MOLECULAR PHYLOGENY OF THE GRASS GENUS BRACHYPODIUM P-BEAUV BASED ON RFLP AND RAPD ANALYSIS

Nuclear genome analysis using RFLPs and RAPDs has been assessed within different species of the genus Brachypodium P. Beauv. and representat ives of other grasses in order to determine the characteristics of the Brachypodium genome and to establish its evolutionary position in rel ation to other Pooideae. Distinctive features of the Brachypodium geno me are its small size, the low amount of repetitive DNA, the lack of r estriction fragment length polymorphisms within the genus for the assa yed probe/enzyme combinations, and the genomic variability demonstrate d at species level by random DNA amplification. These molecular studie s confirm Brachypodium as an isolated ancient genus best placed in its own tribe (Brachypodieae). Its relationships to other tribes-Bromeae, Triticeae, Poeae-are resolved, Brachypodieae being the earliest tribe to diverge from this core of pooids. Within the genus two major Old W orld clades are distinguishable: an annual clade, represented only by B. distachyon; and a perennial clade, represented by all the other spe cies studied (except B. mexicanum). The perennial American species B. mexicanum appears equally attached to these two clades. RFLP data were found to be useful in obtaining phylogenies at generic and higher ran k levels, whereas the highly variable RAPD data were more suitable for resolving interspecific and intraspecific evolutionary pathways.