Sporogenesis and offspring ploidy levels in hybrid Dryopteris ferns

In ferns, apomixis is an important mode of asexual reproduction. Although the mechanisms of fern reproduction have been studied thoroughly, most previous work has focused on cases in which ferns reproduce either exclusively sexually or exclusively asexually. Reproduction of ferns with potentially mixed systems and inheritance of apomixis remains largely unknown.

Three types of spores detected in the experimental plant E_KUR.
Three types of spores detected in the experimental plant E_KUR. Full details in Ekrt and Koutecký.

Ekrt and Koutecký use flow cytometry to assess genome sizes in offspring of pentaploid Dryopteris × critica, a hybrid of triploid apomictic D. borreri and tetraploid sexual D. filix-mas. The hybrid under study is partly fertile and shows unstable sporogenesis. Formation of aborted spores, well-developed reduced spores and unreduced diplospores was recorded in a single sporangium. The well-developed spores germinated in viable pentaploids (from unreduced spores) and half of that (∼ 2.5x) from reduced spores. They conclude that both sexual reduced and apomictic unreduced spores can be produced by a single sporangium and formed viable F2 generation.

Further reading

Ekrt, L., & Koutecký, P. (2015). Between sexual and apomictic: unexpectedly variable sporogenesis and production of viable polyhaploids in the pentaploid fern of the Dryopteris affinis agg. (Dryopteridaceae). Annals of Botany, 117(1), 97–106. http://dx.doi.org/10.1093/aob/mcv152