Abstract
Plants that produce dust seeds can recruit fungi to meet their earliest requirements for carbon and other nutrients. This germination strategy, termed initial mycoheterotrophy, has been well investigated among the orchid family, but there are numerous other plant lineages that have independently evolved mycoheterotrophic germination strategies. One of these lineages is the tribe Pyroleae (Ericaceae). While the fungi associated with mature plants in Pyroleae have been fairly well documented, their mycobionts at the germination and seedling stages are largely unknown. Here, we use an in situ seed baiting experiment along with molecular fingerprinting techniques and phylogenetic tests to identify the fungi associated with seedlings of two Pyroleae species, Pyrola chlorantha and Orthilia secunda. Our results indicate that similar to adult plants, Pyroleae seedlings can associate with a suite of ectomycorrhizal fungi. Some seedlings harboured single mycobionts, while others may have been inhabited by multiple fungi. The dominant seedling mycobiont of both Pyroleae species was a fungus of unknown trophic status in the order Sebacinales. This taxon was also the only one shared among seedlings of both investigated Pyroleae species. We discuss these results juxtaposed to orchids and one additional Pyrola species in the context of ontogenetic shifts in fungal host specificity for mycoheterotrophic nutrition.
Highlights
Dust seeds have evolved independently in at least 12 plant families (Eriksson & Kainulainen 2011)
Based on the analysis of ITS sequences described above, we identified a diversity of fungi from the order Sebacinales associating with multiple seedlings of each Pyroleae species
Additional Sebacinales clade B fungi from P. asarifolia adult plants as well as seedlings collected in Japan (Hashimoto et al 2012) and Austria (Weiß et al 2004) are included in our phylogeny, but do not fall within the same subclade as Sebacinales 1 from this study (Fig. 2)
Summary
Dust seeds have evolved independently in at least 12 plant families (Eriksson & Kainulainen 2011). Owing to their lack of carbohydrate reserves, all dust seeds are dependent on an external carbon source for germination (Eriksson & Kainulainen 2011). A subset of the plant families that produce dust seeds meet their carbon demands via symbiotic associations with fungi. This form of nutrition is referred to as initial mycoheterotrophy (Leake 1994). While some plant species are only ini-.
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