When interspecific prezygotic barriers break down: hybridization between two Potamogeton species (P. wrightii and P. perfoliatus) and comparison of the artificial and natural hybrids

Interspecific hybridization played an important role in speciation and evolution of angiosperms. Although the widespread occurrence of natural hybrids in the genus Potamogeton has been studied intensively, few successful experimental hybridization studies have been reported in this genus. In the present study, critical experimental hybridization was conducted using Potamogeton?×?intortusifolius, a natural hybrid widely distributed in China, and its parents (P. perfoliatus and P. wrightii). The absence of prezygotic barriers between P. wrightii and P. perfoliatus was observed, which contributes to the frequent hybridization of these species in nature. The pollen tube growth rates of P. perfoliatus were much faster than those of P. wrightii in the style of that species. However, the conspecific pollen tubes were competitively advantageous in P. perfoliatus styles. The interspecific hybridization could be applied bidirectionally, and 28 F1 hybrid individuals were successfully obtained from P. wrightii?×?P. perfoliatus, despite the low germination possibility of the hybrid seeds. Both the artificial and natural hybrids exhibited intermediate morphological characters but presented much lower fertility. The sterility of P.?×?intortusifolius is mainly due to its low female fitness. However, the offspring from P. wrightii?×?P.?×?intortusifolius indicated the potential for backcrossing in nature. This is the most successful attempt at artificial hybridization in this genus so far. The possible route for restoration of fertility and the fitness of the hybrids are also discussed in this paper.