Basic Vegetative Growth and Photoperiod Sensitivity of Heading-time Mutants Induced in Rice

Abstract

Out of a large number of heading-time mutants artificially induced from a rice variety Gimb6zu, 83 mutants covering the heading dates from 3 weeks earlier to 2 weeks later than the original variety, were selected without a biased distribution of heading time. These mutants were grown together with the original variety and 32 important Japanese varieties in two kinds of artificially controlled environments, a high-temperature (30°C-short-day-length (10h) and a high-temperature (30°C)-long-day-length (14h): their basic vegetative growih (BVG), which was expressed by the days to heading under 30'C0h, and photoperiod sensitivity (PS), which was expressed by the difference between the days to heading under 30°C-14h and that under 30°C-10h, were estirnated. The estimated BVG and PS were then analyzed for their genetic variations and their relationships with the heading time under the natural conditions in a paddy field in Kyoto (N. L. 35°C01'). The extremely-early-heading varieties cultivated in Hokkaid6 showed small BVG and small PS, the early-heading varieties mainly cultivated in Tohoku and Hokuriku districts generally showed large BVG and small PS, and the intermediate- or late-heading varieties cultivated in the region from Kant6 to Kytish{i districts showed small BVG and large PS (Table 1, Fig. 2).