Inbred Corn Line PHR25

This invention is in the field of corn breeding, specifically relating to an inbred corn line designated PHR25.

The goal of plant breeding is to combine in a single variety/hybrid various desirable traits of the parental lines. For field crops, these traits may include resistance to diseases and insects, tolerance to heat and drought, reducing the time to crop maturity, greater yield, and better agronomic quality. With mechanical harvesting of many crops, uniformity of plant characteristics such as germination and stand establishment, growth rate, maturity, and fruit size is important.

Field crops are bred through techniques that take advantage of the plant's method of pollination. A plant is self-pollinated if pollen from one flower is transferred to the same or another flower of the same plant. A plant is cross-pollinated if the pollen comes from a flower on a different plant.

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

Corn plants (Zea mays L.) can be bred by both self-pollination and cross-pollination techniques. Corn has male flowers, located on the tassel, and female flowers, located on the ear, on the same plant. Natural pollination occurs in corn when wind blows pollen from the tassels to the silks that protrude from the tops of the incipient ears.

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 new 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 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 complement the other. If the two original parents do not provide all of the desired characteristics, other sources can be included in the breeding population. In the pedigree method, superior plants are selfed and selected in successive generations. In the succeeding generations the heterozygous condition gives way to homogeneous lines as a result of self-pollination and selection. Typically in the pedigree method of breeding, five or more generations of selfing and selection is practiced: F.sub.1 .fwdarw.F.sub.2 ; F.sub.2 .fwdarw.F.sub.3 ; F.sub.3 .fwdarw.F.sub.4 ; F.sub.4 .fwdarw.F.sub.5 ; etc.

Backcrossing can be used to improve an inbred line. Backcrossing transfers a specific desirable trait from one inbred or source to an inbred that lacks a trait(s). This can be accomplished for example by first crossing a superior inbred (A) (recurrent parent) to a donor inbred (non-recurrent parent), which carries the appropriate gene(s) for the trait in question. The progeny of this cross is then mated back to the superior recurrent parent (A) followed by selection in the resultant progeny for the desired trait to be transferred from the non-recurrent parent. After five or more backcross generations with selection for the desired trait, the progeny 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 would be selfed to give pure breeding progeny for the gene(s) being transferred.

A hybrid corn variety is the cross of two inbred lines, each of which may have one or more desirable characteristics lacked by the other or which complement the other. The hybrid progeny of the first generation is designated F.sub.1. In the development of hybrids only the F.sub.1 hybrid plants are sought. The F.sub.1 hybrid is more vigorous than its inbred parents. This hybrid vigor, or heterosis, can be manifested in many ways, including increased vegetative growth and increased yield.

The development of a hybrid corn variety involves three steps: (1) the selection of superior plants from various germplasm pools; (2) the selfing of the superior plants for several generations to produce a series of inbred lines, each of which, although different from each other, bred true and are highly uniform; and (3) crossing the selected inbred lines with unrelated inbred lines to produce the hybrid progeny (F.sub.1). During the inbreeding process the vigor of the lines decreases. Vigor is restored when two unrelated inbred lines are crossed to produce the hybrid progeny (F.sub.1). An important consequence of the homozygosity and homogeneity of the inbred lines is that essentially all the hybrid plants resulting from a cross between any two inbreds will be genetically uniform. Once the inbreds that give the best hybrid 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.sub.1 progeny. A double-cross hybrid is produced from four inbred lines crossed in pairs (A.times.B and C.times.D) and then the two F.sub.1 hybrids are crossed again (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 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 obvious: 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 inbred parental lines for producing hybrids.

According to the invention, there is provided a novel inbred corn line, designated PHR25. This invention thus relates to the seeds of inbred corn line PHR25, to the plants of inbred corn line PHR25, and to methods for producing a corn plant produced by crossing the inbred line PHR25 with itself or another corn line. This invention further relates to hybrid corn seeds and plants produced by crossing the inbred line PHR25 with another corn line.

In the description and examples that follow, a number of terms are used herein. In order to provide a clear and consistent understanding of the specification and claims, including the scope to be given such terms, the following definitions are provided:

Predicted RM. This trait, predicted relative maturity (RM),for a hybrid is based on the harvest moisture of the grain. The relative maturity rating is based on a known set of checks and utilizes standard linear regression analyses and is referred to 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.

Selection Index. The selection index gives a single measure of the hybrid's worth based on information for up to five traits. A corn breeder may utilize his or her own set of traits for the selection index. One of the traits that is almost always included is yield. The selection index data presented in the tables in the specification represent the mean value averages across testing stations.

