| Walnut (Juglans regia L.), Walnut (Juglandaceae), Walnut (Juglans), is perennial deciduous angiosperms. Weibei area in arid and semi-arid region of northwest China is one of the precocity walnut cultivars producing areas while it has strong cold air occuring repeatedly in spring, and less rainfall, and then temperature and moisture become the major restrictive factors of walnut production in this area. Temperature and moisture are the most important ecological factors of normal growth and development of plants.Low temperature and water stress can affect the economic productivity of forest, causing large economic losses. On the condition of low temperature and drought stress, studying the physiological and biochemical indexes of walnut, photosynthetic fluorescence characteristics, growth indices for comprehensive evaluation of different cold-hardiness and drought stress about precocity walnut cultivars, screening species of strong resistance, might guide the production to provide the theory basis.The9years old precocity walnut shoots of eleven cultivars were investigated with the method of artificial simulation of low-temperature. Put the materials in15℃(CK),3℃,0℃,-3℃,-6℃,-9℃low temperature and then the physiological and biochemical indexes were investigated and recovering growth situations were observed. Using the recovering rate after statistics of survival to analyse the correlation between survival and physiological and biochemical indicators, filter out the relevant factor for principal components analysis, and synthetically evaluate cold resistance of walnut cultivars combining with fuzzy mathematics method and cluster analysis. Main conclusions were as follows:(1) With temperature decreased, all walnut cultivars shoots recovering rate became lower after low temperature treatment. Especially, the recovering rate of all varieties decreased significantly after-3℃low temperature treatment. Then it was selected as a measure of cold resistance.(2) With the treatment temperature decreased, the relative conductivity of the eleven precocity walnut cultivars shoots rose slowly at first, after a sudden rise, and then flattened, that was showing the "S" curve. The semi-lethal temperatures of the precocity walnut cultivars were gotten based on the relative conductivity trends and the logistic equation, and so Xilin No.3and Liaohe No.3had strongest cold resistance while weakest cold resistance in Xiangling and Xilin No.2.(3) With the temperature decreased, MDA content of all cultivars had different change while increased after-3℃; SOD activity increased at first, then decreased and then increased and decreased again; POD activity showed a trend of decreasing at first and increasing later and decreasing at last; the trend of CAT activity was same with that of POD activity; the content of soluble protein, soluble sugar and praline increased at first and then decreased.(4) The cold-resistance of test walnuts were synthetically evaluated as Liaohe No.3> Xilin No.3> Wen185> Chandler> Zhonglin No.5> Liaohe No.4> Luguang> Zha343> Xifu No.2> Xiangling> Xilin No.2. The eleven walnut cultivars could be divided into four groups by cluster analysis. Liaohe No.3and Wen185had strongest cold resistance;Xilin No.3, Chandler and Zhonglin No.5had stronger one;Liaohe No.4and Luguang had moderate one and Zha343, Xifu No.2, Xiangling and Xilin No.2were the poorest.The one year old precocity walnut seedlings of twelve cultivars were investigated with drought stress. Managed the seedlings in pot and started to stop watering and then let soil naturally drought. Sampled wanut leaves respectively in Od,11d,22d,33d,44d,55d and after rewatering with representing stress days as the degree of stress. Then physiological and biochemical indicators, photosynthetic rate, chlorophyll fluorescence and growth targets were determined. The relative values of different index characters were analysed by fuzzy mathematics method and cluster analysis. Main conclusions were as follows:(1) In the initial stress, every precocity walnut cultivar branch length and rugosity increased considerably during the process of drought stress and rewatering. With the intensification of stress, branch length and rugosity increased non-significantly, while the plants grew significantly again after rewatering and getting normal water supply.(2) With the drought stress increased, the leaf relative water content of every cultivivar kept reducing during the process of drought stress and rewatering and reached normal level after rewatering. The SOD activity of the cultivars increased and decreased in different degrees during drought stress and increased after rewatering. The MDA content, soluble protein content and soluble sugar content decreased or increased during the stress and decreased after rewatering.(3) The photosynthetic rate, chlorophyll fluorescence parameters Fv/Fm and Fv/Fo decreased during drought sress and increased after rewatering, while did not return to normal levels.(4) The drought-resistance of test walnuts were synthetically evaluated as Xinzaofeng> Liaohe No.1>Zhonglin No.5>Wen185>Luguang>Liaohe No.4>Zhonglin No.1> Chandler>Xiangling>Zha343>Xilin No.2>Xifu No.1.The twelve walnut cultivars could be divided into four groups by cluster analysis. Xinzaofeng, Liaohe No.1, Zhonglin No.5had strongest drought resistance.Wen185and Luguang had stronger one. Liaohe no.4, Zhonglin No.1, Chandler, Zha343and Xifu No.1had poorer drought resistance and Xiangling and Xilin No.2were the poorest. |
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