Abstract:

A total of 556 cold−region early Japonica rice varieties from Heilongjiang, Jilin, Liaoning province and Japan were introduced, the field experiments with two sowing dates were conducted in Jiangxi province, where heat tolerance and adaptability were assessed under extreme natural high−temperature conditions, which comprehensively evaluated the high temperature resistance, thereby screening out heat tolerant Japonica rice and provided excellent germplasm resources for Japonica breeding in high−temperature areas. Research indicated that under high−temperature conditions, grain number, filled grain number, spikelet fertility, heat tolerance class, adaptability and high temperature resistance grade of cold−region early Japonica rice had a variation change, among these varieties from different geographical regions, those from Liaoning and Heilongjiang Japonica rice stood out with notably higher grian number and spikelet fertilit compared to others, meanwhile, Liaoning Japonica rice showed the strongest heat adaptability and comprehensive heat tolerance. A total of 30 excellent heat tolerance and adaptability Japonica rice varieties were selected, 13, 2, 11 and 4 varieties were from Heilongjiang, Jilin, Liaoning province and Japan, accounting for 5.26%, 2.94%, 8.53% and 3.60% of the tested material from every geographical origin, respectively. Among these, Tongyu267, Songjing4, Longgrain line, Yanjing34 and Yanfeng47 exhibited the strongest heat tolerance and adaptability, which can be used as the key parents of Japonica rice breeding in high−temperature regions. 

Key words: Cold region Japonica, Extreme high temperature, Heat tolerance, Adaptability, Evaluation