Inheritance and linkage with the k2 and Mdh1-n loci in soybean

Abstract

Mutants for tan saddle seed coat (k2), for yellow foliage (y20), and for malate dehydrogenase [EC 1.1.1.37] 1 null (Mdh1-n) have occurred both separately and concurrently in soybean [Glycine max (L.) Merr.]. This study examines their relationships by testing allelisms, inheritance, and recombination among them. Isoline L67-3483 and genetic type T239 are tan saddle seed coat (k2) mutants, and genetic type T261 is a tan saddle seed coat (k2) and malate dehydrogenase null (Mdh1-n) mutant. Soybean accessions USDA PI 567.391 and PI 567.630A are two Mdh1-n mutants. Inheritance studies indicated that the three k2 mutants were allelic end the three Mdh1-n mutants were allelic. Both k2 and Mdh1-n were inherited as single nuclear recessive alleles. PI 567.630A was homozygous for a chromosome translocation. No linkage was detected between the k2 locus and the translocation breakpoint in PI 567.630A. An approximately 1 ± 1.36% recombination rate between k2 end Mdh1-n was detected in the coupling phase in the crosses of T261 (k2 Mdh1-n) with wild type in about 5,400 F2 plants. In the repulsion phase, however, no recombinants with tan saddle seed and Mdh1-n phenotypes were identified in 3,210 F2 plants from crossing T239 (k2) or L67-3483 (k2) with PI 567.630A (Mdh1-n). These observations indicated that k2 and Mdh1-n are two closely linked loci separated by approximately 1 ± 1.36 cM.