Plants can prepare soils to give other plants protection against pests

It’s known that microbes in the soil can help plants fight pests. Now research published in New Phytologist shows that plants can be used to create anti-pest microbiomes. These collections of microbes can be introduced to new soils, where they can give other plants protection. “Ecologically-based strategies are needed to improve the sustainability of our agricultural systems, and our study emphasizes that the soil is a key component,” write Ana Pineda and colleagues in their paper.

One of the stories of the last decade has been increasing understanding of how microbes in the soil can help prime plants to defend against pathogen and herbivore attack. Pineda and colleagues have followed the research, but when you’re working with a few microbial strains, results can be inconsistent. “An alternative approach is to focus on the complete microbiome,” write the authors. “Several authors have argued that the introduction of more complex soil communities, rather than single species/strains, is necessary to achieve consistent enhancement of crop protection, but so far, evidence of resistance against herbivores either triggered by such microbiome or by a single microbial strain functioning in a complex microbial community, is scarce.”

The team set out to get some of that evidence by using plants to create a beneficial microbiome. The experiment was to use some plants to shape a microbiome that would confer protection to another plant when the microbiome was transferred.

They used a mix of four grass and four forb species to create a microbial community in soil that had benefited chrysanthemum in earlier experiments. Effectively, the team used the plants to farm the microbes for them. Next, they needed to find if these microbes, and not the plants, were aiding chrysanthemums in fighting off herbivores.

Pineda and colleagues sterilised some soil and then introduced soil with the prepared microbiomes to colonise the new soil. They had In chrysanthemums in the soil that should now have had increased protection from herbivore attack. To find out if this was the case, they introduced some thrips, Frankliniella occidentalis, and spider mites, Tetranychus urticae, to attack the chrysanthemums. 

Results were positive but mixed.

“The number of thrips on chrysanthemum plants was strongly reduced by soil inoculation. Fewer thrips were observed on plants growing in soil conditioned by the grass AP and the forb RA, than on plants growing in sterilized soil. The functional group of the plants that conditioned the inocula, however, did not affect the number of thrips on chrysanthemum,” write Pineda and colleagues.

However, the soil did not help the plants defend against spider mites. In addition, the chrysanthemums also set to work altering the microbiome, just as the forbs and grasses used to create the test samples. They also found that the forbs were more helpful in creating beneficial communities than grasses.

Despite the mix of results, the team say that the work shows the proof of concept. The next steps will be to see how to get more predictable results. “A major challenge is how to select conditioning plants that create beneficial soil microbiomes that consistently reduce pests and promote plant growth, within the context of highly diverse and variable soil microbiomes,” Pineda and colleagues conclude. “Hence, the “holy grail” in research on microbiome-induced plant resistance is to find plant species that modify the soil microbiome in a predictable and desirable way.”