, such as high oil content, that cannot readily be combined in a high-yielding single cross hybrid. The present invention, when used as a pollinator, imparts desirable grain quality characteristics, such as high oil content, to the resulting F.sub.1 grain without significant loss of yield. This heretofore was not possible because these desirable grain quality characteristics in hybrids usually have been associated with low yield and poor agronomic characteristics.

Synthetic varieties

Corn has male flowers, located on the tassel, and female flowers, located on the ear, of the same plant. Because of this monoecy, corn plants can be bred by both self-pollination and cross-pollination techniques. Corn is self-pollinated if pollen from one flower is transferred to the same or another flower on the same plant. Corn is cross-pollinated if the pollen comes from a flower on a different plant.

Plants that have been self-pollinated and selected for uniform type over many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny. Cross pollination between two homozygous lines produces a uniform population of hybrid plants that nevertheless may be heterozygous for many gene loci. A cross between two plants that are each heterozygous for a number of gene loci will produce a population of hybrid plants that differ genetically and will not be uniform.

Natural pollination occurs when wind blows pollen from tassels to silks that protrude from tops of the incipient ears on plants of the same genotype and different genotype, resulting in both self- and cross-pollination. When a population of genotypes are combined from all possible intercrosses among a number of selected genotypes and are allowed to open pollinate, the result is called a synthetic variety. A synthetic variety is made up of genotypes which previously have been tested for their ability to produce a superior progeny when crossed in all combinations.

Corn plants may be maintained as an outcrossing synthetic population that is much less homogeneous than a self-pollinated group. Every plant in such a group is certain to be heterozygous at many or most loci, and this heterozygosity must either be maintained during a breeding program or restored at the end of the program, if productivity is to be satisfactory. The main requirement in maintaining a synthetic line is that a sufficient number of plants of heterozygous background be maintained to recover the gene frequencies that are desired for the synthetic population so as to prevent genetic drift toward undesired gene frequencies.

The desirability of high oil content grain

The concentration of oil in most varieties of corn ranges from less than 3.0 percent to 4.5 percent at 0% moisture. Embryos of ordinary corn can contain 30 percent oil, while embryos of high oil corn strains can contain as much as 50 percent oil and are much larger in size than ordinary corn embryos.

There are several reasons for wanting to develop a method for growing corn that is high in oil content. First, corn oil is a premium oil and regularly more valuable than starch, the other major component of corn kernels. Second, high oil corn possesses a higher available energy content than ordinary corn, and thus is a more valuable feed for poultry and livestock. In animal feeding trials it has been found that less high oil corn is required per unit of gain than is required with ordinary corn. In addition, high oil corn requires substantially less soybean meal to balance a typical animal diet, and may be used to replace oil containing additives in animal feed.

Additional impetus was given to breeding corn for high oil by the development of wide-line nuclear magnetic resonance spectroscopy (NMR) and near-infrared spectroscopy (NIR) as analytical tools for the nondestructive analysis of bulk or single kernel samples that can be carried out in as little as two seconds. The development of such tools made it much easier and much quicker to determine the oil content of grain, thereby encouraging experimentation in the area of breeding for high oil.

Thus there exists at present a growing market for corn having high oil, increased protein and other special end-use properties which is not met by corn of standard composition. The diverse types of corn available to plant breeders provides a potential for modification of quality and quantity of grain protein, starch, and oil. Corn now can be developed to more precisely meet the specific nutritional requirements of animals or to meet particular industrial needs.

The TopCross.RTM. grain production system

Unfortunately, high oil is a property that cannot readily be achieved in a high yielding single-cross hybrid. This is because oil content, while being a moderately heritable trait, is influenced by a series of oil genes that have additive effects on oil content and occur at a complex of loci in at least eight linkage groups that influence the amount of oil in the grain progeny. Obtaining a hybrid having all or most of these oil genes can take many years of breeding. Further increasing the difficulty of breeding for high oil content is the fact that the grain yield of higher oil hybrids is generally inferior when compared to elite dent corn hybrids.

A method of producing a high yield of corn having high oil content without requiring years of breeding is described in Bergquist et al. U.S. patent application Ser. No. 07/615,839. The primary aspect of this method, known as the TopCross.RTM. grain production system, is the interplanting of a pollinator corn plant possessing the characteristics for significantly increasing oil and protein levels in the resulting grain with a male sterile hybrid corn plant. The resulting grain possesses an oil content much higher than would be expected for self- or cross-pollination of the fertile version of the hybrid corn plant.

