Effects Of Spraying Exogenous Hormones At Silking Stage On The Grain Yield And Quality Under Post-silking Heat Stress For Waxy Maize

High temperature stress occurs frequently with the aggravation of global warming,which brought a serious threat on maize production.The grain filling of maize often overlaps with the high temperature in the summer,which accelerated the grain filling rate,shortened the filling duration,reduced and the cell division,ultimately resulted in the obstruction of grain formation and development.Therefore,explore the effective ways to alleviate heat stress(HS)is an urgent problem.Exogenous hormones application is an important method in regulating plant growth and development,promoting cell differentiation and delaying senescence,which play an important role in stress resistance.In this study,Jingkenuo 2000 and Yunuo 7 were used as materials to explore the regulatory effects of different types of exogenous hormones and spraying concentrations on the yield and quality formation of waxy maize under post-silking heat stress,which is of great significance to alleviate the injury caused by heat stress.The study could provide theoretical guidance and technical support for high-yield and high-quality cultivation of waxy maize under warming conditions.The main results were as follows:1.Effects of post-silking heat stress on grain yield and quality of waxy maizePost-silking HS significantly decreased the grain weight,grain number,grain yield,and grain starch content by 24.2%,8.0%,25.2%and 10.3%,and the grain protein content increased by 9.6%(mean of Jingkenuo 2000 and Yunuo 7).Post-silking HS enlarged the average starch granule size,decreased the percentage of short chains and ratio of short/long chain of amylopectin in both varieties.The relative crystallinity remains unaffected when plants suffered post-silking HS in both varities.HS reduced the pasting viscosities but increased gelatinization temperatures and retrogradation percentage of flours and starches in general2.Effects of spraying various exogenous hormones at silking stage on grain yield and quality of waxy maize under post-silking heat stressSpraying various exogenous hormones at silking stage had different regulation effects on grain yield and quality under post-silking HS and ambient temperatures(AT).After spraying BR,CTK,GA,and Spm,the yield of the two varieties under HS increased by 32.6%,12.2%,17.5%and 22.0%,respectively;and the yield of the two varieties under AT increased by 29.5%,23.6%,11.8%and 13.1%,respectively.The increase of grain yield was mainly due to the increased grain weight and numbers,and the influence was best for BR among the four exogenous hormones.Under HS,the grain protein content in Jingkenuo 2000 was increased by GA and decreased by Spm,and the value in Yunuo 7 was only increased by BR and unaffected by other hormones.The starch content in Jingkenuo 2000 was increased by BR,CTK and Spm,but it in Yunuo 7 was unaffected by all hormone application.The effects of application of exogenous hormones on starch pasting viscosities and thermal characteristics were different between varieties and temperature conditions.Under HS condition,the average starch granule size was decreased by application of four hormones in Jingkenuo 2000 and only by application of GA in Yunuo 7.The starch viscosisties were improved by four hormones in Yunuo7,and peak and trough viscosities in Jingkenuo 2000 were improved by BR and CTK,and the increase was the highest for BR.Under HS,the ratio of short/long chains was increased by BR in both varieties.The ratio of A/B chains was decreased by BR,CTK,and GA in both varieties,the value was increased in Yunuo 7 and decreased in Jingkenuo 2000 after Spm application.In general,spraying exogenous hormones at silking stage increased the grain yield,grain starch content and pasting viscosities and changed thermal characteristics under HS,alleviate the negative influence of HS,and the effect of spraying BR was better than the other three hormones.3.Effects of spraying different concentrations of BR at silking stage on grain yield and quality of waxy maize under post-silking HSDifferent concentrations(0-0.100 g/L)of BR were sprayed at silking stage can alleviate the effects of HS on grain yield and quality.Under HS condition,spraying different concentrations of BR significantly increased grain weight,grain number and grain yield of the two varieties,and the highest grain yield of Jingkenuo 2000 and Yunuo 7 were under spraying 0.050 g/L and 0.025 g/L BR,respectively.Under HS condition,0.025 g/L and 0.050 g/L BR decreased the protein content in Jingkenuo 2000,the increase of starch content was the highest for 0.025 g/L BR in Jingkenuo 2000 and 0.100 g/L BR in Yunuo 7.Application of different BR concentrations affects the relative crystallinity,molecular weight and amylopectin chain length distribution,pasting viscosities and thermal characteristics,but the regulation effects were different among different BR concentrations and between the two varieties.Under HS condition,application of different concentration of BR significantly reduced the average starch granule size in Jingkenuo 2000,but enlarged in Yunuo 7.In general,application of 0.025-0.050 g/L BR at silking stage favored to improve the pasting viscosities,the retrogradation percentage of flours and starches was significantly reduced by 0.025 g/L and 0.050 g/L BR.Comprehensive consider the effects of BR concentrations on yield and pasting and thermal properties of two hybrids under post-silking HS,0.025-0.050 g/L is recommed concentration in waxy maize production under warm climate.