Evaluation of the potential biocontrol activity of Dicyma pulvinata against Cladosporium fulvum, the causal agent of tomato leaf mould

Cladosporium fulvum, the causal fungus of leaf mould of tomato, is present in most countries that grow tomatoes, and is an economic problem, particularly in Japan. The diverse, complex race structure of C. fulvum in Japan enables the fungus to overcome all resistant commercial cultivars. It was noted that C. fulvum lesions on tomato leaves in the greenhouse were overgrown with white mycelia and that leaf mould did not spread further. Two isolates from the white mycelia, designated 414-2 and 414-3, were identified from morphological and phylogenetic analyses as the mycoparasite Dicyma pulvinata. Scanning electron microscopy of inoculated leaves showed the mycoparasite had coiled around C. fulvum hyphae around stomata. Microscopic analysis revealed that C. fulvum, engineered to express green fluorescent protein, died when entwined by the isolates only when cocultured in the absence of a carbon source. These results indicate that these isolates are mycoparasitic fungi that absorbed nutrients from C. fulvum. Two isolates and four strains were evaluated according to their abilities to control disease caused by C. fulvum, form conidia and produce an antifungal agent. Isolate 414-3 parasitized hyphae of C. fulvum on plants in the greenhouse and inhibited leaf mould caused by all physiological races that cause problems for tomato production in Japan. This indigenous isolate of D. pulvinata may thus serve to control the foliar pathogen C. fulvum.