Characteristics of salicylic acid-induced delay in disease caused by a necrotrophic fungal pathogen in tobacco

Treatment of tobacco with salicylic acid delayed the onset of disease caused by the necrotrophic fungal pathogen, Botrytis cinerea. Inoculation of salicylic acid-treated tobacco with B. cinerea spores resulted in the development of limited necrotic lesions; similar to the hypersensitive response lesions that are normally associated with resistance to avirulent pathogens. In contrast, untreated plants showed watery spreading necrosis that is typical of infection with B. cinerea. Light and scanning electron microscopic examination revealed that B. cinerea hyphae were contained within the hypersensitive-like lesions in the salicylic acid-treated plants during the time-course of the experiment. Intercellular fluid From salicylic acid-treated tobacco was effective at inhibiting the hyphal growth of B. cinerea in vitro. When components of the intercellular fluid with a molecular weight greater than 3000 Da were removed, the intercellular fluid no longer inhibited mycelial growth suggesting that the inhibitory factor is one or more of the extracellular pathogenesis-related proteins. (C) 2000 Academic Press.