Analysis of genotypic diversity in starch thermal and retrogradation properties in nonwaxy rice

A total of 236 nonwaxy rice including 56 landraces (landrace set) obtained from the germplasm center and 180 cultivars and breeding lines (breeding line set) obtained from various breeding programs were studied for the genetic diversity of flour thermal and retrogradation properties, focusing on comparison of the differences between the landrace set and breeding line set. Wide diversity was found in all flour physicochemical properties, e.g. peak temperature (Tp) ranged from 63.2 to 79.8 °C, width at half peak height (ΔT1/2) of gelatinization ranged from 4.7 to 10.5 °C; enthalpy of gelatinization (ΔHg) ranged from 5.6 to 11.4 J/g, and retrogradation percentage (R%) ranged from 0.2% to 54.2%. The breeding line set had a larger range of thermal properties and R% than in the landrace set, whereas the range of retrogradation enthalpy was similar between two sets. The mean for all parameters differed between the two sets; mean ΔT1/2 of the landrace set was smaller than in the breeding line set, whereas other parameters were larger in the landrace set than the breeding line set. Correlation analysis showed that apparent amylose content was positively correlated with ΔHg (r = 0.65, P < 0.001) and R% (r = 0.68, P < 0.001), and negatively correlated with ΔT1/2 (r = −0.28, P < 0.001). All thermal and retrogradation properties themselves were correlated; the correlation between ΔT1/2 and all other parameters was negative, whereas all other pairs were positive.