|Abstract or Summary
- Six winter wheat cultivars were evaluated for their breeding
value in transmitting superior genetic factors for grain yield to subsequent
progeny. The cultivars were selected on the basis of their
potential grain yield and divided into two populations. Population I
was comprised of three cultivars which have been in commercial
production for several years and are regarded as intermediate for
grain yield. Population II was represented by three recently developed
cultivars which have superior grain yielding potential. Each of the
three parents within each population were crossed in a diallel manner
Hence, the parents and subsequent F₁, F₂, and BC progeny made up
the experimental populations. These populations were grown at two
environmentally diverse sites within the state of Oregon. Morphological
characters measured were: (1) tillers per plant; (2) kernels per spike; (3) plant height; (4) weight of 300 kernels; and (5) grain yield.
To detect which parental combination had the greatest potential
for transmitting superior performance to the subsequent progeny for
the components of yield and grain yield, the following parameters
were determined for both populations: (1) the amount and nature of
the genetic variance associated with each population; (2) average combining
ability of each parent within the populations; (3) estimates of heterosis and heterobeltiosis in the F₁ and (4) the possible influence
of the genotype-environmental interactions on the parameters measured.
Also information concerning the desirability of using top crosses and
double crosses rather than single crosses was obtained.
In an effort to compare the relative performance between the
populations, Pullman Selection 101, which is a good general combining
winter wheat cultivar, was used as a tester for both populations. The
values obtained in this investigation reflect the properties of the populations
studied and should not be interpreted as applying to all wheat
Considerable genetic variability was found within both populations
for the characters studied. This variability was largely due to
genetic factors which were additive. Tillers per plant and grain yield
were influenced by both additive and nonadditive genetic variance.
The higher yielding parents in Population II were found to be
higher in their average combining ability for kernels per spike and grain yield per plant whereas the lower yielding parents in Population
I were higher for tiller number, weight of 300 kernels and plant
Parental combinations identified as being promising, for grain
yield in a conventional program, where nearly homozygous lines are
desired, were also the same parental combinations which resulted
in a maximum expression of heterobeltiosis and would be of most
interest in a hybrid program.
The desirability of using multiple crosses to maximize the number
of favorable factors need further study inctuding additional parents
and different combinations plus an evaluation of the performance of
such crosses in later generations.
In this investigation, the single crosses appeared to be the most
promising; however, inbreeding depression due to segregation within
top and double crosses influenced the values obtained. Also, the
population sizes should be increased to measure the total potential of
Significant genotype-environmental interactions were observed
between locations for plant height and weight of 300 kernels. The estimates
obtained for average combining ability, heterosis and heterobeltiosis
for the other characters measured also suggested that it will
be necessary to identify the most promising hybrid combinations based
on the performance of the parents at the specific location. To make the most rapid progress in developing high yielding
cultivars in either conventional or hybrid programs, the wheat breeder
needs to emphasize crosses between unrelated high yielding cultivars.
However, the need to provide superior parental lines which include
such factors as disease resistance, should be evaluated. The development
of elite germ plasm by geneticists will be mandatory if plant
breeders are to continue to improve grain yield.