Abstract

S5-01

Genetic Mapping of a Dominant Gene Conferring Resistance to the Cassava Mosaic Disease (CMD)

Akano² A.O., A.G.O. Dixon¹ C. Mba², E. Barrera² and M. Fregene²   

1.  International Institute of Tropical Agriculture (IITA), PMB 5320, Ibadan, Nigeria

                  Cassava mosaic disease (CMD) is the most important disease of cassava in Africa, and a potential threat to the crop in Latin America where the disease is still not known but the vector has recently been found.  Host plant resistance is the principal method of control, and was first identified in 3^rd back cross derivatives of an inter-specific cross between cassava and M. glaziovii.  This is thought to be polygenic with a recessive component.  Recently, several Nigerian cassava landraces have been identified that show extreme resistance to CMD.  Classical genetic analysis and molecular genetic mapping have demonstrated this extreme resistance is controlled by a major dominant gene.  A bulk segregant analysis (BSA) approach was used to quickly identify a simple sequence repeat (SSR) marker gene linked to the CMD resistance gene.  The SSR marker is located on linkage group R of the male parent-derived molecular genetic map.  The gene has been designated CMD2 and is flanked by two SSR markers and a RFLP marker at 2 and 9 cM respectively.  The use of markers linked to CMD2 to assist marker-assisted breeding for CMD resistance in Latin America and improving the cost-effectiveness of resistance breeding in Africa is discussed.