|Abstract or Summary
- This investigation was motivated by the apparent increase in genetic
variability resulting from the systematic combining of gene pools
represented by winter and spring types of wheats.
It was the objective of this study to provide information regarding
the nature of this genetic variability for nine agronomic characters
in populations resulting from winter x spring crosses. Evaluations
were made for: 1) the amount of total genetic variability; 2) the
nature of the gene action making up this genetic variability using
parent-progeny regression and combining ability analysis and 3) possible
direct and indirect associations for traits which influence grain yield.
Experimental populations which involved parents, Fl, F2 and backcross
generations were grown at two locations where a spring and a winter
environment could be utilized. At the winter site, the research was
evaluated over a two year period.
When the two experimental sites were compared, greater genetic
diversity was observed at the spring site for maturity date, plant height, tillers per plant, kernel weight and grain yield. At the winter
site, heading date, grain filling period, harvest index and kernels per
spike were found to have more total genetic variation.
From the expected mean square values, it would appear that the
winter parents contributed more to the total genetic variation for most
traits measured at both locations. A large genotype-location interaction
was also noted suggesting that estimates of gene action and selection for
adapted plant types can be done only at the specific winter or spring site.
A large portion of the total genetic variation controlling the
traits measured was due to additive gene action. However, at the winter
site there was also a large influence of non-additive gene action associated
with heading date, plant height, harvest index, tillers per plant,
kernel weight, kernels per spike and grain yield.
Of special interest was that at the winter site the most promising
parental combinations could be predicted based on the general combining
ability effects of the individual cultivars for each trait studied. Such
data were not available for the spring site.
Consistent and high correlations were observed between tillers per
plant, kernels per spike and, to a lesser extent, kernel weight and
grain yield at the winter location. Some negative associations were
observed at the spring location between these traits and grain yield
suggesting that yield component compensations were involved in the final
expression of grain yield. The other characters measured did not reflect
significant correlations with yield. When the correlation values were
considered in terms of direct and indirect effects for specific traits,
a large direct effect was noted for the three components and grain yield. The other traits exhibited small or no direct effects on grain yield
but did have a slight influence on grain yield through tillers per plant,
kernels per spike or kernel weight.