Cytogenetic and linkage studies with translocations in soybean [Glycine max (L) Merr]
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The availability of comprehensive genetic linkage maps is of considerable advantage to plant breeders and geneticists as linkage maps reveal linkage relationships among marker genes. Reciprocal translocations are important for assigning linkage groups to chromosomes and for verifying the independence of linkage groups. Isolation of a complete tester set of translocations in soybean is a prerequisite for making maximum use of translocations. The objectives of this study were to (1) cytologically verify the independence of seven soybean translocations, (2) verify whether classical genetic linkage groups 6 and 8 are the same or different, and (3) determine the location of the breakpoints in the KS172-11-3, KS175-7-3, and Clark T/T translocations in relation to mutants of linkage groups 6 and 8. Fourteen F1 progeny from intercrosses of six translocations were analyzed cytologically. The KS172-11-3, KS175-7-3, and Clark T/T translocations were crossed to the same genetic marker types and segregation data from F2 and F2:3 families grown at the Bruner Farm near Ames, Iowa, were analyzed. Cytological analyses confirmed that the six lines were true translocations, and that six of the 20 chromosomes were involved in reciprocal translocations. KS172-11-3, KS175-7-3, and Clark T/T shared one chromosome in common, while PI 189866, KS171-31-2, and L75-0283-4 shared a different chromosome in common. Recombination values showed that Df2 and Y11 of linkage group 6 were linked. Y11 showed loose linkage or may be independent of linkage group 8 loci and the translocation breakpoints, except in Clark T/T where it is linked to the breakpoint. However, Df2 was linked to Ms1 and the breakpoint in Clark T/T. Ms1 was closely linked to the breakpoints while the other loci showed loose linkage or were independent of the breakpoints. Our linkage data suggest that the translocation breakpoint is between Df2 and Ms1, that linkage groups 6 and 8 are the same linkage group, and that the translocated chromosomes in the three translocations are identical. This information will enhance genetic linkage mapping.