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First Report of Powdery Mildew in Greenhouse-Grown Tomatoes in New Jersey

Powdery mildew of tomatoes caused by an Erysiphe sp. has been reported to occur in greenhouses in New York (2). In March and April of 1996, outbreaks of this disease were found in greenhouse-grown tomato plants of cv. PSR55809 at the Cook College campus in New Brunswick, NJ, and in cv. Match in commercial greenhouses in Burlington County, NJ. Identification of an Erysiphe sp. was made by comparative morphology of the conidial state since the perfect stage was not observed. Symptoms included development of patches of white mycelium predominantly on upper surfaces of older leaves followed by chlorosis of tissues colonized by the fungus. Microscopic examination of mycelium revealed the presence of typical Oidium conidiogenous cells and conidia. Conidiogenous cells were short and cylindrical and produce conidia in chains apically. Conidia were hyaline, cylindrical to ellipsoidal, and measured 36 + 4.9 × 16.7 + 2.2 μm (n = 20). Both conidia and symptoms of this powdery mildew are comparable to those previously given for the Erysiphe sp. described in New York (2). Another powdery mildew of tomato, caused by Oidiopsis sicula Scalia, occurs in the western U.S., Mediterranean Basin, Africa, and Asia. However, the conidia of O. sicula are of two types, pyriform and cylindrical, and they are larger than those of an Erysiphe sp. (1). To verify pathogenicity of this Erysiphe sp. to tomatoes, conidia washed from leaves were misted onto uninfected leaves of young tomato plants. After 1 week in a growth chamber (25°C; 80% relative humidity; 12 h of light), typical powdery mildew symptoms were evident on inoculated plants, while unmisted plants remained free of symptoms. Microscopic examination of the fungus on surfaces of leaves confirmed it to be an Erysiphe sp.

References: (1) R. N. Campbell and R. W. Scheuerman. Plant Dis. Rep. 63:1087, 1979. (2) D. M. Karasevicz and T. A. Zitter. Plant Dis. 80:709, 1996.