Effects of spraying exogenous cytokinin or spermine on the starch physicochemical properties of waxy maize exposed to post-silking high temperature

Plant growth regulators (PGR) can be used to alleviate heat injury on the starch quality of crops. In this study, two waxy maize hybrids with exogenous cytokinin or spermine at silking stage were exposed to post-silking ambient temperature (AT; 28/20 °C) and high temperature (HT; 35/27 °C) during grain filling. Results indicated that spraying exogenous cytokinin or spermine increased the grain weight and starch content at both temperature regimes. The starch granule size, amylopectin chain length, and relative crystallinity differed between two hybrids and were affected by PGRs and temperatures. Peak viscosity decreased at HT, unaffected by cytokinin, and increased by spermine at both temperature regimes. The retrogradation percentage at HT with PGR was lower than that without PGR in both hybrids. In conclusion, spraying exogenous cytokinin or spermine at silking stage can increase peak viscosity and reduce retrogradation percentage at HT, thereby alleviating the detrimental effects of post-silking heat injury.