Northeast regions of China (38–558N latitude) play an important role in Japonica rice planting. Heading dates of 10 Japonica rice cultivars
native to the Northeast of China were investigated and their sensitivities to photoperiod and temperature were analyzed. The results showed that
these Japonica rice cultivars were insensitive to photoperiod but strongly sensitive to temperature, i.e. a high temperature can markedly shorten the
heading date. Genetic analyses were conducted on these 10 cultivars using a set of heading date tester lines. All these Japonica cultivars carried a
dominant early heading gene Ef-1, and most of these cultivars carried the photoperiod insensitivity allele e1, and two types of alleles were presented
at the Se-1 locus, including recessive photoperiod insensitivity gene Se-1e and dominant strong photoperiod-sensitivity (PS) gene Se-1n. The PS of
these cultivars carrying E1 or Se-1n can be repressed or weakened by Ef-1 and the recessive allele hd2 they carried. These results provided a
reasonable explanation to the adaptability of Japonica rice to the high latitude environment of the Northeast China, and could be useful for breeding
new cultivars well adapted to the high latitude regions and expanding the rice cultivation range.
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