Testing for Linkage between the Rxp Locus and Nine Isozyme Loci in Soybean

Abstract

Chromosome mapping studies are needed in soybean [ Glycine max (L.) Merr.] to identify the 20 linkage groups. The objective of this research was to identify isozyme loci linked to the Rxp locus. Bacterial pustule of soybean is caused by Xanthomonas campestris pv. glycines . Soybean lines homozygous for the rxp allele are resistant, while the Rxp allele conditions susceptibility to the bacterial disease. Nine isozyme loci were tested for linkage to the Rxp locus. Starch gel electrophoresis analysis was used to assay for the isozymes. The Linkage‐1 computer program was used to estimate recombination distances. On the basis of 650 F 2 plants from reciprocal crosses of ‘Clark 63’ × PI 437477B, a percentage recombination estimate of 15.18 ± 3.81 was obtained with the Rxp locus and a malate dehydrogenase variant. This represents a new linkage group (Linkage Group 20) in soybean. All other linkage tests gave independent assortment.