THE PERFORMANCE OF PURE LINES DERIVED FROM HETEROTIC BREAD WHEAT HYBRIDS

Comparisons of the grain yields of pure lines derived from heterotic hybrides were made with those of the F1 hybrids and their parents for four hand-made crosses, and with the hybrid in the case of the commercial hybrid cultivar Comet. Seventy-five F7 (F6 in the case of Comet) single seed descent lines from each cross were evaluated in hill plot experiments containing five plots of each parent and hybrid per replication. Mid-parent and high-parent heterosis averaged 17% and 10.7% respectively in the four hand-made hybrids. Thus hybrid breeding of wheat could achieve a significant yield advance because the parental genotypes were advanced breeding lines or commercial cultivars. The estimated genotypic value for grain yield of the best pure line derived from each cross was 98, 96, 94, 91 and 85% of the corresponding hybrid mean yield, and even higher yields could be expected from a larger sample of derived pure lines. A hybrid breeding program cannot therefore be justified solely on the basis of yield comparisons between hybrids and pure lines.