Grapevine vein clearing virus Is Prevalent and Genetically Variable in Grape Aphid (Aphis illinoisensis Shimer) Populations.

Grapevine vein clearing virus (GVCV) causes severe stunting and death of cultivated grapevines and is prevalent in native Vitis spp. and Ampelopsis cordata in the Midwest region of the United States. GVCV can be transmitted from wild A. cordata to Vitis spp. by grape aphid (Aphis illinoisensis) under greenhouse conditions, but its prevalence, genetic composition, and genome number in native grape aphids are unknown. In this study, we collected grape aphids from native Vitaceae across the state of Missouri in 2018 and 2019, and conducted diagnostic, genetic, and quantitative analyses. GVCV was detected in 91 of the 105 randomly sampled communities on 71 Vitaceae plants (87%). It was present in 211 of 525 single grape aphids (40%). Diverse GVCV variants from aphids were present on both GVCV-negative and GVCV-positive plants. Identical GVCV variants were found in grape aphids sampled from wild and cultivated Vitaceae, indicating that viruliferous aphids likely migrate and disperse GVCV variants among wild and cultivated Vitaceae. In addition, we found that the number of GVCV genomes varies largely in the stylet and body of individual aphids. Our study provides a snapshot of GVCV epidemics and genetic structure in its mobile vector and sessile hosts. This presents a good model for studying the epidemiology, ecology, and evolution of a plant virus.

North American Grape 'Norton' is Resistant to Grapevine Vein Clearing Virus.

Grapevines (Vitis spp.) host viruses belonging to 17 families. Virus-associated diseases are a constant challenge to grape production. Genetic resources for breeding virus-resistant grape cultivars are scarce. 'Norton' is a hybrid grape of North American Vitis aestivalis and is resistant to powdery mildew and downy mildew. In this study, we assessed resistance of 'Norton' to grapevine vein clearing virus (GVCV), which is prevalent in native, wild Vitaceae and in vineyards in the Midwest region of the U.S. We did not detect GVCV in 'Norton' as either the scion or the rootstock up to 3 years after it was grafted with a GVCV-infected 'Chardonel' grapevine. Upon sequencing of small RNAs, we were able to assemble the GVCV genome from virus small RNAs in GVCV-infected 'Chardonel' scion or rootstock, but not from grafted 'Norton' scion and rootstock. This study unveils a new trait of 'Norton' that can be used in breeding GVCV-resistant grape cultivars, and to investigate genetic mechanisms of 'Norton' resistance to GVCV.

A Natural Reservoir and Transmission Vector of Grapevine Vein Clearing Virus.

Grapevine vein clearing virus (GVCV) is associated with a vein-clearing and vine-decline disease. In this study, we surveyed wild Ampelopsis cordata from the Vitaceae family and found that 31% (35 of 113) of native A. cordata plants are infected with GVCV. The full-length genome sequence of one GVCV isolate from A. cordata shared 99.8% identical nucleotides with an isolate from a nearby cultivated 'Chardonel' grapevine, suggesting the occurrence of an insect vector. To identify a vector, we collected Aphis illinoisensis (common name: grape aphids) from wild A. cordata plants and detected GVCV in the aphid populations. We found that A. illinoisensis is capable of transmitting GVCV from infected A. cordata to Chardonel grapevines in the greenhouse. Upon transmission, GVCV caused severe symptoms on the infected Chardonel 45 days post transmission. We conclude that wild GVCV isolates from A. cordata are capable of inducing a severe disease on cultivated grapevines once they spread from native A. cordata to vineyards via grape aphids. The discovery of a natural reservoir and an insect vector of GVCV provides timely knowledge for disease management in vineyards and critical clues on viral evolution and epidemiology.