Rapid generation advancement in winter wheat

Methods for rapidly advancing wheat generations towards a winter wheat objective, including crossing a winter wheat line with a donor line having a dominant minimal vernalization gene, breeding the offspring from that cross, and selecting to recover wheat plants having the winter growth habit. The breeding process may include selection for the minimal vernalization trait. The offspring resulting from the breeding process may also be crossed with a winter wheat before selection for the winter growth habit. The donor line includes a dominant vernalization gene and also in some cases a gene or genes for a desired trait.

FIELD OF THE INVENTION 
This invention relates to breeding of wheat plants. In particular, it 
relates to methods for rapidly advancing wheat inbreeding generations to 
enhance breeding programs. 
BACKGROUND OF THE INVENTION 
Wheat (Triticum aestivum L.) is the most important human food crop in the 
world. Winter wheat is grown worldwide and accounts for more than 60% of 
U.S. wheat production (Briggle and Curtis (1987) Wheat and Wheat 
Improvement:1). Various cultivars have been developed to accommodate 
different growing conditions, wheat usages and resistance to disease and 
insects. Such improved cultivars have been a significant factor in 
increasing wheat yields and quality as well as stabilizing global wheat 
production. 
Breeding objectives involve creating new genotypes improved in one or more 
important features. These objectives vary widely because the environmental 
conditions that affect wheat production and adversities that limit wheat 
yields differ from one production area to another. The principal 
categories of improvement objectives include yield potential, yield 
stability and grain quality as is generally discussed in Poehlman, (1987) 
Breeding Field Crops, Connecticut: A.V.I. Pub. Co. Inc.). 
One of the most important breeding objectives in wheat breeding is yield 
because it affects the economic return to the farmer. Wheat genotypes 
differ in their inherent yield potential. Several plant characteristics 
have been associated with higher yield potential. The most important have 
been greater spike productivity, kernel weight, spike size, and shorter 
straw. Shorter straw cultivars have been obtained by incorporation of 
dwarfing genes, such as Rht.sub.1 and Rht.sub.2. When only one such gene 
is incorporated, the new wheat cultivar is called a semi-dwarf. 
Another important breeding objective, yield stability, is accomplished by 
breeding for early maturity, lodging and shatter resistance, tolerance to 
drought and soil stress, and resistance to disease and insect pests. Early 
wheat is advantaged because it may escape damage from heat, drought, 
insects, or disease. Early harvest also permits early removal of wheat 
crop in areas where multiple cropping is practiced. The inheritance of 
earliness has been reported as being dominant or partially dominant to 
late maturity and appears to be controlled by a few major genes. 
Resistance to lodging, a bending or breaking of the wheat culm, also 
contributes to a yield stability objective. The development of varieties 
with short, stout stems has increased the length of time that wheat will 
stand without breaking. Short stature may be obtained by 1) selecting for 
quantitative genes that reduce stem length in conventional varieties, 2) 
the use of dwarfing genes, or 3) combinations of the two groups of genes. 
Another element of yield stability is resistance to diseases, such as rust 
diseases, the smuts, foliage diseases, root rot diseases, and viral 
diseases. The rust diseases are among the most destructive plant diseases 
and exist in a gene-for-gene relationship. Resistance to rust disease is 
dominant over susceptibility. 
Several insects are problematic in wheat breeding. The major insect 
problems include wheat stem sawfly, cereal leaf beetle, green bug, and 
Hessian fly. Green bug resistance is conferred by a single dominant, 
biotype-specific gene. The Hessian fly is the most destructive wheat 
insect pest in the USA. In 1915, before the introduction of resistant 
cultivars, an outbreak of the Hessian fly caused an estimated $100 million 
in cross loss (Cartwright and Jones (1953) USDA Farmer's Bull., U.S. Govt. 
Printing Office, Washington, D.C.:1627). More recently, an estimated loss 
of $28 million was reported in the State of Georgia (Hudson et al., (1991) 
Georgia Agric. Exp. Stn. Spec. Publ. No. 70:29.). Virulence in the Hessian 
fly and antibiosis in the wheat host exist in gene-for-gene relationships 
(Hatcherr and Gallum, (1970), Ann. Entomol. Soc. Amer. 63:1400.). 
