Annals of Botany Vol. 72, 551-557 (1993)
Key words: Glutinous rice, X-ray diffraction pattern,
amylopectin, discriminant analysis, Oryza sativa
This study was carried out to analyse the cultivar variability of the X-ray diffraction pattern of glutinous rice starches. Four peaks in the X-ray diffractograms were identified, i.e. 3b, 4a, 4b and 6a. The four peaks were measured from the base line for 71 cultivars and three M3 lines which were irradiated by γ-rays at the rates of 10, 20 and 30 kr, respectively. Glutinous rice starches were classified into two types by discriminant analysis based on the values of 3b/4b, 4a/4b and 6a/4b. the X-ray diffraction type of the three cultivars did not change with the cultivation areas of different latitude, while that of eleven cultivars varied. Degree of crystallinity was estimated using the formula, (Imax-Ii)/Imax, where Imax is the maximum height from background intensity line among cultivars, and Ii represents the four peaks. These ratios indicated that the changes in the order of crystallinity were similar to those with the water content and/or hydration and temperature for gelatinization among and/or within cultivars.