In practice, the seed of the pollinator with improved grain quality traits is blended in small amounts with seed of an elite male sterile grain parent hybrid, but with sufficient pollinator seed to permit abundant pollen production for fertilization of the male sterile grain parent hybrid. The relatively low ratio of pollinator seed to male sterile grain parent seed (less than one pollinator plant to every three grain parent plants) takes advantage of the higher grain yield potential of the elite grain parent hybrid while assuring a sufficient population of pollinator plants to pollinate the male sterile grain parent plants.

Need for superior pollinators

Critical to the success of the TopCross.RTM. grain production system is the use of a pollinator capable of enhancing the grain quality traits of the F.sub.1 offspring. To obtain such pollinators, the corn breeder must select and develop corn plants that have the traits that result in superior inbred and synthetic parental lines.

The pollinator for the TopCross.RTM. grain production system need not be genetically homozygous (inbred) or even uniform in appearance, and need not be selected for genetic combining ability with female plants. However, the pollinator should have uniform desirable grain quality characteristics, such as high oil, that will influence the grain quality characteristics of the F.sub.1 offspring, and the ability to pollinate the female plants. A hybrid obtained by crossing two synthetic populations of different heterotic backgrounds results in a synthetic hybrid with predictable heterozygosity and genetic variability among plants that is particularly useful as a male pollinator in blends with male sterile hybrid grain parents in the TopCross.RTM. grain production system. Some genetic variability is desirable because it extends the flowering period of the pollinator. P55 was developed to achieve these characteristics.

Advantages of synthetic hybrids

The use of synthetic hybrids (such as P55) as TopCross.RTM. grain production system pollinators affords a number of advantages over the use of hybrids produced from single crosses. For instance, synthetic hybrids can be developed more rapidly than commercial hybrids. Specifically, the use of a synthetic population can more rapidly establish stability of dominant oil genes, thereby by-passing the many generations of inbreeding that is required to produce inbreds for making single cross hybrids.

Second, synthetic hybrids often have excellent vigor comparable to that of commercial hybrids. Inbreds, by contrast, typically lose vigor with each successive generation of inbreeding. This is an important advantage of synthetics because pollinator vigor is critical for ample pollen shed at the time of silking in the TopCross.RTM. grain production system. Synthetic hybrid P55 expresses cold vigor in seedling growth stages greater than even most open pollinated synthetic populations.

Third, a synthetic variety, utilizing heterosis in which pollination control is a factor, is more likely to disperse pollen over a longer period of time than a single cross hybrid. The predictable greater variability of synthetic varieties as compared with single crosses permits more flexibility to meet the changing growing conditions typical of field production. In addition, because of the longer flowering period, fewer synthetic pollinators need be developed to be used in blends with many different grain parents.

Fourth, the synthetic hybrid pollinator is more easily produced during periods of heat and drought stress on dryland production than a single-cross hybrid using less vigorous inbred seed stocks. For example, in non-irrigated dryland field tests conducted during 1993 and 1994, production of synthetic hybrid seed remained relatively constant at about 55 bushels per acre despite the fact that rainfall accumulation during the critical months of May, June and July fell from 40.84 cm in 1993 to 13.82 cm in 1994. Over the same period, single cross and seed production using inbred seed stocks fell to less than 25 bushels per acre in 1994 from 55 bushels per acre in 1993.

Fifth, the single cross synthetic hybrid pollinator which results from the cross of two parental synthetic populations, A.times.B, is more quickly produced in a single generation compared to a three-way cross pollinator (A.times.B)C that requires an additional plant generation to produce the hybrid three-way cross pollinator. For example, the A.times.B synthetic hybrid is simply produced in a single plant growing generation in the production of P55 single-cross synthetic hybrid while the three-way cross synthetic hybrid pollinator would require an additional plant generation to produce the final hybrid (A.times.B) crossed to the parental C-population to produce a synthetic three-way hybrid cross designated (A.times.B)C.

