Triticum turgidum L. 6A and 6B recombinant substitution lines: extended linkage maps and characterization of residual background alien genetic variation

  Triticum turgidum L. var ‘durum’ cv ‘Langdon’-T. t. var ‘dicoccoides’ chromosome 6A and 6B recombinant substitution lines (RSLs) and a F₂ population derived from a ‘Langdon’-T. t. var ‘dicoccoides’ disomic chromosome 6A substitution lineבLangdon’ cross were analyzed with the objective of markedly increasing the number of markers assigned to and the resolution of previously constructed 6A and 6B linkage maps. Fifty-seven markers were added to the 6A RSL-population map, which now consists of 73 markers that span 111 cM, and 40 markers were added to the 6B RSL-population map, which now consists of 56 markers that span 123 cM. With the exception of 2 6B loci, all of the loci on the two RSL-population maps were ordered at a LOD score ≥3.0. Thirty-seven orthologous markers were mapped in the two chromosomes and colinearity between them is strongly indicated. The 6A RSL-population map and the F₂-population map are highly similar, indicating that the former population, which consists of 66 lines, can be reliably used for mapping, as was previously demonstrated for the 6B RSL population. In the absence of selection and genetic drift, the lines in a RSL population, except at loci in the substituted/recombined chromosome, should be near-isogenic. An unexpected finding was that at least 26 and possibly 29 of the RFLPs detected in the RSL populations (18% of the markers analyzed) are not located in the substituted/recombined chromosomes. Linkage analysis of the markers disclosed that at least 19 of them are located in six or seven segments that span approximately 10 cM and 17 cM of the genetic lengths of 6B and 6A, respectively, in the 6A and 6B RSL populations, respectively, a finding that suggests that 40 or more alien segments spanning 8–15% of the genetic length of the 13 unsubstituted chromosomes are present in both of the RSL populations. Alien alleles are fixed in many RSLs for most of the markers, in most cases at a frequency consistent with theoretical expectations. Highly distorted segregation favoring the alien allele was detected for all of the markers in 2 of the segments, however. Nine of the markers were among those mapped in the substituted/recombined chromosomes; the linkage data obtained for the other 10 was sufficient to assign them to approximate map positions. Received: 12 June 1997 / Accepted: 6 October 1997