ELIMINATION OF VIRUSES AND HYPERSENSITIVITY TO POTATO VIRUS-Y (PVY-CIRCLE) IN AN IMPORTANT SUDANESE POTATO STOCK (ZALINGE)

Viruses that infect naturally an important Sudanese potato stock Zalinge were detected using enzyme-linked immunosorbent assay, immunosorbent electron microscopy and sap-inoculation to test plants. All of the 19 plants of Zalinge tested were infected with potato leaf roll virus (PLRV) and potato virus S (P VS), and five plants also with potato virus X (PVX). No potato virus Y (PVY), A (PVA) nor M (PVM) were found. The viruses were eradicated with thermo- and chemotherapy using standard procedures. The combination of both therapies did not result in any virus-free plants, but resulted in poor plant survival. Thermotherapy reduced the incidence of PLRV and PVS by 45% and 50%, respectively, and one virus-free plant was obtained. It grew vigorously in the greenhouse, was symptomless and had a significantly increased tuber yield compared to the virus-infected plants. Following sap-inoculation with PVY(O), Zalinge showed mosaic symptoms, developed necrosis in the leaves and stem and died 14 days post-inoculation. However, the plants of Zalinge infected with PVY(N) remained symptomless, which suggested that hypersensitivity was specific to PVY(O). The fast development of lethal necrosis following infection with PVY(O) may contribute to the low incidence of PVY in Zalinge in the field in Sudan.