Analysis On The Correlation Of Disease Index Of Seedling With Adult And Study On The Resistance Mechanism To Cucumber Downy Mildew

This paper studied the correlationship of disease index between seedling which was inoculated with Pseudoperomspora cubensis 4×10 sporangium per milliliter and adult plant which was performed in nature,28 cucumber cultivars were already on trail.Depending on the correlationship, 'Yu cucumber NO.2',resistant to cucumber downy mildew and 'Jinlv NO.3',susceptive,were singled out as representatives.'Yu cucumber NO.2'was inoculated with P.cubensis 4×10^-4 sporangium per milliliter at seedling as well as 'Jinlv NO.3' in further study,physiological index and were measured at preceding and sequential inoculation, in parallel with biochemistrical index.The result shows that:1. The disease index of seedling inoculated with P.cubensis 4×10^-4 sporangium per milliliter(at the condition of 20℃, shading and keep humidity within 24 h) together with adult plant in the field was positive correlation. That was the resistance to cucumber downy mildew between seedling and adult plant had a inherent relation. Consequently the resistant materials could be soon identified and screened by inoculating at seedling stage as a assistant measure.Distinguish 'IL 54','Jinlv No.2' into the susceptive materials, and 'Jinyou 40', 'Zhongnong 12', 'Yuanfeng No.6', 'Yuyi Chunzao cucumber','Jinlv No.6', 'Yu cucumber No.2'et al,were selected as the resistant ones.2. Regress the disease index of seedling and adult and set up regression equation, Y=2.4183X+2.7651,the correlation coefficient is 0.8772,greatly over the r_27(0.01),which is 0.471. When inoculating with P.cubensis at seedling stage, The fading spots come into being at the surface of leaves of 'Jinlv No.3',the susceptive one is earlier than that of 'Yu cucumber No.2',the resistant.The disease index of 'Yu cucumber No.2' and 'Jinlv No.3' accords with the regression equation,and the cultivars were separately representative of the resistant and the susceptive.3. At seedling stage,the content of chlorophyll and soluble sugar were close to the resistance to cucumber downy mildew,and in the light of physiological index which was the measure of resistance.Before inoculating, the content of chlorophyll and soluble sugar of the resistant and the susceptive has a great differece.After inoculating, the maximal content of the resistant and the susceptive still has a great difference.4.At seedling stage,the activities of polyphenol oxidase(PPO) and phenylalanine ammonia lyase(PAL) related to the resistance to cucumber downy mildew,and could be regarded as biochemistrical index which was the measure of resistance.Before inoculating, the activities of PPO and PAL of 'Yu cucumber No.2' and 'Jinlv No.3' had a great difference. After inoculating, the maximal activities of PPO and PAL still had a great difference.