A comparative evaluation of the effect of SSI and Wx allelic variation on rice grain quality and starch physicochemical properties

Near-isogenic lines Nip(Wxb/SSIj), Nip(Wxb/SSIi), Nip(wx/SSIj) and Nip(wx/SSIi) in the japonica rice Nipponbare (Nip) background containing allelic variation in the starch synthase gene SSI and Wx were investigated for cooked rice grain quality, starch morphology, pasting profiles, fine structure and crystallinity characteristics. Rice grains carrying the SSIi allele had poor cooked rice taste in the Wxb background. The introduction of SSIi caused reduced cooked rice grain elongation, especially in the wx background. Starch granule size was reduced in SSIi rice and the viscosity of flour and starch prepared from SSIi rice was markedly increased. Moreover, analysis of the starch molecular structure revealed a remarkable increase in the short amylopectin chains and reduced starch relative crystallinity compared with SSIj rice, which resulted in decreased gelatinization characteristics. These results suggest that SSI allelic variation has multiple effects on rice grain quality, as well as starch fine structure.