Journal de pathologie végétale et de microbiologie

Abstrait

Pathogenicity and Pectinase Activity of Some Facultative Mycoparasites Isolated from Vicia faba Diseased Leaves in Relation to Photosynthetic Pigments of Plant

A Saleem, AHM El-Said, TA Maghraby and MA Hussein

Fourteen dematiaceous hyphomycetes fungi related to 9 genera isolated from diseased leaves of broad bean plant were investigated for their pathogenicity. Eight fungal species (represent 57.15% of total fungi tested) were positive and successfully able to infect broad bean leaves appearing leaf spot symptoms. Among these fungi Alternaria alternata was the most active virulent and produced leaf spots on more than 75% of infected leaves. Six fungal species (42.85%) had negative pathogenicity result and unable to infect the leaves of plant failing to produce any leaf spot symptoms. The photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids) were significantly decreased as a result of the infection of phytopathogenic fungi. The concentrations of photosynthetic pigments were adversely affected by the degree of pathogenicity. Eight phytopathogenic fungi were screened for their abilities to produce pectinase enzyme using cup-plate method. All isolates tested were pectinase producers, but with variable degrees. Three fungal isolates (37.5% of total isolates) exhibited high pectinase activity and these were: Alternaria citri, A. raphani and A. tenuissima. Three other isolates (37.5%) were found to be moderate pectinase activity and these were: Alternaria alternata, Curvularia lunata and Ulocladium botrytis. Cochliobolus spicifer and Stachybotrys atra var. microspora (25%) were low producers of the enzyme. Maximum production of pectinase produced by A. citri and A. raphani was recorded after 8 days at 30°C and pH 6 in the liquid medium supplemented with citrus pectin and ammonium sulphate as carbon and nitrogen sources respectively.