The evolution of the hexaploid grass Zingeria kochii (Mez) Tzvel. (2n=12) was accompanied by complex hybridization and uniparental loss of ribosomal DNA

In the grass tribe Poeae a small group of taxa occur with an exceptionally low chromosome number of 2n = 2x = 4 belonging to the closely related genera Colpodium and Zingeria. To understand the formation of polyploids in this group we analyzed the evolution of allohexaploid Zingeria kochii (2n = 12) and its presumable ancestral species. Genomic in situ hybridization demonstrated that Z. kochii evolved from an interspecific hybrid involving species closely related to contemporary Z. biebersteiniana (2n = 4) and Colpodium versicolor (2n = 4) and a third unknown species. Following allopolyploidization of Z. kochii the biebersteiniana-like parental chromosomes underwent loss of ribosomal DNA. No interlocus homogenization of 45S rDNA took place in Z. kochii and phylogenetic analysis showed that C. versicolor contributed its genome to Z. kochii relatively recently. In situ hybridization was particularly effective in understanding the allopolyploid evolution in Zingeria while the analysis of ITS sequences alone would have resulted in a wrong interpretation of the allopolyploid history of the genus.