Relationships among attributes of pure lines of bread wheat derived from heterotic F₁ hybrids

Abstract

Measurements were made of the number of spikes per unit area, the number of kernels per spike, kernel weight and plant weight in four heterotic hand-made hybrids and the commercial hybrid Comet, together with the parents of the hand-made hybrids, and 75 pure lines derived from each hybrid by single seed descent. Kernel weight exhibited the strongest heterosis, while the incidence of positive heterosis for the remaining yield components varied between crosses. Mid-parent heterosis for plant height was significant for all hand-made hybrids. In both hybrids and pure lines, high yield was associated with intermediate kernel weight and intermediate plant height, but for each trait higher values were observed in the hybrids and pure lines compared with their parents. In terms of both plant height and the major components of yield, viz. kernel number per unit area and kernel weight, the highest yielding pure lines and the hybrids were similar, demonstrating that it is possible to recover homozygous genotypes with the same basic characteristics as the heterotic hybrids from which they were derived. The absence of any consistent pattern on how the best lines obtained their yield suggests that selection for yield based on its components would be unrewarding, except for selection against extremes of kernel weight and plant height.