Abstract
Sixteen soil samples were collected from wheat, barley and yellow corn rhizosphere in Abu-Ghraib, Aqraqof, Latifieh,Tarmiah, Jadriya and of Agriculture in Baghdad university/ Baghdad city. The results found nine phosphate solubilizing bacteria (PSB) isolates (Y1, Y2, Y3, Y4, Y5, Y6, Y7, Y8, Y9), formed clear zones on National Botanical Research Institute's (NBRIP) agar. The solubility index (SI) of PSB isolates ranged from 2.00 to 3.66. Y4 have the highest SI (3.66) followed by Y3 and Y6 (3.33). Phosphate solubilization abilities varying from (20.10-39.00 μg.ml-1), Y4 was the highest (39.00 μg.ml-1) followed by Y3 (37.00μg.ml-1). The results of hydrolytic enzymes production showed that almost all nine isolates are able to produce protease and pectinase, while Y1 and Y2 showed negative results in cellulase production. Maximum ability for hydrogen cyanide (HCN) and indole acetic acid (IAA) production were showed byY3 and Y4 isolates. The isolate Y4 was found to be the most efficient isolate, so it was selected identified as Bacillus cereus using biochemical tests confirmed by VITEC 2 compact system. The results of High performance liquid chromatography (HPLC) revealed that Bacillus cereus produce oxalic acid (2.996), citric acid (9.117) and malic acid (3.734). Bacillus cereus (Y4) enhanced the growth of mung bean plants. A significant increase in branches number (12.33), plant length (83.0cm), fresh weight (27.25 g) and dry weight (1.427g) were obtained compared with control treatments. The main objective of this study is to isolate PSB and evaluate their roles in plant growth promotion. The results showed the high phosphate solubilization efficiency of PSB isolates and the identified isolates was found to be good enough for plant growth promoting.
Highlights
Phosphor (P) availability to plant is limited despite its higher content in soil, in tropical soils.The rapid conversion of supplied chemical phosphate fertilizers into insoluble phosphate sources leads to regularly applying P fertilizers, which are costly and environmentally undesirable
The presence of organic acids in filtrated liquid culture were determined by modern techniques such as HighPerformance Liquid Chromatography (HPLC), Isotachophoresis and enzymatic methods have been used by others to allow more accurate identification of unknown organic acids [6]
Out of 16 soil samples obtained, 9 bacterial isolates formed a halo zone around the bacterial colony during growth in National Botanical Research Institute Phosphorus (NBRIP) agar medium (Figure-1), 6 of them were from wheat rhizosphere (Tab. 2).The 9 bacterial isolates were considered as phosphate solubilizing bacteria (PSB) on the basis of their capability to solubilize the insoluble tri-calcium phosphate (TCP) present in NBRIP agar medium [9]
Summary
Phosphor (P) availability to plant is limited despite its higher content in soil, in tropical soils.The rapid conversion of supplied chemical phosphate fertilizers into insoluble phosphate sources leads to regularly applying P fertilizers, which are costly and environmentally undesirable. Out of 16 soil samples obtained, 9 bacterial isolates formed a halo zone around the bacterial colony during growth in NBRIP agar medium (Figure-1), 6 of them were from wheat rhizosphere (Tab. 2).The 9 bacterial isolates were considered as PSB on the basis of their capability to solubilize the insoluble tri-calcium phosphate (TCP) present in NBRIP agar medium [9]. SI index ranged from 2.00 to 3.66, Y4 isolate reflex the highest value (3.66) followed by Y3 and Y6 (3.33), Y5 (3.00).The isolates ability to release phosphate (P), from tri-calcium phosphate (TCP), in NBRIP broth ranged from 39.00 to 20.10 μg.ml-1, the isolate Y4 showed the highest ability (39.00 μg.ml-1) followed by Y3 (37.00 μg.ml-1)and Y6 (35.00 μg.ml-1).The decline in P-solubilization activity may be due to the nutrients deficiency in the culture medium which needed by phosphate solubilizing bacteria, as a substrates to convert it to organic acid [21]. Bacillus species isolate was identified, to detect its species, by using VITEK2
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