b'Beyond BiologicalsFostering microbial communities is the new frontier in enhanced seed health. Madeleine Baerg, Director of Content, Seed World GroupLEVERAGING THE MICROBIOMEis an extremely excit- Its no different than your gut. So long as your gut is in bal-ing frontier in agriculture that will soon have huge ramifica- ance, that balance is extremely hard to disrupt, Dangl says.tions on plant resilience and productivity, especially aroundInterestingly, its not just foreign bacterial species that have climate change / extreme weather resilience and plant diseasetrouble making inroads into an existing community. Even spe-resistance. Researchers are currently just scratching the surfacecies of bacteria that are ultra-common in soilso common that of how critically important microbial populations are to plantone would think their population should be easy to support and health, resilience to various stresses and ultimate productivity.establishare, in fact, difficult to manipulate. However, big challenges need to be overcome to achieve whatFor example, much work has been conducted on finding couldhopefully soonbe huge gains.supernodulators: rhizobia mutants that produce more nodules We are at the very tip top of an iceberg. The microbiomeon legume roots and, correspondingly, fix more nitrogen. Strains is just as important to plant health as it is to human health, andof supernodulators have been isolated and introduced, yet even were only just starting to understand it even in human health,theydespite rhizobia already being a key player in soils exist-says Jeffrey L. Dangl, the John N. Couch distinguished professoring microbiomes balancehave a very difficult time finding a of biology and an investigator of the Howard Hughes Medicallong-term foothold in the bacterial community. Institute at the University of North Carolina at Chapel Hill.There was a study done in North Africa some time ago. TheThere are two basic paths to leveraging the microbiome: oneresearchers dipped seeds in various strains of rhizobia, then dug is manipulating the microbiome directly; the other is manipulat- up the resulting mature plants to look at the nodules. The oldest ing a plant to improve its ability to recruit and host beneficialnodules are closest to the top of the root. As they went down the bacteria.root looking at the nodules, they could tell the difference via PCR The key issue in anything adding to the microbiome, whetherof the rhizobia. They found the inoculant in usually about the first you apply them or you build a plant to recruit them, is that theyfour to six nodulesthe ones the plant produced earliestbut, have to be able to invade into a pre-existing community, andafter that, it was all a natural strain of rhizobia. That means the they have to be able to persist there, Dangl explains. Those twoinoculant strain had been pushed out of the community. So even thingsinvasion and persistenceare extremely difficult to do.though youre dunking these seeds in your strain of interest, that That, at least in my view, is the nub of the problem and the rate- strain is horribly inefficient in maintaining itself in the environ-limiting step of designing microbials or the plants that recruitment, Dangl says.them at least for now. Promoting PersistenceThe Challenge Currently, the research community is conducting early work on A typical bacterial community on plant roots consists oftwo critical areas that could help with the challenge of persis-between 100 and 300 bacterial species. On leaves, the bacte- tence, Jan Leach, the associate dean for research at Colorado rial population is typically made up of between about 30 andState Universitys College of Agricultural Sciences.150 species and their associated strains. There is huge varia- The first, she says, focuses on trading microbes. tion in the strains within any one of these species, making theFor example, some microbes synthesize chemicals that repel combined metagenome on the leaves or roots on a given plantother microbes; other microbes are helpers that synthesize cultivar extremely complex. The challenge is that these microbialchemicalsan amino acid or a sugar, for examplenecessary communities operate in balance. Unless a major event occursfor others in the community, Leach explains.that interrupts the balance, the communitys natural balanceManipulating the microbiome community itself is very dif-makes it highly resilient to invaders.ficult because these communities have evolved and adapted to 86/ SEEDWORLD.COMDECEMBER 2024'