Like humans, Plants coexist with thousands of species of microorganisms. Étienne Yergeau, a researcher in microbial ecology at INRS, is trying to manipulate these tiny allies of plants to increase their positive effects tenfold.
Plant soil is teeming with life. In fields, one gram of soil contains billions of bacteria from around 10,000 different species and many other microorganisms. Without this microbiota, plants would not survive. “Over time, plants have delegated certain functions to the microbiota, such as defense against certain pathogens, resistance to stress or even aspects of their nutrition,” explains Étienne Yergeau.
With his team, he is studying ways in which the microbiota could be manipulated so that it can help improve the health and productivity of agricultural plants, particularly in the face of challenges such as environmental contamination or climate change. “The microbiota could, for example, provide the plant with nitrogen from the soil, which would reduce the need for fertilizers, or help the plant defend itself against certain diseases,” explains Mr. Yergeau.
Microscopic manipulations
Dispersion remains the most commonly used method to achieve this. It consists of adding new microorganisms to plants or in the soil, in order to modify the microbiota. These microorganisms are chosen for their particular beneficial properties, such as contributing to plant growth or defending against pathogens. It is a bit like adding probiotics to human food to improve health.
This solution remains complicated, because we do not know whether the microorganisms will survive in their new environment or whether they will have the expected effects. Research adopting other approaches is therefore being conducted in parallel, particularly in terms of selection. According to this method, rather than adding microorganisms to a microbiota, we choose some that are already there, and we try to increase their quantity, in order to increase their positive impacts tenfold.
“We do this by putting inputs into the microbiota that promote their multiplication,” says Mr. Yergeau. These can take the form of brewer’s grains, paper pulp, compost or manure. For example, the INRS team is trying to determine which microorganisms would help a plant resist stress induced by drought.
The research teams are also looking at speciation. In nature, microbes exchange bits of DNA through a process called horizontal gene transfer. The researchers want to use this process to modify the functions of certain microorganisms that are already associated with the plant.
“A bacterium could, for example, not be well adapted to live in the soil where a plant is found, but possess a piece of DNA that would be very useful to it,” illustrates Étienne Yergeau. “It could transfer this gene, and therefore the beneficial function, to another bacterium, which is very well adapted to the soil and the environment of the plant.”
Mysteries to be discovered
Étienne Yergeau points out that these processes are all natural. This is precisely one of the main goals: to promote more sustainable agriculture that is better adapted to its environment, while reducing the use of fertilizers and insecticides.
This aims to improve plant health, but also to increase crop productivity and quality. A must to meet the food needs linked to the growth of the world population. The Food and Agriculture Organization of the United Nations has also launched, in 2022, the International Day of Plant Health.
The fact remains that engineering the microbiota is not a simple matter, particularly because it is very diverse and the billions of bacteria and other microorganisms that compose it interact with each other. “We can modify a microbiota for a plant’s growing season, but it is very difficult to change it for the long term,” admits Étienne Yergeau.
Nor can we always be sure that the changes we induce will respond to future environmental conditions, which are difficult to predict. For example, if we try to obtain a microbiota that is extremely well adapted to drought conditions, but this year there is none, we could end up with a less efficient crop than if we had tried nothing.
“Currently, our understanding of the microbiota remains insufficient,” the researcher acknowledges. “To successfully manipulate it to obtain the results we want, we must first learn more about its composition and how it functions.”
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