Author : Truong Hoai Xuan

Summary : The viruses and virus strains naturally occuring in tomato in five locations in the Philippines were identified through indicator plants, modes of transmission, physical properties, electron microscopy, and serology. From the nine different disease-types collected, 11 virus strains belonging to three virus groups were isolated. These were the tobamovirus, cucumovirus, and potyvirus grouped. In the tobamovirus group there were six tomato mosaic virus strains identified, Namely: ToMV-O, TMV-U6, ToMV-A, ToMV-W, ToMV-GY, and ToMV-YF. The last three are new strains and are reported for the first time. Two strains each were found in the cucumovirus group (CMV-O and CMV-Y), and potyvirus group (PVY-O severe and PVY-O mild). One distinct virus, a member of the potyvirus group, was alos isolated and identified as severe strain of tobacco etch virus (TEV-S). ToMV and its strains were isolated from such disease-types as green mosaic (ToMV-O), yellow mosaic (ToMV-A, ToMV-GY, TMV-U6, and ToMV-YF), and white mosaic (ToMV-W). PVY and its strains were isolated from leaf curl diseases and TEV-S from mild leaf distortion. The effects of weather, location, and varieties on the prevalence and severity of these viruses and their aphid vectors were also determined. The effects of CMV-Y on yield of four tomato varieties (Marikit, VC9-1, VC48-1, and VC11-1), were likewise established. At 30 percent infection, there was a corresponding yield loss of 50 percent in the four tomato varieties. Control of ToMV-A by seed treatment and use of attenuated strain were tried. Both methods were found to be effective. The control of the aphid vectors of CMV and PVY by means of granular and emulsifiable insecticides were compared. Their efficacy varied with the varieties. However, the best insecticide-variety combination was Thiodan x Marikit variety.