Analysis On Wheat Freezing Resistance Based On The Responses Of The Physiological Indices To Low Temperature Stress

A pot experiment with twenty wheat cultivars was conducted to investigate the responses of the physiological indices, the grain yield and its constitute factors, the expression of antifreeze protein under low temperature stress, provided the theory basis and the appraisal method for wheat frost resistance breeding. The main findings are as follows.1 Effects of low temperature stress on grain yield and its constitute factors of different wheat cultivars at stem elongation stageLow temperature (-4℃) stress at stem elongation stage resulted in the changes of grain morphology and yield characters. For most of test cultivars, their grain length-width ratio, grain roundness, and sterile spikelets increased, and their grain equivalent diameter, grain area, 1000-grain weight, and grain yield decreased.2 Effects of low temperature stress on physiological indices of different wheat cultivarsThe results indicated that under low temperature stress at seedling and elongation stages, the activities of SOD, CAT, and POD increased, and the content of MDA, the soluble protein and the soluble sugar decreased in functional leaves of each cultivar.3 Correlation analysis between grain yield and physiological indices of wheat after low temperature stress at elongation stageCorrelation analysis indicated that, the SOD, POD and CAT activity had a significant negative correlation with the grain yield; the MDA and soluble sugar had a significant positive correlation with the grain yield after low temperature stress at stem elongation stage. Path analysis indicated that after treated with low temperature at stem elongation stage, the SOD activity and soluble sugar content of functional leaves, especially the SOD activity (direct path coefficient -0.5785), were the dominant factors affecting grain yield.4 Evaluation of wheat freezing resistance at seedling and elongation stages and correlation analysisBased on the value D of seedling stage, value D of stem elongation stage after low temperature stress, the twenty winter wheat cultivars were relatively divided into three groups respectively. Cultivars Jimai19, Jimai20, Liangxing99, Lumai21, Shannong1135, and Shannong8355 belonged to high freeze resistance group, cultivars Liaomai18, Shannong664, Linmai2, and Taishan9818 were of low freeze resistance group, and the other ten cultivars belonged to medium freeze resistance group at seedling stage. Cultivars Jimai19 and Shannong8355 belonged to high freeze resistance group, cultivars Liangxing99, Liaomai18, Linmai2, Weimai8, and Zimai12 were of low freeze resistance group, and the other thirteen cultivars belonged to medium freeze resistance group at elongation stage. Taking the percentage of decreased grain yield due to low temperature stress as the assessment criterion, Cultivars Jimai19, Jimai20, Liangxing99, Shannong1135, Shannong8355, Taishan23, Taishan9818, Wennong6, and Yannong21 belonged to high freeze resistance group, cultivars Linmai2, Weimai8, Yannong19, and Zimai12 were of low freeze resistance group, and the other seven cultivars belonged to medium freeze resistance group.Correlation analysis indicated that, The seedling stage comprehensive assessment index (D value) had a significant negative correlation with the percentage of decreased grain yield(r =-0.5119*), suggesting that the stronger freeze resistance of wheat at seedling stage was beneficial to the higher wheat grain yield, and seedling stage was the critical period to be selected to identify the freeze resistance of wheat.5 Effects of low temperature stress on protein expression of different wheat cultivarsProtein expression analysis indicated that, wheat freezing resistance was related to the protein expression in functional leaf.In conclusion, we can measure the SOD activity and soluble sugar content as the physiological indices, giving priority to the freezing resistance at seedling stage, and take account of the freezing resistance at elongation stage in the wheat freezing resistance breeding.