Potato Growth Promotion Using an Ecological Phosphate Fertiliser Composed of the Phosphate-Solubilising Bacterium Pseudomonas rhizophila S211 and Natural Rock Phosphate

The use of mineral phosphorus solubilising (MPS) bacterial inoculants, alone or supplemented with rock phosphate (RP), supports sustainable agricultural development and food security. This study investigates the combined effect of the MPS plant growth–promoting bacterium Pseudomonas rhizophila S211 and natural RP on potato growth and yield. Several genes potentially responsible for converting the insoluble phosphorus form in the soil into a soluble form for plant uptake were identified in the S211 genome including an open reading frame encoding a membrane-bound pyrroloquinoline-quinone-dependent glucose dehydrogenase (PQQ_mGDH) and a putative pyrroloquinoline quinone (PQQ) biosynthetic operon (pqqABCDEF). Additionally, the P. rhizophila genome harbors resistance genes related to osmotic, alkaline and metallic stresses, suggesting that strain S211 has strong environmental adaptability and RP metal bioremediation potential. The strain S211 showed ability to solubilise tricalcium phosphate (220 μg mL⁻¹) and Gafsa RP (207 μg mL⁻¹) with a decrease in pH (from 7 to 4). The effect of bioinoculant-RP co-supplementation on potato growth was optimised in greenhouse trials on alkaline soil using a mixture design. The results were further validated under field conditions using a randomised complete block design. The highest potato yield (62.6% increase) was obtained with binary mixture fertilisation (S211 inoculation and rock phosphate supplementation) compared with sole RP amendment. Thus, the application of natural RP in combination with MPS plant growth–promoting bioinoculant could be recommended as an ecofriendly alternative to pollution creating and costly chemical fertilisers.