PROPERTIES OF A PREVIOUSLY UNDESCRIBED NEPOVIRUS FROM SOUTH-EAST ANATOLIA

Abstract

SUMMARY A virus with isometric particles ca. 30 nm in diameter and angular contour was isolated by inoculation of sap from a Turkish grapevine showing very mild fanleaf symptoms. In sucrose density gradient centrifugation the virus sedimented as three components: T (empty shells), M (particles containing a RNA species with mol. wt 1.4 x 10 6 Da) and B (particles containing a RNA species with mol. wt 2.2 x 10 6 Da). The coat protein subunits were of a single type with Mr ca. 55.5 kDa. An antiserum with a titre of 1:256 was raised, which did not react with healthy plant antigens. A fragment 1,274 nt in size, representing the 3’ terminal region of genomic RNA-2 was sequenced. Direct comparison analysis with sequences from the same region from GenBank-EMBL databases revealed variable levels of homology with other grapevine nepoviruses, the closest being Grapevine chrome mosaic virus (GCMV) (62% identity at the amino acid level), Artichoke Italian latent virus (AILV) and Tomato blackring virus (TBRV) (49% identity at the amino acid level with both). Based on the determined sequence, specific primers were designed which in RTPCR assays amplified a 343 bp fragment virus from grapevine crude tissue extracts. Infected N. occidentalis leaves had a cytopathology comparable to that of nepovirus infections, typical virus-containing tubules, mostly associated with plasmodesmata. The physicochemical and ultrastructural properties of this virus resembled very much those of nepoviruses. However, it was serologically unrelated to 17 different members of this genus, including all those recorded from grapevines. These results support the notion that the Turkish grapevine virus is a hitherto undescribed member of the genus Nepovirus belonging in subgroup B, for which the name Grapevine Anatolian ringspot virus (GARSV) is proposed.