Resistance in the host is usually dominant and virulence in the insect is 
recessive. Several Hessian fly biotypes have been described that differ in 
their ability to infest wheats with specific genes for resistance. Genes 
for resistance and Hessian fly biotypes have been reviewed recently 
(Patterson et al., (1992) J. Econ. Entomol. 85:307.) 
Various breeding methods have been used extensively to add specific disease 
resistance genes to otherwise susceptible cultivars. Unfortunately, new 
biological forms of the disease pathogen soon arise to which the gene 
transferred does not confer resistance. This is particularly so when there 
is a gene-for-gene relationship between the wheat cultivar and the 
pathogen or pest. The term gene-for-gene relationship refers to an 
interaction between wheat genotypes which control reaction to the pathogen 
and the genotypes for pathogenicity in the pathogen. The interaction 
determines the severity of the infection. Therefore, successful cultivar 
development requires the ability to rapidly transfer genes or linkage 
blocks into desirable genetic backgrounds. Plant breeders must quickly 
introgress new resistance genes into the background of adapted cultivars. 
This requirement for rapid advancement of generations during cultivar 
development is problematic when breeding winter wheat. Although winter 
wheat provides a desirable genetic background for breeding due to its 
ability to harden and withstand freezing temperatures, it can be difficult 
to manipulate during cultivar development because it requires 
vernalization (exposure to near freezing temperatures in the seedling 
stage) before flowering will occur. 
Wheat breeders have accelerated the process of plant improvement by the use 
of off-season nurseries and/or greenhouses, thus allowing more generations 
to be grown per year. Three generations per year have been achieved in 
some spring wheat breeding programs for populations of restricked size 
grown in a greenhouse. However, most winter wheat breeders have been 
limited to one or two generations per year due to the vernalization 
requirement of winter wheat which may be as much as 65 days or longer 
depending upon the genotype. 
Attempts have been made to shorten the generation time of wheat through 
acceleration of seed maturation, germination of immature seeds and green 
vernalization (Mukade, et al. (1973) 4th Int. Wh. Genet. Symp.:439). 
However, these procedures can be tedious in nature and require specific 
steps to be taken for each generation in an attempt to hasten generation 
advancement. Also, these procedures may not be effective with a broad 
spectrium of winter wheat genotypes. 
Other attempts to achieve winter wheat objectives have involved DNA 
transformations. However, wheat transformation is currently difficult and 
relatively expensive (Vasil et al. (1992) Bio/Technology 10:667). 
Unpredicted deleterious somaclonal variation introduced to the recipient 
cultivar through the transformation process may prevent the direct use of 
transformed materials by farmers. 
A need exists for methods providing rapid advancement of generations to 
facilitate cultivar development. 
SUMMARY OF THE INVENTION 
The present invention provides methods for rapidly advancing wheat 
generations towards a winter wheat objective which include crossing a 
winter wheat line with a donor line that has a dominant minimal 
vernalization gene to yield offspring that are heterozygous for the 
minimal vernalization gene and are capable of advancing three or more 
generations per year; breeding the heterozygous offspring; and selecting 
to recover wheat plants having the winter growth habit and/or winter 
hardiness. The offspring resulting from the breeding process may also be 
crossed with a winter wheat line before selection for winter hardiness or 
winter growth habit. The breeding step may include selecting for plants 
carrying the minimal vernalization gene. According to the present 
invention, the donor line may also have a gene or genes for desired 
traits. 
It is an object of this invention to provide methods for rapidly advancing 
wheat generations. 
It is another object of the present invention to provide convenient and 
efficient methods for achieving various breeding objectives which involve 
creating new, improved genotypes. 
It is a further object of the present invention to provide cost-effective 
methods of obtaining improved wheat lines. 
These and other objects, advantages and features are accomplished according 
to the compositions and methods of the following description of the 
preferred embodiment of the present invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
For the purposes of promoting an understanding of the principles of the 
invention, reference will now be made to the preferred embodiments 
thereof, and specific language will be used to describe the same. It will 
nevertheless be understood that no limitation of the scope of the 
invention is thereby intended, such alterations, modifications, and 
further applications of the principles of the invention being contemplated 
as would normally occur to one skilled in the art to which the invention 
relates. 
