Solubilization of iron and calcium phosphates by soil fungi isolated from coffee plantations

Abstract

Almost 900 fungal isolates were obtained from eight coffee plantations in Colombia and Mexico. Of these, 76 isolates showed activity to solubilize Ca₃(PO₄)₂ (PCa) and FePO₄·H₂O (PFe), which had been added to agar in a plate test. Generally, PCa was better solubilized than PFe. Colombian isolates were generally somewhat less effective than Mexican isolates. The two most effective isolates from each country with apparent highest PFe, solubilization potential were selected and cultivated in liquid medium containing PFe, which is more prevalent in tropical soils. The pH value, solubilized P in the medium and P uptake in fungal biomass were determined. After 24 days, Cylindrocarpon didymum and C. obtusisporum (both from Colombia) had solubilized 9.9 and 6.4 mg PO₄ ^3--P L⁻¹ and took up 8.6 and 11.6 mg P in biomass. Penicillium janthinellum and Paecilomyces marquandii (both from Mexico) solubilized 7.0 and 1.9 mg PO₄ ^3--P L⁻¹ and took up 11.3 and 17.3 mg P in biomass. The potential practical use of the four fungal isolates for different strategies in making more P available for coffee growth is discussed.

Keywords:

• Paecilomyces
• Penicillium
• Fusarium
• Cylindrocarpon
• fungal biotechnology

Acknowledgements

The authors express their thanks to Daniela Cela, Ariadna Martinez and Sandra Rocha for their collaboration in the chemical determination procedures; to Cynthia Becerra and Rosa Arias for their collaboration with identifications of fungal isolates in Mexico. Thanks to Nubia Rodriguez and Fernando Ramos for their collaboration in laboratory activities in Colombia. The authors are grateful to the company ‘Química Barquim S.A.’ for their kind donation of iron phosphate. Thanks also to the OAS and CONACyT for the scholarship grant support for the principle author and to the Institute of Ecology A.C. for logistical and economical support. Special thanks are also given to the anonymous reviewer of the article for their highly appreciated comments how to improve the manuscript.