Double-stranded Ribonucleic Acid from Plants Infected with Viruses Having Elongated Particles and Undivided Genomes

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Abstract
Double-stranded RNA (dsRNA) of several members of the poty-, carla-, potex-, and tobamoviruses was purified from 7-30 g of infected tissue by chromatography on CF-11 cellulose. Gel electrophoresis of dsRNA aliquots equivalent to one-tenth of the extracted dsRNA (approximately 0.5 .mu.g) normally resulted in detectable dsRNA bands. Lowest yield of dsRNA was from plants infected with some potyviruses. The size and number of the expected dsRNAs corresponding to the encapsidated single-stranded RNA genomes (the replicative forms) were diagnostic for each virus group analyzed. Other dsRNAs of smaller size (greater mobility) than the replicative form were consistently obtained with most viruses, and were well resolved by electrophoresis on 6% polyacrylamide gels. The presence or absence of additional dsRNAs, together with their size, were useful characteristics for differentiating particular viruss, including strains. Use of appropriate marker dsRNAs is important if results are to be compared and interpreted. Infected plants incubated at 27.degree. C and harvested 10 days postinoculation gave the highest dsRNA yields. Regardless of the host used for virus propagation, dsRNAs were obtained, and no effect of host was observed on dsRNA patterns for each virus tested. Unexpected dsRNAs were found in 6 of 24 uninoculated and apaprently healthy plant species and cultivars. These dsRNAs had molecular weights similar to dsRNAs of plant viruses with single-stranded RNA genomes, and indicate infection by cryptic or latent viruslike agents. Their erratic distribution indicates the need for a careful choice of plant species to be used as disease-free controls.