As indicated above, the present invention provides methods for rapidly 
advancing wheat generations towards a winter wheat objective. The methods 
include crossing a winter wheat line with a donor line having a minimal 
vernalization gene, such as Vrn, breeding the offspring from that cross 
and either directly selecting winter growth habit plants, or crossing the 
offspring resulting from the cross with a winter wheat line to recover 
wheat plants having a winter growth habit. 
According to the present invention, minimal vernalization genes may be used 
to achieve the advancement of three generations or more per year towards a 
winter wheat objective. The present invention capitalizes upon the 
dominance effects of the major genes conferring the spring growth habit 
(Morrison, (1960) Z. VererbLehre 91:141.). In spite of the substantial 
physiological differences between winter wheat and spring wheat, the 
genetic differences between them is relatively minor. The spring growth 
habit is thought to be controlled by no more than five genes, any one of 
which conferring the spring growth habit when a dominant allele is 
present. 
Plant lines heterozygous for a major spring gene (such as Vrn) (Mcintosh 
and Cusick (1987) Wheat and Wheat Improvement:289.) may be grown to 
maturity with minimal vernalization. In this regard, vernalization refers 
to the artificial treatment of seeds before sowing or seedlings after 
germination to hasten flowering, and minimal vernalization is understood 
to mean a period of vernalization lasting no longer than about seven to 
ten days. Because the heterozygotes require only a minimal vernalization 
period, three generations or more per year may be achieved toward a winter 
wheat objective. Selection may be practiced during the breeding process 
for a Vrn gene and any desired gene(s) that are detectable under 
greenhouse conditions. After the final cross and identification of the 
gene(s) of interest, the selection can be reversed in relation to the 
dominant minimal vernalization gene so that the recessive gene types are 
favored and the winter growth habit is recovered. Resulting populations 
may then be directed to fall planted field nurseries for evaluation by 
standard field breeding methods. 
Generally, the invention provides methods for new winter wheat cultivars 
which include crossing a winter wheat line having a winter growth habit 
with a donor line. It is understood that a "line" is a group of plants 
with characteristics that are distinct, uniform and stable. A line is 
preferably an inbred line which exhibits desirable characteristics such as 
yield, maturity, disease resistance and other agronomic or quality 
characteristics. Once a line is identified as being superior it may be 
named, increased, and made available commercially as a cultivated variety, 
or cultivar. 
The winter wheat line may be any winter wheat, preferably an adapted, 
winter hardy wheat which provides a good genetic background. The donor 
line may be any wheat line having a dominant minimal vernalization gene. 
In one embodiment of the invention, the donor line may be obtained by 
crossing a wheat line having a desired trait with a spring wheat line 
requiring only minimal vernalization to yield the donor line. 
In one embodiment of the invention, the donor line is a spring wheat line 
having a dominant Vrn gene. Offspring of crosses between donor and winter 
wheat parents are heterozygous, Vrn/vrn. Such heterozygotes have a spring 
growth habit and are capable of advancing three or more generations per 
year. According to the invention, a breeding process may be performed with 
the heterozygous offspring. The ability of the offspring to advance three 
or more generations per year due to the Vrn gene, is an improvement over 
the parent winter wheat line which is capable of only one or two 
generations per year due to the vernalization requirement. 
The methods of the present invention may be used to rapidly advance 
inbreeding generations with or without selection. The breeding process may 
include selecting for plants carrying the minimal vernalization gene. It 
may also include selecting for and/or identifying plants which contain a 
desired trait or traits. After the final cross and identification of the 
desired genes, selection is reversed in relation to the minimal 
vernalization gene to favor the fully recessive types and recover the 
winter growth habit. 