According to the invention, there is provided a novel synthetic corn hybrid, designated P55, that when used to pollinate an elite male sterile hybrid grain parent, produces commercial grain exhibiting improved quality grain traits, including high oil and protein. Furthermore, when P55 is used to pollinate male sterile hybrid grain parents that are harvested as whole plants at approximately 50% plant moisture, it produces commercial fodder that expresses improved feeding quality traits, including improved feed efficiency and rate of weight grain.

P55 is characterized by excellent cold tolerant seedling vigor for rapid emergence in cold soils and excellent early-season adaptability facilitating nicking with early maize hybrids to condition fast dry-down and superior grain quality in the grain arising from the recipient female grain parent. The invention thus relates to the seeds, plants and plant parts of P55; to tissue culture comprising regenerable cells of a plant part of P55; to plants regenerated from regenerable cells of the tissue culture of P55; to a method of producing P55 by crossing synthetic LP41.1B-Lancaster and LP44.1A-Reid synthetics; and to a method of producing high oil TopCross.RTM. grain using P55 as a pollinator in a TopCross.RTM. seed blend.

In the description and examples that 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:

Anthesis. The period or act of flowering.

Backcross. The cross of a hybrid to either one of its parents. The offspring of such a cross is referred to as the backcross generation.

Backcross Method of Breeding. A system of breeding carried out by several generations of backcrossing to one of the parents of a hybrid and subsequent selection. The characteristics of the recurrent parent are retained for the most part, and characteristics from the nonrecurrent parent are added.

Bulk Method of Breeding. The growing of segregating generations of a hybrid of self-pollinating crops in a bulk, with or without mass selection, followed by individual plant selection in F.sub.6 or later generations.

Combining Ability. The ability of a genetic strain, when crossed with another strain, to produce a high proportion of desirable individuals.

Cytoplasmic Inheritance. Transmission of hereditary characters through the cytoplasm as distinct from transmission by genes carried by chromosomes. Detected by differing contribution of male and female parents in reciprocal crosses.

Diallel Cross. The crossing in all possible combinations of a series of genotypes.

Donor parent. The parent from which one or a few genes are transferred to the recurrent parent in backcross breeding.

Ear Height. The ear height is a measure from the ground to the top developed ear node attachment and is measured in centimeters.

Elite. This term characterizes a plant or variety possessing favorable traits, such as, but not limited to, high yield, good grain quality and disease resistance.

Embryo. The rudimentary plant in a seed. The embryo arises from the zygote. In high oil corn breeding, increases in oil content are accompanied by increases in embryo size.

Endosperm. The nutritive tissue formed within the embryo sac in seed plants. It commonly arises following the fertilization of the two primary endosperm nuclei of the embryo sac by the two male sperms. In a diploid organism the endosperm is triploid.

Express. To manifest a genetic character trait.

F.sub.1. The first generation of a cross.

F.sub.2. The second filial generation obtained by self-fertilization or crossing inter se of F.sub.1 individuals. Subsequent generations are F.sub.3, F.sub.4, F.sub.5, etc.

GDD Shed. The number of growing degree days or heat units required for an inbred line or hybrid to reach anthesis or pollen shed from the time of planting. Growing degree days are calculated by the Barger Method, where the heat units for a 24-hour period are: ##EQU1## The highest maximum used is 86 degrees F. and the lowest minimum used is 50 degrees F. For each hybrid it takes a certain number of GDDs to reach various stages of plant development. GDDs are a way of measuring plant maturity.

Genotype. The fundamental genetic constitution of an organism.

Germ. The embryo of the corn kernel that contains most of the oil found in the kernel.

Grain. Mature corn kernels produced by commercial growers for purposes other than growing or reproducing the species.

Grain Parent. Male sterile, elite hybrid that comprises a large majority of the plants in a TopCross.RTM. production field.

Grain Parent Seed. Corn seed used to produce grain parent plants.

Grain Quality. The general quality of shelled grain as it is harvested based on the color of the harvested grain, any mold on the grain, and any cracked grain.

Grain Quality Trait. Any attribute of grain that is of commercial value. Such traits relate to the intermediate or final use of grain and include but are limited to the quantity or quality of oil, protein, starch, pigmentation, and fiber found in corn grain. Such traits also encompass physical attributes of the grain itself, such as grain texture, size, or hardness, among others. Certain of these compositional or physical attributes of grain correlate with functional attributes as well which are of commercial importance, such as susceptibility to breakage and spoilage, among others.

