Estimating paternal efficiency in an agamic polyploid complex: pollen stainability and variation in pollen size related to reproduction mode, ploidy level and hybridogenous origin in Pilosella (Asteraceae)

Abstract

Pollen quality was evaluated in Pilosella plants sourced from the field and representing various cytotypes (diploid to octoploid), reproduction modes (sexuality, facultative apomixis and seed sterility or semisterility) and status of origin (basic species, hybridogenous intermediate species and recent hybrids). Two methods of non-vital pollen staining were compared, providing a similar pattern of variation in pollen stainability and pollen size. A complex influence of ploidy level, reproduction mode and plant origin on pollen quality was found. Sexual biotypes had high and equable pollen stainability whereas apomictic and (semi)sterile plants were more variable in this trait. Nevertheless, the sexual, apomictic and (semi)sterile plants did not significantly differ in pollen stainability, while the impacts of both ploidy level and plant origin were significant. Apomictic triploids had low pollen stainability and heterogeneously sized pollen, most likely resulting from disturbed meiosis. The other biotypes, including higher odd-ploid cytotypes, displayed various patterns of pollen quality partially depending on the hybridogenous origin. Whereas high pollen quality was detected in most of the apomictic hexaploids and heptaploids, including recent hybrids, serious pollen dysfunction was found in most octoploids. Seed (semi)sterility was not strongly associated with reduced pollen quality. Either blocked or unstable pollen production was occasionally recorded, predominantly among recent hybrids. Despite autonomous apomixis independent of pollen, most apomictic biotypes displayed fairly high pollen stainability and pollen size homogeneity, implying sufficient production of viable reduced pollen. Most representatives of this agamic polyploid complex, including facultative apomicts, might efficiently mate as both male and female parents in natural populations.