Improving Rice Cooking and Eating Quality: Alternate Wetting and Moderate Drying Irrigation Reduces Protein Content Under High Nitrogen

ABSTRACT High nitrogen (N) application usually increases protein content to impair rice cooking and eating quality. Mitigating this deterioration under high N conditions remains to be explored. Alternate wetting and moderate drying irrigation (AWMD) can interact with N fertilizer to improve rice quality. To investigate the effects of AWMD on rice protein content and cooking and eating quality, Nanjing 9108 (NJ9108), a superior‐tasting japonica variety, was planted. With 150 kg N hm −2 applied as the base‐tiller fertilizer, four panicle‐stage N rates (0, 70, 140, and 210 kg hm −2 , denoted as 0, 70, 140, and 210 N, respectively) were tested. Two irrigation regimes of conventional irrigation (CI) and AWMD were implemented during the grain‐filling stage. The results showed that increasing panicle N fertilizer enhanced the contents of protein and total amino acids (TAAs) in milled rice, as well as the activities and gene expressions of the key enzymes involved in protein synthesis. Compared with CI, AWMD increased the contents of protein and TAAs and enzymatic activity and gene expressions under 0 and 70 N treatments, but it reduced these parameters at high panicle N rates (140 and 210 N). Principal component analysis indicated that expression levels of OsAAT and OsAlaAT1 genes and TAAs content can be key parameters for evaluating protein synthetic capacity in rice grains. Correlation analysis revealed that the measured parameters related to protein synthesis had a significant negative correlation with rice cooking and eating quality. These results suggest that the AWMD regime can alleviate the decline in rice cooking and eating quality by reducing protein content at high panicle N fertilizer levels. The taste quality of superior taste japonica rice can be improved by adopting the AWMD regime under high panicle N fertilizer conditions.