Grapevine Fleck Virus ELISA Development Kit

Maculavirus is a new genus of plant viruses typified by Grapevine fleck virus (GFkV). A possible second member is Grapevine redglobe virus (GRGV). Maculaviruses are phloem-limited non-mechanically transmissible viruses with isometric particles c. 30 nm in diameter that have a rounded contour and prominent surface structure. Vectors, if any, are unknown. GFkV preparations contain two centrifugal components, T, made up of empty protein shells and B, which contains 35% RNA. The coat protein (CP) has a molecular mass of 24 kDa. The genome is a single-stranded RNA that has c. 50% cytosine residues. It is 7564 nt in size, excluding the poly(A) tail and contains four putative open reading frames (ORF) that encode a 215.4 kDa polypeptide with the conserved motifs of replication-associated proteins of positive-strand RNA viruses (ORF1), the CP (ORF2), and one (GRGV) or two (GFkV) proline-rich polyproteins of 31.4 kDa (ORF3) and 15.9 kDa (ORF4), respectively, with unknown function. Replication-associated proteins and CP are phylogenetically related to those of members of the genera Tymovirus and Marafivirus. GFkV-infected grapevine cells contain vesiculated mitochondria, the possible site of RNA replication. In the natural host, GFkV particles accumulate in great quantity, sometimes in crystalline arrays in phloem cells.

Infection of French-American hybrid grapevines by GLRaV-3 is latent, and information about the impact of the virus on the performance of these cultivars is scarce. This study compares several performance indices between Vidal blanc and St. Vincent grapevines that were naturally infected and those free of GLRaV-3. Virus infection did not affect grapevine vigor, but was linked to an approximately 5% reduction (p < 0.001) in average berry weight in both cultivars. Titratable acidity was 5 and 9% higher (p < 0.001) in the fruit from virus-positive St. Vincent and Vidal blanc grapevines, respectively, three to seven days prior to harvest. Also included in the study were Vidal blanc plants naturally infected by GLRaV-3 and grapevine fleck virus (GFkV). Plants with both viruses had a 7% reduction in average berry weight and titratable acidity levels were 14% higher compared to healthy plants (p < 0.001). Graft-indexing on Vitis vinifera L. cv. Cabernet Franc and Vitis rupestris Scheele cv. St. George indicators produced typical leafroll and fleck symptoms, respectively. These results suggest that latent infections in these French-American hybrid cultivars cannot be attributed to the low virulence of the viral strains, but probably to host tolerance.