marker-assisted selection in wheat - ictsd

Chapter 7 – Marker-assisted selection in common beans and cassava 109major traits of agronomic interest even ina subset of elite parents used for breedingis beyond the resources available for beanand cassava research. Association mappingand linkage disequilibrium mapping,which rely upon non-random associationof candidate genes or markers on a high resolutionmap with a phenotype of interestin a non-structured collection of genotypes,have been proposed as a way aroundthis problem. Association mapping can beused to discover new marker-trait associationsor to validate associations that werefound through conventional genetic mapping.The GCP is facilitating associationmapping of traits of agronomic importancein cassava and beans with the goal of discoveringmore useful markers for a widerrange of genotypes.The need to strike a balance betweenMAS and field-based selectionOccasionally the question is raised: whichis better, MAS or conventional selection?This very question betrays a falsedichotomy that hinders progress. By itself,MAS is seldom an adequate selection tooland therefore must be combined withconventional phenotypic selection. Theobjective should be to develop the optimalbalance between conventional and molecularbreeding, and the “best” balance willbe unique to each situation, crop, selectionscheme, environment and opportunities fordifferent selection methods. More emphasisis needed on combined selection systems,rather than viewing MAS as a replacementfor phenotypic or field selection.ReferencesAfanador, L.K. & Hadley, S.D. 1993. Adoption of a mini-prep DNA extraction method for RAPDmarker analysis in common bean. Bean Improv. Coop. 35: 10–11.Akano, A.O., Dixon, A.G.O., Mba, C., Barrera, E. & Fregene, M. 2002. Genetic mapping of a dominantgene conferring resistance to cassava mosaic disease. Theor. Appl. Genet. 105: 521–525.Asiedu, R., Hahn, S.K., Bai, K.V. & Dixon, A.G.O. 1992. Introgression of genes from wild relativesinto cassava. In M.O. Akoroda & O.B. Arene, eds. Proc. 4 th . Triennial Symp. Internat. Soc. Trop.Root Crops-Africa Branch, pp. 89-91. Nigeria, ISTRC-AB/IDRC/CTA/IITA.Awale, H.E. &. Kelly, J.D. 2001. Development of SCAR markers linked to Co-42 gene in commonbean. Ann. Rep. Bean Improv. Coop. 44: 119–120.Babu, L. & Chatterjee, S.R. 1999. Protein content and amino acid composition of cassava tubers andleaves. J. Root Crops .25: 163–168.Beaver, J.S., Rosas, J.C., Myers, J., Acosta, J., Kelly, J.D., Nchimbi-Msolla, S.M., Misangu, R.,Bokosi, J., Temple, S., Aranud-Santana, E. & Coyne, D.P. 2003. Contributions of the bean/cowpea CRSP to cultivar and germplasm development in common bean. Field Crops Res. 82:87–102.Beebe, S., Velasco, A. & Pedraza, F. 1999. Marcaje de genes para rendimiento en condiciones de altoy bajo fósforo en las accesiones de frijol G21212 y BAT 881. VI Reunião Nacional de Pesquisa deFeijão. Salvador, Brazil.Beebe, S., Skroch, P.W., Tohme, J., Duque, M.C., Pedraza, F. & Nienhuis, J. 2000. Structure ofgenetic diversity among common bean landraces of Mesoamerican origin based on correspondenceanalysis of RAPD. Crop Sci. 40: 264–273.Beebe, S., Rengifo, J., Gaitan, E., Duque, M.C. & Tohme, J. 2001. Diversity and origin of Andeanlandraces of common bean. Crop Sci. 41: 854–862.