Heat Units. A measure of the relative heat experienced by crops, expressed in degree days. Heat units is a function of the daily temperature highs and lows, and is calculated as: ›(Max. Temp.(<86 Degrees F.)+Min. Temp.(>50 Degrees F.))/2!-50. If Max. Temp. 86 degrees Fahrenheit or greater than 86 degrees Fahrenheit, then 86 is used and if Min. Temp. is 50 degrees or less, then 50 is used. Heat units accumulated daily and cannot be less than 0.

Heterozygous. A genetic condition existing when different alleles reside at corresponding loci on homologous chromosomes.

Homozygous. A genetic condition existing when identical alleles reside at corresponding loci on homologous chromosomes.

Hybrid. (1) The progeny of a cross fertilization between parents belonging to different genotypes. (2) The first generation offspring of a cross between two individuals differing in one or more genes. (3) A hybrid is the result of a cross between two or more components.

Hybrid Vigor. The phenomenon in which the cross of two stocks produce hybrids that show increased vigor-heterosis compared to the parent stocks.

Inbred. A substantially homozygous individual, variety or line.

Inbred Line. (1) A line produced by continued inbreeding. In plant breeding a nearly homozygous line usually originating by continued self-fertilization, accompanied by selection. (2) A relatively homozygous line produced by inbreeding and selection.

Kernel. The corn caryopsis comprising a mature embryo and endosperm which are products of double fertilization.

Line. (1) A group of individuals from a common ancestry. (2) A narrowly defined group that is a variety.

Male Sterility. A condition in which pollen is absent or non-functional in flowering plants.

Moisture. The moisture is the actual percentage moisture of the grain at harvest.

Pedigree. A record of the ancestry of an individual, family, or strain.

Pedigree Breeding. A system of breeding in which individual plants are selected in the segregating generations from a cross on the basis of their desirability and on the basis of a pedigree record.

Percent Oil. The oil concentration of a corn kernel expressed on a dry weight basis.

Percent Yield. The percent yield is the yield obtained for the hybrid in terms of percent of the mean for the experiments in which it was grown.

Phenotype. (1) Physical or external appearance of an organism as contrasted with its genetic constitution (=genotype); (2) a group of organisms with similar physical or external makeup; (3) the observed character of an individual without reference to its genetic nature.

Plant Height. A measure of the height of the hybrid from the ground to the tip of the tassel and is measured in centimeters. The data herein is given in percentage of mean of the experiments in which the hybrid was grown.

Pollen. A structure which contains the two haploid sperm nuclei which fuse with the egg nucleus and polar nuclei found in the ovule to give rise to the embryo and endosperm of the mature corn kernel.

Pollinators. Male fertile corn plants used to pollinate male sterile hybrid corn plants.

Pollinator Seed. Corn seed that, when sown, germinates to produce pollinator plants.

Population. In genetics, a community of individuals which share a common gene pool. In statistics, a hypothetical and infinitely large series of potential observations among which observations actually made constitute a sample.

Recurrent Parent. In backcross breeding, used to refer to the parent to which the first cross and successive backcrossed plants are crossed.

Seed. Mature corn kernels produced for the purpose of propagating the species.

Seed Parent. A corn line that is pollinated by pollen from pollinator plants, with hybrid corn seed resulting from this pollination.

Seedling Vigor. The visual rating (1 to 5) of the amount of vegetative growth after emergence at the seedling stage (approximately five leaves). A higher score indicates better vigor.

Self-fertilization. The fusion of the female egg cell of one individual with a male sperm cell of the same individual.

Single Cross. A cross between two genotypes, usually two genetically different inbred lines or synthetic lines.

Stay Green. The measure of plant health near the time of black layer formation (physiological maturity). A low score on a scale of 1 to 5 indicates better late-season plant health.

Synthetic Hybrid. Any offspring of a cross between two genetically unlike synthetic individuals or unlike individuals.

Synthetic Population. A genetically heterogeneous collection of plants of known ancestry created by the intermating of any combination of inbreds, hybrids, varieties, populations, races or synthetics.

Synthetic Variety. A variety produced by crossing inter se a number of genotypes selected for good combining ability in all possible hybrid combinations, with subsequent maintenance of the variety by open pollination.

Test Cross. A cross of a double or multiple heterozygote to the corresponding multiple recessive to test for homozygosity or linkage.

