Microsatellite analysis of wheat chromosome 2D allows the reconstruction of chromosomal inheritance in pedigrees of breeding programmes

The dwarfing gene Rht8 and the photoperiodic insensitivity gene Ppd-D1 are linked on the short arm of chromosome 2D of bread wheat and play an important role in determining the geographic adaptation of modern wheat varieties. The genes are believed to originate from the old Japanese variety 'Akakomugi' and have been distributed throughout the world by diverse breeding programmes. Twelve microsatellite loci previously mapped on wheat chromosome 2D were used for a retrospective analysis of 59 wheat varieties with known pedigree, to trace the transmittance of the chromosomal region around these genes during extended breeding programmes. Within the range of the screened varieties 100 alleles were detected at the 12 microsatellite loci. For each microsatellite locus, a screen over varieties was performed to find the alleles corresponding to the parental variety 'Akakomugi'. A comparison of wheat varieties carrying the 192-bp allele, at locus Xgwm261-2D which is diagnostic for the presence of the gene Rht8, with the varieties without Rht8, showed linkage disequilibrium of 'Akakomugi' alleles for a segment of chromosome 2D which comprised at least 28 cM. Selection was accompanied with a linkage drag of 'Akakomugi' alleles in the neighbouring loci to Rht8. A diminution of the segment of chromosome 2D originating from 'Akakomugi' during several pedigree generations was observed. Varieties of the early generations were found to carry the whole short arm of chromosome 2D of 'Akakomugi', while the varieties of further selections possessed smaller segments including the diagnostic allele at locus Xgwm261-2D. Our results demonstrate that microsatellites can be successfully used for studying the inheritance of chromosomes within pedigrees of breeding programmes.