Studies On The Mechanism Of Interaction Between Rapeseed(Brassica Napus)Varieties And Sclerotinia Sclerotiorum

Studies on the mechanism of interaction between rapesced(Brassica nap us) varieties and Sclerotinia sclerotiorum Abstract White rot of rapeseed is world-wide disease caused by S.sclerotiorum, which affects the production of rapeseed seriously all around the world. As a result, the breeding and application of varieties resistant to S.sclerotiorum has attracted increasing attention of the scientists and researchers in the world. The author has made some tentative studies ranging from isolation of S. sclerotiorum strains, the screening of resistant resources of rapeseed to S.sclerotiorum, the mechanism of resistance of rapeseed to S.sclerotiorum to the mechanism of pathogenesis of S.sclerotiorum with the expectation of providing foundation for resistance-oriented breeding. The results were described as following: The determination of 600 rapeseed resources?resistance to S.sclerotiorum was made by use of mycelia inoculation. The results showed that there were 3 high-resistant varieties(resources), 50 middle-resistant varieties, 246 low-resistant varieties, 240 low-susceptible varieties, 42 middle-susceptible varieties, 19 high-susceptible varieties. The assay of the ability for producing oxalic acid and pathogenicity of 17 S.sclerotiorum isolates indicated that the ability for producing oxalic acid of each S.sclerotiorum isolates was correlated positively with it抯 pathogenicity with the correlated 2 coefficient being 0.9872; as for the ability for producing oxalic acid and pathogenieity, SS5, SS18 are the two strongest isolates, while SS4, SS15, SS19 are the three weakest isolates; there is a significant interaction between rapeseed and the isolates of S. sclerotiorum. The role of cell wall-degrading enzymes and toxin produced by S.sclerotiorum in pathogenicity to rapeseed was studied respectively after seperating them. The enzyme liquid failed to cause the disease symptom while the toxin could lead to the obvious disease lesion, so toxin (oxalic acid) is a pathogenicity determinant. It was observed by means of electronic microscope that toxin resulted in the apparent change in ultrastructure of rapeseed leaf including the damage of chloroplast membrane, dilated, disordered grana lamellae; the damage of mitochondria membrance and eventually vacuolated mitochondria; the contract of cell nuclein. The effect of toxin on ultrastructure is heavier and faster on susceptible varity than resistant one. Tow resistant varieties including M004, Xiang You 15 and three susceptible varieties including 98C40, 84039, SW038 were chosen for biochemical measuring in different time after inoculation with S. sclerotiorum. Before inoculation with S.sclerotiorum, there is no difference of soluble sugar content in leaves between resistant varieties and susceptible ones, while the content of soluble protein and phenolices in leaves of resistant varieties is higher than that of susceptible ones, After inoculation with S.sclerotiorum, the soluble sugar content in both resistant varieties and susceptible varieties decreased, but the 3...