Test Weight. The measure of the weight of the grain in pounds for a given volume (bushel) adjusted for percent moisture.

TopCross.RTM. Grain Production System. The proprietary method of commercial high oil corn production of E.I. DuPont de Nemours and Company, Inc.

Variety. A subdivision of a species. A group of individuals within a species which are distinct in form or function from other similar arrays of individuals.

Yield (Bushels/Acre). The yield in bushels/acre is the actual yield of the grain at harvest adjusted to 15.5% moisture.

P55 is a yellow dent corn, high oil single cross synthetic hybrid having superior agronomic characteristics and the ability to impart desirable grain quality traits to a first generation grain when used as a pollinator in the TopCross.RTM. grain production system.

Synthetic hybrid P55 is produced by planting synthetic populations LP41.1B and LP44.1A, allowing one synthetic to pollinate the other, and harvesting the resulting seed. Either synthetic parental population may be used as female parent or the male parent. Preferably, synthetic LP41.1B should be the female of the cross and synthetic LP44.1A should be the male of the cross because of the larger seed size grade-out resulting from the LP41.1B seed parent in hybrid synthetic production. Production planting of the male and female synthetics can be made at the same time due to the fact that male pollen is shed at the same time the female silks are receptive to the pollen.

LP41.1B and LP44.1A were produced by conducting a series of crosses, selfings and backcrosses beginning with the crossing of LH51 and LH59 with ASKC28 (for LP41.1B) and the crossing of LH132 and B73 with ASKC28 and B73 with UHOC3 (for LP44.1A). During the random mating generation of development of LP41.1B and LP44.1A, test crosses were made to a hybrid grain parent tester and the resulting grain was analyzed to identify normal grain type segregants with favorable dominant oil genes expressing high oil in the genetic segregants.

When produced according to the method disclosed herein, both LP41.1B and LP44.1A breed true, that is, produce a P55 synthetic hybrid that is both reproducible and usable as a high oil TopCross.RTM. pollinator.

CHARACTERISTICS OF P55

Synthetic corn hybrid P55 most closely resembles maize synthetics ASKC28, ASKC20 and UHO in characteristics of plant type, ear type, kernel type and usage, but P55 is considerably earlier in maturity and expresses moderately higher grain test weight with normal grain and dent phenotype that expresses a moderately hard starch.

P55 synthetic hybrid has the following characteristics, based on data primarily collected at El Paso, Ill.:

P55 is adapted over a wide area of the northern corn belt and can be used advantageously in seed blends with male sterile hybrids from approximately 100-115 relative maturity based on the Minnesota Relative Maturity Rating System for harvest moisture of the grain. P55 cold test vigor was excellent in laboratory tests, exhibiting 95% emergence compared to 90% emergence for ASKC20, 92% emergence for UHOC3, and 83% emergence for ASKC28. Kernel size-out is also very good for P55, with approximately 59 percent of the kernels falling in the medium flat category.

Although P55's primary use would be as a pollinator in the TopCross.RTM. grain production system with blends of early maturing corn hybrid male sterile grain parents, it is also an acceptable male to be crossed to later maturing full season high oil pollinators to develop medium maturity pollinators for expanding the use of its genetics to fuller season maturity grain parents.

Pollen production is good with P55. Under extreme heat and drought stress, P55 may top fire and have some tassel blasting (necrosis of top leaves and tassel, respectively). It sheds pollen for approximately eighteen days and should be planted in 8 to 20 percent blends to ensure adequate pollen in commercial production of TopCross.RTM. grain where it is used as a male pollinator.

P55 has shown uniformity and stability within the limits of environmental influence for all traits as described in Table 1. P55 has expressed segregation for red and white cob color because of the genetic differences of LP41.1B and LP44.1A synthetic parent populations. P55 is a synthetic hybrid that has been maintained by hand and cross pollination in isolated fields with continued observation of high oil for uniformity of dominant high oil genetics. Although segregating for cob color, glume color and plant height in test crosses, P55 synthetic has consistently expressed high oil across different environments.

P55 is an early-medium maturity flowering synthetic hybrid, broadly adapted to the corn growing areas of the Northern United States and Southern Canada. P55 has expressed high oil and excellent cold soil seedling vigor that conditions low grain moisture in the grain of the male sterile hybrid grain parents.

