marker-assisted selection in wheat - ictsd

Chapter 18 – Marker-assisted selection in crop and livestock improvement 367IntroductionThe tremendous advances made in molecularmarker techniques in the past twodecades have led to increased understandingof the genetic basis of many agriculturaltraits in a variety of plant and animal species.The use of these techniques has alsomade it possible to accelerate the transferof desirable traits among varieties and tointrogress novel genes from related wildspecies.DNA markers have many advantagesover conventional approaches available tobreeders. They are especially advantageousfor traits that are otherwise difficult to tag,such as resistance to pathogens, insects andnematodes, tolerance to abiotic stresses andquality parameters. They offer great scopefor improving the efficiency of conventionalbreeding by carrying out selectionnot directly on the trait of interest but onlinked genomic regions. Additionally thesemarkers are unaffected by environmentalconditions and are detectable during allstages of growth (Mohan et al., 1997).Molecular marker techniques have thereforemoved beyond their early projectedrole as tools for identifying chromosomalsegments and genes to uncovering manypossibilities for easing the transfer of genesinto desired cultivars and lines. MAS generatedgreat enthusiasm as it was seen as amajor breakthrough, promising to overcomemany limitations of conventionalbreeding processes (FAO, 2003). However,despite advances in the theory of MAS,direct utilization of the information it providesfor selecting superior individuals withcomplex traits is still very limited (Young,1999; Ferreira, 2003). Nevertheless, thereis still optimism about the contributionsof MAS, which is now balanced by therealization that genetic improvement ofquantitative traits using this tool may bemore difficult than previously considered(FAO, 2003). In 1999, Young reviewed thedevelopment of MAS, analysing in detailits main drawbacks, many of which remaintoday. He concluded that because MAStechnology was so challenging it should notbe a reason for discouragement but, instead,reason for more ingenuity and better planningand execution.Recent developments in high-throughputgenotyping, single nucleotide polymorphism(SNP) and the integration of genomictechnologies are advances that will play animportant role in the development of MAS asan effective tool for sustainable conservationand increased use of crop genetic resources(Ferreira, 2006). However, research teams,funding agencies, commodity groups andthe private sector will need to work togetherto develop MAS technology further andensure that breeders have the best availabletools. Also, the tools and strategies willneed to go beyond markers themselves toinclude genome-based knowledge derivedfrom model systems, high-throughput costeffective technology, as well as better technologiesand strategies for handling largevolumes of information.The purpose of this chapter is to discussthe access to and utilization of MAStechnology by breeding programmes,with special emphasis on strategies to helpstrengthen research capacity and partnershipsin developing countries. Wheneverpossible, recommendations are presentedto help guide decisions that may contributeto enhancing the access and successful useof MAS by national programmes.Perceptions about the use of MASin Crop and Livestock ImprovementAs MAS is still an evolving technology,there are not many detailed studies availabledescribing the state-of-the-art of its