Study On Cold-Hardiness Mechanism Of Mulberry

Mulberry which belongs to deciduous trees or shrubs mainly produce fruit. Mulberry fruit, also known as mulberry, is not only nutritious, delicious taste, but also very rich in nutritional value and health care function. In recent years, mulberry as a new type of industry, have developed rapidly in many provinces, but due to different cultivated regions, cold hardiness is different among different mulberry varieties. In the introduction and cultivation of mulberry, especially in the alpine region, the low temperature affected the yield and planting area of fruit mulberry, therefore it is significantly important to study mechanism of cold resistance of fruit mulberry, select proper identification of cold resistance index, explore and evaluate of cold resistance of fruit mulberry varieties and screen for cold resistant variety of fruit mulberry, introduction, breeding and promotion. This thesis aimed to study the influence of low temperature stress on membrane permeability, membranous peroxide, antioxidant enzymes activity, osmotic regulation substances in twigs of15mulberry cultivars, and the principal component analysis and membership function method were used for the comprehensive evaluation, and the results were as follows:1Under lower temperature stress, the trend of physiological and biochemical indexes of different mulberry cultivars are basic consistent. Electrical conductivity, MDA content and POD activity with lower temperature stress has been an increasing trend and although the SOD activity of the five mulberry varieties such as Bei fang hong have also been rising,the trend of the rest varieties is dropping after increasing, but their SOD activity remained higher than the control level. Soluble protein content and the content of soluble sugar showed increase at first among them, soluble protein content showed a rising trend. Except of a few varieties showed a slightly lower soluble sugar content than the contrast, the level of soluble sugar of the rest varieties maintained higher than the control. Proline content changed extent among varieties and although the general trend of Proline content is rising, their peak temperature is different.2In the process of continuous cryogenic stress, the trend of physiological and biochemical indexes of different mulberry cultivars are basically the same. Among them, the content of MDA and membrane permeability has been an uptrend. The variation of SOD and POD activity is volatile and varieties presents different change trend, but the whole shows ascendant trend. The trend of soluble protein content was lower increase at first, but overall maintain significantly higher than the level of control. The content of soluble sugar and proline changed extent and their rule are not consistent, but proline content is rising; Except a few species of soluble sugar content reduced after the low temperature stress of6d, the rest maintained in the level of higher than those of control.3Based on the principal component analysis and fuzzy mathematic function method, the cold hardiness of15mulberry varieties is divided into three levels:Bei fang hong, Bai yu wang, Ning xia hong, Lv shen zi,Tian sheng1, Hong guo1and8632belong to high cold resistance varieties; Da10, Hong guo2, Tai wan72C002and Ri ben hu cheng belong to medium cold resistance varieties; Taiwan46C019, Ao yu, Yi chuan hong and Hong bao shi belong to low cold resistance varieties.