Association of closterovirus-like particles and high molecular weight double-stranded RNA with grapevines affected by leafroll disease

Abstract

Grapevines exhibiting symptoms typical of leafroll disease were shown to contain closterovirus- like particles in phloem tissue. Particles were readily fragmented in negatively stained preparations and had a modal length ofabout 1400 nm. Electrophoretic separation of nucleic acid species isolated from grapevine phloem tissue indicated the presence of a high molecular weight (MW) component in diseased, but not in healthy, vines. This nucleic acid had a MW of about 8 × 10⁶ and was shown to be double-stranded RNA (dsRNA) by its differential digestion by RNase A in low salt but not high salt conditions. The levels of this dsRNA varied considerably depending on the tissue sampled and the time of sampling, being greatest in phloem extracts from dormant cuttings. The molecular size of this dsRNA, and its consistent association with closterovirus-like particles in affected vines, suggest that it may be the replicative form of this virus. Grapevines affected by corky bark disease also contained a high MW dsRNA similar in electrophoretic mobility to that isolated from vines affected by leafroll disease.

Keywords:

• grapevines
• Vitis vinifera
• leafroll
• corky bark
• closterovirus particles
• double-stranded RNA