SYNERGISTIC EFFECT OF ARBUSCULAR MYCORRHIZA AND PHOSPHATE SOLUBILIZING BACTERIA ON WHEAT GROWTH AND PHOSPHORUS ACQUISIION UNDER FIELD CONDITIONS

ABSTRACT
Two field experiments were conducted on distinct soil types, sandy and loamy, to assess the impact of phosphate-solubilizing bacteria (PSB) Azospirillum brasilense and Bacillus subtilis, applied individually or in combination with the arbuscular mycorrhizal (AM) fungus Glomus sp., on phosphorus (P) acquisition from low-bioavailability sources (rock phosphate, RP) and the yield of wheat (Triticum aestivum var. Sakha 94). The experimental design included two blocks: one inoculated with AM fungi and one without. Each block was subdivided into eight treatments, comprising four bacterial inoculation (non-inoculated control, individual strains, and their mixture) and two fertilizer treatments (control and RP application at 77.5 kg P₂O₅ ha⁻¹). Shoot dry weight was measured at the vegetative stage, while P uptake and yields of straw and grains were recorded at ripening. Soil available P and alkaline phosphatase activity were analysed after harvest. Results demonstrated that combined inoculation with bacterial strains and AM fungi significantly enhanced straw and grain yields compared to single inoculations or controls, in both soil types. However, plant responses varied with soil texture and nutrient status. In sandy soil treated with RP, the highest straw yields (7.03 and 7.00 ton ha⁻¹) were achieved with A. brasilense or B. subtilis combined with AM fungi, while the highest grain yield (3.97 ton ha⁻¹) was observed with B. subtilis plus AM fungi. In loamy soil, the greatest straw and grain yields (21.79 and 9.80 ton ha⁻¹) were recorded with A. brasilense plus AM fungi. Combined inoculations also improved P uptake in straw and grains relative to non-inoculated or singly inoculated treatments. Notably, the increase in alkaline phosphatase activity and available soil P was greater in sandy soil than in loamy soil, highlighting the stronger stimulatory effect of AM fungi under nutrient-deficient conditions.