Heterosis and combining ability in crosses of different height categories in bread wheat

Heterosis, inbreeding depression and combining ability were analysed in an eight-parent diallel in F1 and F2 generations, involving diverse height categories of spring wheats belonging to tall, d1 d2 and d3 groups. Grain yield showed maximum heterosis (91⋅83%), followed by ears per plant (44⋅44%), 100-grain weight (14⋅52%), heading (–13⋅38%)) plant height (–23⋅35%) and spikelets per ear (5⋅94%). Manifestation of yield heterosis was through ears per plant. The intermediate height categories (d1 and d2) showed superiority over other height groups with high heterosis and less inbreeding depression for several characters related to yield. Combining ability analysis also showed superiority of d1, and d2 height groups. Height, grain weight and spikelets per ear showed additive gene action, whereas ears per plant and yield per plant were mostly non-additive. Plant height and 100-grain weight showed negative g.c.a. effects in semidwarfs. In general, the five categories of height could not be directly related to any consistent trend in the magnitude of g.c.a. effects for heading, ears per plant, rust incidence, leaf drying and productivity, nor for reciprocal effects for any of the characters.