Locating the w1 Locus on the Satellite Chromosome in Soybean1

Abstract

F2 data of field‐grown plants of a cross between translocation 172‐11‐3 (purple flower, W1) and type collection line T93A (white flower, w1) of soybean [Glycine max (L.) Merr.] revealed a significant deviation from the expected ratio of 3 purple: 1 white. To determine the cause(s) of the abnormal ratio, the chromosome number and constitution of the F2 progenies of another cross involving 172‐11‐3 and T161 (white flower) were determined. Translocation 172‐11‐3 has cytologically recognizable interchange chromosomes, and the short interchange chromosome was present as a univalent in 46% of the pollen mother cells (PMCs) in interchange heterozygotes. Sixty‐five percent of the F2 progeny were disomics of the N/N, N/T, and T/T types, 18% were trisomics, 16% were 40‐chromosome plants with a duplication‐deficiency gamete, and 1% were 42‐chromosome plants. Assuming that the univalent was lost in the cytoplasm 50% of the time, the observed number of N/N and N/T plants fit the expected, but the number of T/T did not. A recombination frequency of 1.9% between w1 and the breakpoint was calculated. The F2 data of duplex trisomic hybrids indicated that the w1 locus was on the satellite chromosome. The breakpoint on the long arm of the satellite chromosome is distal to the w1 locus. Our data indicated no linkage between the breakpoint and the genes y10 (chlorophyll deficiency) and t (pubescence color).