GRAPEVINE DEFORMATION VIRUS A NOVEL NEPOVIRUS FROM TURKEY
I. Cigsar, M. Digiaro, K. Gokalp, N. Abou Ghanem-Sabanadzovic, A. De Stradis, D. Boscia, G.P. Martell
A virus with isometric particles ca. 30 nm in diameter and angular contour was recovered by mechanical transmission from a grapevine with fanleaf-like symptoms growing at Nevsheir (Cappadocia, Turkey). In sucrose density gradient centrifugation this virus (laboratory code: isolate N66) sedimented as three components, T (empty shells), M, and B, both of which consisted of apparently intact particles. Virus preparations contained two RNA species with mol. wt. 2.6·106 Da (RNA-1) and 1.3·106 Da (RNA-2). The coat protein (CP) subunits were of a single type with Mr of c. 53,000. An antiserum with a titre of 1:1024 was raised, which did not react with healthy plant antigens. A fragment 1,175 nt in size from the 3’ terminal region of RNA-2 was sequenced, which comprised part of the CP cistron. Comparison analysis with GenBank sequences from the same region revealed variable levels of homology with other grapevine nepoviruses, the closest being Arabis mosaic virus (ArMV, 69% identity at the amino acid level) and Grapevine fanleaf virus (GFLV, 58% identity at the amino acid level), both belonging in subgroup A of the genus Nepovirus. Based on the determined sequence, specific primers were designed, which in RT-PCR assays amplified a 240 bp fragment from grapevine crude tissue extracts. The physicochemical properties of isolate N66 and the cytopathology of infected Chenopodium amaranticolor tissues resembled very much those of nepoviruses. In gel double diffusion tests isolate N66 proved serologically unrelated to 16 different nepoviruses. A distant positive reaction was obtained with ArMV in immunodiffusion (serological differentiation index = 4) and immunoelectron microscopy tests and when leaf extracts from infected grapevines or C. quinoa were tested in ELISA with commercial antisera to ArMV. These results support the notion that isolate N66 is a hitherto undescribed virus species belonging in subgroup A of the genus Nepovirus, serologically related to but distinct from ArMV, for which the name Grapevine deformation virus (GDefV) is proposed.