Regulation of Grain Number in Wheat: Genotypic Difference and Responses to Applied Abscisic Acid and to High Temperature

Abstract

Floret infertility was induced by the application of abscisic acid ((�)-ABA) directly to the developing wheat spike, but only for applications over a 3-6-day period during pollen meiosis, not earlier or later. Yield components affected included loss of up to 20% of florets, senescence of the tip of the spike and the prevention of ear emergence. The major effect, however, was failure of grain in apparently competent florets. Cultivars differed in both their sensitivity to (�)-ABA and in the yield components affected. Also, for at least one cultivar (Triticum durum cv. Durati), the yield components affected changed over the 6-day period around pollen meiosis. High temperature (27°C average) for 7 days over the period of meiosis also reduced grain set and in some cultivars florets were lost. The variety most sensitive to high temperature was also most sensitive to (�)-ABA but there were differences in the yield components affected. Direct action of (�)-ABA in the spike and a possible indirect effect on assimilate supply are discussed.