Since 1994, tomato (Lycopersicon esculentum Mill.) grown in Mérida State, located in the Venezuelan Andes, have been consistently affected by a gray leaf spot disease with symptoms on leaves, petioles, and stems. Yield is reduced, and in some cases entire crops have been destroyed over short time. Because of its prevalence, distribution, and severity, the disease has become the major factor limiting tomato production in this region. Disease symptoms were commonly observed on seedlings and plants. On leaves the disease first appeared as circular to elongated dark specks. As the spots enlarged, they became gray and bright. Old lesions dried and usually cracked. Severely infected leaves turned yellow and then died and dropped. Lesions on petioles and stems were elongate. Disease severity was generally higher following the beginning of fruiting. The fungus was isolated from leaves, petioles, and stems of tomato cv. Rio Grande on 2% water agar acidified with lactic acid. On potato-carrot agar, conidiophores and conidia were produced with the characteristics of Stemphylium. Two species of Stemphylium, S. solani G. F. Weber and S. lycopersici (Enjoji) W. Yamamoto, cause gray leaf spot symptoms on tomato. Based on morphology, size, and the length/width ratio of the conidia, the fungus was identified as S. solani (1). Inoculations done by spraying a conidial suspension on plants of tomato cv. Rio Grande produced symptoms similar to those observed in the field. S. solani was consistently isolated from experimentally infected tissues, thus confirming Koch's postulates. This is the first report of S. solani causing gray leaf spot on tomato grown in the Andes of Venezuela.
Reference: (1) G. F. Weber. Phytopathology 20:513, 1930.
