INSECT TRANSMISSION OF SWEET-POTATO DISEASE AGENTS IN NIGERIA

Two infective agents were separated from a sweet potato disease complex in Nigeria. One is a nonpersistent virus [a filamentous rod (850 nm)] which is transmitted most efficiently by the aphids Myzus persicae and Aphis gossypii and less efficiently by A. citricola. It is latent in sweet potato [Ipomoea batatas L.] but produces marked vein-clearing and leaf twisting in I. setosa. Following infection, symptoms disappear after about 8 new leaves are produced. The disease is referred to as sweet potato vein-clearing. The 2nd agent is transmitted by the whitefly, Bemisia tabaci. It also is latent in the sweet potato cultivars tested. In I. setosa it produces mild chlorosis and severe stunting of the plant. The disease is referred to as sweet potato chlorotic stunt. In combination the 2 disease agents produce severe symptoms in sweet potato. Depending on the cultivar, vein-clearing, puckering, leaf strapping, chlorosis and stunting may occur. Dual infection in I. setosa results in stunting, severe chlorosis followed by necrosis of older infected leaves and a severe reduction in leaf lamina.