Moderate drought stress followed by re-watering enhances wheat starch biosynthesis, improving granule size...

Wheat growth is often restricted by drought, but crops have a water compensation effect. This study explored the effects of rewatering after different degrees of drought stress in the early stage of grain-filling (1-10 days post anthesis) on starch synthesis, yield, starch particle size distribution and physicochemical properties of two wheat varieties with different drought tolerance. Compared to the well-watered control (CK; soil relative moisture 70-75 %), mild drought followed by re-watering (MR; soil relative moisture 50-55 %) enhanced the activity and gene expression level of XN836 and XN979 starch synthases, increased the content of starch and sucrose, accelerated the conversion of sucrose to starch and thereby raised the wheat yield. Concurrently, MR increased starch granule size, swelling power, and water solubility, while decreasing relative crystallinity, short-range molecular degree of order, gelatinization temperature, and gelatinization enthalpy, ultimately improving starch quality. Dynamic rheology further revealed enhanced elastic behavior in starch under MR treatment. In contrast, severe drought followed by re-watering (SR; soil relative moisture 35-40 %) exhibited the opposite trends in both cultivars. Furthermore, XN836 demonstrated superior recovery capacity following drought and re-watering compared to XN979. These findings provide a theoretical basis for adaptive wheat management strategies under future climate change scenarios.