Abstract

Cassava bacterial blight (CBB) is caused by Xanthomonas axonopodis pv manihotis (Xam) a major cassava disease in all cassava growing area of the world. Resistance to the disease is found in Manihot esculenta and, in addition, has been introduced from a wild relative, M. glaziovii. We introduced a novel method of screening large population of cassava accessions in a screen-house environment using planting tray with a planting tree that can accommodate 68 different cassava stems cuttings in one planting tray. A total of 1,090 cassava accessions were screened with this method in the screen-house. The experimental design was augmented with randomized complete block design (ARCBD). Out of 490 land races cassava accessions that were assessed for susceptibility to CBB, 14.3 % were resistant to the disease. Land races populations were more susceptible to CBB infection having 30.1% highly susceptible and 12.3% susceptible cultivars.  Six hundred cassava accessions of the improved and the new improved were screened in the greenhouse.  Within the improved cultivars, 11.1% showed very strong resistance and 30.1% were resistant to the bacterial infections while 4.3% of these improved cassava accessions were observed as being highly susceptible to the disease and 36.6% were tolerant. Our results demonstrated that resistance to CBB is broadly distributed in cassava germplasm and for quick evaluation, the planting tray system should be employed.

Key words: CBB, Xanthomonas axonopodis pv manihotis, Manihot esculenta, resistance, susceptibility.