b"BEYOND BIOLOGICALS FOSTERING MICROBIAL COMMUNITIES IS THE NEW FRONTIER IN ENHANCED SEED HEALTH.BY: MADELEINE BAERG, DIRECTOR OF CONTENT, SEED WORLD GROUPL everaging the microbiome is an extremely exciting frontier inroots and, correspondingly, fix more nitrogen. Strains of supernod-agriculture that will soon have huge ramifications on plantulators have been isolated and introduced, yet even theydespite resilience and productivity, especially around climate change /rhizobia already being a key player in soils existing microbiomes extreme weather resilience and plant disease resistance. Researchersbalancehave a very difficult time finding a long-term foothold are currently just scratching the surface of how critically importantin the bacterial community. microbial populations are to plant health, resilience to various stressesThere was a study done in North Africa some time ago. The and ultimate productivity. However, big challenges need to be over- researchers dipped seeds in various strains of rhizobia, then dug come to achieve what couldhopefully soonbe huge gains.up the resulting mature plants to look at the nodules. The oldest We are at the very tip top of an iceberg. The microbiome is justnodules are closest to the top of the root. As they went down the as important to plant health as it is to human health, and were onlyroot looking at the nodules, they could tell the difference via PCR of just starting to understand it even in human health, says Jeffrey L.the rhizobia. They found the inoculant in usually about the first four Dangl, the John N. Couch distinguished professor of biology andto six nodulesthe ones the plant produced earliestbut, after an investigator of the Howard Hughes Medical Institute at thethat, it was all a natural strain of rhizobia. That means the inoculant University of North Carolina at Chapel Hill.strain had been pushed out of the community. So even though you're There are two basic paths to leveraging the microbiome: one isdunking these seeds in your strain of interest, that strain is horribly manipulating the microbiome directly; the other is manipulatinginefficient in maintaining itself in the environment, Dangl says.a plant to improve its ability to recruit and host beneficial bacteria. The key issue in anything adding to the microbiome, whetherPROMOTING PERSISTENCEyou apply them or you build a plant to recruit them, is that theyCurrently, the research community is conducting early work on two have to be able to invade into a pre-existing community, and theycritical areas that could help with the challenge of persistence, Jan have to be able to persist there, Dangl explains. Those two thingsLeach, the associate dean for research at Colorado State Universitysinvasion and persistenceare extremely difficult to do. That,College of Agricultural Sciences.at least in my view, is the nub of the problem and the rate-limitingThe first, she says, focuses on trading microbes. step of designing microbials or the plants that recruit them atFor example, some microbes synthesize chemicals that repel least for now.other microbes; other microbes are helpers that synthesize chemi-calsan amino acid or a sugar, for examplenecessary for others THE CHALLENGE in the community, Leach explains.A typical bacterial community on plant roots consists of betweenManipulating the microbiome community itself is very dif-100 and 300 bacterial species. On leaves, the bacterial populationficult because these communities have evolved and adapted to one is typically made up of between about 30 and 150 species and theiranother. But we're beginning to understand that you might be able associated strains. There is huge variation in the strains within anyto substitute one microbe for another to fulfill a necessary chem-one of these species, making the combined metagenome on theical pathway, she says, which would therefore make the invader leaves or roots on a given plant cultivar extremely complex. Thebacteria more attractive to the existing community.challenge is that these microbial communities operate in balance.Another avenue of research is syn-comms: synthetic bacterial Unless a major event occurs that interrupts the balance, the commu- communities. Where one bacteria might not be able to break into nitys natural balance makes it highly resilient to invaders.an existing community, a whole purpose-built community might It's no different than your gut. So long as your gut is in bal- have a stronger chance at invasion and persistence.ance, that balance is extremely hard to disrupt, Dangl says. One of the things that people are exploring is, can we make Interestingly, its not just foreign bacterial species that havea synthetic community? Can we put the microbes together, if we trouble making inroads into an existing community. Even speciesunderstand what it takes for them to survive and colonize in that of bacteria that are ultra-common in soilso common that onecommunity, in that environment? Leach says. would think their population should be easy to support and establishEven if a syn-comm cant ever be engineered to adequatelyare, in fact, difficult to manipulate.establish itself in a real-world setting, the fundamental knowledge For example, much work has been conducted on finding super- gained from this research will lay the groundwork for major future nodulators: rhizobia mutants that produce more nodules on legumesteps forward. 20ISEED WORLD EUROPEISEEDWORLD.COM/EUROPE | FEBRUARY 2025"