Suppression of the defence-related oxidative burst in bean leaf tissue and bean suspension cells by the necrotrophic pathogen Botrytis cinerea

The interaction of two selected isolates of Botrytis cinerea with bean suspension cells and bean leaf discs was compared in relation to levels of reactive oxygen intermediates (ROI). Isolate B 1.7 was arrested by a hypersensitive-like necrosis of bean leaf tissue. According to its inability to spread and produce conidia on the bean leaf tissue it was classified as non-aggressive. The second isolate induced a fast expanding light brownish necrosis of the leaf tissue. It was able to produce conidia on bean leaf discs and was classified as aggressive. The generation of superoxide was followed biochemically in inoculated bean cell suspensions. Both isolates induced a similar early superoxide peak approximately 18-h post inoculation (hpi). While the non-aggressive isolate induced a much stronger secondary superoxide burst at 33 hpi, the level of superoxide of suspension cells inoculated with the aggressive isolate was below the control level. This is the first report on the occurrence of a biphasic oxidative burst in plant cells induced by a fungal pathogen. Such a suppression of superoxide generation was also observed in bean leaf discs inoculated with the aggressive isolate. An oxidative burst-suppressing agent was extracted from inoculated cell culture medium and determined as 2-methyl-succinate (2-MS) by GC/MS analysis. The compound was detected approximately 20 hpi in the aggressive fungus-plant interaction. 2-MS was able to suppress the hypersensitive response-like necrosis on leaf discs as well as the second superoxide burst in suspension cells when inoculated with the non-aggressive isolate. The early superoxide burst at 18 hpi was not affected. The results confirm the important role of enhanced production of ROI in plant resistance reactions, also for a necrotrophlike B. cinerea.