A framework linkage map of bermudagrass (Cynodon dactylon x transvaalensis) based on single-dose restriction fragments

This study describes the first detailed linkage maps of two bermudagrass species, Cynodon dactylon (T89) and Cynodon transvaalensis (T574), based on single-dose restriction fragments (SDRFs). The mapping population consisted of 113 F1 progeny of a cross between the two parents. Loci were generated using 179 bermudagrass genomic clones and 50 heterologous cDNAs from Pennisetum and rice. The map of T89 is based on 155 SDRFs and 17 double-dose restriction fragments on 35 linkage groups, with an average marker spacing of 15.3 cM. The map of T574 is based on 77 SDRF loci on 18 linkage groups with an average marker spacing of 16.5 cM. About 16 T89 linkage groups were arranged into four complete and eight into four incomplete homologous sets, while 15 T574 linkage groups were arranged into seven complete homologous sets, all on the basis of multi-locus probes and repulsion linkages. Eleven T89 and three T574 linkage groups remain unassigned. In each parent consensus maps were built based on alignments of homologous linkage groups. Four ancestral chromosomes were inferred after aligning T89 and T574 parental consensus maps using multi-locus probes. The inferred ancestral marker orders were used in comparisons to a detailed Sorghum linkage map using 40 common probes, and to the rice genome sequence using 98 significant BLAST hits, to find regions of colinearity. Using these maps we have estimated the recombinational length of the T89 and T574 genomes at 3,012 and 1,569 cM, respectively, which are 61 and 62% covered by our maps.