A.A. Raji, A.G.O. Dixon and T.A.O Ladeinde
Eleven landraces suspected to be sources of resistance to cassava mosaic disease (CMD) and cassava green mite (CGM) were selected from IITA’s collection of Nigerian landraces, and assessed together with an improved CMD resistant cultivar (TMS 30572) and a susceptible check (Isunikankiyan) for their levels of genetic diversity, for possible utilization in the breeding program. Large genotypic variation was observed among the landraces for their reactions to CMD and CGM and to a lesser extent for CBB. In addition, there were significant genetic variations among these landraces for various agronomic and food quality traits. Additional sources of resistance to CMD and CGM far better than the popular improved cultivar, TMS 30572, were identified. Sources for low cyanogenic potential and mealiness of boiled storage roots were also identified. Principal component analysis using the correlation matrix of 53 agrobotanical characteristics identified five distinct groups of clusters among these cultivars. Within each group, genotypes are genetically related and between groups, genotypes are unrelated suggesting that some of the landraces may have emerged from different genetic backgrounds with different sources of genes for desirable traits like disease and pest resistance TMS 30572, an improved cultivar and an offspring of the Manihot glaziovi derivative, clone 58308(sole source of resistance to CMD), is genetically unrelated to the sources of resistance to ACMD identified among the landraces. It is important to make an extensive and complete collection of local germplasm in Africa. Local cultivars generally outyield improved cultivars and usually carry genes for adaptation to local conditions, especially tolerance to drought, resistance to diseases and pests, and posses preferred root quality as this study shows.