Sequence variation at a microsatellite locus (XGWM261) in hexaploid wheat (Triticum aestivum) varieties

The wheat microsatellite XGWM261 is of interest to wheat breeders because of its linkage to a commercially significant reduced height gene (Rht8). Previous studies have indicated that there are three major alleles at the XGWM261 locus and that the majority (90%) of varieties are homozygous, generating PCR products of 192,174, or 165 bp. As a preliminary investigation of heterozygosity and sequence variation at the XGWM261 locus in Australian wheat varieties, we cloned and sequenced PCR products from 24 hexaploid varieties of significance in Australian breeding programmes. Three major alleles of 192, 174 and 164 bp were found, but a165 bp allele was not detected. Prior genotyping via electrophoretic methods had indicated that 2 of the 24 (8%) varieties were heterozygous. Our results indicate that 6 varieties (25%) carry 2 or more of the major alleles. It is not clear whether this results from heterozygosity within individual seeds, or from heterogeneity of breeding stocks. With respect to the microsatellite region itself, we found that the 174 bp and 164 bp alleles actually represent (CT)₁₁AG and (CT)₆AG motifs (respectively) rather than(CT)₁₂ and (CT)₇. This finding has diagnostic potential. A further 2 varieties also carry an interrupted (CT)_nCC(CT)_n microsatellite not previously recorded. It is unclear whether this represents a separate allelic lineage or is simply the result of replication error. This revised version was published online in July 2006 with corrections to the Cover Date.