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Polyploidy is widely recognized as a major mechanism of sympatric speciation in plants, yet little is known about its effects on interactions with other organisms. Mycorrhizal fungi are among the most common plant symbionts and play an important role in plant nutrient supply. It remains to be understood whether mycorrhizal associations of ploidy-variable plants can be ploidy-specific. We examined mycorrhizal associations in three cytotypes (2x, 3x, 4x) of the Gymnadenia conopsea group (Orchidaceae), involving G. conopsea s.s. and G. densiflora, at different spatial scales and during different ontogenetic stages. We analysed: adults from mixed- and single-ploidy populations at a regional scale; closely spaced adults within a mixed-ploidy site; and mycorrhizal seedlings. All Gymnadenia cytotypes associated mainly with saprotrophic Tulasnellaceae (Basidiomycota). Nonetheless, both adults and seedlings of diploids and their autotetraploid derivatives significantly differed in the identity of their mycorrhizal symbionts. Interploidy segregation of mycorrhizal symbionts was most pronounced within a site with closely spaced adults. This study provides the first evidence that polyploidization of a plant species can be associated with a shift in mycorrhizal symbionts. This divergence may contribute to niche partitioning and facilitate establishment and co-existence of different cytotypes., (© 2013 The Authors. New Phytologist © 2013 New Phytologist Trust.)

Background and Aims: One of the prerequisites for polyploid research in natural systems is knowledge of the geographical distribution of cytotypes. Here inter- and intrapopulational ploidy diversity was examined in the Gymnadenia conopsea aggregate in central Europe and potential explanations and evolutionary consequences of the observed spatial patterns investigated., Methods: DAPI flow cytometry supplemented by confirmatory chromosome counts was used to determine ploidy in 3581 samples of the G. conopsea aggregate from 43 populations. The fine-scale spatial pattern of cytotype distribution (intra- and interploidy associations) was analysed with univariate and bivariate K-functions., Key Results: Gymnadenia tissues undergo a progressively partial endoreplication, which accounts for about 60 % and 75 % of the total genome in G. conopsea and G. densiflora, respectively. Flow cytometric profiles are therefore species-specific and can be used as a marker for rapid and reliable species recognition. Two majority (4x, 8x) and three minority (6x, 10x, 12x) cytotypes were found, often in mixed-ploidy populations (harbouring up to all five different ploidy levels). The scarcity of the minority cytotypes (about 2·7 %) suggests the existence of strong pre- or postzygotic mating barriers. Spatial structure was observed in plots of populations with the highest cytotype variation, including clumping of individuals of the same ploidy and negative association between tetra- and octoploids., Conclusions: The remarkable ploidy coexistence in the G. conopsea aggregate has reshaped our perception of intrapopulational ploidy diversity under natural conditions. This system offers unique opportunities for studying processes governing the formation and establishment of polyploids and assessing the evolutionary significance of the various pre- and postzygotic mating barriers that maintain this ploidy mixture.

The genus Reynoutria is represented by four taxa in the Czech Republic: Reynoutria japonica var. japonica, R. japonica var. compacta, R. sachalinensis and R. xbohemica. By using flow cytometry, cytological variability within the genus is described based on 257 Reynoutria samples. The varieties of R. japonica are cytologically uniform, var. japonica is exclusively octoploid (2n = 8x = 88) and var. compacta occurs only as a tetraploid (2n = 4x = 44), but R. sachalinensis and R. xbohemica exhibit some variation in chromosome numbers. Reynoutria sachalinensis is predominantly tetraploid (2n = 4 x = 44), but also occurs occasionally as hexaploid and octoploid cytotypes. The most common ploidy level in R. xbohemica is hexaploid (2n = 6x = 66), but tetraploid and octoploid clones were also found. The four taxa occurring in the Czech Republic are described briefly and the possible origins of the cytotypes discussed.