*Correspondence: licy@yzu.edu.cn (C.L.)

The formation process of starch in the wheat grain is influenced by both genetic characteristics and environmental factors, which can affect starch quality. Waxy wheat Yangnuo1 (YN1) and non-waxy wheat Yangmai15 (YM15) were subjected to heat stress of day (35 °C) / night (25 °C) at early, medium, and late grain filling stages using artificial intelligence temperature control. Heat stress increased the short chain content of amylopectin in both cultivars and decreased their amylose contents. The effect of heat stress on wheat amylopectin structure was most pronounced in 16–20 days after anthesis (DAA).

The crystallinity and enthalpy of starch decreased, as did the swelling potential, solubility and transmittance, but the retrogradation degree showed an opposite trend after heat stress. Compared with YM15, YN1 exhibited superior physical and chemical properties as well as anti-aging properties of starch and consequently had greater thermal stability under heat stress due to its higher degree of branching.

The most sensitive stage to heat stress for yield was 6–10 DAA, resulted in significant decreases in grain number and 1000-grain-weight, followed by 16–20 DAA, resulted a significance only in 1000-grain-weight.

Our study indicated that heat stress during the early stage of grain filling resulted in a decrease in both grain weight and yield, whereas during the middle stage of grain filling, which led to a decline in starch quality, especially in non-waxy wheat.