Molecular phylogeny of the grass genusBrachypodiumP. Beauv. based on RFLP and RAPD analysis

Abstract

Nuclear genome analysis using RFLPs and RAPDs has been assessed within different species of the genusBrachypodiumP. Beauv. and representatives of other grasses in order to determine the characteristics of theBrachypodiumgenome and to establish its evolutionary position in relation to other Pooideae. Distinctive features of theBrachypodiumgenome are its small size, the low amount of repetitive DNA, the lack of restriction fragment length polymorphisms within the genus for the assayed probe/enzyme combinations, and the genomic variability demonstrated at species level by random DNA amplification. These molecular studies confirmBrachypodiumas 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 World clades are distinguishable: an annual clade, represented only byB. distachyon;and a perennial clade, represented by all the other species studied (exceptB. mexicanum). The perennial American speciesB. mexicanumappears equally attached to these two clades. RFLP data were found to be useful in obtaining phylogenies at generic and higher rank levels, whereas the highly variable RAPD data were more suitable for resolving interspecific and intraspecific evolutionary pathways.