The Effect of Speckled Leaf Blotch on Apical Development and Yield in Winter Wheat in New Zealand

Abstract

Speckled leaf blotch (Mycosphaerella graminicola) reduced yield in a winter wheat trial by 18 per cent. Detailed analyses of the effects of disease on yield components showed that disease reduced both grain number per ear and grain weight. The reduction in grain number per ear was due to a decrease in grain number per spikelet, and this occurred for both main stem and tillers, and occurred equally at each spikelet position on the ear. The effect of disease on grain number was traced back to an earlier reduction in floret primordium number per ear, especially floret number per spikelet. It was suggested that floret primordium production was affected by the reduced assimilate supply to the developing apex. The effects of disease on yield could therefore be attributed to effects on plant development both before and after anthesis. The disease effects on yield were not necessarily associated with the time of maximum disease severity. Plots with the early phase of disease epidemic only showed a significant reduction in yield, but there was some evidence of compensation for early reductions to yield potential in the later-determined yield components. We suggest, therefore, that an effective disease-control programme must take into account the possible early effects of disease on yield potential.