Leafroll virus spread is primarily via which pathway?

• A. Grafting and mealy bugs
• B. Wind-dispersed seeds
• C. Root grafting between vines
• D. Water splashes from rain

Answer: (A)

Leafroll virus in grapevines spreads mainly through infected planting material and by vectors that feed on the plant’s phloem. When grafts or cuttings come from an infected vine, the virus is introduced into the new plant, so using certified virus-free material is key to preventing spread. Mealybugs (and other phloem-feeding insects) acquire the virus from an infected vine and transmit it to healthy vines as they feed, making them the primary natural spread mechanism in the field. Seeds are not a reliable route for this virus, since grapevines are clonally propagated and the virus isn’t seed-transmitted. Water splashes don’t effectively move the virus between plants, and while root grafts between vines can occur, they are not the main pathway driving widespread transmission compared with infected propagation material and insect vectors.