UNENCAPSIDATEDD DOUBLE-STRANDED-RNA ASSOCIATED WITH MEMBRANE-VESICLESIN ISOLATES OF ALTERNARIA-SOLANI

Double-stranded RNA (dsRNA) elements of 8.3 and 5.5 kbp were detected in three of Eve geographically distinct isolates of Alternaria solani. Variation with respect to the number of dsRNA segments was detected a mong isolates of the fungus. No virus-like particles were purified fro m the mycelium, or observed in ultra-thin sections of hyphae. Utilizin g differential centrifugation or density gradient centrifugation for s ubcellular fractionation, dsRNA was found associated specifically with fractions containing 80-100 nm spherical membrane vesicles. Similar v esicles were observed in cytoplasm of hyphae by electron microscopy. T reatment of dsRNA-containing fractions with ribonuclease A did not deg rade the dsRNA, suggesting that it is located inside the vesicles. The re was no correlation between the radial growth of the isolates in lab oratory media and the presence or absence or dsRNA.