Studies on Ralstonia solanacearum in Cameroon
Studies were conducted on Ralstonia solanacearum (EPPO A2 List) in Cameroon in 2005. 110 strains of R. solanacearum were recovered from wilted tomato (Lycopersicon esculentum), sweet and hot pepper (Capsicum annuum and C. chinense), potato (Solanum tuberosum), huckleberry (Solanum scabrum), Amaranthus spp. and sesame (Sesamum spp.) plants. Bacterial wilt is widely distributed in Cameroon, but results showed that disease incidence and severity were higher in the lowlands near Yaoundé and in the highlands near Bafoussam which are the main vegetable cropping areas of Cameroon. Out of these 110 strains, 44 representative strains were characterized according to the new phylotype classification system*. Strains isolated from Cameroon clustered into phylotypes I (Asian), II (American) and III (African). Lowland tomato strains (regions with humid forests) belonged to phylotype I and were quite homogeneous. Strains belonging to phylotype II were more diverse but included race 3/biovar 2 strains (associated with potato brown rot and tomato wilt). Strains from potatoes growing in the highlands of West Cameroon (areas with a temperate climate) fell into both phylotype II (race 3/biovar 2) and phylotype III. It is felt that these strains attacking potato and tomato crops in temperate highlands could pose an economic threat throughout Central Africa. The EPPO Secretariat previously had no information on the situation of R. solanacearum in Cameroon.
The situation of Ralstonia solanacearum in Cameroon can be described as follows: Present, widespread.
* New hierarchical classification scheme proposed by Fegan and Prior (2005) based on molecular characteristics (sequence analysis of ITS region, endoglucanase (egl) gene, and hrpB gene).
- Phylotype I: strains from Asia belonging to biovars 3, 4 and 5.
- Phylotype II: strains from America belonging to biovar 1/race 1, biovar 1/race 2 (Moko disease), biovar 2/race 3 (that includes potato and tomato strains found in temperate areas), biovar 2T.
- Phylotype III: strains from Africa and the Indian Ocean belonging to biovars 1 and 2T.
- Phylotype IV: strains from Indonesia, some strains from Japan and Australia belonging to biovars 1, 2, and 2T.
Fegan M, Prior P (2005) How complex is the Ralstonia solanacearum species complex? In C Allen, P Prior and AC Hayward (Ed.) Bacterial wilt disease and the Ralstonia solanacearum species complex. APS Press (US), pp 449-461.
Mahbou Somo Toukam G, Cellier G, Wicker E, Guilbaud C, Kahane R, Allen C, Prior P (2009) Broad diversity of Ralstonia solanacearum strains in Cameroon. Plant Disease 93(11), 1123-1130.