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Evaluation of soybean nodule microbiome for biocontrol applications

Amitava Mitra: University of Nebraska

<div>Legume nodules are known to harbor a host of bacteria besides the Rhizobia. In an effort to identify beneficial bacteria for plant disease control we are studying soybean nodules as the source of these bacteria as our metagenomics analysis of a single soybean nodule identified a large number of diverse bacterial species. Surface sterilized single soybean nodule was used to isolate nodule associated bacterial species. A total of 569 colonies were tested individually against two bacterial and one fungal pathogens on solid media plates for inhibition of pathogen growth. From the initial screening, 56 colonies were selected based on significant growth inhibition of three selected plant pathogens. These colonies were further tested on three other bacterial and two fungal pathogens on solid plates. Fifteen colonies from these were also tested in tomato seedlings against two bacterial pathogens. Both soil and stem inoculation methods were used to infect tomato plants. Bacterial metabolites were extracted from 15 colonies with ethanol and ethyl-acetate and used to treat tomato seeds. Treated seeds was tested for resistance against two bacterial pathogens. Results show that many soybean nodule associated bacteria strongly inhibit growth of plant pathogens in both in vitro and in vivo assays. Furthermore, the treated plants grew better than untreated control plants. All 56 colonies are being identified by 16s RNA sequencing and MALDI-TOF assays. Efforts are being made to establish a cocktail of these bacteria that can be used for broad-spectrum disease management.</div>