Abstract
Delayed sowing (DS) is an important measure for adapting to global warming, but its effect on rice quality is poorly understood. To evaluate the influence of DS on the starch structure and quality of rice, this study conducted field experiments by sowing two indica rice cultivars on two different sowing dates in both Hanyuan and Chongzhou, Sichuan Province, China, from 2017 to 2018. The delayed sowing period experienced a mean temperature reduction of 1.87-2.99℃ during the grain-filling stage compared to the conventional sowing period. The amylose content (AC), starch content (SC), branching degree (BD), proportion of amylopectin A chain (DP 6-12), 1022/995 cm(-1) ratio, Z-average molecular weight (Mz)/ number average molecular weight (Mn), and weight average molecular weight (Mw)/Mn were significantly (p < 0.05) and negatively correlated with both chalky rice rate (CRR) and chalkiness degree (CD) but positively correlated with appearance value (AV), taste value (TV), and comprehensive score (CS) of cooked rice. Meanwhile, starch granule average diameter (SGAD), volume-based percentage of large starch granules (D > 8 μm) (VPLSG), average amylopectin chain length (AACL), 1045/1022 cm(-1) ratio, proportions of amylopectin B2 (DP 25-36) and B3 (DP ≥ 37) chains, and crystallinity degree (CRD) significantly (p < 0.05) reduced with eating quality of rice but positively associated with rice chalkiness. Compared to conventional sowing, the 1022/995 cm(-1) ratio, amylose content (AC), BD, A chain proportion, Mw/Mn, and Mz/Mn were significantly (p < 0.05) increased by delayed sowing treatment in both study sites. DS also reduced the VPLSG, AACL, CRD, B2 and B3 chains proportions, and 1045/1022 cm(-1) ratio. This contributed to reductions in CRR and CD, as well as increases in the AV, TV, and CS of cooked rice across study sites. No significance was observed in milling quality of rice. Therefore, delayed sowing improved the appearance and eating qualities of rice by altering its components and structural characteristics of starch.