Onion is one of the most important vegetable crops in China, yet its yields and quality are increasingly threatened by severe soil salinization and by frequent outbreaks of basal rot driven by intensive farming and continuous cropping. However, effective, environmentally friendly measures that address both problems remain scarce.
A team led by Xueping Li at the Institute of Plant Protection, Gansu Academy of Agricultural Sciences, set out to build a microbial consortium that degrades salt and alkali, controls basal rot, and promotes onion growth. Their starting point was the soil itself. From the rhizosphere of diseased onion plants in Jingtai County, Gansu Province, they isolated 20 salt- and alkali-degrading strains. Two of them, LAB2 and LAB3.2, tolerated both 10% NaCl and pH 10.0, and in liquid culture LAB3.2, LAB2 and MX38 lowered alkalinity by 12.3–17.6%, while SYP202, LAB2, MFL22 and MX50 reduced salt content by 10.61–19.26% after 72 hours.
The researchers then combined the most promising isolates with biocontrol and plant-growth-promoting properties from the Culture Collection of Biocontrol and Plant Growth-Promoting Strains for Specialty Crops in Gansu Province established by their team, plate confrontation assays were performed to ensure that no member antagonized another. Of the three candidate consortia assembled, the one designated A3 performed best: it released 99.13 mg/L of potassium, fixed 0.225 g/L of nitrogen, produced 39.54 siderophore units and 10.66 mg/L of indole-3-acetic acid, and inhibited Fusarium oxysporum, the dominant basal rot pathogen, by 95.15%. The consortium comprised Staphylococcus sciuri LAB2, Exiguobacterium acetylicum LAB3.2, Bacillus velezensis MP6, B. halotolerans SYP202, and Trichoderma harzianum M3. An orthogonal design then established the optimal ratio of M3: LAB3.2: LAB2: MP6: SYP202 as 9: 9: 3: 7: 5. In pot experiments, onion seedlings inoculated with the pathogen and then treated with the A3 consortium showed a control efficacy of 73.3% against basal rot. Soil pH fell by 0.5 units and soluble salt concentration dropped by 44.46 mS/cm, and treated plants were taller, with thicker stems and longer roots than untreated controls.
"Onion fields on salt-affected soils need a solution that works on two fronts at once, because the disease and the soil problem are not separate," said Xueping Li, corresponding author for the team. "What surprised us was that two salt- and alkali-tolerant strains we isolated from the rhizosphere could be combined with a fungal biocontrol agent and two Bacillus strains without losing either function. Compatibility, not just individual performance, turned out to be decisive in the final formulation."
The team published these findings in Microbiology China in 2026.
The next step is to move from pots to fields. The current results come from a single cultivar and a single isolate of the pathogen under controlled conditions; performance under variable field salinity, native microbial communities and real irrigation regimes remains to be tested. The team is also examining how the consortium reshapes the rhizosphere microbiome and soil nutrient status across a full growing season, and is working on a stable, scalable fermentation process for regional biofertilizer production.
"Onion growers in Gansu and across the northwest need products that are affordable, stable and easy to apply," Li said. "A consortium like this one only matters if it can be produced consistently and still works in a farmer's field. That is the work ahead of us."
This work was supported by the Fourth Batch of Longyuan Young Talent Program of Gansu Province and the Joint Venture Project (GYLS-2026-Y001).
