marker-assisted selection in wheat - ictsd

390Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishor laboratory-based phenotypic selectionmethods. When perfect markers are availableto screen for a particular trait, suchmarkers are preferred. However, for traitsthat cannot be screened conveniently usingtraditional approaches and even when perfectmarkers are not available, if markers areavailable with close linkages to the trait(s)of interest, these can be used to increasethe desirable allele frequency for the targetgene. MAS-related activities in both wheatand maize at CIMMYT are conductedas collaborative projects involving bothbreeders and biotechnologists. The breedersuse information coming from wheat MASactivities to define better their parentalcrossing block materials and to make selectivecrosses using parents identified bymarkers. Moreover, segregating early generationprogenies in certain crosses areselected in the field based on whole plantphenotype, which are then further refinedby sampling leaf tissue from field-taggedplants and processing for MAS assays in thelaboratory. Only those entries that containthe target genes identified with MAS areadvanced to the next generation. This enablesbreeders to reduce population sizes forthe traits under evaluation and accumulatecertain gene combinations in elite backgrounds.The material thus generated isadvanced through several cycles of selfingand eventually used in field screening toidentify the best performing lines.Economics of MASEstablishing the capacity to conductMASFor MAS to be a viable option for a plantbreeding programme, adequately equippedlaboratory facilities must be in place andappropriately trained scientists must beavailable. Therefore, one of the first decisionsfacing research managers consideringMAS is whether to invest in biotechnologyresearch capacity.Economic theory suggests that the mostefficient level of research investment canbe determined with the help of a researchproduction function that relates researchinputs to research outputs. At the nationallevel, the research production function canbe thought of as a meta-function encompassingthe frontiers of many smallerfunctions, each representing a differentlevel of research capacity distinguished bycomplexity and scope (Figure 1) (Brennan1989; Byerlee and Traxler, 2001; Maredia,Byerlee and Maredia, 1999; Morris et al.,2001). Movement outwards along themeta-function, accomplished by addingsubprogrammes and thereby increasingthe number of researchers and the extentof available research infrastructure, is associatedwith changes in focus and increasesin the capacity of the national researchprogramme.For a plant breeding programme, addingnew biotechnology-based subprogrammesis equivalent to taking a series of discretesteps involving increased complexityand cost. These steps have the effect ofmoving the programme from one level ofresearch capacity to the next. These levelsof research capacity can be broadly characterizedas follows:• Biotechnology product user. Here, theresearch programme imports germplasmproducts developed using biotechnologyand incorporates them into its conventionalcrop improvement schemes, eitherby backcrossing them into local germplasmor by testing them for potentialimmediate release.• Biotechnology tools user where theresearch programme imports biotechnologytools and uses them, ifnecessary, after adapting them to local