No abstract

No abstract

No abstract

INDEXWORDSManihot esculenta, cassava, Manihot glaziovii, ceara rubber, Xanthomonas manihotis, cassava bacterial blight, cassava mosaic disease, heritability, genotypic correlation, correlated response to selection. SUMMARYThe two most serious diseases ofcassava (Manihot esculenta CRANTZ) are cassava mosaic disease (CMD) and cassava bacterial blight (CBB) (Xanthomonas manihotis STARR). Clone 58308, derived from the third backcross of the interspecific cross of cassava (M. esculenta) x ceara rubber (M. glaziovii), showed a high level of resistance to both diseases. Crosses of 58308 with several other clones which varied from susceptible to moderately susceptible to both diseases gave progenies with a significant genotypic correlation between resistance to both diseases (r = 0.90) apparently due to linkage. The heritabilities of resistance to the diseases were esfimated at 5&70% for CMD and 25-65 % for CBB. Resistance to both diseases is assumed to be polygenic. The correlated response to selection for CMD and for CBB was estimated.

The improved cassava mosaic-resistant cassava variety TMS 30395 produced significantly higher root yields under field conditions than its susceptible parent Isunikakiyag, irrespective of whether it was established from mosaic-free or mosaic-infected planting material. Significant reductions in fresh root yield, root number, root size, top fresh weight and starch content in both varieties resulted from plants established from CMD-infected planting material. For the variety Isunilokiyan, yield reduction was greater in plants established from clonal CMDinfected cuttings than in those established from disease-free cuttings but which later became infected through vector transmission.