Abstract: 【Objective】Clarifying the influence of heat stress durations at grain formation stage on grain yield and starch quality of waxy maize, which could afford a theoretical basis for waxy maize starch quality improvement.【Method】The pot trials were conducted at Yangzhou University in 2014 and 2015. After artificial pollination, heat stress treatments (35℃) were introduced by intelligent greenhouse and the heat stress durations were 1-5 d, 1-10 d, and 1-15 d after pollinations (DAP), respectively. The grain yield, grain protein and starch content, starch physicochemical parameters (starch granule size and distribution, chain-length distribution, crystallinity, pasting and thermal properties) were analyzed using Suyunuo 5 and Yunuo 7 as materials.【Result】Heat stress at grain formation stage reduced grain number and weight, which induced yield loss and the loss at 1-5, 1-10 and 1-15 DAP was 39.3%, 47.4%, 50.9%, respectively. Heat stress increased protein content and decreased starch content in grains, respectively. High temperature increased the starch average granule size and the granule size gradually decreased with the prolongation of heat stress durations. The starch maximum absorption wavelength, crystalline structure and setback viscosity present typical waxy character. Heat stress at grain formation stage increased the proportion of long-chains in amylopectin, and the values were the highest and the lowest at 1-10 DAP heat stress conditions for Suyunuo 5 and Yunuo 7, respectively, among different treatments. Relative crystallinity in response to heat stress durations was different between two varieties and two planting years. Generally, 10 d heat stress did not affect the pasting characteristics, while the peak, trough, breakdown, and final viscosities and pasting temperature were increased by 1-5 and 1-15 DAP heat stress and the increase of peak, trough and breakdown viscosities were the highest in 1-15 DAP heat stress. Compared with control, heat stress decreased gelatinization enthalpy and increased the other thermal characteristics. The gelatinization enthalpy was the lowest in 1-15 DAP heat stress, gelatinization temperatures were the highest in 1-5 DAP heat stress, and retrogradation percentage were similar among different heat stress durations.【Conclusion】Heat stress at grain formation reduced the grain yield and the reduction was gradually severe with the prolongation of heat stress durations. High temperature suppressed grain starch accumulation and increased the protein content. Starch pasting and thermal properties were changed as the starch granule size enlarged and proportion of long-chains in amylopectin increased. Among different heat stress durations, the peak and breakdown viscosities were the highest and setback viscosity was the lowest when high temperature was introduced at 1-15 DAP. The gelatinization temperatures were the highest under 1-5 DAP heat stress conditions and no difference was observed for retrogradation percentage among three heat stress treatments.

Key words: grain formation stage, waxy maize, heat stress, grain yield, starch quality