Abstract
Arbuscular mycorrhizal fungi (AMF) are a group of soil microorganisms that establish symbioses with most land plant species. “Root trap culture” generally has been used for isolating a single regenerated spore in order to establish a monospecific, native AMF line. Roots may be co-colonized with multiple AMF species; however, only a small portion of AMF within roots sporulate, and do so only under certain conditions. In this study, we tested whether young thalli (<2 mm) of the liverwort Marchantia paleacea harbour monospecific AMF, and can be used as a vegetative inoculant line. When M. paleacea gemmae were co-cultivated with roots obtained from the field, the young thalli were infected by AMF via rhizoids and formed arbuscules after 18 days post-sowing. Ribosomal DNA sequencing of the AMF-colonized thalli (mycothalli) revealed that they harboured phylogenetically diverse AMF; however, new gemmae sown around transplanted mycothalli showed evidence of colonization from phylogenetically uniform Rhizophagus species. Of note, mycothalli can also be used as an inoculum. These results suggest that the young thalli of M. paleacea can potentially isolate monospecific AMF from field soil in a spore-independent manner.
Highlights
The mutualistic relationship established by mycorrhizal fungi has a substantial impact on the nutrition, growth, and productivity of host plants [1,2,3]
To establish a method for the isolation of individual Arbuscular mycorrhizal fungi (AMF), we investigated the timing that would allow small thalli to be colonized by only a few AMF individuals at the early colonization stage
In the preliminary trials for setting up cultivation conditions enabling young M. paleacea thalli to be rapidly and uniformly colonized by AMF, we found that brightly-coloured soils enabled the thalli to grow up so as to leave from the soil, which eventually inhibited uniform AMF colonization
Summary
The mutualistic relationship established by mycorrhizal fungi has a substantial impact on the nutrition, growth, and productivity of host plants [1,2,3]. RDNA sequencing of AMF mycorrhizas has shown evidence of the coexistence of diverse species of the genus Glomus species in bluebell (Hyacinthoides nonscripta L.) roots, using family-specific primers, but found very few Glomus spores within the associated rhizosphere [18]. This indicates that the majority of AMF colonize roots in a vegetative manner [19,20], and that their functionality cannot be assessed by inoculation studies in a spore-dependent manner. Considering that roots inevitably host numerous AMF species, a smaller plant size (i.e., a lower cell number for colonization) may be more suitable for the isolation of a single AMF. AMF-colonized thalli (i.e., “mycothalli” [24]) can feasibly inoculate other plants
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