Abstract
Many agricultural soils are deficient in plant available phosphate and hence not able to sustain optimal crop productivity. The problem is due to the ability of many soils to fix phosphate in a wide range of soil pH and ecological conditions. There is a need to search for more environmental friendly alternatives to improve soil fertility and crop production in phosphate deficient soil. The aim of this study was to isolate, screen, and characterize phosphate solubilizing actinomycetes found in different types of soil with varied pH from various sites in Iran. Phosphate solubilizing ability of the actinomycetes was evaluated both on modified Pikovskaya's (PVK) agar and into broth media containing Christmas Island Rock Phosphate (CIRP). The abilities of each isolate to solubilize phosphorus was evaluated from day 1 to day 14 after inoculation. Streptomyces spp. were identified morphologically under scanning electron microscope (SEM). About 31% (22/70) isolates of actinomycetes were found to have the ability to solubilize (CIRP). Isolates IA15 and IA31 showed high solubilizing index (SI) on agar medium whereas isolates IA61, IA59, IA38, IA35, and IA31 were determined to have high CIRP solubilizing ability in broth medium. Isolates IA11, IA31, IA10, and IA61 had high pH decrease in broth medium after 14 days of inoculation. A gradual decrease in pH was observed over a 14 day period of incubation, suggesting a slow release of phosphate from CIRP. The mechanism of solubilization was related to pH decrease in broth medium. In general, majority of phosphate solubilizing actinomycetes revealed superior ability to solubilize CIRP. Key words: rock phosphate; solubilizing phosphate; Streptomyces spp
Highlights
Many agricultural soils are deficient in plant available phosphate and not able to sustain optimal crop productivity
Qualification of Pi release: Isolates IA61 showed high Pi released on modified PKV agar medium while isolates IA22, IA15, and IA31 were significantly lower Pi release on 1st day of inoculation (Table 2)
Whereas at 7th days after inoculation, IA22 showed the highest Pi released followed by IA15, IA61, and IA27 on modified PKV agar medium
Summary
Many agricultural soils are deficient in plant available phosphate and not able to sustain optimal crop productivity. Among phosphate solubilizing microorganisms (PSM), Actinomycetes are of prime interest since these filamentous sporulating bacteria are able to develop in diverse form of soils (Salcedo et al, 2014). They produce various substances including (anti-fungi, insecticides, anthelminthics, and phytohormone-like compounds that could be useful for plant growth (Castanheira et al, 2014). After nitrogen (N), phosphate (P) readily is a major nutrition element limiting plant growth in world-wide agricultural soils especially for crop production (Brännvall et al, 2014). The favorable effect of rock phosphate has made this material an attractive element for application in agriculture (Barea et al, 2002)
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