High Temperature during Grain Filling Impacts on Leaf Senescence in Waxy Maize

Waxy maize (Zea mays L. sinensis Kulesh) is frequently exposed to high temperatures (higher than 35.0 degrees C) during grain filling in southern China. This pot trial was conducted to study the effect of heat stress during grain filling on grain yield, dry matter (DM) accumulation and translocation, and leaf senescence of plants. Post-pollination plants of Suyunuo 5 and Yunuo 7 (waxy maize varieties) were planted under high temperature (35.0 degrees C) and ambient temperature conditions (daytime temperatures during grain filling were 29.0 and 28.2 degrees C in 2014 and 2015, respectively). The decrease rate of grain yields for Suyunuo 5 and Yunuo 7 were 31.3 and 21.9% due to the reduced grain number and weight, respectively, indicating that Suyunuo 5 was more sensitive to heat stress. Heat stress decreased dry matter accumulation aft er pollination (DMA). The photosynthate of vegetative organ post-pollination translocated to grain decreased by 36.1 and 55.9% for Yunuo 7 and Suyunuo 5, respectively. However, the translocation amount and rate of assimilates pre-pollination increased, with greater increase observed in Suyunuo 5. The malondialdehyde (MDA) content was increased by heat stress 25 and 20 d after pollination in Yunuo 7 and Suyunuo 5, respectively. Leaf chlorophyll (Chl), carotenoid (Car), and soluble protein contents were decreased, and the activities of antioxidant enzymes (superoxide dismutase [SOD], catalase [CAT], and peroxidase [POD]) were suppressed by heat stress in both varieties. The findings suggested that reduced DMA and accelerated leaf senescence under heat stress post-pollination result in the grain yield loss.