Chemical desiccation of wheat plants as a simulator of post-anthesis stress

Abstract

Chemical desiccation (with magnesium chlorate) of wheat, applied 14 days after anthesis, was evaluated as a screen for post-anthesis drought tolerance, in terms of sustained translocation-based kernel growth in the absence of photosynthesis. Thirty-eight and 26 wheat varieties were tested in 1979/1980 and 1980/1981, respectively. In each year the effect of chemical desiccation was studied in a non-stress environment as compared with the effect of post-anthesis drought stress in a drought environment. In both years, the extent of injury to kernell weight by drought stress was significantly and positively correlated, across varieties, with the extent of injury to kernel weight by chemical desiccation. Of the plant attributes studies, the main one associated across varieties with tolerance in kernel growth to post-anthesis stress was small kernel size. The significant negative association found between the extent of injury to kernel weight by chemical dessication or by drought stress and kernel number per spike or days to anthesis, was also mediated, at least partly, through kernel size. A significant positive association was found across varieties between the extent of injury to kernel weight by stress and the extent of compensation in kernel growth for the reduction (by excision) of kernel number per spike. This association seemed also to be mediated partly by kernel size, with a larger compensation observed in small-kernelled varieties. Kernel weight was negatively correlated across varieties with the number of kernels per spike. No correlation was revealed between the extent of injury by stress to kernel weight and non-stress kernel weight per spike. It was therefore concluded that the selection for smaller kernel weight as a post-anthesis stress-adaptive trait is not necessarily antagonistic to the maintenance of a large since size and high potential yield.