A Phytotoxic Activity in Extracts of Broth Cultures of Mycosphaerella fijiensis var. difformis and Its Use to Evaluate Host Resistance to Black Sigatoka. Gloria C. Molina, Associate Research Scientist, Department of Plant Pathology, Honduran Foundation for Agricultural Research (FHIA), Apartado Postal 2067, San Pedro Sula, Honduras. J. P. Krausz, Head, Department of Plant Pathology, Honduran Foundation for Agricultural Research (FHIA), Apartado Postal 2067, San Pedro Sula, Honduras. Plant Dis. 73:142-144. Accepted for publication 8 August 1988. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/PD-73-0142.

Crude extracts from 28-day-old coconut (Cocos nucifera) and soybean (Glycine max) broth cultures of Mycosphaerella fijiensis var. difformis caused tissue necrosis on treated banana (Musa acuminata) and plantain (Musa acuminata × M. balbisiana) plants. The phytotoxic activity could be extracted by either chloroform or ethyl acetate. Phytotoxic activity was evaluated by either dipping cut leaf tips of banana and plantain plants developed from meristem cultures into a 1:10 aqueous dilution of the extract or by puncturing the leaf with a sharp needle through a 20-?l droplet of the diluted extract placed on the leaf surface. Extract from uninoculated broth cultures showed no phytotoxic activity. Relative levels of field resistance to M. fijiensis var. difformis in seven banana and plantain differential cultivars were strongly inversely correlated with the area of necrotic tissue in extract-treated plants. The diluted extract failed to cause a phytotoxic reaction on eight treated plant species that were not of the genus Musa.