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A Peach Isolate of Prunus Necrotic Ringspot Virus. E. L. Civerolo, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; S. M. Mircetich, Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 62:529-532. Accepted for publication 9 December 1971. DOI: 10.1094/Phyto-62-529.

A multicomponent isolate of Prunus necrotic ringspot virus (NRSV-P) was mechanically transmitted from graft-inoculated peach seedlings to cucumber. For purification, NRSV-P was stabilized by the extraction of cucumber tissue in 0.02 M NaDIECA-0.01M Na₂EDTA₂ and the acidification of the extract to pH 5 with 10% HCl. Virus was concentrated by two cycles of differential centrifugation. Rate zonal sedimentation of partially purified NRSV-P preparations in sucrose density gradients resolved three or four components. Infectivity was associated with the most rapidly sedimenting portion of a major 70-80 S component. This component consists of at least two sedimenting species. The faster-sedimenting species was predominant in NRSV-P preparations 5 days after infection, whereas the slower sedimenting species was predominant 7 days after infection. The average ribonucleic acid (RNA) content of this centrifugally heterogenous component is ca. 18-19% RNA as determined spectrophotometrically. Electron microscopic examination of NRSV-P negatively stained with potassium phosphotungstate, uranyl acetate, and uranyl oxalate, or fixed with 2% glutaraldehyde, mainly revealed irregularly shaped particles and only a few particles resembling virus particles with well-defined structure.