USE OF CHEMICAL DESICCANTS AND SENESCING AGENTS TO SELECT WHEAT LINES MAINTAINING STABLE GRAIN-SIZE DURING POSTANTHESIS DROUGHT

This study was initiated to test whether stopping current photosynthesis by spraying plants with a desiccant or a senescing agent at the beginning of grain filling may provide a simple technique to select wheat lines that maintain stable grain size (kernel weight) through high contribution of the stem reserves during post-anthesis drought. Several desiccants and senescing agents were compared, and all chemicals were found to induce uneven desiccation or senescence of the ears and a large reduction in kernel weight when the chemicals were applied to whole plants (ears included). However, when only leaves and stems were sprayed, one senescing agent, potassium iodide (KI), had comparable effects on grain growth to manual defoliation and was judged to be the best chemical for field use. In two field experiments, the reductions in kernel weight due to the KI treatment under irrigated conditions were significantly correlated with the reductions in kernel weight due to drought. Wheat lines with low reductions in kernel weight under the irrigated KI treatment also best maintained stable kernel weight under drought. These lines had the highest levels of stem sugars at the beginning of grain filling. However,as KI was sprayed only on leaves and stems, ear photosynthesis may also have partly compensated for the loss of leaf photosynthesis. The KI treatment also consistently ranked varieties for kernel weight stability in the 2 years of the study. It was concluded that the KI treatment shows promise as a selection technique to identify wheat lines maintaining stable kernel weight during drought through high contribution of the stem reserves and/or ear photosynthesis.