Residual sexuality of the apomict Pilosella rubra under natural conditions in the Krkonoše Mts

Because of residual sexuality, a maternal facultatively apomictic plant is able to produce more than just apomictic progeny. The production of such non-apomictic progeny has been studied in open-pollinated Pilosella rubra, a hexaploid species of hybridogenous origin. The mixed-species population was studied in montane grasslands in the Krkonoše Mts (the Sudetes). Progeny from achenes that were collected in the field were grown (2800 plants) and their DNA ploidy level was determined. Based on maternal/progeny comparisons regarding ploidy level and morphology, most of the progeny was formed apomictically (91.0%), while the remainder (9.0%) consisted of trihaploids and various hybrids. In previous garden crossing experiments, the residual sexuality of P. rubra was 11.9%, not significantly different from the value found in the present study. Most of the hybrid progeny grown from seeds originated from a conjugation of parental reduced gametes (n+n hybrids) except for the octoploid hybrid of P. rubra with any of the tetraploid taxa (2n+n hybrid). The range of variation in DNA content within particular progeny categories/cytotypes reflected the origins of the progeny. Examination of the species/cytotype composition of the population from which the achenes of P. rubra were collected, revealed hybrids of P. rubra established in the field and identified the co-occurring Pilosella species, some of which were the putative paternal parents of these hybrids. Based on a combination of morphology and ploidy level, hybrids of hexaploid P. rubra with the following Pilosella species were identified there: the tetraploid P. officinarum (hybrid P. ×stoloniflora, pentaploid, hexaploid and octoploid plants, one of the hybrid plants was a somatic mosaic (4x+8x)), the diploid P. lactucella (tetraploid hybrid), the tetraploid P. floribunda (pentaploid hybrid) and the tetraploid P. iserana (pentaploid hybrid). The facultatively apomictic P. rubra readily hybridizes as a maternal parent under field conditions, especially in species-rich populations. The progeny arising from these interspecific crosses increases the population diversity and may affect the evolution of such populations.