Differential interactions among isolates of peanut stunt cucumovirus and its satellite RNA

The interactions of seven isolates of peanut stunt cucumovirus (PSV) originating from North America, Europe and Africa, and two variants of PSV satellite RNA (sat RNA) were analysed. Electrophoretic and immunoblot analyses of the coat protein (CP) and Northern blot hybridization analyses of the viral RNAs showed that isolates PSV F352, 1339 and 1507 belonged to subgroup I, and isolates PSV W, Su and B to subgroup II. The seventh isolate, robinia mosaic virus (RoMV) clustered with subgroup I isolates by CP analysis, but was related to both subgroups by RNA hybridization analysis. The ability to support the accumulation of two newly described sat RNA variants, P4 and P6 sat RNAs, was not related to PSV isolate classification: neither PSV W nor RoMV were helper viruses for these PSV sat RNAs. Symptom modulation by both sat RNAs was the same: the presence of sat RNA did not modify the symptoms induced by subgroup I isolates but exacerbated the symptoms induced by subgroup II isolates in both tobacco and cowpea. Sat RNAs P4 and P6 contained 393 nucleotides, and differed only in three nucleotide substitutions. This resulted in marked differences in infectivity, level of accumulation and relative encapsidation between both the sat RNAs. Accumulation levels and relative encapsidation of sat RNAs was also affected by the isolate of helper virus.