Chlorpyrifos- and Carbofuran-Tolerant Phosphate-Solubilising Arthrobacter oxydans and Bacillus flexus Improved Growth and Phosphorus Content in Potato in Pesticide-Amended Soils

Phosphate-solubilising bacteria are an important component of sustainable agriculture but their number and performance are reduced due to the presence of pesticides in soils. The potato requires a high amount of phosphorus making it a fertilizer-demanding crop. Therefore, the present study was conducted with the aim to develop pesticide-tolerant phosphate-solubilising bacterial inoculants for improving growth and phosphorus content in potato. Phosphate-solubilising bacteria were isolated from potato rhizosphere and screened for pesticide tolerance, phosphate solubilisation in the presence of pesticides and growth promotion of potato in pesticide-amended soils. Nineteen phosphate-solubilising bacteria isolated from potato rhizosphere showed phosphate solubilisation ranging from 115 to 747 µg ml⁻¹ with significant difference among the isolates. Out of 19 isolates tested for tolerance against two commonly used pesticides in potato, two isolates showed tolerance up to 7.5 μl ml⁻¹ (3 times the recommended dose) of chlorpyrifos and 0.75 g ml⁻¹ (2 times the recommended dose) of carbofuran. These two pesticide-tolerant bacterial isolates also showed phosphate-solubilisation in the presence of chlorpyrifos and carbofuran, although the phosphate-solubilising ability decreased significantly with increased pesticide concentrations. The isolates were identified as Arthrobacter oxydans PR₁PSB₂ and Bacillus flexus PR₂PSB₁ based on phenotypic features, biochemical tests, and matrix-assisted laser desorption/ionisation-time of flight mass spectroscopy (MALDI-TOF–MS). The bacterial treatments Arthrobacter oxydans PR₁PSB₂ and Bacillus flexus PR₂PSB₁ alone or in combined application exhibited a significant increase in the growth parameters, phosphorus (P) content, and soil available P over the uninoculated control under greenhouse conditions in potato in the presence of pesticides. However, the plant growth promotion and P content decreased with an increase in pesticide concentrations. Pesticide-tolerant phosphate-solubilising Arthrobacter oxydans and Bacillus flexus from potato are reported for the first time.