Incidence of potato viruses and bacterial wilt disease in the west Amhara sub-region of Ethiopia.
A survey of virus diseases and bacterial wilt was carried out in four major potato growing administrative zones in the west Amhara sub-region of Ethiopia in 2008. Leaf samples with symptoms suggestive of virus infection were collected from 38 randomly selected fields in 16 locations, whilst for bacterial wilt detection tuber and stem samples were collected from 23 and 12 fields in 15 and 12 locations, respectively. Disease incidences were visually assessed in the field and the identities of the pathogens were confirmed by laboratory testing using double antibody sandwich (DAS)-ELISA for viruses, and nitrocellulose membrane (NCM)-ELISA kits for Ralstonia solanacearum. In addition, an enrichment procedure was used to determine latent infection by R. solanacearum. Virus disease incidence varied from zero to 100% in different potato growing systems, whilst bacterial wilt incidence as high as 25% was recorded in farms in the west Gojam and north Gonder zones when assessed based on visual field symptoms. Results of laboratory testing for viruses confirmed the occurrence of at least five viruses, with Potato virus S (PVS) being the most widely distributed. Other viruses identified included Potato virus X (PVX), Potato virus M (PVM), Potato leaf roll virus (PLRV) and Potato virus Y (PVY), in order of importance. Mixed infections with two or more viruses were also detected. Potato virus A (PVA) was not detected in any of the samples tested. Latent infection by R. solanacearum was found in various potato fields, including experimental plots, farmers' seed potato production fields, suggesting the need to consider strict quarantine measure and restrict the free movement of seed tubers.