Combining ability of cassava genotypes for cassava mosaic disease and cassava bacterial blight, yield and its related components in two ecological zones in Ghana
Breeding for resistant genotypes is the best strategy to offset the destructive effects of cassava mosaic disease (CMD) and cassava bacterial blight (CBB). Two sets of diallel parents were selected for the forest and the savannah ecological zones in Ghana based on good levels of resistance to CMD and CBB. Both sets were crossed in a half-diallel design. The first set of seven progenitors and their 21 F1 progenies were planted in a randomised complete block design (RCBD) with three replications in two different locations for two seasons in the forest ecology. The second set of five progenitors and their 10 F1 progenies were planted in a RCBD with three replications in two locations in the coastal savannah ecological zone of Ghana. Both experiments were evaluated for CMD and CBB resistance, fresh root yield, dry root yield, root number, harvest index, dry matter content, plant height at maturity and height at first branching, levels of branching and plant vigour. Results of the combined analysis of variance revealed that the environment effect was significant for all the traits. General combining ability and specific combining ability effects were significant for most of the traits. Narrow sense heritability was significant for plant vigour, root number, CMD and CBB in both the zones. CMD and root number also had a predictability ratio of close to one, indicating the importance of additive gene effects.
Genetic variability of three cassava traits across three locations in Ghana
Peprah Bright Boakye1*, Ofori Kwadwo 2, Asante Isaac K. 3 and Elizabeth Yaa Parkes 1,4
1 Crops Research Institute, Fumesua, Kumasi, P. O. Box 3785, Ghana.
2 Department of Crops Science, University of Ghana, Legon.
3 Department of Botany, University of Ghana, Legon.
4 International Institute of Tropical Agriculture, Ibadan, Nigeria.
Accepted 27 May, 2013
A study was conducted to assess the extent of genetic variability, broad-sense heritability and correlations for fresh root weight, root number and top weight of five cassava genotypes across three locations in 2 years. Combined analysis of variance revealed highly significant genotypic effect for all the traits. Genotype x environment interaction was also significant for all the traits studied indicating considerable but, varying response of the genotypes to the environments. High broad-sense heritability and genetic advance as percent of the mean were observed for fresh root weight, suggesting that the trait is primarily under genetic control and that a simple recurrent phenotypic selection scheme would be rewarding. Phenotypic coefficients of variation values were larger than their corresponding genotypic coefficient of variation values for all traits. Correlations between the three traits were highly significant and positive indicating that simultaneous progress for the three traits is feasible.