Abstract
There are concerted efforts in promoting cassava production in sub Saharan Africa as a staple food crop as well as income earner at both household and commercial level. These efforts can bear meaningful results if breeding strategies are properly coordinated. Efficient breeding methods require a thorough understanding of the genetic background of planting materials. Therefore, a genetic study was conducted to establish the genetic basis of cassava genotypes for root weight, root number/plant, root length (cm), above ground weight, harvest index, cassava mealy bug and cassava green mite by mating six cassava genotypes using a diallel method. The generated F1s were evaluated using a randomized complete block design (RCBD) replicated thrice. The analysis of variance revealed highly significant (P< 0.001) genetic variation among the genotypes for all the traits except for cassava mealy bug, indicating the presence of high variability among genotypes. Thus, selection among these genotypes could lead to good progress for the improvement of the target traits. Mean squares for both general combining ability (GCA) and specific combining ability (SCA) were highly significant for all traits except for harvest index and cassava green mite for GCA and SCA respectively which suggested involvement of additive and non-additive component of heritable variance in the inheritance of all these traits. However, the proportions of additive variance to the total genetic variances (that is, 2δ2gca/(2δ2gca + δ2sca) showed that crossing for these traits and making selection from such crosses, about 41 to 100% of the improvement would be expected to come from SCA and less than 59% from GCA which indicated a greater role played by non-additive genes. Overall, results indicated that it would be readily possible to breed for high yield from this set of genotypes. Key words: Breeding, combining ability, gene action.
Highlights
The importance as well as challenges of cassava production are well known worldwide
For cassava green mite (CGM), significant positive combining ability effects were considered as low, non-significant as average and significant negative as high (Saleem, 2008)
The study has found that the best rated general combiners based on general combining ability (GCA) effects were Mulola for average root number, fresh root weight and above ground weight and Maunjili for fresh root weight, harvest index and cassava green mite which means that these could be good parents to use when breeding for genotypes for the said traits. 01/1313 was the worst combiner for all the traits studied except cassava green mite
Summary
The importance as well as challenges of cassava production are well known worldwide. The acclaimed advantages accrued to cassava production include staple food crop and source of income for the rural communities, industrial raw material, and earner of foreign exchange (Cock, 1985). Cassava brown streak virus disease (CBSD) are the important diseases (Dixon et al, 2003) These diseases can affect plant establishment and vigour, inhibit photosynthetic efficiency and cause pre-harvest or postharvest deterioration. Severe occurrences of both insect pests and diseases often lead to a considerable loss in yield potential of cassava. Combining ability is the relative ability of an inbred line or a clone, when crossed to another inbred line or clone, to transmit desirable traits or specific trait to the generation (Chaudhari, 1971) It helps to predict the performance of a particular line when used as a parent in a hybrid and facilitates the selection of superior parents for hybrid combination and for studying the nature of genetic variation (Russel, 1985). Information on combining ability is needed in order to identify suitable parents (among the following; Mulola, 01/1313, Depwete, 01/1316, Silira and Maunjili) and superior genotypes which can be hybridized for the development of elite cultivars and hybrid varieties that would ensure sustained production and productivity by smallholder farmers in Malawi
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