ABSTRACT
Some fungi of Alternaria spp. are known as foliar pathogens. Essential for this host range is the production of host-specific toxins, which are involved in the development in a few destructive diseases. A. alternata tobacco pathotype also produces host-specific and nonhost specific toxins. Toxic substances with host specific toxicity were released from germinating spores of this pathogen in 24 hr after germination. AT-toxin was partially purified from culture filtrate the fungus. It was shown to have host specific toxicity at cultivar level in leaf bioassay with tobacco cultivars Beinhart 1000.1, Shiroenshu 601 and Shiroenshu 1.