Survival of Colletotrichum dematium in soil and infected mulberry leaves

Overwinter survival of Colletotrichum dematium, the causal agent of mulberr y anthracnose, was examined in Japan. Conidia and infected mulberry leaves were mixed with soil and placed on the ground in early December. Viability of conidia declined rapidly under field conditions-they could not be recove red within 30 days-whereas conidia placed indoors or outdoors under a roof protected from rain and snow survived longer. When a suspension of soil inf ested with conidia was used to inoculate detached healthy leaves, no infect ion was detected after 65 days of incubation, suggesting that conidia in so il are not a significant form of overwintering inoculum. When infected or l atently infected leaves incubated in soil under field conditions were used as inoculum on leaves, it was shown that the fungus remained viable for at least 150 days. The fungus in infected leaves maintained under laboratory c onditions at different temperatures survived for at least 90 days at 25 and 35 degrees C and for 600 days at 0 degrees C. These results suggest that C . dematium can overwinter in infected or latently infected leaves, and that these leaves can be a source of primary inoculum the following year. Hence , the elimination of fallen leaves in the field in autumn may be an effecti ve way to prevent occurrence of the disease the following year.