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Etiology

Strawberry Pallidosis Disease: Distinctive dsRNA Species Associated with Latent Infections in Indicators and in Diseased Strawberry Cultivars. N. Yoshikawa, Assistant professor, Faculty of Agriculture, Iwate University, Morioka 020, Japan; R. H. Converse, Research plant pathologist, United States Department of Agriculture, Agricultural Research Service, Horticultural Crops Research Unit, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331. Phytopathology 80:543-548. Accepted for publication 12 December 1989. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1990. DOI: 10.1094/Phyto-80-543.

Double-stranded RNA (dsRNA) was extracted from Fragaria plants and analyzed by electrophoresis on 5% polyacrylamide gel, followed by silver stain. The dsRNA band patterns were determined for a virus-tested clone of strawberry cultivar Northwest and for nongrafted plants of several common strawberry virus indicators, including seedling line Alpine of Fragaria vesca var. semperflorens and cultivars UC-10, UC-11, and UC-12 of F. virginiana. No dsRNA bands in the M_r range above 4 ? 10⁶ were found in these plants. On the other hand, plants of indicator cultivars UC-4, UC-5, and UC-6 of F. vesca, maintained in our greenhouse and thought to be virus free, contained two dsRNA bands of M_r 4.3 and 4.6 ? 10⁶ similar to those found in plants infected with known pallidosis isolate Rip 157. Some smaller dsRNAs also occurred in each case. DsRNA bands of M_r 4.3 and 4.6 ? 10⁶ were found in Alpine seedlings after leaf grafting with leaflets of our clones of UC-4, UC-5, and UC-6, UC-10 plants grafted with leaflets from these same clones of UC-4, UC-5, and UC-6 plants developed symptoms of leaf distortion and chlorosis that were very mild but typical of pallidosis disease, suggesting that these clones were contaminated with pallidosis agent. Eight additional pallidosis isolates induced leaf distortion, chlorosis, and dwarfing in UC-10 plants but no obvious symptoms in UC-4, UC-5, UC-6, or seedling Alpine plants. All eight pallidosis isolates examined had two to four dsRNAs in the M_r range of 4.3 to 5.2 ? 10⁶ and, depending on the isolate, one to 10 dsRNAs ranging from M_r 1.0 to 2.3 ? 10⁶. Until now, pallidosis agent has been detected in strawberry plants only by graft indexing in the absence of viruses that would confound or obscure the symptomatology associated with the pallidosis agent. The electrophoretic band patterns of dsRNA associated with pallidosis are sufficiently distinct to permit its tentative identification in strawberry plants with multiple virus infections.