Invasion of Non-phloem Tissue in Nicotiana clevelandii by Potato Leafroll Luteovirus Is Enhanced in Plants also Infected with Potato Y Potyvirus

Abstract

Nicotiana clevelandii plants doubly infected with potato leafroll luteovirus (PLRV) and potato Y potyvirus (PVY) developed more severe symptoms than plants infected with either virus alone. Compared with singly infected plants, the PLRV concentration was increased up to eightfold by the double infection and the proportion of leaf parenchyma protoplasts that could be stained with fluorescent antibody to PLRV was increased from 0.2 to 1.4%. The concentration of PVY was unaffected by the double infection. In potato plants, in contrast, double infection with PVY did not increase PLRV concentration and none of the parenchyma protoplasts obtained from singly or doubly infected leaves could be stained with fluorescent antibody to PLRV. PLRV seems restricted to phloem tissue in potato but also invades a few parenchyma cells in N. clevelandii, a process that is accentuated in plants also infected with PVY.