Preferably the desired trait is controlled by expression of a single 
dominant gene, but may be recessive or polygenic. The desired trait may 
relate to any one of several breeding objectives, including yield 
potential, yield stability, or grain quality. The desired trait may 
include resistance to disease, including wheat rush diseases, septoria 
tritici, septoria nodorum, powdery mildew, helminthosporium diseases, 
smuts and bunts, fusarium diseases, bacterial diseases, viral diseases, 
and others. The desired trait might provide improved yield, milling and 
baking ability, early maturity, or lodging resistance. The desired trait 
may be conferred by a dwarfing gene, including Rht. It may be grain color 
R (red wheat) or r (white wheat) glume color, halriness, photoperiod 
response, homoeologous pairing, or male sterility M. The desired trait may 
included resistance to insect infestation, including Hessian fly, wheat 
stem soft fly, cereal leaf beetle, and green bug. Such traits are 
preferably conferred by a dominant gene such as the H21 gene for 
resistance to the Hessian fly Mayetiola destructor, (Say)! but may be 
recessive or polygenic. Cytoplasmic traits such as male sterility (CMS) 
for hybrid wheat production may also be recombined with different nuclear 
genotypes. Fertility restorer for CMS Rf is also a trait of importance. 
Where a particular Vrn gene and the gene of interest from a donor are 
discovered to be closely associated on the same chromosome, it will be 
preferable to use a different Vrn gene for the initial cross. In the case 
of close association of the genes, the difficulties related to repulsion 
phase linkage in the initial cross of a spring habit wheat by a donor or 
the coupling of the genes following cross over recombinations in later 
generations might significantly increase the effort required to utilize 
this method. However, these problems could be avoided by using a different 
Vrn gene. For example, if a gene for a trait such as Hessian fly 
resistance were located on the long arm of chromosome 5A near the Vrn1 
locus, then a spring habit wheat line with a gene at the Vrn3 locus on the 
long arm of chromosome 5D or the Vrn5 on the short arm of chromosome 7B 
might be used instead to initiate the crossing program (Mcintosh and 
Cusick, 1987). This would not be possible in the case where the gene for 
introgression was already linked to a Vrn gene in a spring habit donor. In 
this case, crossover recombination would be the only way to effect the 
transfer into winker wheat. 
Crosses made according to the methods of this invention may be accomplished 
by such conventional methods as are required to circumvent 
self-pollination. As is well known, the wheat flower is bi-sexual: wheat 
plants are practically always self-pollinated because the wheat anthers 
are located inside the florets and pollen is shed before flowers open. 
Generally, crosses can be accomplished as follows: Male anthers are 
removed from a plant to create a female plant. The head of the female 
plant is then covered to protect contamination. Pollen grain from anthers 
of the desired male plant are deposited on the stigmas of the female plant 
which remains covered to prevent contamination. 
The techniques of the present invention may be used to facilitate various 
mating schemes including single, three way, four way, or more complex 
crosses. Numerous crossing and selection methodologies may be practiced 
including backcrossing, recurrent selection as well as other breeding 
schemes. It is understood that the term recurrent selection means a 
breeding system designed to increase the frequency of favorable genes of a 
quantitatively inherited characteristic by repeated cycles of selection. 
In backcross breeding schemes, a gene for a favorable trait may be added 
to an otherwise favorable cultivar. The most significant feature of the 
backcross is that it provides a means for changing an allele and a 
cultivar without otherwise affecting cultivar performance. 
During the breeding process, selection may be made for the spring growth 
habit, i.e., minimal vernalization, by growing plants under a minimal 
vernalization regime. The minimal vernalization regime includes 
temperatures above 10.degree. C., with temperatures not falling below 
10.degree. C. for more than about 7 to 10 days. Plants lacking a dominant 
vernalization gene will not flower under the minimal vernalization regime. 
At the same time, selection and/or screening for a desired trait may be 
carried out. For example, when the desired trait is insect resistance, 
plants may be exposed to the insect during the breeding process and 
seedlings may be screened for symptoms of infestation. 
Various breeding methods may be utilized. For example, the heterozygous 
offspring may be back crossed with the recurrent parent having the winter 
growth habit. In a breeding scheme, a succession of backcrosses can be 
utilized to add a gene for a desirable character to an otherwise desirable 
parent, or the backcross may be made to concentrate genes for a 
quantitative character. The purpose of a backcross is to recover the 
genotype of the recurrent parent, except for the addition of a gene for 
the superior character. A recurrent parent is either an original parent or 
a genetic equivalent. The backcross is most useful if the character being 
added is simply inherited, dominant, and easily recognized in the hybrid 
plants. Backcrossing is a form of inbreeding, and the features of the 
recurrent parent are automatically recovered after successive backcrosses. 
