Crosses between four near isogenic lines for height reducing genes Rht1 and Rht2 and one agronomically superior dwarf line, including generations through F3 with reciprocal backcrosses constituted the experimental materials. Mean, range and standard deviation values for eleven traits pertaining to the different generations were obtained. Heterosis and inbreeding depression along with broad and narrow sense heritability estimates for the traits provided information regarding nature of gene action. Possible relationship between selected traits were also determined. The amount of genetic diversity between crosses depended upon the number and specific dwarfing genes involved. A limited number of traits were different in crosses involving either Rht1 or Rht2 isolines. This may have resulted since 'Yamhill Dwarf also carries the Rht1 allele. For generations, differences were detected for all eleven traits measured. The cross involving the standard height isoline (rht1rht2) and Yamhill Dwarf registered the highest mean values for plant height, grain yield, 300-kernel weight and biological yield; but had the lowest value for harvest index. Increased grain yield was more a function of higher "biological yield" than "harvest index" in all crosses and populations examined. Consistent and positive associations were also found between grain yield and biological yield; however the same was not true for grain yield with harvest index where little or no associations were detected for any of the crosses. Heterosis estimates were high for most traits in rht1Rht2/Yamhill Dwarf cross and low in the cross Rht1rht2/Yamhill Dwarf. Inconsistent broad and narrow sense heritability estimates were observed in several crosses for most traits measured. The one exception was for 300-kernel weight, being relatively high and consistent in all crosses except Rht1Rht2/Yamhill Dwarf. In some instances, negative narrow sense heritability estimates were realized. This was particularly true for the cross between the standard height isoline (rht1rht2) and Yamhill Dwarf. Also, depending on the cross and trait measured, larger narrow sense heritability estimates were obtained when compared to the broad sense estimates. This could reflect some sampling error or a large genotype X environmental interaction which was observed.

Grain yield and grain protein are often negatively associated in wheat. When yield increases and grain protein decreases, there can be an adverse effect on the milling and baking quality if the desired end product is bread flour. It has been suggested that this inverse association is the result of selecting for a higher harvest index (ratio of grain yield to total biomass), to enhance grain yield. Parents, Fl, F2, and F3 generations of three crosses and reciprocal backcrosses of one cross were space-planted to study the association of grain protein content with grain and biological yields, harvest index, and related traits. Selection P5221, a high protein selection, was a common parent in crosses with three different genotypes. Differences were observed among generations within crosses for biological yield, grain yield, harvest index, grain protein content, grain hardness, and protein yield. The coefficients of variation for the measured traits were low for the three crosses. No associations between grain protein content and grain yield were observed in the populations studied. The largest association detected was between harvest index and grain protein. The r values ranged from -0.39 to -0.46, and rho was not different from -0.50 in two of the crosses. Path coefficient analyses revealed that this association was mostly due to the direct effect of harvest index on grain protein content, with little direct or indirect effect via other plant traits. In the cross P5221/ORCR 8313, biological yield exhibited a moderately large (0.64) direct effect on grain protein content; however this was offset by the negative indirect effect of tiller number. The R2 of the path analyses were relatively small for the three crosses, indicating that most of the variation in grain protein content was not explained by the variables included in the analyses. A possible negative association between grain protein content and harvest index, although moderate, suggests that selection for high yield should not be based on further increases of harvest index because grain protein could decrease.

Five winter wheat cultivars and their diallel crosses were evaluated for plant height, harvest index, deading-maturity duration, the components of yield, (spikes per plant, spikelets per spike, kernel weight and kernels per spikelet)and total plant yield. Two diverse locations, Moro, a dryland site (250 mm annually) located in central Oregon and the Hyslop Agronomy Farm, a high rainfall site (over 1000 mm annually) located in the Willamette Valley, were utilized for one and two cropping seasons, respectively. Three rates of seeding were used as main plots in a split-plot design that was replicated four times. A modified blend method of seeding was used to simulate solid seeding conditions. Experimental seeds were planted 30.5 centimeters apart within the row over a filler cultivar in equally spaced (30.5 centimeters) rows. The data were analyzed by analysis of variance, Griffing's diallel analysis (Method 4, Model 1), correlation, path-coefficient analysis and by parent progeny regression. The correlation between grain yield, its components, harvest index, maturity-duration and plant height was dependent on the particula. r environment of the test. The re waspoorcorrelationbetween yield, tiller number and seed size under all the conditions of these studies. Negative associations between the components of yield indicated the sequential compensatory behavior of these characters under all environments. It would be very hard to select for large grain and short stature wheat because of the positive correlation between plant height and seed size within this population. The low correlations of yield with tiller number and seed size were mainly caused by indirect negative effects through one or more of the other yield components. Harvest index, maturity-duration and plant height had very small direct or indirect influences on grain yield. It was concluded that maximum yield would be obtained from a plant type which produces enough tillers to cover a particular unit of field area with large, fertile spikes, having medium to large kernels and semi-dwarf stature. No significant differences existed between parents and single crosses in the expression of the yield components. Nevertheless, hybrids outyielded their parents in grain yield and demonstrated that heterosis for complex traits was a consequence of multiplicative relationships among the components of these traits. Significant interactions between the genotypes and locations, seeding rates and years were observed in the expression of all characters studied. These interactions indicated that using data from non-competitive conditions to assess performance under competitive conditions could not be justified. Also, limiting the number of testing sites may lead to unsound generalizations and erroneous recommendations regarding gene action estimates of yield and the components of grain yield and three associated characters. Under non-competitive conditions, estimates of the additive type of gene action were more significant and contributed larger effects than the non-additive type for all traits. As competition increased at higher seeding rates, the effects of specific combining ability became more important in the expression of yield, number of spikes, spikelets per spike, and plant height. Heritability estimates confirmed these results except for yield. Of the agronomic characters, harvest index, maturity-duration and plant height, only harvest index showed some promise as a selection criterion under noncompetitive conditions. A breeding procedure utilizing the component approach consisted of selecting early generations under spaced planting with emphasis on avoiding extreme values in any of the components of yield. The balanced combinations of the components of yield should be tested under solid seeding conditions.

Sept.-Oct. issue includes list of theses and dissertations for U.S. and Canadian graduate degrees granted in crop science, soil science, and agronomic science during the previous academic year.