Introgression of genes for dry matter content from wild cassava species

Cassava cultivars often have poor resistance to biotic stresses and lack good quality traits. Wild species of cultivated crops have frequently been used as an important source of genetic diversity. Cassava breeders are becoming increasingly interested in incorporating genes of wild relatives. In 2000 the International Center for Tropical Agriculture (CIAT) initiated a programme to introgress genes for several root yield and quality traits from wild cassava relatives into its germplasm collection. The objectives of this study were to evaluate one resulting inter-specific cross with high variability for dry matter content (DMC) and to assess the effect of such a cross on other yield related traits. Crossing of the elite cultivar MTAI 8 to the wild relative Manihot tristis increased the percentage DMC above the normal average of about 35%, with percentage DMC ranging from 34.39 to 42.73. The crosses, however, were accompanied by some detrimental effects, most noticeable the reduction in harvest index (HI). It is apparent that when selecting for DMC, caution should be taken and HI and fresh root yield should be monitored. Regression analysis singled root weight, percentage DMC and fresh root yield out as the most important contributors to dry root yield. Principal component analysis indicated that root weight, roots per plants and DMC contributed most to storage root yield.