Differences in the Sterility of Japanese Rice Varieties under Short-day Conditions and Seasonal Changes

Abstract

Nine Japanese paddy rice varieties were cultivated in a phytotron under a natural photoperiod with a day/night temperature regime of 30/22°C on Ishigaki Island which belongs to the subtropical climate, in the southernmost part of Japan. The sterility rates of all varieties were less than 10% when sown in June, but were higher for most varieties originating from the western region of Kanto when sown in September. September sowing accelerated the time to rice heading, resulting in shorter anthers and higher rates of sterility when anther lengths were less than 1.7 mm. Kyushu varieties (e.g., “Shinrei” and “Nishihomare”) had a short basic vegetative growth period and high photosensitivity. As these varieties generally have short anthers, when heading occurred noticeably earlier with September sowing, their anthers became even shorter and there was an increase in sterility. Tohoku and Hokuriku varieties (e.g., “Hitomebore” and “Fukuhikari”) have a long basic vegetative growth period and low photosensitivity. When sown in September, shortening of days to heading and anthers of these cold-resistant long anther varieties was negligible and their fertility remained high. The Kyushu varieties “Minaminishiki” and “Yumehikari,” which both have long anthers, maintained high fertility even when sown in September. Although both “Fukuhikari” and “Shinrei” were cultivated year-round, the sterility of “Fukuhikari” remained stable and low throughout the year, whereas that of “Shinrei” varied inversely with seasonal differences in the number of days to heading.