Selection of New Check Rice Varieties for Evaluating High Cold Tolerance and the Development of Breeding Lines with High Cold Tolerance in the Tohoku Region of Japan

To select new check rice varieties for evaluating cold tolerance at the booting stage higher than 'Very-tolerant', precisely, cold tolerance was investigated using a deep-water irrigation system at 7 breeding stations for 5 years from 2004 to 2008. Judging from the percentage sterility, new check varieties from pre-existing 'Very-tolerant' to 'Very-tolerant 9' in the very-early heading group ('Yumekogane' class) and from 'Very-tolerant' to 'Very-tolerant 11' in the very-early ('Kakehashi' class), early, early-to-moderate and moderate heading groups were selected. Using the new check varieties, new breeding lines with high cold tolerance and good agronomic traits were developed.