Microsatellite high-density mapping of the stripe rust resistance gene YrH52 region on chromosome 1B and evaluation of its marker-assisted selection in the F-2 generation in wild emmer wheat

A new stripe rust resistance gene, YrH52, derived from the unique Mount Her mon population of wild emmer wheat (Triticum dicoccoides) in Israel, was pr eviously located on chromosome 1B. The main objectives of the present study were to increase marker density in the vicinity of the YrH52 gene using ad ditional microsatellite markers, and to evaluate the accuracy and efficienc y of marker-assisted selection on this gene in the F-2 generation. By means of 70 additional microsatellite primer pairs, 150 individuals of the F-2 m apping population were genotyped. Among 202 marker loci, 20 were found to b e linked to the YrH52 gene with log-likelihood (LOD) scores ranging from 3. 84 to 58.82, and linkage distances ranging from 0.33 to 41.39 cM. A genetic map was constructed of chromosome 1B, consisting of 23 markers and the YrH 52 gene, with a total map length of 149.5 cM. Most of the markers were loca ted in the region close to YrH52, which was flanked by Xgwm413 and Xgwm273a with map distances of 1.3 and 2.7 cM, respectively. The accuracy and effic iency of marker-assisted selection were calculated as AMAS and EMAS, respec tively, for homozygous resistant genotypes of YrH52 gene in the F-2 generat ion. AMAS and EMAS for homozygous resistant genotypes of the YrH52 gene in the F-2 generation showed linear and significant negative correlation with the map distance between marker and target gene or between the two bracketi ng markers. It was concluded that the YrH52 region on chromosome 1B is sign ificantly more enriched by microsatellite markers than the previously publi shed map; that a single microsatellite marker is efficient for marker-assis ted selection of homozygous resistant genotypes of YrH52 gene in the F-2 ge neration when the map distance is < 5.0 cM; and that when two markers are u sed AMAS can be dramatically improved and becomes relatively stable, wherea s EMAS will not be obviously improved and will still vary linearly with map distance.