Distribution of the Rice Diversity Panel 1 accessions by subpopulation group for cold tolerance at germination.

Cold tolerance described as the “Germination Index” was calculated as the ratio of the mean percentage of seeds with coleoptiles >5 mm under cold treatment to the mean percentage of seeds with coleoptiles >5mm under warm treatment. The temperate japonica and tropical japonica accessions were significantly more tolerant than accessions classified as indica and aus, the INDICA subspecies. Based on the Student’s t-test (p<0.05) there were no differences between indica and aus subpopulations.