Malakisi tobacco veinal necrosis, a strain of potato virus Y isolated from nicotiana tabacum L.cultivar speight G.28 in western Kenya
A tobacco virus disease, causing mainly mottling, vein-clearing and necrosis on leaves and stem bias recently noticed throughout the tobacco growing areas in Western Kenya and seemed to have a serious effect on leaf losses, mainly on cultivar 'Speight G.2S', which is the main cultivar grown in Western 'Kenya. Field symptoms consist of green vein-banding, vein-clearing and mottling with pale yellow spots.on a green background which in advanced stage changed into extreme white mottling. On 'Speight G.2B', severe veinal and stem necrosis occured. In this work, the new virus strain on tobacco has been isolated, characterized and identified. It has been reffered to as the Malakisi Tobacco veinal necrosis strain (M-TVNS) . Electron microscope examination showed that M-TVNS is a filamentous particles about 742 nm long. The results on symptomatology and host-range through mechanical inoculation, transmission through seed of. Nicotiana tabacum cultivars and the aphid Myzus persicae' Sulz', ultra-violet absorption, and serological reactions suggest that the M-TVNS is strain of PVY Reactions on differential hosts used by de Bokx (1931) and Kahn and Monroe (1963) showed that M-TVNS is different from all the three groups of PVY strains as reported by de Bokx (1931). Its ability to induce systemic necrosis on leaves, veins and stem of root- knot resistant cultivar 'Speignt G.28» identify it S R as a MsNr strain described by Gooding and Tolin (1973).