Abstract
The duration of reproductive phase (DRP), which was defined as the number of days from panicle initiation to heading, was investigated for 8 cultivars of Oryza sativa L. including 2 japonica and 6 indica varieties at Kagoshima. The DRP was determined by observing the panicle initiation stage under a stereoscopic microscope and the heading stage with the naked eye. DRP of cultivars were examined under two conditions, natural daylength and constant short daylength (10h day/14h dark). Results obtained are as follows: (1) DRP was shortest in early maturing followed by medium and late maturing varieties in this order. The DRP shortened by short-day treatment also varied with the cultivar in the same order. (2) There was a significant difference in DRP among cultivars and treatments with a p\<0.01 according to the analysis of variance. These results show that the DPR varied with the cultivars and growth condition. On the other hand, in some cultivars such as TEPI, MIRITI, BINASHAIL, DPR were not differ influenced by short-day treatments suggesting that the DPR of some cultivars are not sensitive to short-day treatment.
