Novel Wx alleles induced by chemical mutagens in rice, Oryza sativa L.

From mutant pools of two Taiwanese elite japonica cultivars, Tainung 67 and Taikeng 8, we identified 13 mutant lines possessing opaque endosperm with relatively low amylose contents (AC) ranging from 1.5% to 7.1%. Because of different AC, paste viscosities of these 13 mutant lines differed, as revealed by palatability and physicochemical properties. The mutated gene conferring opaque endosperm was isolated from the F-2 population of one mutant line, WY1x indica cv. Taichung Sen 17', by positional cloning, revealing a G3018 -> A3018 substitution at exon 9 of Waxy leading to a non-synonymous mutation from alanine to valine. Two additional alleles were identified from the other 12 mutant lines, for which single-nucleotide substitutions G2708 -> A2708 and G3029 -> A3029 occurred in exons 8 and 9, leading to non-synonymous mutations from arginine to histidine and glutamic acid to lysine, respectively. The three novel wx alleles had different effects on grain quality, specifically on eating and cooking quality, and could be applied in rice breeding programmes to develop new low AC varieties by marker-assisted selection.