Analysis of Genotypic and Environmental Effects on Rice Starch. 2. Thermal and Retrogradation Properties

Eight rice varieties with wide diversity in apparent amylose content (AC) were selected and planted in the early (HZE) and late season (HZL) in Hangzhou and in the winter season in Hainan (HN) for two consecutive years to study the genotypic and environmental effects on starch thermal and retrogradation properties of grain. Genotypic variation (all at P < 0.01) accounted for >56% of the total variation for onset (T o), peak (T p), and completion (T c) temperature, width at half-peak height (ΔT 1/2) of gelatinization, enthalpy (ΔH r) of retrograded starch, percentage of retrogradation (R%), and 45.8% for enthalpy (ΔH g) of gelatinization. Seasonal variation accounted for about one-fifth for T o, T p, and T c and one-third for ΔH g, but less for T 1/ 2, ΔH r, and R% of the total variation, indicating that T o, T p, T c, and ΔH g were highly affected by seasonal environment in addition to the genotypic variation. The T o, T p, T c, and ΔH g in HZL were much smaller than those in HZE and HN. Correlation analysis for the eight genotypes showed that AC was significantly correlated with ΔH g (r = −0.83, P < 0.01) and R% (r = 0.734, P < 0.05). ΔH g was also positively correlated with T c (r = 0.878, P < 0.05), but it did not have any correlation with ΔH r, whereas the latter was positively correlated with R% (r = 0.994, P < 0.001). The intercorrelation of T o, T p, T c, and ΔT 1/ 2 themselves was significant at P < 0.001. The correlation analysis results suggest that there are different molecular mechanisms to regulate thermal properties (T o, T p, T c, and ΔH g) and retrogradation properties (ΔH r and R%) as affected by environmental conditions. The implications of the results for rice breeders and starch-based food processors are discussed. Keywords: Rice; starch; gelatinization temperature; thermal property; retrogradation; environment