Abstract
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.
Highlights
Fungal plant pathogens are a group of microorganisms that show a very high versatility during their infection cycles [1]
Gherbawy [7] studied the pathogenicity of Alternaria species collected from several Egyptian crops on tomato fruits. 62% of isolates were pathogenic to wounded tomato fruit
The pathogenicity of selected species was assayed on 20 days broad bean plants by spraying of leaves, which were grown in a glasshouse for 15 days
Summary
Fungal plant pathogens are a group of microorganisms that show a very high versatility during their infection cycles [1] This versatility allows them to infect a wide variety of crops [2]. They employ diverse strategies to infect and colonize the plants, and they establish a complex interaction between fungus species and their hosts [35]. Gherbawy [7] studied the pathogenicity of Alternaria species collected from several Egyptian crops on tomato fruits. The spot form isolates were responsible for higher levels of disease than net form isolates. Kumar et al [9] studied the pathogenicity of eleven Alternaria solani isolates, the causal agent of early blight of tomato. Plant-fungi interaction (Pathogenicity) was carried out in many investigations in several parts of the world and several plants [12,13,14,15,16,17,18]
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