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 cause d by the necrotrophic fungal pathogen, Botrytis cinerea. Inoculation of sal icylic acid-treated tobacco with B. cinerea spores resulted in the developm ent of limited necrotic lesions; similar to the hypersensitive response les ions that are normally associated with resistance to avirulent pathogens. I n contrast, untreated plants showed watery spreading necrosis that is typic al of infection with B. cinerea. Light and scanning electron microscopic ex amination revealed that B. cinerea hyphae were contained within the hyperse nsitive-like lesions in the salicylic acid-treated plants during the time-c ourse of the experiment. Intercellular fluid From salicylic acid-treated to bacco 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 myc elial growth suggesting that the inhibitory factor is one or more of the ex tracellular pathogenesis-related proteins. (C) 2000 Academic Press.