marker-assisted selection in wheat - ictsd

Chapter 6 – Targeted introgression of cotton fibre quality quantitative trait loci using molecular markers 75Table 3Identification of the 19 targeted regions mapped on 15 different chromosomes and comprising oneor several co–localized fibre quality QTL from G. barbadense for introgression into a G. hirsutumgenetic backgroundCarrier chromosomeChromosomelength(cM)Target interval(cM)Target size(cM)Traitc14 197 28–57 29 Lengthc3 153 32–67 35 Length, fineness90–138 48 Length, strength, finenessc4 190 102–118 16 Finenessc22 139 112–139 27 Finenessc5 360 78–101 23 Strengthc6 296 137–144 7 Length, finenessc25 183 44–73 29 Length, strengthc16 168 65–117 52 Strength, fineness, colourc23 173 45–66 21 Strength (elongation –, colour –)113–135 22 Length, strengthc10 192 0–21 21 Fineness78–120 42 Length, fineness, colourc20 268 88–161 73 Elongation, finenessc26 195 67–143 76 Length (colour –)A01 233 16–54 38 Length171–209 38 Strengthc18 158 32–46 14 FinenessA03 271 209–234 25 Strength, uniformityTotal 3176 Total 636Note: All targeted QTL show a positive contribution from the G. barbadense allele, except for a few negative cases indicatedin brackets. The target region is defined as situated between the two loci flanking the QTL peak LOD value at a one LODconfidence interval.along chromosome 3 for QTL for fibrestrength and fineness, and chromosome 23for QTL for fibre strength and length.The chromosome regions carryingco-localized QTL (corresponding to asingle or to several traits measured on asingle or on several populations) whosepositive alleles derived from the G. barbadensedonor genome, were reduced to19 QTL-rich regions that were carriedby 15 different “carrier” chromosomes(Table 3). Altogether, the confidence intervals(one LOD) of the involved QTL-richregions delimited a total length of 636 cM(20 percent of the carrier genome), or11.5 percent of the total genome (Table 3).Eleven non-carrier chromosomes weredevoid of positive QTL, or harboured negative(positive alleles derived from the G.hirsutum alleles) QTL.MAS in the BC 3 and BC 4 generationsand allelic transmission throughoutgenerationsThe early selection of BC 3 and BC 4 plantsusing SSR markers that framed the 19 targetedregions of interest made it possibleto choose those plants that showed anallelic constitution with as many introgressedloci within the targeted regions aspossible. In total, 43 BC 3 plants out of 411(11.4 percent) and 37 BC 4 plants out of 450(8.2 percent) were retained based upon theinformation provided by the markers, i.e.without any phenotypic selection at thisstage. These plants were backcrossed to therecurrent parent (and self-pollinated in thecase of the BC 4 plants).The allelic transmission observed in thefour groups of BC 4 derived from fourdifferent BC 1 plants is given in Table 4.