2001 Volume 70 Issue 1 Pages 54-58
Heading time of rice cultivars, Koshihikari and Kirarimiyazaki, in the early-season-culture depends on climatic factors during the period from transplanting stage to panicle formation. Effect of short days given at various stages was examined by pot-experiments in Miyazaki Prefectural Experiment Station. When the two cultivars were grown in short days from transplanting, Koshihikari, which normally heads later than Kirarimiyazaki headed one day earlier than Kirarimiyazaki. It was thought that this reversed heading between Koshihikari and Kirarimiyazaki was due to the difference in photoperiodic sensitivity, Koshihikari was sensitive to photoperiod from 30 days before the first panicle formation stage to panicle formation, especially 18-19 days before the first panicle formation. The same was also the case in Kirarimiyazaki, but the heading of this cultivar was less hastened by short-day treatment than that of Koshihikari. It was thought that the reversed heading between Koshihikari and Kirarimiyazaki in 1998 was due to the high temperature during April and May, which accelcrated the vegetative growth(panicle formation) and made Koshihikari more responsive to short days than Kirarimiyazaki.
