Grapevine leafroll-associated virus 3

Grapevine leafroll-associated virus 3 (GLRaV-3) is a positive-sense single-stranded RNA plant virus in the family Closteroviridae, genus Ampelovirus.^[1][2]

Grapevine leafroll-associated virus 3
Virus classification
(unranked):	Virus
Realm:	Riboviria
Kingdom:	Orthornavirae
Phylum:	Kitrinoviricota
Class:	Alsuviricetes
Order:	Martellivirales
Family:	Closteroviridae
Genus:	Ampelovirus
Species:	Ampelovirus trivitis

It is the principal causal agent of grapevine leafroll disease (GLD), a globally distributed disease complex that reduces yield and fruit quality in Vitis vinifera. Natural transmission is by mealybugs and soft scale insects; the virus is also disseminated via infected propagation material.

Taxonomy and classification

GLRaV-3 belongs to the genus Ampelovirus within the family Closteroviridae.^[1] Viruses of Ampelovirus characteristically have long flexuous filamentous particles and are transmitted by mealybugs or soft scale insects. GLRaV-3 shares these features and has been continually refined in classification as more variants were discovered.

Genome and molecular biology

The genome of GLRaV-3 is around 18–19 kb, encoding approximately 12 ORFs including the replication module (papain-like protease, methyltransferase, helicase, RdRP), HSP70h, the major coat protein (CP) and minor coat protein (CPm), plus small accessory ORFs.^[1] There is substantial genetic variation among isolates: multiple phylogenetic groups have been defined, and certain variants lack ORF2 or have divergent genomic regions.^[2]

Symptoms and disease

In red-fruited grape cultivars, GLD symptoms typically include interveinal reddening of leaves with green veins, leaf rolling downward, and delayed ripening of fruit. In white-fruited cultivars, symptoms may be less dramatic—leaf chlorosis (yellowing) and rolling may occur.^[3]

Infected vines can show reduced sugar accumulation (Brix), increased acidity, lower anthocyanin in red grapes, lower vigor, and diminished yield—often tens of percent compared to healthy vines.^[4]

Transmission and epidemiology

GLRaV-3 is spread primarily via two routes: (1) through infected propagation material (grafts, cuttings, rootstocks), and (2) via insect vectors—especially mealybugs (family Pseudococcidae) and certain soft scale insects (Coccidae).^[4] For example, experiments with the vine mealybug (Planococcus ficus) demonstrated semipersistent transmission: acquisition and inoculation within ~24 h, retention up to several days, and first-instar crawlers being more efficient than adults.^[5]

Management

There is no cure for infected vines, so management focuses on prevention and containment. Key strategies include:

1. Planting certified virus-tested (“clean”) propagation material.^[3]

2. Mapping and removing (roguing) infected vines early to minimise spread.^[4]

3. Controlling vector populations (mealybugs and scales) using integrated pest management: monitoring, insecticide treatments upon crawler emergence, biological controls, and pheromone-based mating disruption.^[3]