Final report : production, extraction and purification of mycotoxin produced by Mycosphaerella fijiensis var. difformis and evaluation of its use for screening for resistance to Black Sigatoka

Different culture media and solvents for extraction of the phytotoxic component were evaluated. Coconut and soybean broths proved to be the best media among those evaluated. The phytotoxic component was best extracted by either chloroform or ethyl acetate. The biological activity of the toxin was observed on meristem cultured plantlets, inoculated with M. fijiensis culture extracts. Phytotoxic activity was expressed by necrosis from the point of inoculation. Necrosis was evident 24 hours after introduction of the extracts from M. fijiensis inoculated broths. No necrosis was observed on plants treated with extracts from uninoculated broths. Banana and plantain varieties with known levels of susceptibility and resistance in the field to M. fijiensis were subsequently treated with the phytotoxic extracts. Results showed that resistant varieties developed smaller necrotic areas compared to susceptible ones. This indicates the potential use of the phytotoxic extract as a tool for early screening of bananas and plantains against Black Sigatoka. Purification has been done and led to identification of the specific fraction causing necrosis on infected leaves. (Author abstract)