Alternaria alternata strawberry pathotype cause Alternaria black spot desease of strawberry (Morioka-16). This pathogen produces three host-specific toxins, AF-toxin I, II, and III (1, 2, and 3). These toxins expressed different biological activities as shown in Table 1. These chemical structures were determined by chemical derivation and spectroscopic analyses. Each toxin were a mixture of three stereoisomers. Major component was (2E,4E,6Z)-stereochemistry (1a, 2a, and 3a) in each case. The structure of 2b was very similar to those of AK-toxin I and II (6 and 7). (2E,4Z,6E)-stereoisomers (1b, 2b, and 3b) were minor component in our AF-toxin series. The presence of secondary hydroxy group (OH) seems to be very impotant for the toxicity to japanese pear (Nijisseiki).
