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Detection of dsRNA from Cleistothecia and Conidia of the Grape Powdery Mildew Pathogen, Uncinula necator. Ossmat I. Azzam, Graduate Research Assistant, and Dennis Gonsalves, Professor, Department of Plant Pathology, Cornell University, New York State Agricultural Experiment Station, Geneva 14456. Plant Dis. 75:964-967. Accepted for publication 11 February 1991. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0964.

Double-stranded RNA species ranging in molecular weight from 0.95 to 6.3 106 were detected in grapevines in New York. We recently showed that two of the species (Mr = 5.3 and 4.4 106) are associated with rupestris stem pitting disease. In this report, we show that the other eight detectable dsRNA species are associated with the powdery mildew fungus, Uncinula necator. These dsRNAs associated with the powdery mildew fungus were previously detected in leaves and epidermal stem tissue of grapevines infected with powdery mildew. The same dsRNA species were also detected from extracts of isolated cleistothecia and conidia of U. necator devoid of plant tissue. Isometric and rigid rodlike particles were observed in single cleistothecia preparations when examined under transmission electron microscopy.