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There has been very little effort to incorporate foliar microbiomes into plant conservation efforts even though foliar endophytes are critically important to the fitness and function of hosts. Many critically endangered plants that have been extirpated from the wild are dependent on regular fungicidal applications in greenhouses that cannot be maintained for remote out-planted populations, which quickly perish. These fungicides negatively impact potentially beneficial fungal symbionts, which may reduce plant defenses to pathogens once fungicide treatments are stopped. We conducted experiments to test total foliar microbiome transplants from healthy wild relatives onto fungicide-dependent endangered plants in an attempt to mitigate disease and reduce dependency on fungicides. Plants were treated with total microbiome transplants or cultured subsets of this community and monitored for disease severity. High-throuhgput DNA screening of fungal ITS1 rDNA was used to track the leaf-associated fungal communities and evaluate the effectiveness of transplantation methods. Individuals receiving traditionally isolated fungal treatments showed no improvement, but those receiving applications of a simple leaf slurry containing an uncultured fungal community showed significant disease reduction, to which we partially attribute an increase in the mycoparasitic Pseudozyma aphidis. These results were replicated in two independent experimental rounds. Treated plants have since been moved to a native habitat and, as of this writing, remain disease-free. Our results demonstrate the effectiveness of a simple low-tech method for transferring beneficial microbes from healthy wild plants to greenhouse-raised plants with reduced symbiotic microbiota. This technique was effective at reducing disease, and in conferring increased survival to an out-planted population of critically endangered plants. It was not effective in a closely related plant. Plant conservation efforts should strive to include foliar microbes as part of comprehensive management plans.
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Supplemental figures and code
Fig S1 - Community similarity vs. infection load; Fig S2 - NMDS of donor and recipient communities; Fig S3 - Barcharts of taxonomic profiles; Code used to generate figures from raw data; Clustal alignment of pathogen with voucher specimen; Permanova tables
Interesting and important study! It's too bad there wasn't an autoclaved (or otherwise sterilized) slurry treatment to parse out possible effects of slurry biochemistry vs the effects of living foliar endophytes to increase disease resistance. I'm thinking about all of the phytochemicals that are also present in that slurry.
Thanks for the feedback. We actually performed exactly the experiment you suggest (0.2 um filtered slurry) to test the phytochemical aspect. This was reported in the 2nd paragraph of the Methods section.