Abstract
The effect of short-day treatment on the cool-weather tolerance at the flowering stage was examined in 14 varieties of rice from the south of Tohoku district, Japan, and 3 varieties from Yunnan Province, China. The plants were exposed to 8-hour short days for 14 days from the 5.5 leaf stage (short-day plot; SDP) or natural-day lengths throughout the experimental period (NDP). On the day of heading, they were exposed to 17.5°C for 15 days. The number of days to heading in SDP was 28 days less on average than in NDP. In the varieties with a longer period to heading in NDP, the period was reduced more markedly by a short-day treatment (r=0.926, n=17). The variation of heading date among varieties in SDP was smaller than in NDP. Although the cool-weather tolerance at the flowering stage in SDP was higher in varieties with longer periods to heading in NDP, with greater reduction in the number of days to heading by short-day treatment, and with a longer duration of sunshine, from 3 days before to 5 days after heading (r=0.666, 0.536 and 0.741, each, n=16), there was a highly significant positive correlation (r=0.830, n=16) in the cool-weather tolerance between SDP and NDP. Therefore the short-day treatment was considered to be laborsaving for growing materials for the test of cool-weather tolerance.
