• Thanakorn Saengsanga
  • Tarntip Rattana
  • Sutat Termsaithong
Keywords: Phosphate solubilizing bacteria, Rubber tree, Rhizosphere


Even though soils generally contain a large amount of total phosphorous (P), only a few amount is immediately available for plant uptake. Phosphorous deficient is widespread in all major crop production and is the main growth-limiting factor in many tropical and subtropical areas, especially in Thailand. Long term single application of chemical fertilizers in high level affected on soil properties, plant and productivity. However, soil microbe activities involve the process of de-compostition of organic matter, production of phytohormones, secondary metabolites and mineralization macro nutrients from soil to the plant. Beneficial bacteria like phosphate solubilizing bacteria (PSB) has been documented to solubilize insoluble phosphate into soluble form for plant growth through the secretion of organic acids. The present study aimed at screening the PSB from root rhizosphere of rubber trees (Hevea brasiliensis Muell Arg) in Nongki district, Burirum province, Thailand on Pikovskaya’s agar medium, specific culture medium. Obtained PSB were then examined for their extracellular enzyme production such as amylase, cellulase, lipase and protease by plate assays. Our result revealed that seven isolates of PSB were retrieved from rhizosphere of rubber tree. The phosphate solubilization index was examined by using tri-calcium phosphate (TCP) as sole phosphorus source. Solubilization index by the isolates were observed in ranging from 2.28 to 2.88, which were determined in PVK medium supplemented with 0.5% (w/v) of TCP after incubation at 30°C for 5 days. The result showed that the highest SI (2.88) was obtained from strain NRRU-S5 followed by NRRU-T18 (2.86), NRRU-S16 (2.78) and lowest of SI was observed by strain NRRU-S17 (2.28), respectively. Furthermore, all of the PSB strains were qualitative estimated in liquid PVK medium supplemented with 0.5% (w/v) of TCP. Phosphate solubilization by the strains were ranged from 35.8 to 192.5 µg/mL by Vanado-molybdate- yellow color method. The result confirmed that the NRRU-T18 was the best phosphate solubilizer by releasing soluble phosphate at the highest level of 192.5 µg/mL. The NRRU-S5, NRRU-S19, and NRRU-S16 were solubilized 168.8, 162.5 and 103.3 µg/mL, respectively. The lowest (35.8 µg/mL) phosphate solubilization was found in NRRU-S17. Finally, the enzymatic productions by PSB were analyzed. The result revealed that NRRU-S17 and was able to produce amylase and protease while NRRU-T18 and NRRU-T12 were able to produce cellulase and amylase, respectively. In conclusion, this study is preliminary screening and selection for PSB strains from rhizosphere of rubber tree plantation for the future study that could lead to the development of an effective microorganisms as bio-fertilizer for improving phosphorus plant nutrition.


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