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BACKGROUND Maize is frequently subjected to simultaneous water (drought or waterlogging) and heat (HS) stresses during grain formation in southern China. This work examined the effect of high temperature combined with drought (HD) or waterlogging (HW) during grain formation on the starch physicochemical properties of two waxy maize hybrids, namely Suyunnuo5 (SYN5) and Yunuo7 (YN7). RESULTS: Heat stress enlarged the starch granule size, and water stresses aggravated this effect. Heat stress reduced the ratio of small molecular weight fractions for both hybrids, and HD aggravated this reduction only in SYN5. Relative crystallinity in SYN5 was increased by stresses but in YN7 it was unaffected by HD, reduced by HS, and increased by HW. Fourier‐transform infrared (FTIR) spectrometry results showed that the 1045/1022 cm−1 ratio in SYN5 was not influenced by HW but was increased by other stresses, and that in YN7 it was increased by all stresses, with the highest value induced by HW. Peak viscosity was decreased, whereas gelatinization temperatures and retrogradation percentage were increased by all of these stresses. These effects were exacerbated by combined heat and water stresses. The maximum decomposition rate was severely increased by HW. CONCLUSION: Drought or waterlogging at grain formation stage aggravated the detrimental effects of HS on the starch physicochemical properties of waxy maize. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

• Waterlogging decreased starch granule size. • Waterlogging increased the proportion of long-chains and high-molecular-weight molecules in amylopectin. • Ordered structure of waterlogged starch decreased peak and breakdown viscosities. The grain formation stage is a critical stage that affects grain starch quality and frequently overlaps the rainy season in southern China for waxy maize production. Two waxy maize varieties were grown under control and waterlogging conditions during grain formation (1–15 days after pollination) to probe the effects of oversaturated soil moisture on starch structural and functional characteristics. Results indicated that waterlogging during grain formation decreased the size of starch granule, proportion of large granule (d > 15 μm) and ratio of medium-length chains (DP 10–24) in amylopectin, whereas the percentage of high-molecular-weight molecules were increased. Compared with the control, the percentage of ordered starch was increased by waterlogging for both varieties. The changes in starch internal structure under waterlogging had no influence on thermal stability, increased the maximum thermal decomposition ratio and pasting temperatures, and reduced pasting viscosity characteristics in both varieties. [ABSTRACT FROM AUTHOR]