Potential use of rock-phosphate-solubilizing bacteria associated with wild rice as inoculants for improved rice (Oryza sativa)

Abstract

A study was conducted to isolate P-solubilizing bacteria from the rhizosphere of three wild rice species and to test their ability to mobilize P from rock phosphate (RP). Inoculated seeds or seedlings of eight different strains were grown in soils supplemented with a P fertilizer mixture (PFM) consisting triple super phosphate (TSP) and RP, each providing equal amounts of P₂O₅. Crop growth, NaHCO₃-extractable P, crop P uptake and yield were compared with two uninoculated controls, with either TSP or PFM added. In the pot experiment, P availability varied from 20 to 48 mg P kg⁻¹ soil. Yields ranged between 4.8 and 6.6 g per pot and were not significantly different between treatments. In the field experiment, shoot P accumulation in inoculated and TSP-control treatments at the heading stage ranged between 79–129 mg and 219 mg per pot, respectively. Dual inoculants comprising Staphylococcus scirui, Bacillus pumilus, Bacillus subtilus and Bacillus cereus increased yield by about 29% over PFM-controls (324 g m⁻²) but those yields were 21% lower than TSP-controls (510 g m⁻²). Therefore, application of inoculants combined with PFM is not a viable alternative for TSP under the tested conditions because yield was limited by the P availability.

Keywords:

• P-solubilizing bacteria
• rock phosphate
• rice
• wild rice

Acknowledgements

We thank Mr A.S.U. Liyange, Plant Genetic Resource Centre, Gannoruwa, Peradeniya for providing information on the locations of wild rice, farm manager and the staff of the sub-campus, Mahailluppallama for maintaining field trials, Ms C.S. Gunarathne and Mr C. Ekanayake for technical assistance. The financial support was provided by the Council for Agricultural Research and Policy, Sri Lanka.