Isolation of plant growth promoting bacteria from paddy (Oryza sativa) rhizosphere

Abstract

Plant growth promoting rhizobacteria (PGPR) is the bacteria that inhabit the plant rhizosphere and have an ability to promote the growth of plant, and could increase crop yield by fixing atmospheric nitrogen, and solubilizing insoluble phosphate into the form that available for plant's uptake. This project aimed to isolate two types of PGPR including nitrogen fixing bacteria (NFB), and phosphate solubilizing bacteria (PSB) on selective media namely Burk's medium, and Pikovskaya medium, respectively. Total of 391, and 59 colonies of NFB, and PSB respectively were successfully isolated. Ten colonies of NFB were selected due to its ability to grow relatively faster than the other colonies and namely as P-NF1, P-NF2, P-NF3, P-NF4, P-NF5, P-NF6, P-NF7, P-NF8, P-NF9, and P-NF10, while nine colonies of PSB were selected based on the diameter of halo zone formed on Pikovskaya agar and namely as P-PS1, P-PS2, P-PS3, P-PS4, P-PS5, P-PS6, P-PS7, P-PS8, and P-PS9. The cellular morphology of all the isolates were then characterized by performing the gram staining. Seven of the NFB isolates are gram-negative rod, while the other three are gram-negative cocci, gram-positive rod, and gram-positive cocci each. On the other hand, three of the PSB isolates are gram-negative rod, and six isolates are gram-positive rod. The ability of the isolates in fixing nitrogen and solubilizing phosphate were evaluated by the determination of nitrogen fixing ability on Burk's medium, and by measuring the phosphate solubilizing activity using phosphate solubilization index (PSI) test. It was discovered, all the nine PSB are able to fix nitrogen with eight of the isolates show the high nitrogen fixing activity, while one of the isolates has low activity. The highest phosphate solubilization activity was shown by P-PS3 with SI 6.75 while for NFB, P-NF7 have the highest phosphate solubilization activity with SI 2.50. Results suggest that PGPR from paddy rhizosphere especially P-PS3 and P-NF7 are good candidates as biofertilizer in promoting plant growth.