A Chronological Study on Grapevine Leafroll-Associated Virus 2 in Australia.

Area of Science:

• Plant Pathology
• Virology
• Horticulture

Background:

• Grapevine leafroll disease is a global concern impacting grapevine health.
• Previous research in Australia primarily focused on GLRaV-1 and GLRaV-3, neglecting GLRaV-2.
• GLRaV-2 is associated with graft incompatibility and vine decline, posing a risk to viticulture.

Purpose of the Study:

• To document the temporal occurrence and incidence of grapevine leafroll-associated virus 2 (GLRaV-2) in Australia since 2001.
• To identify grapevine varieties and rootstocks affected by GLRaV-2.
• To analyze the phylogenetic diversity of GLRaV-2 in Australia and its association with symptoms.

Main Methods:

• Analysis of 11,257 grapevine samples collected across Australia from 2001 onwards.
• Detection of grapevine leafroll-associated virus 2 (GLRaV-2) using molecular methods.
• Metagenomic sequencing to identify co-infections with other viruses and viroids.

Main Results:

• An overall incidence of 2.7% for GLRaV-2 was recorded across 11,257 samples.
• GLRaV-2 was detected in 18 grapevine varieties and Vitis rootstocks, with Chardonnay showing decline on sensitive rootstocks.
• Four phylogenetic groups of GLRaV-2 were identified in Australia, with one isolate on Grenache exhibiting severe leafroll and necrosis.

Conclusions:

• GLRaV-2 is present in Australia, with a low but notable incidence.
• The virus can cause symptomless infections or severe decline, particularly in conjunction with specific rootstocks.
• The presence of multiple GLRaV-2 phylogenetic groups and its association with graft incompatibility highlight the ongoing risk to Australian viticulture, especially where hybrid rootstocks are used.