Fungal sensitivity to and enzymatic degradation of the phytoanticipin α-tomatine

alpha-Tomatine, synthesized by Lycopersicon and some Solanum species, is toxic to a broad range of fungi, presumably because it binds to 3 beta-hydroxy sterols in fungal membranes. Several fungal pathogens of tomato have previously been shown to be tolerant of this glycoalkaloid and to possess enzymes thought to be involved in its detoxification. In the current study, 23 fungal strains were examined for their ability to degrade cc-tomatine and for their sensitivity to this compound and two breakdown products, beta(2)-tomatine and tomatidine. Both saprophytes and all five nonpathogens of tomato tested were sensitive, while all but two tomato pathogens (Stemphylium solani and Verticillium dahliae) were tolerant of alpha-tomatine (50% effective dose > 300 mu M). Except for an isolate of Botrytis cinerea isolated from grape, no degradation products were detected when saprophytes and nonpathogens were grown in the presence of alpha-tomatine. All tomato pathogens except Phytophthora infestans and Pythinm aphani-dermatum degraded alpha-tomatine. There was a strong correlation between tolerance to a-tomatine, the ability to degrade this compound, and pathogenicity on tomato. However, while beta(2)-tomatine and tomatidine were less toxic to most tomato pathogens, these breakdown products were inhibitory to some of the saprophytes and nonpathogens of tomato, suggesting that tomato pathogens may have multiple tolerance mechanisms to alpha-tomatine.