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

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.

Moisture. The moisture is the actual percentage moisture of the grain at harvest presented in percent of the mean for the experiments in which the hybrid was grown.

GDU Shed. The GDU shed is the number of growing degree units (GDU) or heat units required for an inbred line or hybrid to reach anthesis or pollen shed from the time of planting. Growing degree units are calculated by the Barger Method, where the heat units for a 24-hours period are: ##EQU1## The highest maximum used is 86.degree. F. and the lowest minimum used is 50.degree. F. For each hybrid is takes a certain number of GDUs to reach various stages of plant development. GDUs are a way of measuring plant maturity. The data is given in percent of the mean for the experiments in which the hybrid was grown.

Stalk Lodging. This is the percentage of plants that do not stalk lodge, i.e., stalk breakage, as measured by either natural lodging or pushing the stalks and determining the percentage of plants that break off below the ear. This is a relative rating of a hybrid to other hybrids for standability. The data are given as the percentage of the mean for the experiments in which the hybrid was grown.

Root Lodging. The root lodging is the percentage of plants that do not root lodge; i.e., those that lean from the vertical axis at an approximate 30.degree. angle or greater would be counted as root lodged. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Barren Plants. This is the number of the plants per plot that were not barren (lack ears). The data is converted to percent of the mean for the experiments in which the hybrid was grown.

Stay Green. Stay green is the measure of plant health near the time of black layer formation (physiological maturity). A high score indicates better late-season plant health. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Test Weight. This is the measure of the weight of the grain in pounds for a given volume (bushel) adjusted for percent moisture. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Cob Score. The cob score is a rating of how well the grain is shelled off the cob and how badly the cob is broken up going through the combine. This is given as a 1 to 9 score with 9 being good. A high score indicates that the grain shells off of the cob well, and the cob does not break. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Grain Quality. This is a 1 to 9 rating for the general quality of the shelled grain as it is harvested based on the color of the harvested grain, any mold on the grain, and any cracked grain. High scores indicate good grain quality. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Seedling Vigor. This is the visual rating (1 to 9) of the amount of vegetative growth after emergence at the seedling stage (approximately five leaves). A higher score indicates better vigor. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Early Stand Count. This is a measure of the stand establishment in the spring and represents the number of plants that emerge on a per-plot basis for the hybrid. The data is given in percentage of mean of the experiments in which the hybrid was grown.

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 inches. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Ear Height. The ear height is a measure from the ground to the ear node attachment and is measured in inches. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Dropped Ears. This is a measure of the number of dropped ears per plot and represents the number of plants that did not drop ears prior to harvest. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Brittle Stalks. This is a measure of the stalk breakage near the time of pollination of the hybrids, and is an indication of whether a hybrid would snap or break at the time of flowering under severe winds. Data are presented as percentage of plants that did not snap. The data is given in percentage of mean of the experiments in which the hybrid was grown.

Inbred corn line PHR25 is a yellow dent corn with superior characteristics and provides an excellent parental line in crosses for producing first generation (F.sub. 1) hybrid corn. Inbred corn line PHR25 was selected from the cross B83/207. Both B83 and 207 are Pioneer proprietary inbreds. The cross (B83/207) was produced when B83 was used as the female parent in a 207 isolation field grown at Woodstock, Ontario. As a female, B83 was detasseled and allowed to cross-pollinate with the male, 207. The hybrid, B83/207, was selfed and a bulk of the seed was saved and planted in the Woodstock breeding nursery. Standard pedigree ear-row selection and selfing was practiced with selection for acceptable agronomic traits and uniformity during the line development process. Test crosses to appropriate testers were made and evaluated in topcross yield tests. The inbred had good testcross performance and appeared acceptable as a male parent. Additional ear-row selection was practiced up through the F16 stage. PHR25 was evaluated as a line per se and in additional crosses by Pioneer Hi-Bred International, Inc. northern research stations. One particular cross showed promise in Woodstock testing. This hybrid was tested widely across the Northern Corn Belt.

The inbred is adapted to the northern United States and may advantageously be used in producing hybrids of approximately 80 to 90 relative maturity based on the Minnesota Relative Maturity Rating System for harvest moisture of the grain. PHR25 sheds adequate amounts of pollen to be an acceptable male. It averaged 1.38 gm per plant (93% of experiment mean) over 14 locations in parent research testing. PHR25 has questionable cold test as a female with below-average ear and grain quality with soft-textured grain. Thus, its primary use will be as a male in the production of hybrids.

