Isolation of phosphate solubilizing bacteria and their effect on growth of wheat (Triticum aestivum L.)

Understanding of the morpho-physiological and biochemical traits that form the basis of uptake of P as required by plants is of paramount importance in the selection / production of desirable materials. The study was under taken to identify phenotypic flexibility for PSB inoculation in the locally available gene pool in wheat cv. Inqalab-91) (Triticum aestivum L.) The experiment was comprised of three phases. In first phase, isolation of phosphate solubilizing bacteria (PSB) was carried out from rhizosphere, soil and roots of wheat. These PSB isolates, WPs-5 (isolated in the experiment) CPs-1, CPs-2, CPs-3, LPs-3, Ca-18, AP, IFA1 and IFA2 were characterized by (a) gram staining, (b) zone diameter measurement, (c) IAA production and (d) ARA activity. All PSB strains were gram negative, rod shaped, motile, fast grower and vary in IAA production and ARA activity. Zone diameter was also measured for qualitative evaluation and it ranges from 20-81 mm. It was observed that PSB strains were obtained only 1.2% of 50-80 bacterial colonies, found from wheat rhizosphere samples. No PSB strain was found in soil and root samples of wheat. Results showed highest percentage of PSB have been found in rhizosphere than soil and roots of wheat plants. Only one PSB WPs-5 was isolated from rhizosphere of wheat plant and eight PSB strains were taken from NIBGE culture collection. These PSB isolates were characterized by gram staining. After characterization, these phosphate solubilizing bacterial (PSB) strains were named. Strains isolated from wheat called WPs-5 and the strains taken from NIBGE culture collection were named CPs-1, CPs-2, CPs-3 (chickpea), LPs-3 (lentil). It was found that only 1.2% PSB strains obtained in wheat from total bacterial colonies observed. No PSB strain was found in soil and in root sample of wheat. Results showed highest percentage of PSB have been found in rhizosphere of wheat plants. In second phase, spe c trophotometric quantification of solubilized P by phosphate solubilizing bacterial strains was carried out by phospho-molybdate method. One PSB strain (WPs-5) isolated in the experiment, CPs-1, CPs-2, CPs-3, LPs-3, Ca-18, AP, IFA1, IFA2 (obtained from NIBGE culture collection) were used for this quantification. PSB strain Ca-18 is a standard bacterial strain already used in Biopower (a commercial product of Biofertilizer Division, NIBGE, Faisalabad). Available phosphorus solubilized by PSB strains ranges from 62-126.5 mug ml-1. Highest value of phosphate was solubilized by PSB strain WPs-5 followed by CPs-3 strain. In third phase, effect of these PSB strains on wheat plants was determined by a pot trial. A lab experiment was conducted in Completely Randomized Design (CRD) with single factor factorial arrangement. The experiment was consisting of twelve treatments with three replicates. Out of twelve treatments, three were without inoculation (T1, T2, T3) and seven treatments (T4, T5, T6, T7, T8, T9, T10) were inoculated with CPs-1, CPs-2, CPs-3, LPs-3, WPs-5, Ca-18 and AP respectively (PSB strain). Treatments T11 and T12 were inoculated with non- phosphate solubilizing bacterial strains IFA1, IFA2 respectively. The morpho- physiological traits were evaluated periodically along the plant growth. The results revealed that applied PSB strains considerably enhanced seedling emergence, establishment and phosphate availability to plants and consequently promote plant growth of wheat plants. Favourable effect of PSB inoculation on ion accumulation is important feature of this study causing an improvement in growth and yield of plants. PSB inoculation caused an extensive increase in concentration of total nitrogen (N), total phosphorus (P) and other cations such as Na+, K+ and Ca+2. Phosphate solubilizing bacterial strains CPs-1, CPs-2 and Ca-18 had maximum positive effect on shoot length, shoot dry weight, root area and number, size and ARA activity of root of wheat plants. Treatments inoculated with non-phosphate solubilizing bacterial strains IFA1, IFA2 showed minimum values in all the parameters. Improved growth traits identified here, were vigorous growth of seedling, sustained photosynthetic area, better branching behaviour, and more production of green tissues. A combination of these characters may be used for improving P-deficiency in wheat plants by PSB inoculation. It has been concluded, that efficient phosphate solubilizing bacteria may be used as biofertilizer for the improvement of crop yield by P-uptake. So there is great scope for improving P- deficiency in crop plants by PSB inoculation, if the above given criteria of PSB inoculation are incorporated in the high yielding germplasm through conventional breeding and biotechnological techniques.