The only selection practiced is for the one superior trait contributed by 
the recurrent parent. The plant selected from the final backcross progeny 
will be heterozygous for the desired trait. 
According to the methods of the present invention, the back cross procedure 
may be repeated at least two more times, resulting in at least three 
generations in a twelve month period. Each time, a selection for progeny 
having a spring growth habit may be employed. It is understood that 
various breeding methods may be employed here. Thus, the offspring may be 
crossed with other various lines or with each other. Various wheat 
objectives may be screened for or selected. 
After offspring have been obtained and the final selection for the trait of 
interest has occurred, the selection is then reversed so that recessive 
winter habit types are favored to recover the winter growth habit. 
The offspring from the final back cross may then be evaluated by standard 
field breeding methods. Conventional methods may be used to establish a 
stable inbred line. For example, the seeds from a candidate plant may be 
planted in a head row (i.e., about 100 plants). The plants from the head 
row will be evaluated for the desired traits such as disease resistance or 
increased yield. The head row plants produce breeder seeds. The breeder 
seeds are planted and grown to make foundation seed. Where plants grown 
from the foundation seed have the desired characteristics, they will yield 
registered seed and, from these, certified seed. 
A dynamic wheat germplasm "toolbox" consisting of a Vrn gene with genes of 
any number of various disease or insect resistance (or any other genes of 
importance) in the background of the best adapted elite winter germplasm 
available is contemplated. This "toolbox" may be accessed to "repair" new 
and promising elite materials that are deficient in one or more 
characters. Exceptional segregates with the character of interest and a 
Vrn allele may be used as an upgraded "tool" for the greenhouse germplasm 
"toolbox" to "repair" future elite lines. 
In another embodiment, the methods of the present invention may also be 
used to rapidly introgress a recessive gene, but would require some 
additional effort since the trait of interest would not be phenotypically 
detectable in heterozygous individuals. The basic procedure would be 
essentially the same as for a dominant gene, but would require crossing 
with a number of random plants in each segregating generation. 
Self-pollinated seeds from these individual parent plants could then be 
grown concurrently with the backcross derived first filial generation (F1) 
plants. The second filial generation (F2) progeny plants could then be 
tested for the recessive trait. Families exhibiting the trait of interest 
would descend from heterozygous parent plants. Records of parent plants 
could then be referenced to determine which backcross families would be 
expected to be segregating for the gene to be transferred. 
The segregating families would then be selected to repeat the process of 
crossing random individuals for the next generation and the 
non-segregating families would be discarded. In the case of the transfer 
of a single recessive gene, in each generation it would be necessary to 
cross with at least five random spring habit plants from segregating 
families in order to be confident (P&lt;0.05) of at least one plant being 
heterozygous for the gene of interest. Sixteen or more plants from a 
segregating family would be necessary to begin each backcrossing cycle so 
that one could be confident (P&lt;0.05) of recovering at least five spring 
habit plants for crossing. In practice, twenty five plants or more are 
recommended to start each cycle, when working with a recessive gene. An 
increased number of plants helps protect against the effects of poor 
germination or other growing problems and enhances the probability of 
recovering the desired genotypes. 
Rapid generation advance via Vrn genes according to the present invention, 
provides an efficient means to manipulate genes introduced to wheat via 
DNA transformation technologies. Transfer of genes to adapted types 
according to this invention is easier and less expensive than repeated 
attempts at transfers in each new wheat background. 
The methods of this invention may also be used to facilitate a recurrent 
selection program for improved yield by modifying the technique proposed 
by Frey et al. ((1988) Crop Sci. 28:855.) to account for unvernalized 
winter habit segregates by measuring yield on the basis of individual 
plant yield per se. Precise determination of quantitatively inherited 
traits, such as yield, may not be possible with small populations in 
greenhouse or hill plot experiments. However, breakthroughs in wheat yield 
improvement have historically resulted from certain specific crosses that 
have demonstrated a high frequency of very exceptional segregates. Crosses 
of this nature may represent the favorable recombination of relatively 
large and positive linkage blocks from the parents. The methods of the 
present invention may be used to effectively screen large numbers of 
crosses in early generation greenhouse and hill plot experiments to 
quickly identify these very outstanding crosses and recycle selections 
into the recurrent selection program. Tillering potential may be a major 
influence on per se yield in a 10 cm pot or a space planted field 
transplant, and that high tillering types may prove to be more tolerant to 
Hessian fly infestation, as well as a number of other production hazards. 
