Patterns of morpho-phenological and genetic variation of Brachypodium distachyon (L.) P.Beauv. complex in Tunisia

The genus Brachypodium is generally considered taxonomically difficult because of the high levels of phenotypic variation and frequent hybridization between its species. In this study, the patterns of genetic variation of 180 lines of B. distachyon (B. distachyon, B Stacei and B. hybridum) collected from diverse regions in Tunisia were investigated using 18 morpho-phenological traits and 15 SSR markers. Our results showed that the polyploid species B. hybridum is the most abundant in Tunisia. Moreover, considerable morphological variation was revealed for the majority of analyzed traits. The variation was found to be more pronounced within B. hybridum, than its two progenitors. Importantly, we found that B. distachyon was characterized by early maturity, B. stacei differed from the two other species by plant height, whereas the allotetraploid species was mainly characterized by traits related to biomass production. At the molecular level, the fifteen SSR marker were found to be very informative in terms of polymorphism and allelic diversity (P = 100%, Na = 20.3 and Ne = 10.8). B. hybridum was found to be much variable than B. stacei and B. distachyon (He = 0.86, He = 0.78 and He = 0.58, respectively). FCA and Bayesian clustering showed a clear separation between the three species, which suggests the high usefulness of SSR markers used in our study in the delimitation between B. distachyon, B. stacei and B. hybridum.