1 College of Plant Protection，Shenyang Agricultural University，Shenyang 110866，Liaoning，China；2 Institute of
Plant Protection，Chinese Academy of Agricultural Sciences，Beijing 100193，China
Abstract：Toxin-producing condition optimization and determination of crude toxin biological activity
and its physical，chemical properties were carried out on Colletotrichum orbiculare. The results showed that
different culture conditions had different influences on pathogenic toxin activity. The Richard culture medium with
pH 6 ，culture temperature at 25℃，in dark，and shaking continuously for 20 d were the best toxin-producing
conditions. The watermelon stem inoculated by crude toxin could produce the same acute symptom as the bacteria
did，which had inhibitory effect on seed radicle growth and seed germination； and also a collapsing role on
seedling. That toxin is the main pathogenic factor in the process of watermelon anthrax bacteria infection. Among
the 10 kinds of selected plants inoculated by crude toxin，the symptoms of muskmelon，summer squash and
strawberry were significant，while no symptoms were seen on tomato，eggplant and pepper.
