Effect Of Three Exogenous Materials On Cold-resistance Capability Of Watermelon (Citrullus Lanatus Mansf.)

Low temperature stress caused watermelon membrane-lipid peroxidation. In order to study the effects of exogenous substance on chilling-resistance of watermelon (Citrullus Lanatus Mansf.)seedlings and germination seeds, to research its physiological mechanism and variation rule of protection enzymes activity and chlorophyll fluorescence characteristic , cv. Jinxin 1 and Xinong 8 et al as basic testing material were treated by H2O2 , SA(salicylic acid ) and oxalic acid at seed stage and 3-true leaf stage. In addition, the application of several chilling appraisal ways was discussed. The main result showed as follows.1. H2O2 , SA and oxalic acid can reduce damage by chilling stress in watermelon germination and seedling stage.2. H2O2 , SA and oxalic acid can improve capability of chilling-resistance. Activities of peroxidase (POD) and catalase (CAT) and superoxide dismutase (SOD) increased, malondialdehyde(MDA) contents decreased and high resistance to chilling were acquired after three exogenous substance treatment. But suitable treated stage is seed germination stage, because of economy and convenience.3.Photoinhibition of the photosystemⅡoccur at low temperature and poor light, and chlorophyll fluorescence characteristic show some significant changes. The photosystemⅡwere damaged severely by 5℃ low temperature, it contained three stage of activation of protection mechanism, lost activities of PSⅠand that of PSⅡ. In addition, the content of chlorophyll decreased with long time chilling stress. The results showed that the decrease of capability of photosynthesis result from long time chilling stress.4.The extent of electrolyte leakage of cells membrane was affected by low temperature tolerance. The increment of cells membrane leakage was significant by 5℃ low temperature, and 15℃ is very sensitive to low temperature for watermelon. 5.The capability of chilling-resistance treated by oxalic acid under 5℃ low temperature is better than those of treated by SA, because of high activities of protection enzyme and low leakage of cells membrane.6. The capability of chilling-resistance of ten watermelon varieties were comprehensive evaluated by analysis of comprehensive value, and Gankang, Xinda and Jinxin show better effects of chilling-resistance among ten varieties.7. It is impersonal and reliable to appraise watermelon chilling-resistance for analysis of function index to chilling-resistance, analysis of comprehensive value and analysis of grey related degree. The index of chilling injure is not effective for indistinctive difference of varieties.