Effects of exogenous hormones on floret development and grain set in wheat

At specific stages during floret development. solutions of IAA. GA(3), zeatin and ABA were injected into the leaf sheath around the young spike of wheat (Triticum aestivum L.) to study the regulating effects of exogenous hormones on floret development. Zeatin promoted floret development and significantly increased the number of fertile florets as well as grain set, especially at the stage of anther-lobe formation. Zeatin also increased the sugar concentrations in spikes at anthesis. In contrast, IAA, GA(3) and ABA inhibited floret development, with different patterns for each of the hormones. IAA inhibited the development of the whole spike and all florets in the spikelets such that grain loss occurred in all positions in the spikelets. GA(3) increased the number of fertile florets per spike, but decreased grain set of the third floret in each spikelet, especially when applied at terminal spikelet formation. ABA inhibited floret development, and decreased the number of fertile florets and grain set at almost all development stages, except at anther-lobe formation. The inhibitory effect of ABA was mainly on the first and third florets in each spikelet.