First Report of Angular Leaf Spot Caused by Phaeoisariopsis griseola on Phaseolus coccineus in Argentina

Plant Disease
Sebastian StengleinL D Ploper

Abstract

Angular leaf spot (ALS), caused by Phaeoisariopsis griseola (Sacc.) Ferraris, is one of the most destructive and widespread problems of common bean (Phaseolus vulgaris L.) in Tucumán and other northwestern provinces of Argentina (4). Symptoms similar to those of ALS were observed during April 2005 on most plants of runner bean (P. coccineus L.) in an 80-ha field in Tafí del Valle, Tucumán (2,000 m above sea level). Leaf lesions were brown to gray, irregular to angular to circular, and 0.5 to 1 cm in diameter. Lesions on pods were oval to circular with reddish brown centers surrounded by darker brown borders. Conidia in vivo were curved cylindrical to obclavate with one to five septa and measured 25 to 60 × 3.5 to 7 μm. The conidiophores were 100 to 250 μm high and clustered together to form synnemata measuring 20 to 50 μm in diameter. The pathogen was isolated by placing conidia from diseased leaves onto potato dextrose agar (PDA) at pH 6. Colonies measuring 2 to 3 mm in diameter composed of dense, dark olive mycelium developed after incubation in the dark at 24 ± 2°C for 3 to 4 days. Pathogenicity of the isolate was tested with conidia obtained from the second subculture of 14-day-old colonies on PDA. Conidial suspensions of 2...Continue Reading

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