Genome size discriminates between closely related taxa Elytrigia repens and E-intermedia (Poaceae : Triticeae) and their hybrid

Flow cytometric and karyological investigations were performed on the closely related taxa Elytrigia repens and E. intermedia (Poaceae: Triticeae) from the Czech Republic. DNA-hexaploids clearly prevailed among 238 examined plants and amounted to 96.2% of all samples. 2C-values +/- s.d. for hexaploid Elytrigia repens and E. intermedia were estimated at 23.27 +/- 0.20 pg and 27.04 +/- 0.24 pg respectively. Genome size thus allowed reliable separation of the two species (difference ca. 16%) as well as the identification of hybrid individuals. Natural hybridization in E. repens - E. intermedia alliance seems to be quite a common phenomenon as indicated from a large proportion (one sixth) of hexaploid samples with intermediate 2C-values. Previously, the crosses were most probably overlooked or misidentified due to their weak morphological differentiation. New nonaploid cytotypes (2n=9x=63) were revealed for both species as well as for the hybrid (determined on the basis of morphological characters only), representing the first records from the field. Fusion of unreduced and reduced gametes of the hexaploids is the most plausible mode of nonaploid origin.