ObjectivesThis study explored influences of foliar application of 6-benzylaminopurine (6-BA) on floral development and grain-setting of wheat with expectation of providing references for the chemical regulation of increases in the number of grains per spike and improving the yield.

MethodsField experiments were conducted in the Science and Technology Demonstration Park of Henan Agricultural University (113°59′ E, 34°86′ N) during the 2012–2013 and 2013–2014 growing seasons of wheat. The experiments involved the wheat cultivar Yumai49-198 and two foliar applications, water (CK) and 6-benzylaminopurine (6-BA), which were applied 25 days after the jointing stage. Samples were collected and observed under an EMZ-TR dissecting microscope to record: the young spikelets’ differentiation process of the main stem and the characteristics of young spikelet differentiation at different stages. At the mature stage, we recorded the number of grains at different spikelet positions (basal, central and apical), the number of grains on each spikelet, and that at different floret positions at each spikelet using conventional test methods.

ResultsThis comprehensive study was analyzed in detail floret development in wheat as affected by foliar spraying 6-BA and found that the grain-setting rates of fertile floret on the basal, central and apical spikelet positions were increased by 8.4%, 15.1%, and 10.6% respectively compared with the control treatment which spraying water. The basal spikelet floret’s degeneration rate of spraying 6-BA was decreased by 24.4%, and the infertility rate was decreased by 73.0%. The central spikelet floret’s degeneration rate of treatment was decreased by 14.7% and the infertility rate was decreased by 76.0%. The treatment can restrain the degeneration and infertility rate of the basal and central spikelet floret, and also can restrain the infertility rate of the apical spikelet floret to promote producing seeds. This kind of spraying has no obvious effect on the degeneration of apical spikelet floret. Further, the spraying 6-BA can significantly promote florets grain-setting at different floret position of the different spikelet, especially promote producing seeds of the 3rd and 4th floret positions which are weak florets.

ConclusionsWe have demonstrated that prior to the degeneration peak of winter wheat florets (25 days after their jointing stage), the degeneration rates and the abortion rates of fertile florets at basal and central spikelet positions can be significantly reduced by foliar application of exogenous 6-BA (10 mg/L). In addition, the foliar application of 6-BA also improved the grain set rate of fertile florets per spike and the final grain number by inhibiting the abortion rate of fertile florets at the apical spikelet position. This study showed that exogenous application of the hormone 6-BA has the potential to reduce the percentage of fertile florets that fail to develop into grains (i.e. reducing the number of florets that never become grains).