Assessment of cassava root and stem rots in ecozones of togo and evaluation of the pathogen virulence

Among the diseases of cassava (manihot esculenta crantz),root and stem rots are important in different ecozones of west africa. this study on the prevalence of cassava root and stem rot diseases was carried out in forest and wet savanna ecozones of togo and the causing pathogens were isolated,identified and pathologically characterized. cassava rots were found in both the ecozones,but were more frequently observed in the forest than in the wet savanna zone. a total of 39 fungal strains were isolated from diseased root and stem samples collected from cassava fields. botryodiplodia theobromae,fusarium sp.,sclerotium rolfsii and pythium sp. were the fungi isolated from the rotted cassava roots and stems. b. theobromae was the most frequently isolated fungus (51.3% of the isolated root rot pathogens),followed by fusarium sp. (33.3% of the isolates),while s. rolfsii and pythium sp.,were less frequently found. virulence tests on cassava stem cuttings and on cassava roots of field plants revealed only b. theobromae strains extremely virulent when inoculated into stem cuttings,whereas most of the fungi were highly virulent when inoculated into both cassava stem cuttings and roots of field plants,except s. rolfsii strains,which were less virulent when inoculated into stem cuttings. a pathogenic specialization of strains for roots or stems seemed to occur.