Inheritance of resistance to cassava green mite and other useful agronomic traits in cassava grown in Zambia

Cassava green mite (CGM) Mononychellus tanajoa (Bondar) (Acari: Tetranychidae) is a major arthropod pest causing significant loss in the yields of storage roots and planting materials of cassava in Zambia. Its control has been mainly based on the use of exotic predatory mites as biological control agents, which unfortunately, have not established well in Zambia due to the lack of suitable host genotypes and harsh weather conditions. The current study was aimed at breeding cassava for improvement of morphological traits that are associated with resistance to CGM, which can also enable cassava genotypes to provide shelter and ensure continuous survival of natural enemies of CGM, and to determine the inheritance of these traits by assessing combining ability and therefore the type of gene action involved in their expression. Using a 5 × 5 half diallel mating design, full-sib cassava genotypes were generated out of which 300 were selected and evaluated in the field. Data were collected for CGM density, CGM leaf damage and cassava mosaic disease severity, plant growth habit, leaf morphological traits, storage root yield and root dry mass. Both general and specific combining ability effects were significant (P < 0.01) for the reaction of the F 1 progeny to CGM, and for the various plant morphological traits that were measured, suggesting that both additive and non-additive gene effects play a role in the expression of the traits.