A Method for Estimating the Suitable Area and the Time of Transplanting or Direct-seeding to Avoid Marked Dull Endosperm by Predicting the Amylose Content of Low-amylose Rice Varieties in the Tohoku Region

Abstract

A method for estimating the suitable time and area for transplanting or direct-seeding rice to avoid the incidence of marked dull endosperm was investigated by predicting the amylose content of low-amylose rice varieties using a model for estimating developmental stages. Three low-amylose rice varieties were transplanted or direct-seeded at three locations in the Tohoku region of Japan three times a year for three years. A high negative correlation was found between the temperature during the ripening period and the amylose content of milled grains. Marked dull endosperms were observed in the grains containing less than 10% amylose. The amylose content with respect to transplanting or direct seeding date was estimated using a model for estimating heading dates and a regression model explaining the relationship between the temperature during the ripening period and the amylose content. The root mean square error quantified by the difference between the predicted values of amylose content by this method and the measured values was 0.88-1.67%. It was possible to estimate the suitable time for transplanting or direct-seeding to avoid marked dull endosperm by estimating the dates on which the amylose content was predicted to be 10-15%. Furthermore, the results estimated by this method suggested that the suitable area and time of cultivation to avoid marked dull endosperm could be expanded by an appropriate combination of transplanting and direct seeding.