A favorable linkage combination in the soybean

Very little information is available on linkage between desirable genes in the soybean [Glycine max (L.) Merr.]. The cultivars Douglas and Tracy-M carry different alleles for resistance to phytophthora rot (caused by Phytophthora megasperma Drechs. f. sp. glycinea Kuan and Erwin), and are tolerant to the widely used herblcide metribuzin [4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one]. If genes controlling these traits are linked, selection efficiency could be increased when cuitivars having these genes in coupling phase are used in crosses. The objective of this study was to verify this linkage and determine recombination frequencies. A soybean breeding line was used in reciprocal crosses with Douglas and Tracy-M. The F3 lines from these crosses were evaluated for reaction to hypocotyl inoculations with P. megasperma and to a 125μgL−1 concentration of metribuzin in a hydroponic system. Similar segregation ratios from reciprocal crosses indicated little or no cytoplasmic effects in reaction to either the pathogen or herbicide. The results indicate that the alleles Rpsl in Douglas and Rpsl-b in Tracy-M are closely linked with Hm, with recombination estimates of 5 percent and 6 percent, respectively.