marker-assisted selection in wheat - ictsd

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Chapter 6 – Targeted introgression of cotton fibre quality quantitative trait loci using molecular markers 69INtroductionAmong the four species of Gossypium thatproduce seeds with spinnable fibres calledcotton, Gossypium hirsutum dominates theworld’s cotton fibre production, accountingfor approximately 90 percent of total worldproduction. The second most cultivated species,G. barbadense, includes superior extralong, strong and fine cottons. However,compared with G. hirsutum, the marketingadvantage of “high quality” G. barbadensecottons is offset by their lower productivityand a narrower adaptability to harshenvironments. Breeding approaches withinthese two species have essentially relied onhybridization and selection methods (subsequentto simple or complex crosses, apedigree system, sometimes combined withrecurrent selection, is applied). AlthoughG. hirsutum and G. barbadense displaycomplementary characteristics, attempts toutilize deliberate interspecific G. hirsutum/G. barbadense recombinations throughconventional breeding have had limitedimpact on cultivar development.In the past 10–15 years, DNA markersfor analyses of QTL and MAS have receivedconsiderable attention by plant and animalbreeders (Dekkers and Hospital, 2002).However, following an initial keen interestand promises for molecular-based breedingapproaches, the successful application ofthis technology has been shown to dependon the reliability and accuracy of the QTLanalyses, which in turn are strongly affectedby both population size and environmentalfactors (Schön et al., 2004). Examples ofapplied MAS in breeding programmes arestill scarce, particularly when complextraits (yield components, product quality)are under consideration.In the case of cotton, it is only recentlythat the results of efforts to gain a betterunderstanding of the genome and themolecular basis of fibre quality have beenpublished. Most of the earlier efforts incotton molecular breeding concentratedon interspecific hybridization, due to thefact that, intraspecifically, the major speciesG. hirsutum displayed a very lowlevel of molecular variability (Brubakerand Wendel, 2001). Based on studies ofinterspecific G. hirsutum x G. barbadensepopulations, published reports relate (i) tothe construction of high-resolution geneticmaps (Lacape et al., 2003; Rong et al.,2004); and (ii) to the identification of fibrequality-related QTL (Jiang et al., 1998;Kohel et al., 2001; Paterson et al., 2003;Lacape et al., 2005). In parallel, data haveaccumulated describing the cotton fibretranscriptome (reviewed by Wilkins andArpat, 2005). These studies confirmed thatkey fibre quality properties, such as length,fineness and strength, are controlled quantitatively,thus complicating conventionalbreeding for fibre improvement.Within the framework of a marker-assistedbackcross introgression scheme aimed attransferring fibre quality traits from a lowproductivityline of G. barbadense (donor)into a productive line of G. hirsutum (recipient),a saturated genetic map of tetraploidcotton was first developed (Lacape et al.,2003). This chapter describes how molecularmarkers were used in the early BC 1 and BC 2generations to identify QTL-rich regionsinvolved in determining fibre quality, asrecently reported by Lacape et al. (2005),and how MAS was actually implemented inthe later BC 3 and BC 4 generations.MethodologyThe major milestones (Figure 1) in themarker-assisted backcross selection processincluded the construction of two geneticmaps from the BC 1 and BC 2 populations,the detection of fibre quality QTL from
70Marker-assisted selection – Current status and future perspectives in crops, livestock, forestry and fishFigure 1Schematic representation of the marker-assisted backcross selection schemeG. hirsutum x G. barbadense(var. Guazuncho 2) (var. VH8 -4602)BC 1 generation:1160 loci (RFLP + SSR + AFLP)phenotypic data and QTL mappingNo selectionF 1 xBC 1 xG.hG.hBC 2 generation: 200 plants514 loci (SSR + AFLP)200 BC 2 + 200 BC 2 S 1 phenotypic data and QTL mappingNo selectionBC 2BC 2 S 1BC 3 x G.hxG.hBC 3 generation:411 plants with 35 SSR loci and43 plants with 340 AFLP lociMarker selectionBC 4 generation:450 plants with 50 SSR loci and 37 plants with 340 AFLP lociMarker and phenotypic selectionBC 4 x G.hBC 4 S 1BC 5PyramidingQTL - NILsthree phenotyping data sets (BC 1 , BC 2 andBC 2 S 1 ) and the actual marker-based selectionin the BC 3 and BC 4 generations, followedby the analysis of marker-trait associationsin the BC 3 and BC 4 generations.Plant materialThe initial interspecific cross involved theG. hirsutum variety Guazuncho 2 andthe G. barbadense variety VH8-4602.Guazuncho 2 is a modern pure lineG. hirsutum variety created in Argentina andwas chosen as a recipient in the backcrossgenerations for its good overall agronomicperformance. VH8-4602, a G. barbadensevariety of the Sea Island type, was thedonor parent for superior fibre quality, inparticular for length (+9 to +12 mm as comparedwith Guazuncho 2), strength (+12 to+16 g/tex) and fineness (-30 to -50 millitex);conversely its fibre colour indices (reflectanceand yellowness) are of lower value. 1The plant material used in the multigenerationQTL analyses included threepopulations: BC 1 , BC 2 and BC 2 S 1 (Lacapeet al., 2005). The first backcross generation(BC 1 ), consisted of 75 plants grownin a greenhouse in Montpellier (France)during the summer of 1999; these servedas female parents for the second backcrossto Guazuncho 2. Two hundred individualfield-grown BC 2 plants that had shown asatisfactory production of BC 3 seeds andoriginating from 53 different BC 1 plantswere used in 2000. Open pollinated seedsharvested from BC 2 plants were grown as200 BC 2 S 1 progenies in 2001 under fieldconditions in Brazil. Each BC 2 S 1 line was11 tex = 1 gram/kilometre
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iiiContentsAcknowledgementsForeword
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Section v - marker-assisted selecti
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viiForewordSince almost the beginni
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ixAbbreviations and acronymsAATFAB-
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xiFIVIMSFNPFSCFSILGABIGASGCAGCPGDPG
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xiiiOBMOECDOIEOPVPAGEPBRsPCRPGRFAPI
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xvContributorsAmalia BaroneProfesso
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xviiElcio Perpétuo GuimarãesSenio
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xixAndrea SonninoSenior Agricultura
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Chapter 1Marker-assisted selection
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Chapter 1 - An overview of the issu
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Section VMarker-assisted selectioni
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Chapter 19Technical, economic and p
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This book provides a comprehensive
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