ORIGIN OF HIGHLY POLYPLOID SPECIES: DIFFERENT PATHWAYS OF AUTO- AND ALLOPOLYPLOIDY IN 12-18X SPECIES OF AVENULA (POACEAE)

Polyploidy belongs to the most striking factors in plant evolution. To address the role of allo- versus autopolyploid speciation in natural polyploids, we studied species of the oatlike genus Avenula, which contains diploids and polyploids with up to 22x valence. We conducted DNA sequence analyses of plasmid-cloned ITS repeats of nuclear ribosomal (nr) 35S DNA, complemented by cytogenetic studies including fluorescence in situ hybridization (FISH) with nr and satellite (sat) DNAs in 12–18x polyploid species from SE Europe and Asia Minor. Altogether, four different ITS repeat types are involved in their parentage. One is confined to Avenula armeniaca and the second shared between A. armeniaca and Avenula blaui, none of which is known from extant diploid species. The latter repeat type is characteristic of A. blaui but prevails also in one of the A. armeniaca accessions, as a result of hybridization and/or genetic introgression with an ongoing process of sequence change in favor of A. blaui repeats. The two...