The inbred PHR25 has shown uniformity and stability for all traits as described in the following variety description information. It has been self-pollinated and ear-rowed a sufficient number of generations with careful attention paid to uniformity of plant type to ensure genetic homozygosity and phenotypic stability. The line has been increased both by hand and in isolated fields with continued observations for uniformity. No variant traits have been observed or are expected in PHR25.

Inbred corn line PHR25 has the following morphological and other characteristics (based primarily on data collected at Johnston, Ia.):

Inbred corn PHR25 most closely resembles 207 in characteristics of maturity, plant type, ear type, kernel type, and usage.

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 parent corn plant is the inbred corn plant from the line PHR25. Further, both first and second parent corn plants may be from the inbred line PHR25. Thus, any methods using the inbred corn line PHR25 are part of the invention: selfing, backcrosses, hybrid breeding, and crosses to populations. Any plants produced using inbred corn line PHK05 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.sub. 1) corn hybrid seed and plants with superior characteristics.

As used herein, the term "plant" 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.

Tissue culture of corn is described in European Patent Application, publication number 160,390, incorporated herein by reference. Corn tissue culture procedures are also described in Green and Rhodes, "Plant Regeneration in Tissue Culture of Maize," Maize for Biological Research (Plant Molecular Biology Association, Charlottesville, Va. 1982), at 367-372. Thus, another aspect of this invention is to provide for cells which upon growth and differentiation produce the inbred PHR25.

Corn is used as human food, livestock feed, and as raw material in industry. The food uses of corn, in addition to human consumption of corn kernels, include both products of dry- and wet-milling industries. The principal products of corn dry-milling are grits, meal, and flour. The corn wet-milling industry can provide starch, syrups, and dextrose for food use. Corn oil is recovered from corn germ, which is a by-product of both dry- and wet-milling industries.

Corn is also used extensively as livestock feed primarily to beef cattle, dairy cattle, hogs, and poultry.

Industrial uses of corn are mainly from corn starch from the wet-milling industry and corn flour from the dry-milling industry. The industrial applications of corn starch and flour are based on functional properties, such as viscosity, film formation, adhesive properties, and ability to suspend particles. The corn starch and flour have application in the paper and textile industries. Other industrial uses include applications in adhesives, building materials, foundry binders, laundry starches, explosives, oil-well muds, and other mining applications.

Plant parts other than the grain of corn are also used in industry. Stalks and husks are made into paper and wallboard and cobs are used for fuel, to make charcoal.

The seed of inbred corn line PHR25, the plant produced by the inbred seed, the hybrid corn plant produced from the crossing of the inbred, hybrid seed, and various parts of the inbred and hybrid corn plant can be utilized for human food, livestock feed, and as a raw material in the industry.

In the examples that follow, the traits and characteristics of inbred corn line PHR25 as a line and in hybrid combination are given. The data collected on inbred corn line PHR25 is presented for the key characteristics and traits.

The data in Table 1 shows the relative hybrid performance of PHR25 compared to H51 which is a Pioneer proprietary parent used in some early hybrids commercially sold in the northern United States. This data was obtained across eight inbred testers where the hybrids involving PHR25 and H51 were grown in the same experiment (each line was crossed to the same inbreds). The data was averaged across all testers and replications and would include experiments grown by five Pioneer Hi-Bred International, Inc. northern corn research stations.

The data shows that both lines make hybrids of similar maturity (RM) but that PHR25 hybrids tend to be a little drier at harvest (lower predicted RM) but flower a little later (GDU shed). PHR25 hybrids have better stalk lodging resistance than H51 crosses but tend to have poorer seedling vigor and early stand counts.

In specific hybrid combinations, PHR25 has shown outstanding yield performance relative to other commercially sold hybrids of similar maturity.

The data in Table 2 shows the electrophoresis results for PHR25 and its parents B83 and 207. The electrophoresis results show that PHR25 and 207 contain the same alleles for 19 loci. These tests were based on 10 plants for each inbred. Although the lines have the same electrophoresis pattern, the inbreds are distinctly different for other traits. PHR25 is earlier to flower, has drier grain at harvest, poorer roots, poorer staygreen, and poorer grain quality than 207 as an inbred. Also B83 and 207 were only different at two loci for the alleles present.

Inbred seeds of PHR25 have been placed on deposit at the American Type Culture Collection (ATCC), Rockville, Md. 20852, under deposit accession number 40415 on Jan. 13, 1988. A Plant Variety Protection Certificate has also been applied for with the United States Department of Agriculture.

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.