Genome mapping of polyploid tall fescue (Festuca arundinacea Schreb.) with RFLP markers

Genetic mapping using molecular markers such as restriction fragment length polymorphisms (RFLPs) has become a powerful tool for plant geneticists and breeders. Like many economically important polyploid plant species, detailed genetic studies of hexaploid tall fescue (Festuca arundinacea Schreb.) are complicated, and no genetic map has been established. We report here the first tall fescue genetic map. This map was generated from an F2 population of HD28-56 by 'Kentucky-31' and contains 108 RFLP markers. Although the two parental plants were heterozygous, the perennial and tillering growth habit, high degree of RFLP, and disomic inheritance of tall fescue enabled us to identify the segregating homologous alleles. The map covers 1274 cM on 19 linkage groups with an average of 5 loci per linkage group (LG) and 17.9 cM between loci. Mapping the homoeologous loci detected by the same probe allowed us to identify five homoeologous groups within which the gene orders were found to be generally conserved among homoeologous chromosomes. An exception was homoeologous group 5, in which only 2 of the 3 homoeologous chromosomes were identified. Using 12 genome-specific probes, we were able to assign several linkage groups to one of the three genomes (PG1G2) in tall fescue. All the loci detected by the 11 probes specific to the G1 and/or G2 genomes, with one exception, identified loci located on 4 chromosomes of two homoeologous groups (LG2a, LG2c, LG3a, and LG3c). A P-genome-specific probe was used to map a locus on LG5c. Comparative genome mapping with maize probes indicated that homoeologous group 3 and 2 chromosomes in tall fescue corresponded to maize chromosome 1. Difficulties and advantages of applying RFLP technology in polyploids with high levels of heterozygosity are discussed.