Potential microbial candidate strains for management of nutrient requirements of crops

Abstract

Zinc (Zn) and phosphorus (Pi) are essential for optimum plant growth. Upon application, they get fixed in the soil matrix. Application of more than one microbe for each nutrient is often difficult. Azotobacter (31), Azospirillum (38), Bacillus (19) and Pseudomonas (82) strains were isolated from diverse crop production systems and were evaluated for solubilization of ‘Zn’ and ‘Pi’ in vitro from insoluble zinc (ZnO, ZnCO3) and phosphorus [tricalcium phosphate (TCP)], respectively. After 15 days of incubation, 15 strains solubilized zinc and produced >50 cm2 solubilization zone on solid media. In broth culture, with ZnO as zinc source, B116 could release maximum available Zn (13.12 ppm) and with ZnCO3, B118 could release highest available Zn (16.3 ppm). Pseudomonas strain PIII-105 released highest available 'Pi' (14.8 ppm) and solubilization of Zn and Pi corresponded with fall in pH of the medium except in case of B116. Two (2) strains of Azospirillum, 6 strains each of Bacillus and Pseudomonas showed a clearance zone area of >50 cm2with both Zn sources. Similarly, 2 strains each of Azospirillum and Bacillus and 3 strains of Pseudomonas solubilized TCP. Azospirillum strains As-20, As-22; Bacillus strains B113, B118; and Pseudomonas strains P17, P33 and PIII 105 solubilized both Zn and P sources showing their ability to supplement both essential nutrients to plants. Interestingly,Azospirillum is already known to supplement nitrogen also. Key words: Multi-nutrient management, zinc carbonate, zinc oxide, tricalcium phosphate,Pseudomonas, Bacillus, Azospirillum.