Estimating rice amylose content from Wx alleles and weather data and determining suitable cultivation areas for new high-yield, low-amylose lines in Tohoku region of Japan

Abstract

　The demand for ready-made meals is growing rapidly. Low-amylose rice is preferred for its stickiness and softness after cooking and cooling. In addition, processors demand a stable amylose content for reliable production. However, existing low-amylose cultivars have variable amylose contents and low yields. A Waxy allele, Wx-mq, which confers a stable low amylose content, has been used in low-amylose cultivars such as ‘Kiraho’, from which ‘Iwate 144’ and ‘Iwate 147’, with improved yield performance, have been developed. To identify suitable growing regions, we developed an equation using Ridge regression to predict amylose content from alleles at the Wx locus and weather conditions during the grain filling stage. The equation can predict amylose content with RMSE = 1.1 ％ and R² = 0.992 of lines with both Wx-b (middle-amylose) and Wx-mq (low-amylose) alleles. The equation was combined with a rice development model and applied to the Tohoku region of northeastern Japan. Using 30-year-average amylose content and stability, the equation identified northern Iwate Prefecture and northeastern Aomori Prefecture as suitable for growing the variety. Simulations conducted for later-maturing low-amylose cultivars currently under development suggested that these cultivars would have a higher amylose content than ‘Iwate 144’ and ‘Iwate 147’. Thus, cultivars with a wide range of maturities will contribute to increased production through the expansion of suitable locations. We conclude that selecting the appropriate maturity group according to climate is important to meeting the requirements for stable amylose content and high yield of low-amylose cultivars, and will contribute to large-scale planting of new low-amylose cultivars with reliable amylose content.