Two phosphate-solubilizing analogue-resistant mutants of Azotobacter chroococcum showed a positive interactive effect on sunflower (Helianthus annuus). Plant height, leaf area, seed mass, seed yield, protein and oil content increased significantly by inoculation with A. chroococcum mutants. Both levels of fertilizers applied (80N + 30P2O5 and 80N + 60P2O5 kg/hm2 showed increased seed yield. Likewise, inoculation resulted in a significantly higher yield. Application of P-solubilizing A. chroococcum strains with the lower fertilizer level showed no significant difference on plant growth parameters when compared with the higher fertilizer level, indicating that inoculation of P-solubilizing Azotobacter strains can reduce the necessary levels of fertilization from 60P2O5 to 30P2O5 kg/hm2.

Department of Microbiology Haryana Agricultural University Hisar 125 004 India

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