BENEFITS OF P55 AS A POLLINATOR

In field tests of the TopCross.RTM. grain production system using P55 as the pollinator and a male sterile hybrid grain parent, plants of both varieties were allowed to grow unmolested to maturity. Both varieties were allowed to continue to grow and natural cross-pollination occurred by the action of wind as is normal in most grasses, including corn (i.e., excluding wheat). Of course, only pollen from the male parent synthetic hybrid, P55, was available for pollination of the male sterile hybrid grain parent; the tassels, or pollen bearing flowering parts, of the grain parent having been rendered sterile by genetic/cytoplasmic mechanisms.

The fields where high oil TopCross.RTM. grain was produced were well isolated from other corn fields to prevent any accidental contamination with ambient pollen. Such isolation techniques may be accomplished by timed delay with other hybrid corn production fields or by using a space distance pattern of more than 70 m from normal corn, well known to those skilled in the art of the seed corn industry.

Both varieties comprising the corn seed blend were allowed to continue to grow and be harvested. The ears harvested from the male sterile grain parent expressed the higher grain yield potential of the elite male sterile grain parent and the high oil, protein and grain density qualities of the pollen parent. The grain from the male parent variety ears can also be harvested along with the grain of male sterile grain parent for high oil corn use.

Because the same oil source (i.e. ASKC28) was used in the development of the LP41.1B-Lancaster and LP44.1A-Reid parental populations, only modest heterotic effects for yield were expressed in P55. The low grain yields expected from synthetic hybrid P55 pollinator dictated the need for a low percent of pollinator in the pollinator-grain parent seed blend so as to maximize yield, but a high enough percent to produce sufficient pollen to maintain the higher yield potential of the elite male sterile grain parent hybrid.

The field tests discussed below indicated that P55 induces superior grain quality characteristics to TopCross.RTM. grain of the male sterile hybrid grain parent as a result of being pollinated by P55. That is to say, the grain quality traits and high oil characteristics of P55 were transferred to the grain of the male sterile hybrid grain parent.

In the two examples that follow, the characteristics of TopCross.RTM. grain produced using P55 as a pollinator are provided.

1995 Strip Test Trials

First year (1995) strip test trials were conducted in El Paso, Ill., comparing the characteristics of grain from various Pfister hybrids rendered male sterile and pollinated by P55 with the characteristics of grain produced from grow outs of the same Pfister hybrids in their fertile state. The hybrids used were Pfister hybrids 2320, 3001, 3034, 3333, X528, X577, X591, X592 and X642. These results are presented in Table 2.

Traits obtained from the strip test data include the following:

"Grain yield", expressed in bushels per acre for both the grain produced by the pollination of the male sterile hybrid by P55 and for the grow out of the fertile hybrid.

"Moisture percent", expressed as a percentage of total kernel weight for both grain produced from the pollination of the male sterile hybrid by P55 and for the grow out of the fertile hybrid. Moisture Percent was determined by distillation on a Brown-Duvel moisture tester manufactured by the Seed Trade Reporting Bureau of Chicago, Ill. Electronic moisture testers were calibrated against the moisture determinations of the Brown-Duvel moisture tester in field harvest tests.

"Oil Percent", expressed as a percentage of the total kernel dry weight for both grain produced from the pollination of the male sterile hybrid by P55 and for the grow out of the fertile hybrid. Thus oil percent is a measure of the content of oil in the grain at harvest. Oil percent was determined by NIR on a dry matter basis (0% moisture).

"Protein percent", expressed as the percentage of protein in the grain on a dry matter basis as determined by NIR for both grain produced from the pollination of the male sterile hybrid by P55 and for the grow out of the fertile hybrid.

Grain yield, moisture percent, oil percent and protein percent for the grain produced by the male sterile/P55 blends are also expressed as a percent of the same traits from the fertile grain parent grow outs (% of GP).

1997 Strip Test Results

Second year (1997) strip test trials were conducted in El Paso, Ill., comparing the characteristics of grain from various Pfister hybrids rendered male sterile and pollinated by P55 with the characteristics of grain produced from grow outs of the same Pfister hybrids in their fertile state. The hybrids used were Pfister hybrids 2020, 2025, 3034, X623 and X777. The results are presented in Table 3.