Tillering may also be a major component of yield stability in the 18 cm. 
rows which are commonly used by soft red winter wheat producers. 
In the following example, an apparent single gene from the FL85238-G28-G4 
parent was used to effect the minimal vernalization requirement. If more 
than one Vrn gene were utilized in the initial cross, a lower minimum 
number of heterozygous plants would be necessary in each generation since 
spring habit segregates would be much more frequent. However, winter habit 
segregates would be less frequent in later generations. It is therefore 
preferred to use a single Vrn gene to initiate the crossing and to follow 
throughout the breeding generations. 
The skilled artisan will be able to ascertain, with a minimum amount of 
experimentation, the various desired genetic backgrounds and genes for the 
various traits that may be incorporated into those backgrounds in 
accordance with the methods of the present invention. 
The following specific example is provided for purposes of illustrating the 
invention, and no limitations on the invention are intended thereby.

EXAMPLE 
Materials and Methods 
IN8138I1-16-5-50 is a Purdue University soft red winter wheat experimental 
line that possesses superior winter hardiness but is susceptible to 
Hessian fly biotype "L". This line was chosen as the recurrent parent in a 
backcrossing program to transfer H21, a dominant Hessian fly resistance 
gene carried on the chromosome arm 2RL of `Chaupon` rye (Secale cereal L.) 
(Friebe et al., 1990). KS86HF012-23-6, a hard red winter wheat germplasm 
line developed at Kansas State University which carries the translocation 
2BS/2RL, was used as the donor of H21. FL85238-G28-G4 is a University of 
Florida experimental soft red winter wheat line that can be grown with 
minimal vernalization (less than seven days) and probably possesses one of 
the major Vrn genes or an allele. It is unknown whether FL85238-G28-G4 
possesses a named Vrn gene or a gene as yet undescribed. However, it is 
not essential to know which minimal vernalization gene is present in order 
to utilize the gene to effect the desired rapid generation advancement. 
FL85238-G28-G4 was chosen as the source for the minimal vernalization gene 
because of its good soft wheat quality and the package of assembled 
disease resistance genes that allow it to perform well in the warm and 
humid conditions of southeastern USA. 
Hessian fly Biotype L was used to screen segregating families because it 
has the greatest number of genes for virulence of Hessian fly biotypes 
identified to date (Sofa, 1981). Biotype L can infest wheats with genes H3 
to H8 and H11. Wheat seedlings were grown in greenhouse flats 
54.times.36.times.8 cm. and tested for Hessian fly resistance as described 
previously (Maas et al., (1989) Crop. Sci. 29:23.) 
Germinating seeds were placed in a controlled chamber maintained at 
4.degree. C. to 5.degree. C. after planting to break dormancy and enhance 
the uniformity of germination, thus reducing the probability of late 
germinating plants that may escape Hessian fly infestation. Presumably, 
this period could provide some minimal vernalizing effect for certain Vrn 
alleles and may be responsible for causing an earlier heading date in the 
greenhouse than otherwise would have been observed. No other cold chamber 
treatment was used for plants carrying the Vrn gene during the generations 
of backcrossing. Several plants of the IN8138I1-16-5-50 recurrent parent 
were vernalized using standard vernalization techniques, 4.degree. C. to 
5.degree. C. for 60 days or longer. Transplants were moved to the 
greenhouse at weekly intervals so that synchronous flowering would be 
assured for each crossing generation. 
Seedlings without obvious symptoms of infestation (stunting, dark green 
color) were removed from the flat and examined for the presence of dead 
first instar larvae behind the lead sheath to avoid advancing non-infested 
susceptible escapes. Resistant plants were transplanted into 10 cm plastic 
pots containing greenhouse soil. The unvernalized resistant transplants 
and vernalized plants of the recurrent parent were grown to maturity under 
a 24 hr. photoperiod. For the first six weeks in the greenhouse, night 
temperatures were held near 10.degree. C., when possible, while an attempt 
was made to keep day time temperatures below 25.degree. C. Subsequently, 
night temperatures were increased to 20.degree. C. until harvest. After 
pollination, day temperatures were allowed to vary between 25.degree. C. 
and 35.degree. C. All-purpose fertilizer was applied regularly as a liquid 
solution three or four times per growing cycle. 
