Mild alternate wetting and drying modulates cooking and eating quality of rice under low to normal nitrogen dose

Cooking and eating quality (CEQ) is a key indicator for evaluating rice quality, and its formation is determined by the combined effects of starch polymers and protein. This study explored the fine structure of starch polymers and the crystalline order of starch, along with protein content, and their impact on CEQ under water‑nitrogen interactions. Field experiments were conducted exposed to three N doses, 180 (low, LN), 270 (normal, NN), and 360 kg ha^-1 (high, HN) under conventional irrigation (CI) and alternate wetting and drying irrigation (AWD). Results indicated that starch crystalline orderliness and protein content were key determinants of CEQ in rice. The biosynthesis of longer amylopectin chains increased crystalline orderliness, whereas concurrent protein accumulation further decreased CEQ (pasting, thermal, and texture properties). Conversely, the accumulation of short amylopectin chains and amorphous polymers reduced starch crystalline order, and together with decreased protein content, effectively modulated CEQ. The results of water-nitrogen interaction further indicated that AWD synergistically optimized carbon and nitrogen metabolism, promoting the synthesis of short amylopectin chains; however, this synergistic effect was contingent upon nitrogen dose (low and normal nitrogen). This study provides mechanistic insights into the structural basis of rice CEQ improvement via water-nitrogen interactions.