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Molecular marker-assisted selection of three intractable traits of maize and sorghum in Kenyan genetic backgrounds: myth or reality? K. Ngugi, Z. Muthamia, R. Folkertsma The Kenya Agricultural Research Institute (KARI) is applying molecular marker-assisted selection (MAS) to enhance conventional breeding efforts to improve drought tolerance and insect resistance in maize, and Striga resistance or tolerance in sorghum. The rationale of using molecular markers instead of conventional selection is that all three traits are quantitatively inherited and are difficult to select in the field using standard selection criteria. This paper discusses ongoing research in MAS of these three traits. For insect resistance and tolerance in maize, mapping populations were generated from the CML123 donor line from the International Maize and Wheat Improvement Center (CIMMYT) and K64R, an agronomically elite line originally from Zimbabwe but widely adapted in Kenya. In this case, an F2 of 250 individuals was genotyped with 150 restriction fragment length polymorphism (RFLP) and 60 simple sequence repeat (SSR) markers. For drought tolerance in maize, an F3 of 311 individuals from CML 16, a drought-tolerant line from CIMMYT, and K64R were genotyped with 50 SSR and 150 RFLP markers. Maps were constructed using Mapmaker ver. 3.1 software. Analysis of quantitative trait loci (QTLs) was done using the composite interval method exploring the four genetic models. Appropriate flanking SSR markers were used to conduct foreground and background MAS. Crosses were also made between marker-selected genotypes with fixed QTL for drought tolerance and insect resistance with farmer-selected germplasm. In sorghum, earlier research done by the International Centre for Research in the Semi-Arid Tropics (ICRISAT) in western Kenya and Mali had identified three QTLs from two independent mapping populations associated with Striga resistance in a resistant line, N 13. These QTLs that explain between 14 and 44% of the total phenotypic variation for Striga resistance are being introgressed through three backcross generations into locally adapted, farmer-preferred sorghum varieties. Molecular markers flanking these three QTLs are being used to select for Striga resistance. In both maize and sorghum, the benefits, if any, of marker-assisted selection as compared with conventional breeding are yet to be proved and verified at the small-scale farm level. |