- Volume 66, Issue 2, 1985

Viroid-like RNA was isolated from some samples of grapevine leaves (Vitis vinifera L.). When inoculated to cucumber, this RNA induced symptoms that were identical to those induced by hop stunt viroid (HSV). It had a molecular size similar to that of HSV, and hybridized with a 32P-labelled DNA probe for the cucumber isolate of HSV (HSV-c, pCP-55). This hybridization suggests high (> 55%) sequence homology with HSV. The HSV-related sequence was detected not only in the infected cucumber plants but also directly in RNA extracted from grapevine plants. The result indicates that viroid-like RNA, closely related to HSV, is present in grapevines in Japan.

Following nitrous acid mutagenesis of cowpea mosaic virus (CPMV) virion RNA, a mutant has been isolated which is able to grow in Phaseolus vulgaris but is unable to grow in the ‘Early Red’ or ‘Blackeye Early Ramshorn’ varieties of cowpea (Vigna unguiculata). Dot blot analysis failed to detect virus-specific RNA in ‘Blackeye Early Ramshorn’ plants which had been inoculated with mutant 7A-4, indicating that no CPMV RNA synthesis had occurred. Supplementation experiments showed that the mutation was located in B RNA.

The four RNA species of a French strain of beet necrotic yellow vein virus (BNYVV) have lengths of 7100, 4800, 1800 and 1500 nucleotides, as measured by agarose gel electrophoresis in denaturing conditions. Translation of purified RNA in a reticulocyte cell-free system revealed that RNA-2 encodes the 22000 mol. wt. coat protein. Cloned cDNA copies of each of the four viral RNA species have been used to show that BNYVV RNA-3 and RNA-4 share no sequence homology with RNA-1 and RNA-2. Thus, RNA-3 and RNA-4 cannot be subgenomic messengers derived from the larger RNA species.

Dot blots of dsRNA from European and American hypovirulent (H) strains of the chestnut blight fungus, Endothia parasitica, were hybridized with 32P-5′-end-labelled fragments of denatured dsRNA of French, Italian and American origins. Although dsRNA from European or American strains reacted well with labelled RNA probes from strains from the same continent there was little or no cross-hybridization between RNA from strains from different continents.