Yield Comparisons TopCross.RTM. Grain Versus Hybrid Self

In the first year (1995) trials, blends of 8-9 percent pollinator seed and 91-92 percent male sterile hybrid seed were planted and grown to maturity. Grain from both the male sterile hybrid plants and the pollinator plants were harvested. The mean yield of grain produced by the pollination of the male sterile hybrids by P55 was 94 percent of the yield of grain from the fertile grain parents in eight comparisons. In one comparison, the yield achieved from a blend of P55 and Sdms-cytoplasmic male sterile grain parent hybrid Pfister X591-Sdms (140.4 Bu/A) was slightly more than the yield obtained from a grow out of fertile Pfister Hybrid X591 (132.3 Bu/A).

In the second year (1997) trials, the mean yield achieved in five different comparisons from a blend of 8-9 percent P55 and 91-92 percent Pfister Hybrid sterile grain parents was 102% of the yield obtained from planting the fertile Pfister hybrids alone.

Oil Comparisons--TopCross.RTM. Grain Versus Hybrid Self

Comparisons of the oil content of TopCross.RTM. grain were made against the oil content of grain from fertile hybrids. The oil contents of grain produced in first year (1995) strip tests of Pfister male sterile hybrids 2320-Sdms, 3001-Sdms, 3034-Sdms, 3333-Sdms, X528-Sdms, X577-Sdms, and X591-Sdms, X592-Sdms and X642-Sdms pollinated by P55 are presented in Table 2. The overall mean oil content of the TopCross.RTM. grain was 165% higher--or 3% higher in absolute terms (7.6% compared to 4.6%) --than the overall mean oil content of the grain from the fertile checks of the nine hybrids in tests made at El Paso, Ill.

In second year (1997) comparisons (Table 3), the mean oil content of grain produced by male sterile Pfister Hybrids 2020-Sdms, 2025-Sdms, 3034-Sdms, X623 and X777-Sdms pollinated by P55 was 167 percent higher (7.3 percent compared to 4.4 percent) than the mean oil content of grain produced from the self pollination of the fertile hybrid alone.

Moisture Comparisons--TopCross.RTM. Grain Versus Hybrid Self

Conventional high oil hybrids traditionally express higher grain moisture at harvest and are slower to dry down than lower-oil dent hybrids of the same maturity. To test this concept of higher moisture associated with higher oil content of grain, comparisons were made of moisture at harvest of grain resulting from the pollination by P55 of male sterile Pfister hybrids and grain resulting from the self pollination of the comparable fertile Pfister hybrids.

In first year trials (Table 2), grain moisture at harvest from the sterile grain parent hybrids pollinated by P55 was higher than the grain moisture from the fertile grain parent hybrids alone in all nine comparisons. Since higher oil content resulted in higher moisture content in all nine comparisons, the first year data supported conventional theory regarding the relationship between higher oil content with accompanying larger germs and higher grain moisture.

In second year trials (Table 3), grain moisture at harvest from the sterile grain parent hybrids pollinated by P55 was higher than the grain moisture from the fertile grain parent hybrids alone in only one of six comparisons. The overall mean grain moisture was lower for the TopCross.RTM. grain: 15.9 percent compared to 16.5 percent. The second year data did not support the theory that higher moisture is associated with higher oil content.

Protein Comparisons--TopCross.RTM. Grain Versus Hybrid Self

In first year (1995) strip tests protein content of the TopCross.RTM. grain (i.e., the grain resulting from the pollination of the male sterile hybrid by P55) was compared to the protein content of grain produced from open pollinated fertile hybrid checks. Analysis of population means indicated that P55 significantly increased protein in the TopCross.RTM. grain compared to the grain from the fertile hybrid grain parent checks. For example, mean protein level from grain produced by the pollination of Pfister Hybrid X642 by P55 was 109 percent higher (10.6 percent compared to 9.7 percent) than the protein level in grain produced by the self pollination of fertile X642. Mean protein level from grain produced by the pollination of Pfister Hybrid X528 by P55 was 117 percent higher (11.0 percent compared to 9.4 percent) than the protein level in grain produced by the self pollination of fertile X528.

In second year (1997) trials (Table 3), the overall mean grain protein content of the grain resulting from the pollination of the five male sterile hybrids by P55 was 109 percent higher than the overall mean grain protein from grain produced by the hybrid selfs (10.1 compared to 9.2).