Ten F1 plants of the cross: KS86HF012-23-6/FL85238-G28-G4 were grown in the 
greenhouse between July and November. These F1's were transplanted at 
intervals in order to synchronize flowering with fully vernalized 
IN813811-16-5-50 plants. The three way cross: 
IN8138I1-16-5-50//KS86HF012-23-6/FL85238-G28-G4 was made. The three way 
F1's generated from this cross were screened for resistance to Hessian fly 
biotype L. IN8138I1-16-5-50 was used as the seed parent in this cross and 
in subsequent generations of backcrossing, so that both the H21 gene and 
the Vrn gene would be genetic markers to insure that no self-pollinated 
plants were advanced. Plants lacking the H21 gene would not survive the 
Hessian fly infestation, and plants lacking the Vrn gene would not flower 
under the minimal vernalization regime. The resistant three way F1 
seedlings were grown in the greenhouse from November 1991 to March 1992 
and backcrossed to the IN8138I1-16-5-50 recurrent parent. The BC1 plants 
were screened to Hessian fly and transplanted to the field in April 1992, 
and BC2 crosses were made in June using vernalized IN8138I1-16-5-50 plants 
that had been transplanted to the field. The BC2 F1 plants were selected 
for Hessian fly resistance and grown to produce BC2 F2 seed. The BC2 F2 
families were tested to verify that the Hessian fly resistance was 
present. 
Results and Discussion 
In a backcrossing program, progeny of heterozygous dominant individuals 
backcrossed to the recessive recurrent parent are expected to segregate in 
a ratio of 1:1. This was observed for both the H21 gene and the Vrn gene 
(data for the Vrn gene not presented). At least one plant in each 
generation was found to be both resistant to Hessian fly and also capable 
of flowering without vernalization (Table 1). 
TABLE 1 
______________________________________ 
Reaction of progeny to Hessian fly biotype L during 
successive generations of a backcrossing program to introduce 
the H21 gene into the background of IN8138I1-16-5-50 by using 
a Vrn gene to avoid lengthy vernalization periods each generation. 
No of. Number of plants 
Cross Parentage Seeds Resistent 
Susceptible 
______________________________________ 
BC0 generation - November to March 
92898A IN8138I1-16-5-50// 
6 2 4 
KS86HF012-23-6/ 
FL85238-G28-G4 
BC1 generation - March to July 
922642A 
IN8138I1-16-5-50*2// 
16 10 6 
KS86HF012-23-6/ 
FL85238-G28-G4 
BC2 generation - July to November 
922816A 
IN8138I1-16-5-50 *3// 
5 2 3 
KS86HF012-23-6/ 
FL85238-G28-G4 
BC2 F2 progeny test - November 
922816A1 
IN8138I1-16-5-50 *3// 
35 31 4 
KS86HF012-23-6/ 
FL85238-G28-G4 
______________________________________ 
The use of procedures according to this invention are illustrated in the 
Example by a backcrossing program, employing a Vrn gene for the transfer 
of the dominant H21 gene for resistance to Hessian fly Mayetiola 
destructor, (Say)! biotype "L" into the background of IN8138I1-16-5-50, a 
winter hardy, experimental soft red winter wheat line susceptible to 
biotype L. BC2 F1 individuals heterozygous for both the H21 gene and a Vrn 
gene were developed within twelve months. 
This Example provides merely one illustration of one embodiment of the 
invention. The methods of this invention may be used to create a dynamic 
germplasm "toolbox" consisting of any of a number of genes for various 
resistances or other traits in association with a Vrn gene in the 
background of adapted elite winter wheats. These methods may also be used 
to facilitate other crossing schemes or recurrent selection. 
While the invention has been described in detail in the foregoing 
description, the same is to be considered as illustrative and not 
restrictive in character, it being understood that only the preferred 
embodiments have been shown and described, and that all changes and 
modifications that come within the spirit of the invention are desired to 
be protected. 
All publications cited herein are hereby incorporated by reference in their 
entirely as if each had been individually incorporated by reference and 
fully set forth.