In Vitro Selection of Rock Phosphate Solubility by Microorganism from Ultisols in South Sulawesi, Indonesia

Abstract

Phosphorus (P) is the second most required nutrient of plants, but its availability in ultisols is relatively low. Source of P can be found from rock phosphate (RP) which has low solubility level. Use of microbial solubilizing phosphate such as bacteria, fungi or combination of both is potential to increase availability of P. This research was aimed to find bacterial or fungal isolates that are high potential in solubilizing of RP. In vitro selection was conducted to obtain indigenous bacteria or fungi from Ultisols of South Sulawesi. Selection of microbes for their capability to solubate rock phosphate qualitatively, conducted through measuring the solubility index (SI) and solubility efficiency (SE) on pykovskaya solid medium and on National Botanical Research Institutes phosphate-bromophenol blue (NBRIP-BPB) medium. The results of this study indicated that from SI and SE highest values, four high potential isolates were selected namely, Aspergillus niger JTM 2, Bacillus sp JTM 3, Aspergillus niger JTM 6 and Pseudomonas sp JTM 10. Ability of solubilizing phosphate from the four isolates was then tested in liquid medium pikovskaya either in single or mixed combination. Solubilizing phosphate of RF was determined according to [1] method. The results of test on solid media indicate that Bacillus sp JTM 3 and Pseudomonas sp JTM 10 have SI and SE higher than both Aspergillus niger JTM 2 and Aspergillus niger JTM 6. Futhermore, test on Pikovskaya liquid media confirmed that Aspergillus niger JTM 6 and Pseudomonas sp JTM 10 gives the higher results than other single isolates and control, whereas the combination of isolates Bacillus sp JTM 3 and Aspergillus niger JTM 2 indicated significantly higher solubilizing phosphorus production than all other treatments.