Use of morphological characters to identify cassava mosaic disease and cassava bacterial blight resistance

摘要

Diseases are among the major constraints that prevent cassava's (Manihot esculenta sp. L.) optimum yield. Both the improved cassava breeds and local germplasms in the International Institute of Tropical Agriculture, Ibadan expressed wide genetic variability in morphological characters and diseases resistance. The current criteria for disease resistant varieties among the cassava cultivars appeared to be cumbersome. Attempts were made to identify and classify the clones based on the morphological traits expressed by the improved breeds and the landraces. Genotypes were scored for resistance to cassava mosaic disease (CMD) and cassava bacteria blight (CBB) attacks in the field. It was evident that identification of cassava genotypes using morphological characters is reliable. Some genotypes were resistant to CMD and CBB attack. It was found that pigmentation and level of branching confers resistance to cassava against CMD and CBB attack. CBB incidence was highly correlated (P<0.001) with both pith and hardwood thickness. The negative relationship between CBB severity and sprouting was very significant (P<0.001) for 3, 6, and 9 days after planting (DAP). CMD incidence showed a high correlation (P<0.001) with CMD severity. A similar result was observed in the relationship between CBB incidence, showing a strong correlation (P<0.001) with CBB severity.