Genomic heterogeneity and host recovery of isolates of Malva vein clearing virus.

Malva vein clearing virus (MVCV), a tentative species of the genus Potyvirus, was identified as the causal agent of viral symptoms in Malva sp. weed plants. Amplified viral genomic fragments corresponding to approximately 20% of the 3' terminal region of its genome were obtained using non-species specific, genus-specific reagents. The sequences of the PCR fragments were determined. BLAST and phylogenetic analyses of the deduced amino acid sequence indicated that MVCV is a distinct species of the genus Potyvirus and close to Pea seed-borne mosaic virus (PSbMV) with which it forms a new phylogenetic cluster within the genus. The results show that MVCV is a definitive member of the Potyvirus genus. Specific MVCV PCR primers were designed and validated as diagnostic tools, and used to assess the variability of the species. Much variation was found and this was not correlated with either the geographical origin of the isolates, or the severity of the symptoms. Recovery from viral symptoms was observed in natural and experimental hosts. Tests in experimental hosts showed that it was a true viral recovery, in that the virus was absent and the recovered tissues could not be infected. This is the first reported example of true viral recovery of a potyvirus in a natural system.