Genetic and physical analysis of a single Festuca pratensis chromosome segment substitution in Lolium perenne

Molecular marker analysis and genomic in situ hybridisation (GISH) were use d to examine the process of chromosome segment introgression in BC2 diploid hybrids (2n=2x=14) between Lolium perenne and Festuca pratensis. Two genot ypes having what appeared to be the same, single, introgressed chromosome s egment of F. pratensis in the L. perenne background were crossed with diplo id L, perenne to produce a recombinant series for the introgressed region. Physical and genetic analysis of this series showed that, while recombinati on seemed to be possible at all points along the chromosome arm, the rate o f recombination varied depending on relative position: more recombination w as detected in the interstitial region as compared with the centromeric or telomeric regions. The implications of these results for the use of GISH an d molecular marker analysis in the measurement of linkage drag in backcross breeding programmes is discussed.