- Parental and segregating populations derived from four winter x
spring wheat crosses were investigated to obtain information concerning
the inheritance and association of earliness, grain yield and yieldrelated
traits. Feasibility of selecting in early generations for these
characteristics was also evaluated. Four winter wheat cultivars
(Hyslop, Yamhill, Bezostaia 1, and Sprague) and one spring wheat
cultivar (Inia 66) were chosen on the basis of their relative maturity
and contrasting agronomic characteristics. Parents, F₁ s, F₂' s,
and reciprocal backcrosses to both parents were planted in the fall
in a space-planted randomized complete block design. The two environmentally
diverse locations selected were the Hyslop Agronomy
Farm, Corvallis, Oregon (1000 mm of rainfall) and Sherman Experimental
Station, Moro, Oregon (250 mm of rainfall). The effectiveness
of early generation selection for the measured characteristics was
evaluated by growing F₃ lines identified as the earliest 1% and the
highest yielding 1% of F₂ individuals in each cross. These were
grown along with the parents, F₁s, BC₁ s, BC₂ s and F₂' s under
space-planted conditions at Hyslop Agronomy Farm. A study with
the same populations was conducted by vernalizing and planting in the
spring to gain further information on earliness.
Analyses of variance were conducted for all characteristics
measured. Frequency distributions for days to heading of F₁, F₂,
backcross generations and parents were examined. From the data
collected, estimates of F
-midparent deviations, degree of dominance,
heritability in the narrow sense and genetic advance under
selection were determined for each cross. The data were further
analyzed by parent-progeny regression, correlation and path-coefficient
analyses, polynomial and multiple regressions.
Partially dominant major genes, varying in number between one
to five depending on the particular cross, appeared to influence heading
date. Modifying factors also seemed to affect the date of heading.
The gene action involved in the inheritance of earliness was primarily
additive indicating that selection for earliness would be effective as
early as the F₂ generation under both high and low rainfall conditions.
Estimates of additive and nonadditive gene action suggested both were
equally important in determining the yield components. Higher heritability
estimates for the components of yield indicated that there was
more genetic variability associated with the yield components than yield per se. Occurrence of additive genetic variation by location
interaction implied that selection should be practiced simultaneously
under different environments if wide adaptability of potential lines is
desired. Since pronounced additive effect by year interactions occurred
for the yield components, delayed selection for these traits
may not be productive.
Positive correlations were obtained between yield and the number
of days to heading when all generations were combined. However,
in the F₂ generations, it appeared possible to select for the desired
earliness with high yields as indicated by the low association between
these two traits.
The path-coefficient analyses suggested that tiller number had
the highest direct effect on grain yield. However, because of a negative
association between tiller number and kernel weight, selection
pressures would have to be balanced between these two components.
In most cases, linear relationships existed between grain yield and
seven measured traits, respectively. The result of regression
analyses also showed that grain yield may be described best as a
linear function of its components.