First and fourth authors: National Institute of Sericultural and Entomological Science, 1-2 Owashi, Tsukuba, Ibaraki 305-8634, Japan; and second and third authors: National Institute of Agro-Environmental Sciences, 3-1-1 Kan-nondai, Tsukuba, Ibaraki 305-8604, Japan
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Accepted for publication 30 November 1999.
Colletotrichum dematium, the causal agent of mulberry anthracnose, was examined to produce phytotoxins in vitro and in planta. Raw and autoclaved mulberry leaves infected with the fungus, as well as the fungus incubated with several solid or liquid media, were extracted with acetone. Extracts obtained from the fungus grown on raw and autoclaved mulberry leaves caused brown necrotic lesions on susceptible mulberry leaves when they were placed (10 μl) on the wounded adaxial surface. Whereas, no extracts obtained from media, except inoculated medium containing homogenized mulberry leaves, induced the necrosis, suggesting that the fungus produced phytotoxins in planta and that some components in mulberry leaves may be indispensable substrates for producing the toxins. The phytotoxins obtained from the diseased leaves induced necrosis on nonhost plants leaves as well as on mulberry leaves. The toxins were present in the border of anthracnose lesions on the leaves, and the sensitivity to the toxin correlated with that to the fungus infection in each susceptible or resistant mulberry cultivar. These results suggest that the phytotoxins are host nonspecific and play a role in fungal pathogenesis in the development of the lesions. Four toxic compounds were isolated and purified from anthracnose lesions. However, due to the low yield, the chemical structure of the compounds could not be identified.
© 2000 The American Phytopathological Society