Spraying exogenous synthetic cytokinin 6-benzyladenine following the waterlogging improves grain growth of waterlogged maize in the field

6-Benzyladenine (6-BA, a synthetic cytokinin) could improve the ability to resist adversity. However, very little attention has been given to its role in alleviating waterlogging damages on grain growth. A field experiment was performed to investigate effects of exogenous 6-BA after waterlogging for 6 days at the third leaf stage (V3-WL + 6-BA) or the sixth leaf stage (V6-WL + 6-BA) on grain filling, and endogenous hormone of summer maize hybrids DengHai605 (DH605) and ZhengDan958 (ZD958), which were planted popularly in China. Exogenous 6-BA alleviated waterlogging damages on grain filling by improving grain weight and volume, which was beneficial to yield increase. Grain yield of DH605 under V3-WL + 6-BA and V6-WL + 6-BA increased by 16% and 12%, respectively, compared with that of V3-WL (waterlogging at the third leaf stage) and V6-WL (waterlogging at the sixth leaf stage), while the corresponding values for ZD958 increased by 20% and 15%, respectively. Moreover, exogenous 6-BA alleviated waterlogging damages on grain endogenous hormone content by increasing levels of endogenous indole-3-acetic acid, zeatin riboside, and gibberellic acid, and decreasing level of abscisic acid in grain of waterlogged summer maize during grain-filling periods. Clearly, exogenous 6-BA improved grain-filling characteristics, and endogenous hormone, resulting in a significant yield increase of waterlogged summer maize.