That AF - toxin produced by Alternaria fragriae causes the black spot ofstrawberry is a bost -selective toxin which is only pathogenic to strawberry cv. Morioka-16 and Japanese pear cv- Nijisseiki. The toxin comprises parts Ⅰ, Ⅱ andⅢ,with partiallydifferent chemical structures and pathogenicity. AF-toxin Ⅰis under protection of the AF-toxin Ⅱ. AF-toxin induces susceptibility of the host and destroys host cell,resulting inplasma membrane invagination and damage, electrolyte leakage and electric potential ofm...