Comprehensive evaluation of low temperature and waterlogging stress of direct-seeding rice at bud stage and seedling stage using membership function method

【Objective】Under the double stress of low temperature and waterlogging stress, some rice varieties area were evaluated, evaluation of the ability of early rice varieties to withstand low temperature and waterlogging stress during bud stage and seedling stage in double cropping rice area of Guangxi was conducted, and screened out the rice varieties suitable for early rice direct seeding, so as to provide reference for suitable early rice varieties of direct seeding in Guangxi.【Method】Based on the artificial simulated low temperature environment, the germination seeds of 25 tested rice varieties were treated with low temperature and waterlogging daily average temperature 5℃(12 h light+12 h darkness), water depth of germination box was 5 cm and control daily average temperature 5℃(12 h light+12 h darkness), water depth of germination box was 3 mm.The seeds of tested varieties after accelerating germination were cultured for 10 d.After this treatment, the seeds were restored to 28℃and continued to grow for 10 d.The seedling rate, root length, root numbers, seedling height, fresh weight per plant, above-ground fresh weight and root fresh weight were measured, and their low temperature and waterlogging tolerance abilities were comprehensively evaluated by membership function analysis and correlation analysis.【Result】Seedling rate stress coefficient of 25 rice varieties was different, the variation was 0-1.00, the average stress coefficient was 0.935.Through the correlation analysis of stress coefficient, there was significant positive correlation between seedling rate and above-ground fresh weight per plant under stress(P< 0.05, the same below), and positive correlation with other traits, but the correlation did not reach significant level(P> 0.05, the same below).Seedling height was extremely positively correlated with root length, above-ground fresh weight and root fresh weight(P< 0.01, the same below), and significantly positively correlated with root number and plant fresh weight.According to the average results of membership function, the tested varieties were divided into three types:strong, medium and weak tolerance.There were nine varieties with strong tolerance, they were:Guiyu 12, Wushansimiao, High quality farm seed 2, Guiyu 9, Jinsimiao, Xiangzhou fragrant rice, Hexifengzhan, Y liangyou 1, Guiyu 11.Compared with the medium tolerancetypes and weak tolerance types, the rice varieties with strong tolerance hadimprovement in root length, root number, root fresh weight and seedling height.Compared with the control, under the condition of low temperature and waterlogging stress(LT+W), all measurements of plant traits were decreased, and the root length decreased the most, reaching 19.0%, followed by root fresh weight and root number, which decreased by 18.2% and 16.3% respectively.【Conclusion】The key indexes of tolerance to low temperature and waterlogging stress of direct seeding early rice are seedling rate, root indexes(root length, root number and root fresh weight) and seedling height.Nine varieties such as Guiyu 12 can be directly used in the production of direct seeding rice in Guangxi, and can also provide materials for the study of the mechanism of rice tolerance to low temperature and waterlogging and the cultivation of suitable direct seeding rice varieties.