Movement of plant viruses in mixed infections

The effects of mixed infections on virus movement were examined in various plant hosts. Tobacco mosaic virus (TMV) remained confined to primary local lesions on leaves of N gene tobacco plants inoculated with TMV only. In the presence of potato leafroll virus (PLRV), however, TMV moved systemically and caused systemic necrotic lesions on young leaves. TMV could be rub-transmitted from the systemic necrotic lesions but not from non-necrotic areas of dually infected plants. Stem necrosis caused collapse of some dually infected plants. Regrowth from the base of such plants was initially non necrotic but necrotic lesions developed on young leaves much later. TMV could not be rub-transmitted but could be graft transmitted from non necrotic regrowth. In Phaseolus vulgaris cv. Ouray, infection with beet curly top virus (BCTV) did not affect TMV movement or symptoms. TMV remained confined in the local lesions on primary leaves. In contrast, localized infection of Ouray beans with TMV did affect BCTV infection. It caused more severe BCTV symptoms and an 8-10 fold increase in BCTV concentration. Furthermore, BCTV escaped the phloem cells and invaded the parenchyma cells of both roots and shoots of co-infected plants. Some potato clones that could not be infected with PLRV alone were systemically infected with PLRV when co-infected with potato virus X (PVX) and/or potato virus Y (PVY). Co-infections with PVX and/or PVY also increased the concentration of PLRV in some susceptible clones, but it did not facilitate transmission of PLRV or the escape of PLRV from phloem tissues. Infection with PLRV did not observably affect the movement and concentration of PVX and PVY. It also did not cause the movement of PVX into non-inoculated leaf tissue of cultivars Saco and USDA seedling 41956, nor did it effect movement of PVX from local lesions in Gomphrena globosa.