Patterns of genetic variation in Pilosella echioides and its selected relatives: results of variation in ploidy level, facultative apomixis and past and present hybridization
Abstract
We used allozymes to elucidate the genetic variation of Pilosella echioides and P. rothiana in the Pannonian Basin and its relationship with morphology and modes of reproduction. The former species consists of sexual diploid, apomictic tetraploid, and very rare sexual tetraploid populations; the latter is exclusively tetraploid and apomictic.
As expected, we detected the highest intra-population variation in diploid populations of P. echioides. Nonetheless, 73 % of populations of tetraploid P. echioides and 64 % of P. rothiana consisted of 2-7 multilocus allozyme genotypes, the means being 5.75 in P. echioides and 2.64 in P. rothiana.
Both the proportion of distinguishable genotypes (G/N) per population and genotype diversity (D) per population significantly differed between diploid P. echioides (means 0.415 and 0.828, respectively) on the one hand and tetraploid P. echioides (means 0.252 and 0.387, respectively) and P. rothiana (means 0.213 and 0.347, respectively) on the other. Rather surprisingly, we found an excess of homozygotes (positive F (IS)) in diploids, which indicates inbreeding.
Tetraploids of P. echioides have most likely originated from only a few polyploidization events and have spread thanks to agamospermy-at least populations from the NW part of the area under study seem to be monophyletic. Genetic differences within the putatively hybridogeneous species P. rothiana are small.
It seems plausible that it has a common origin and that it spreads independently of its parents (P. echioides and P. officinarum). A certain level of genetic diversity can be caused by residual sexuality or less likely by repeated polytopic hybridization between P. echioides and P. officinarum.
Pilosella sterrochaetia is reported here from Hungary for the first time. It is an extremely rare primary diploid hybrid between diploid P. echioides and P. leucopsilon.
Its intermediate nuclear genome size also confirms its hybrid origin.