The Study On Conditions Of Toxin Production And Its Pathogenesis Of Sclerotinia Sclerotiorum In Sunflower

Because S.sclerotiorum in sunflower shows a complicated pathogenesis, causes serious symptom and is difficult to control, hypha growth, toxin-generated conditions and pathogenic mechanism of S.sclerotiorum toxin were studied in sunflower. The results showed that there was a positive correlation between the hypha growth and the the amount of carbon source under a appropriate condition. The optimum temperature for hypha growth was 20℃ , the optimum pH value was pH 4.0~8.0.The best carbon source, nitrogen source were amylum and NH4Cl. The accumulation of oxalic acid toxin was related to carbon source and its precursor. The optimum temperature for the toxin production was 25℃ , the optimum pH value was pH6.0. The best carbon source was latose. The best nitrogen source was asparagin and glutamic acid. hypha growth and toxin accumulation were up to max value after cultured 10 days. The pathogenesis of S.sclerotiorum toxin were studied at plant, tissue, cell, physiological and biochemistry leval. The results showed that S.sclerotiorum toxin can damage and inhibit seed germination, plulmar axis growth and seedling growth and also induced lesions of sunflower leaves in vitro. After being treated with toxin in sunflower leaves, the damage of the cell membrane was examined by the electrical conductivity method. The results showed that the toxin could damage cell membrane of sunflower leaves, then made the function of cell membrane turbulent. The effects of S.sclerotiorum toxin on peroxidase (POD), polyphenoloxidase (PPO) and phenylalanine ammonialyase(PAL) activities of the leaves from different sunflower cultivars were detected. The results showed that the activity of POD was increased and the activity of PPO was decreased after being treated with toxin in sunflower leaves. The activity of PAL was increased under the low concentration of toxin. Howewer, when the anount of toxin was enough high, it inhibited the activity of PAL. The role of cell Wall-degrading enzymes and toxin produced by S.sclerotiorum in pathogenicity to sunflower was studied respectively after separating them. The virulence of S. of S.sclerotiorum was related to the cell Wall-degrading enzymes and toxin. Toxin could increase the activity of the cell Wall-degrading enzymes, which resulted in host cell disaggregated rapidly and degree of host disease aggravated.