Variation in Starch Properties in Ratoon Rice and Their Relationship with Rice Quality

Ratoon rice is characterized by higher production combined with enhanced rice quality. However, the relationship between the differences in the structure and properties of the starch and variations in the ratoon season and rice quality is still unclear. In this study, we conducted a field experiment in 2023 to assess the relationship between rice quality differences and starch characteristics of four different hybrid rice varieties (Longjingyou1212: LJY1212; Taoyouxiangzhan: TYXZ; Liangyou6326: LY6326; Fengliangyouxiang1: FLYX1) in the ratoon season. In terms of appearance, the chalkiness degrees and chalky grain percentage of LJY1212 (0.6%, 2.3%) and TYXZ (1.2%, 6.0%) were 53.5% and 53.9% lower than those of LY6326 (2.4%, 10.0%) and FLYX1 (1.6%, 7.8%), indicating that the appearances of LJY1212 and TYXZ were better than those of LY6326 and FLYX1. The average amylose contents of LJY1212 (18.5%) and TYXZ (19.0%) were 10.8% higher than those of LY6326 (17.7%) and FLYX1 (15.7%), and there was no significant difference in protein content between the varieties in the ratoon season. Regarding the starch microstructure, the starch granules of LJY1212 and TYXZ in the ratoon season were arranged more closely. The average ratios of 1045/1022 cm−1 of LJY1212 (0.77) and TYXZ (0.76) were 7.0% higher than those of LY6326 (0.71) and FLYX1 (0.72), indicating that the internal orders of LJY1212 and TYXZ’s starch were better than those of LY6326 and FLYX1. The average relative crystallinities of LJY1212 (24.8%) and TYXZ (24.5%) were 5.2% lower than those of LY6326 (25.7%) and FLYX1 (26.6%). The relative crystallinity of starch decreased with the increase in amylose content, while the short-range order degree, gelatinization temperature, and gelatinization enthalpy increased with the increase in amylose content. Therefore, the LJY1212 and TYXZ varieties, with better rice qualities, are recommended for planting in southern China.