Natural hybridization between Elymus repens and Elymus hispidus assessed by AFLP analysis

Hybrid speciation within the genus Elymus is analyzed and discussed. The supposed hybrid origin of Elymus x mucronatus between Elymus repens and Elymus hispidus was tested. In this aim, pollen viability and AFLP variation of putative progenitors and progenies from two natural populations were studied. Pollen fertility of hybrids ranging from 0 to 91.95% (average 59.50%) indicates the occurrence of F1 hybrids and backcross hybrids. Seven EcoRI/MseI AFLP primer combinations generated a total of 477 AFLP fragments (300 polymorphic) for 48 parental and hybrid individuals. UPGMA and principal coordinates analysis of the AFLP data set show that hybrids are closer to E. hispidus than to E. repens and suggest unidirectional introgression towards E. hispidus. AFLP fragments of the hybrid taxon were additively inherited from the parental species and no hybrid-specific bands were identified. AFLP analysis validates the hybrid status of E. ×mucronatus. Populations in which E. repens, E. hispidus and their hybrids co-occur still progress from early hybridization stages of F1 hybrids to an advanced hybridization stage of a well-established hybrid swarm. E. ×mucronatus is potentially self-sustaining by predominant vegetative reproduction by rhizomes and partial fertility leading to the development of mature seeds. We propose to consider Elymus ×mucronatus as a new species of hybrid origin in the Polish flora.