Foliar Brassinolide Sprays Ameliorate Post-Silking Heat Stress on the Accumulation and Remobilization of Biomass and Nitrogen in Fresh Waxy Maize

Abstract

Heat stress (HS) during grain filling is an extreme environmental factor and affects plant growth and development. Foliar application of exogenous brassinolide (BR) is an effective practice to relieve HS injuries, but the influence on the accumulation and remobilization of biomass and nitrogen is still unclear. In the present study, the effect of foliar BR application at the silking stage on the accumulation and remobilization of biomass and nitrogen in fresh waxy maize under ambient (28/20 °C) and high (35/27 °C) temperatures during grain filling were studied in a phytotron using heat-sensitive Yunuo7 (YN7) and heat-tolerant Jingkenuo2000 (JKN2000) as materials. HS reduced the fresh ear yield by 21.8% and 19.8% in YN7 and JKN2000, respectively, but fresh grain yield was only reduced in the heat-sensitive hybrid (6.9%) and unaffected in the heat-tolerant hybrid. BR application improved the yields of fresh ears (11.3% and 10.9% in YN7 and JKN2000, respectively) and grains (19.9% and 13.2% in YN7 and JKN2000, respectively) under HS, and the increases were higher in YN7. HS decreased the post-silking biomass accumulation by 67.3% and 51.8%, and nitrogen deposition by 61.9% and 50.5%, in YN7 and JKN2000, respectively. The remobilization of pre- and post-silking biomass and nitrogen were increased and decreased by HS in YN7, respectively, but both were unaffected in JKN2000. Under HS, BR application increased the remobilization of post-silking biomass and nitrogen in both hybrids. The grain nitrogen concentration was increased by HS but decreased by BR application in both hybrids. The harvest index of biomass and nitrogen was increased by HS, and it was improved in YN7 and unaffected in JKN2000 by BR application under HS. In conclusion, BR application at the silking stage can relieve HS injuries on fresh waxy maize yields by improving the remobilization of biomass and nitrogen to grain and increasing the harvest index, especially in the heat-sensitive hybrid. Therefore, foliar BR application is a simple, feasible, efficient practice in fresh waxy maize production and is worth popularizing, especially under warmer climates.