Field application of two plant growth promoting rhizobacteria with potent antifungal properties
Introduction
In recent years the use of microbial inoculants as biofertilizers and biocontrol agents in the agriculture industry has been increasing considerably. Microbial inoculants are favoured to reduce environmental pollution caused by chemicals and pesticides. Plant growth promoting rhizobacteria (PGPR) can be nitrogen fixing or have properties that enhance growth of crops (Islam et al., 2013, Yadegari et al., 2010). The strains in most of the cases produce the plant growth factors (Reetha et al., 2014, Kang et al., 2014). In soil, phosphates are generally present in the form of insoluble phosphate like tri-calcium phosphate or hydroxy-apatite or rock phosphates as the phosphorus combines with several chemical compounds. PGPR are also reported to solubilize the insoluble phosphates by producing organic acids (Bajpai and Sundara, 1971, Ghosh et al., 2016). Sometimes they also exhibit antimicrobial activities and inhibit the growth of plant pathogens (Johnson and Carl, 1972, Higa, 1999, Morales et al., 2008, Nourozian et al., 2006). Biological control of the pathogens is accomplished either directly or by competition for specific nutrients (Neeno-Eckwall et al., 2001). Agrawal and Agrawal (2013) showed that the strains of Bacillus isolated from the tomato rhizosphere increased the seed germination and seed vigour index significantly. Rhizobacteria can produce siderophores, antibiotics or promote induced systemic resistance (ISR) in plants which is a key defense pathway (Choudhary et al., 2007). In this study we report two PGPR strains VBLR10 and VBLR39 which showed maximum sequence similarities with Bacillus subtilis and Cellulosimicrobium cellulans respectively in 16s rRNA gene sequence homology which have PGP activities including antifungal activities and their effects were tested in field applications.
Section snippets
Isolation and screening of the PGPR strains
Rhizospheric soils i.e. the soil particles adhered to healthy root surfaces of the fresh and healthy Solanum lycopersicum (tomato) plants were collected for the isolation of PGPR strains. The nature of the soils was alluvial type and was collected from the surface of the gently uprooted healthy roots. The soil samples were dried under aseptic conditions, powdered and was suspended in sterilized water for isolation of desired strains. The strains were initially isolated in nutrient agar (NA)
Isolation of the PGPR strains
Out of innumerable bacterial strains isolated in NA plates, 42 rhizobacterial strains were randomly picked up for further studies. Among the 42 rhizobacterial strains, isolated from the tomato rhizosphere, 16 could grow in the nitrogen free Burk's plates indicating their putative nitrogen fixing phenotype. Later, two strains viz., VBLR10 and VBLR39 were finally selected for their maximum growing ability in Burk's broth among the primarily screened strains (Fig. 1a).
Antifungal activity of the strains
The CFSs of both the PGPR
Conclusions
The two isolates described in this study enhanced plant growth in the field and were demonstrated to have good PGP attributes. VBLR39 was found to have activities like phosphate solubilization, chitinase production, IAA production and siderophore production. VBLR10 showed phosphate solubilization and IAA production ability. Both strains showed remarkable antifungal activities.
Acknowledgements
S.B.S. is thankful to the University Grants Commission, India (Ref. No.: 22/12/2013 (ii) EU-V) for financial support.
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