marker-assisted selection in wheat - ictsd

396Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishprogramme cannot absorb the higher upfrontcosts associated with MAS, or thatit can absorb them only by forgoing otherpotentially profitable breeding projects), itmakes sense to choose conventional selection,because it generates the largest IRR.Implications for developingcountriesWhen discussing policy implications ofMAS efforts in developing countryscenarios, it is appropriate to consider theexperience gained over the past severaldecades, mainly in industrialized countries.In advanced countries, the private sectorhas made significant investments in MASefforts while there are a few publiclyfundedresearch groups using MAS inbreeding routinely and these are restrictedto a few target crops (Eagles et al., 2001;Dubcovsky, 2004; William, Trethowan andCrosby-Galvan, 2007). Information aboutthe traits and the breeding strategies usedin MAS applications in large agribusinessenterprises are not publicly available freely.To date, significant investments have beenmade in biotechnology applications onlyfor widely grown crop species such as rice,maize, wheat, soybean, cotton and canola.While GM crops and their implications arenot the focus of this chapter, it is reasonableto assume that technologies associated withGM crops offer significant potential foraddressing biotic and abiotic stress tolerancein widely grown cereals and legumes as wellas species that are important but thus farneglected such as tef, millets, yams and othertuber crops in the developing countries. Forexample, GM technologies that can makeone crop species perform better are likelyto be valuable with slight modificationsto enhance the performance of a neglectedcrop species. When useful GM varieties of aparticular crop are made available, they alsobecome prime candidates to apply MASbasedintrogression of the introduced geneconstruct/s to other well adapted cultivarsin different agro-ecological regions.Reports indicate that two rice varietieswith improved bacterial blight resistancehave been developed with MAS approachesand deployed in Indonesia (Toenniessen,O’Toole and DeVries, 2003). Moreover,rice varieties carrying multiple diseaseresistance genes are being developed byseveral national programmes with technicalbackstopping by the International RiceResearch Institute (IRRI) (Hittalmani etal., 2000). There are also reports describingthe use of MAS in China for improving certainquality traits in rice (Zhou, P.H. et al.,2003) and wheat (Zhou, W-C. et al., 2003)and fibre related traits in cotton (Zhang etal., 2003), but it is not clear whether theseare one-time research efforts or there iscontinued activity using MAS.Although it is not possible to obtainentirely reliable estimates of the costs,benefits and cost-effectiveness of MASapplications, the costs associated with MASare frequently considered as the main constraintto their effective use by many plantbreeders, especially in small- to mediumscalebreeding enterprises. However, newmarker technologies, especially thosebased on single nucleotide polymorphisms(SNPs) and associated ongoing large-scalegenome sequencing projects, should enablethe development and deployment of genebasedmarkers in the near future (Rafalski,2002). SNPs are defined as single base differenceswithin a defined segment of DNA atcorresponding positions. These SNP-basedpolymorphisms are known to be abundantlypresent in human as well as in plantgenomes. Consequently, the potential existsto develop SNP markers associated withmany important traits in a diverse array of