The Preliminary Physiological And Biochemical Studies Of Disease Resistance To Sclerotinia Sclerotiorum In Brassica Napus

Sclerotinia disease affects the production of rapeseed seriously. As a result, the breeding and application of varieties resistant to S.Sclerotiorum has attracted increasing attention of the researchers. Some primary studies were made about physiological and biochemical change at seedling and adult plant stage with 5 resistant and susceptible varieties, hoping to supply some proof for resistant disease breeding to rape seed. The results were described as follows:1 After infection by S. Sclerotiorum, the rapeseed cultivars enhanced the uptake of ³²P-labelled phosphate in leaves. Furthermore, the uptake in resistant cultivars was higher than in susceptible ones before inoculation. The absorbed ³²P-labelled phosphate was transported and accumulated to the leaves inoculated with S.sclerotiorum.2 Sugars contents and invertase activity in resistant rapeseed cultivars were increased faster and higher than susceptible ones after oxalic acid treatment. At adult plant stage, contents of soluble sugar and activity of invertase in resistant cultivar were lower than in susceptible ones.3 Abscisic acid and salicylic acid are important signaling molecules in the induction of disease resistance and the establishment of systemic acquired resistance (SAR) in plant. Before inoculation with S.sclerotiorum, the contents of ABA and SA in leaves of rapeseed cultivars with different resistance to S.sclerotiorum had no significantly difference. The contents of ABA or SA in For-infected seedlings of resistant cultivars were higher, but never both higher in these materials.4 Under oxalic acid treatment, the products of lipid peroxidation monodialdyhyda (MDA) in cotyledons of resistant cultivar was significantly lower than that of susceptible one. And the defense enzymes activities rose under mild stress of oxalic acid treatment, but declined under serious stress. What's more, the activity of defense enzymes in cotyledons of resistant cultivar rose higher and faster than that of susceptible one. At maturing stage, the defense enzymes activities were increased and the MDA content was also increased after inoculation with S.sclerotiorum. The change of SOD, PPO and PAL activities was significant in susceptible cultivars while the change of POD activity was significant in resistant cultivars. The POD isozyme-zymogram was simple and significant. After inoculation with S.sclerotiorum the isoenzyme bands intensified and new isoenzyme bands added. The number of isoenzyme bands was involved in resistance mechanism.5 The contents of soluble proteins and total free amino acids in cotyledons of rapeseed cultivars were increased under oxalic acid treatment. At first time, the change of soluble proteins content was more susceptive in resistant cultivar than in susceptible one. Later, it increased slowly. The change of free amino acids was not susceptible between resistant and susceptible cultivars. At adult plant stage, soluble proteins contents were decreased while total free amino acids contents were increased. However, the changes of soluble proteins and total free amino acids contents were more susceptible insusceptible cultivar than in resistant one.