Photoperiod sensitivity gene controlling heading date in rice cultivars in the northernmost region of Japan

Rice is grown in diverse environments at latitudes ranging from 53^°N to 40^°S. In Japan, Hokkaido is the northernmost rice cultivation region(42–45^°N latitude). Only extremely early maturing (heading) varieties that have extremely low photoperiod sensitivity are adapted to this area. Heading date is the most important trait in adaptation to this particular environment. Also, the efficient manipulation of heading date is a crucial component of rice improvement. To determine the genetic basis for heading date among cultivars grown in Hokkaido, the heading behaviour was analyzed. Clear segregations were observed. To estimate the photoperiod sensitivity of the genes involved, the cultivars and F₁ plants from crosses between the cultivars were grown under different daylength conditions. The results indicated that the genes controlling heading date are photoperiod sensitive, suggesting they play important roles in the northernmost rice cultivation regions in Japan, to which only cultivars with extremely low photoperiod sensitivity are adapted. This revised version was published online in August 2006 with corrections to the Cover Date.