USE OF RECOMBINANT SUBSTITUTION LINES IN THE CONSTRUCTION OF RFLP-BASED GENETIC MAPS OF CHROMOSOMES 6A AND 6B OF TETRAPLOID WHEAT (TRITICUM-TURGIDUM L)

RFLP-based genetic maps of chromosomes 6A and 6B of Triticum turgidum have been constructed using data obtained by the study of Triticum tur gidum var 'durum' cv 'Langdon'-T. t. var 'dicoccoides' recombinant sub stitution lines (RSLs) supplemented with data obtained from F-3 famili es derived from 'Langdon'-dicoccoides 6A and 6B disomic substitution l ines. The average RFLP frequencies detected for the two chromosomes in a test of 45 DNA clones with six restriction enzymes were 56% and 53% , respectively, and a subset of 32 clones gave frequencies of 75% and 72%, respectively. Seventeen loci were mapped in 6A and 18 in 6B. With the possible exception of 5 loci in the centromeric region of 6A, all of the mapped 6A and 6B loci are located in the same arm as are homol ogous loci in hexaploid wheat, and the linear order of the loci is the same in the two chromosomes, except possibly close to the centromere. Major differences in genetic distances exists between homologous loci located in the proximal regions of the 6AL and 6BL linkage groups, ho wever, the distances being much larger in the former than in the latte r. The 6B maps that were constructed using data from both the RSL and the F-2 populations and using data from the RSL population alone close ly resemble one another, indicating that the 6B RSL population, compos ed of 85 lines, can be reliably used for genetic mapping. Additional s tudies must be conducted before the utility of the 6A RSL population, composed of 66 lines, can be adequately assessed.