Hey readers!

This week we move from native Bacillus strains tested against Fusarium in Colombian strawberry fields, to a Pseudomonas hiding inside soybean nodules, purple bacterial biomass used as a nitrogen source, and a new three-strain bacteria inoculant targeting drought stress.

Four very different stories, but all showing just how many ways microorganisms can be selected, formulated and used in agriculture.

Let's dive in!

Researchers in Colombia screened 350 bacterial isolates from eight strawberry farms across two municipalities in Cauca looking for microorganisms capable of suppressing Fusarium oxysporum. Five Bacillus isolates stood out, all inhibiting the pathogen by around 80% or more in vitro, with the highest numerical inhibition coming from Bacillus nakamurai UCBF3 at 85.07%.

During liquid biomass production, however, the B. nakamurai strains produced a viscous biomass that was difficult to recover by centrifugation and difficult to homogenize into the formulation. Weighing biological performance against how easily each strain could be produced and formulated, the researchers took Bacillus thuringiensis UCBF2 and Bacillus subtilis UCBF11 to the field, at 84.95% and 79.72% inhibition. Both were formulated on talc with guar gum, powdered milk and yeast extract, and tested individually and together in strawberry at a single site in Sotará with three blocks.

After 90 days, the combined treatment produced the longest roots, reaching 11.67 cm, compared with 8 cm in the untreated control and 6.33 cm in plants given F. oxysporum alone. On the severity index the pathogen-only treatment reached 66%, against around 46% where the bacteria were applied.

In the rhizosphere microbiome after treatment, the relative abundance of F. oxysporum never exceeded 33% in soils receiving the bioinputs, against around 50% in the untreated control and 58% where the pathogen had been inoculated. The study does not establish that these changes caused the disease suppression, and the authors state that they did not investigate the antagonistic mechanisms or the metabolites behind the inhibition.

What the study offers is a view of a potential biological strategy for controlling F. oxysporum in strawberry, starting with native isolates selected in the laboratory and taking two of them through formulation and open field evaluation.

BioWorks has launched BioRain Ax, a liquid microbial inoculant designed to help crops perform under limited water conditions.

The product combines three bacteria: Priestia megaterium, Bacillus subtilis and Bacillus paralicheniformis. According to BioWorks, the microorganisms colonize the rhizosphere and help improve soil structure, water retention and nutrient availability, supporting a stronger and deeper root system.

What makes this product interesting is the way it has been positioned. Many microbial inoculants are sold around broad benefits such as plant growth, nutrient uptake and general stress tolerance. BioRain Ax is much more specific: its main agronomic target is water stress.

BioWorks has also reported results from a watermelon trial on 2.47 acres, with the product applied through drip irrigation at transplanting. Treated fruit came out around 14.5% heavier than the control, and the report presents the less cracking and the more uniform size as visual observations rather than measurements. No replication is stated.

BioWorks reports these results as an early indication of how the consortium may perform under field conditions. The product can be applied to the soil or through irrigation systems and is currently available in the United States, in all states except California.

Three microorganisms are combined and commercialized around one clearly defined field problem, helping crops make better use of limited water.

Researchers at RIKEN and Kyoto University grew the marine purple photosynthetic bacteria Rhodovulum sulfidophilum, lysed and dried the biomass, and tested whether that material could replace conventional nitrogen fertilizer on broccoli.

The dried biomass contained 11.0% nitrogen with a C/N ratio of 4.50, and it released that nitrogen gradually. In soil incubations it released around 68 to 72% over 30 days, against 95 to 99% for inorganic fertilizer. The field experiment therefore also included bacterial biomass applied at 1.5 times the standard nitrogen rate.

In the field, across two broccoli seasons at Kizugawa, growth and yield were broadly comparable to both organic and inorganic fertilizer treatments, while unfertilised plots produced significantly lower yields. It was a single site with three replicates per treatment.

The clearest difference appeared in nitrous oxide. In laboratory soil incubations at matched nitrogen rates the biomass emitted less N₂O than inorganic fertilizer at every measurement, 72.7% less on day 3 and 44.0% less by day 19, though these are incubation results rather than full season field measurements.

The authors conclude that processed bacterial biomass could serve as an alternative nitrogen source for vegetable production, combining slower nitrogen release with lower N₂O emissions than inorganic fertilizer under the conditions tested.

Southern blight can cost more than 40% of a soybean crop under favourable conditions, and it is hard to manage because Agroathelia rolfsii survives in warm, moist soils while the fungicides used against it bind to soil and spread unevenly.

Researchers at Virginia Tech went looking in an unusual place. Pseudomonas sp. JDE115 came from nodules on soybean, the structures normally sampled for rhizobia, and the same group had described it in an earlier paper before testing it here against the fungus.

In dual culture it suppressed fungal growth by 91.1%. In broth it stopped sclerotia from germinating altogether, and under the electron microscope those sclerotia showed partial collapse, with the outer rind thinned and its organised structure lost.

The strain works on several fronts: siderophores that lock up iron, protease, hydrogen cyanide, and antifungal volatiles, mainly 1-undecene and dimethyl disulfide. Pure 1-undecene applied at 100 µL almost completely suppressed the fungus.

In the greenhouse, control plants collapsed by day 15 while every treated plant stayed symptom-free. That test ran in steam-sterilised soil, so it did not measure JDE115 against an intact native soil microbiome, which the authors list alongside persistence and field validation as the next steps.

The curious part of this study is where the strain came from. A soybean nodule normally investigated for nitrogen-fixing rhizobia was also harbouring a bacteria with multiple mechanisms for suppressing a soilborne fungal pathogen.