STUDIES OF YIELD AND YIELD COMPONENTS IN HYBRID WINTER WHEAT (TRITICUM AESTIVUM L.) (NEBRASKA)

The objective of this investigation was to evaluate the heterosis and performance stability of 15 wheat hybrids in comparison with their respective parents. All hybrids, produced by the use of a chemical hybridizing agent, and their parents were planted at five locations in Nebraska, 1982, under standard on-farm seeding rates. A randomized complete block design with three replications was used and the combined analysis of variance over locations was utilized for analysis of the data. Two linear contrasts were included in the analysis of variance for each cross group to measure midparent and highparent percent heterosis. Stability tests were conducted to compare the performance stabilities between hybrids and their parents. Hybrids generally seemed to be more damaged by the severe environmental stresses and diseases than their parents. Of the 15 hybrids tested, six produced more grain yield than their higher-yielding parents. Hybrids that produced the highest yields and highest heterosis values came from parents that produced medium yields. Hybrid RH 792847, with higher mean performance but a lower regression coefficient than its parent values, showed increased phenotypic stability and responded productivity to environmental changes in a predictable way. Higher-yielding hybrids RH 812258, RH 801924 and RH 803044 with higher mean performance, and similar regression coefficients and coefficients of determination to those of their parents, could be described as productive hybrids with average sensitivity to environmental changes. Heterosis for other agronomic traits was less than that for yield itself. Correlations between heterosis values for grain yield and other agronomic traits indicated similar trends to those for phenotypic correlations between yield and these traits. Significant correlations were recorded between heterosis values for yield and number of spikes/m(\u272), and for yield and hectoliter weight, with the high-yielding hybrids having somewhat higher correlations than the lower-yielding hybrids. However, heterosis values for yield components were not significantly correlated with each other. Only a few wheat hybrids had heterosis values large enough to be of economic importance