marker-assisted selection in wheat

Chapter 6 – Targeted introgression of cotton fibre quality quantitative trait loci using molecular markers 77Figure 3Graphical genotypes (26 chromosomes) of a BC 1 plant (No. BC1/16) (upper panel) and of twoselected BC 4 plant (Nos. BC 4 /104 and BC 4 /419) (lower panel) derived from itBC 1/16c25 c16 c23topc26A01topA01botc3topc4c3botc6c23botc20A03BC 4 /104 BC 4/419c25 c16 c23topc25c26A01botc6c23botA03The two possible allelic forms, homozygous Gh/Gh and heterozygous Gh/Gb, are denoted in dark grey and black respectively.Regions in black are introgressed with G. barbadense alleles. Light grey areas indicate portions of unknown alleliccomposition. Boxed areas represent the localization of QTL-rich regions localized on 15 carrier chromosomes shown to theleft (11 non-carrier chromosomes are shown to the right). Arrows indicate the regions totally or partially introgressed.Fibre characteristics of BC 3 and BC 4generation plantsOwing to the limited number of individualsand the unbalanced frequenciesof genotypic classes in the BC 3 and BC 4material, significant marker-trait associationswere less frequent than observedfrom the BC 1 and BC 2 data. For example,markers mapped along five, nine and sixchromosome regions contributed (P=0.01),respectively, to length, strength or finenessvariation using BC 4 marker-trait data,as compared with 15, 12 and 21 from theBC 1 and BC 2 data (Table 2). However,the majority of significant associations,particularly those determined in the BC 4generation, were observed within previouslydetected regions (not shown). Usingfibre strength as an example, out of the eightstrength QTL-harbouring regions on chromosomesc3bot, c5, c16, c23sup, c23bot,c25, A01 and A03 identified from the combinedBC 1 and BC 2 data (Table 3), theBC 4 data confirmed significant marker-traitassociations in five of these regions, i.e. formarkers mapped on chromosomes c3bot,