Harvest Index and Spike Index in Crosses between Wheat Genotypes with Different Spike Architecture

Crosses between vulgare wheat genotypes with different spike architecture were examined for total biomass per plant, grain mass per plant, and harvest index. The genotypes with branched spikes (turgidum type) and tetrastichon spikes were equal or superior to those with normal spikes in total biomass per plant but inferior in grain mass per plant. Consequently, they had significantly lower harvest indices. In the F 1 and F 2 generation, high heterosis for total biomass per plant occurred in all crosses between the genotypes with branched and normal spikes. There was heterosis for grain mass per spike in most crosses, but it was not as high as for total biomass. This investigation confirmed earlier findings that genetic changes towards the branched or the tetrastichon spike do not increase the potential for grain yield. Since, however, the crosses between the genotypes with branched and normal spikes showed high heterosis for grain mass per plant, lines with highly fertile but normal spikes may be expected in the segregating generations as a result of a genetic change in sink capacity. The genotypes with branched and tetrastichon spikes produced higher biomass per spike but lower spike index than the genotypes with normal spike. This may be an indication that the increase in vegetative area of the spike does not necessarily have a positive effect on grain mass per spike.