Tassel-Silk Synchronization--P55 Pollen Shed Dates Compared to Grain Parent Silk Extrusion Dates

The success of the TopCross.RTM. grain production system is primarily based on the synchronization of pollen shed from the pollinator with the extrusion of silks from the male sterile grain parent hybrid, which is termed nicking.

Table 4 presents results of tassel-silk date observations and growing degree days (GDD) to tassel shed and silk flowering for P55 pollinator and Pfister Hybrid 2020, respectively. As shown in the table, in 1997 strip tests the pollination period of P55 began July 18 and ended August 4, an eighteen (18) day period. The peak pollination date, i.e., the date during which 50% cumulative pollen shedding was achieved, occurred on July 22 (the result of 1196 GDD). By comparison, the peak silk extrusion date for Pfister Hybrid 2020 was one day later--July 23 (the result of 1218 GDD). These data indicate that the nicking of TopCross.RTM. pollinator P55 with male sterile Pfister Hybrid 2020-Sdms is acceptable.

Dry Down Comparisons--Oil, Protein and Moisture in Grain Produced From Hybrid Self Pollination, Hybrids Pollinated by P55, and Self-Pollinated P55, Each Harvested Over Time

Table 5 presents the oil content, protein content and moisture of grain produced from Pfister Hybrids 2020 and 2020-Sdms (columns one and two), grain produced from Pfister Hybrids 2020 and 2020-Sdms pollinated by P55 (columns three and four), and grain produced from self-pollinated P55 (column five) when the grain was harvested 39 days after flowering and then harvested on selected days to and beyond the onset of physiological maturity (i.e., black-layer).

Pfister Hybrid 2020-Sdms pollinated by P55 (column four) expressed 7.31% oil content of the grain as early as 716 GDD after flowering, thus indicating a very high level of oil while the plant foliage was green and actively growing. This permits an early harvest for silage and/or earlage while maintaining a high energy recovery from the grain.

A comparison of the protein content data shows little difference in protein at 39 days after flowering (9.7%) through 77 days (9.4%), suggesting the physiological make-up of the seed is basically complete at the early (39 day) harvest date.

A comparison of moisture over the course of 43 days (August 29 to October 7) illustrates the rate of dry down. The moisture data indicates that the rate of dry down of grain resulting from the self-pollination of fertile hybrid 2020 (column one) was faster than the rate of dry down of grain resulting from the pollination by P55 of male sterile hybrid 2020 (column four). For example, at 39 days after pollination, both types of grain contained about 52% moisture, but after 77 days the TopCross.RTM. grain had 30% moisture while the self-pollinated hybrid had only 23% moisture.

The rate of dry down of self-pollinated P55 grain (column five) was slower than the rate of dry down of grain from Pfister hybrid 2020 pollinated by P55 (column three). For example, grain produced from self pollinating P55 achieved 24% moisture in 82 days whereas grain resulting from the pollination by P55 of male sterile hybrid 2020 achieved 20% moisture over the same time period.

DEPOSIT INFORMATION

Applicant has made available to the public without restriction, a deposit of at least 2500 seeds of synthetic hybrid P55 with the American Type Culture Collection (ATCC), Rockville, Md. 20852, ATCC Deposit No. 209429. Synthetic parental seed stocks of LP41.1B-Lancaster and LP44.1A-Reid have also been made available to the public without restriction from a deposit of at least 2500 seeds of each synthetic population with the American Type Culture Collection (ATCC) under Deposit No. 209029 for LP41.1B and No. 97888 for LP44.1A.

The seeds deposited with the ATCC were taken from the same deposit maintained by DuPont TopCross International, Box 19, 90 North Fayette Street, El Paso, Ill. 61738, since prior to the filing date of this application. The deposit 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 effective life of the patent, whichever is longer, and will be replaced if it becomes nonviable during that period.

ASKC28 and UHOC3 have been previously deposited with ATCC. LH51, LH59, LH132, B73, ASKC28 and UHOC3 are publicly available maize materials.

Although the foregoing invention has been described in some detail by way of illustration and examples for purposes of clarity and understanding, it will be obvious that certain modifications and alternative embodiments of the invention are contemplated which do not depart from the spirit and scope of the invention as defined by the foregoing teachings and appended claims.