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 Zalin ge were detected using enzyme-linked immunosorbent assay, immunosorben t electron microscopy and sap-inoculation to test plants. All of the 1 9 plants of Zalinge tested were infected with potato leaf roll virus ( PLRV) and potato virus S (P VS), and five plants also with potato viru s X (PVX). No potato virus Y (PVY), A (PVA) nor M (PVM) were found. Th e viruses were eradicated with thermo- and chemotherapy using standard procedures. The combination of both therapies did not result in any v irus-free plants, but resulted in poor plant survival. Thermotherapy r educed the incidence of PLRV and PVS by 45% and 50%, respectively, and one virus-free plant was obtained. It grew vigorously in the greenhou se, was symptomless and had a significantly increased tuber yield comp ared to the virus-infected plants. Following sap-inoculation with PVY( O), Zalinge showed mosaic symptoms, developed necrosis in the leaves a nd stem and died 14 days post-inoculation. However, the plants of Zali nge infected with PVY(N) remained symptomless, which suggested that hy persensitivity was specific to PVY(O). The fast development of lethal necrosis following infection with PVY(O) may contribute to the low inc idence of PVY in Zalinge in the field in Sudan.