Application of embryo culture in germinating African cassava mosaic disease resistant gene mapping population

In a study to map out the genes confering resistanceto African cassava msaic disease (ACMD), a cost-effective protocol for zygotic embryo culture developed at the International Institute of Tropical Agriculture(IITA) using 1/2 strenght Murashige and Skoog's basal media, was employed to germinatethe F1 populations. The F1 crosses wee generated from cross combinations between ACMD resistant and susceptible and local cassava germplasm. These crosses were TMS 30572 x TME 117, TMS 30572 x TME 4, and TMS 30555 x TME 3, giving three mapping populations. Four weeks after explanting embryo axes, progenies of the F1 cross of TMS 30555 x TME 3 perfomed best with 88% of the explanted embryos poducing two or more nodes, followed by those of the F1 cross TMS 30572 x TME 4, with 79%, and TMS 30572 x TME 117, germilings had 4 to 5 nodes, and 3, 5, and 9% in F1 crosses of TMS 30572 x TME 117, TMS 30572 x TME 4, and TMS 30555 X tme 3, respectively

Genetic mapping of a dominant gene conferring resistance to cassava mosaic disease

Cassava mosaic disease (CMD) is the most-important disease of cassava (Manihot esculenta) in Africa, and is a potential threat to Latin American (LA) cassava production. Although this viral disease is still unknown in LA, its vector – the whitefly – has recently been found. The disease is best controlled through host-plant resistance, which was first found in third backcross derivatives of an interspecific cross between cassava and Manihot glaziovii, and is thought to be polygenic. Recently, high levels of resistance were also found in several Nigerian cassava landraces. Classical genetic analysis and molecular genetic-mapping of the landraces showed that a major dominant gene confers this resistance. Bulk segregant analysis (BSA) was used to quickly identify a simple sequence repeat (SSR) marker linked to the CMD-resistance gene. The marker, SSRY28, is located on linkage group R of the male-parent-derived molecular genetic map. The gene, designated as CMD2, is flanked by the SSR and RFLP marker GY1 at 9 and 8 cM, respectively. To our knowledge, this is the first report of qualitative virus resistance in cassava, and of molecular markers that tag CMD resistance in cassava. We discuss the use of markers linked to CMD2 for marker-assisted breeding of CMD resistance in Latin America and for increasing the cost-effectiveness of resistance breeding in Africa