Soil microorganisms with potential for alleviation of abiotic stresses in combination with plant growth promotion would be extremely useful tools in sustainable agriculture. To this end, the present study was initiated where forty-five salt tolerant bacterial isolates with ability to grow in high salt medium were obtained from the rhizosphere of Triticum aestivum and Imperata cylindrica. These bacteria were tested for plant-growth-promoting rhizobacteria traits in vitro such as phosphate solubilization, siderophore, ACC deaminase and IAA production. Of the forty-five isolates, W10 from wheat rhizosphere and IP8 from blady grass rhizosphere, which tested positive in all the tests were identified by morpholological, biochemical and 16SrDNA sequencing as Bacillus safensis and Ochrobactrum pseudogregnonense respectively and selected for in vivo studies. Both the bacteria could promote growth in six varieties of wheat tested in terms of increase in root and shoot biomass, height of plants, yield, as well as increase in chlorophyll content. Besides, the wheat plants could withstand water stress more efficiently in presence of the bacteria as indicated by delay in appearance of wilting symptoms increases in relative water content of treated water stressed plants in comparison to untreated stressed ones, and elevated antioxidant responses. Enhanced antioxidant responses were evident as elevated activities of enzymes such as catalase, peroxidase, ascorbate peroxidase, superoxide dismutase and glutathione reductase as well as increased accumulation of antioxidants such as carotenoids and ascorbate. Results clearly indicate that the ability of wheat plants to withstand water stress is enhanced by application of these bacteria which also function as plant growth promoting rhizobacteria.
A total of 18 bacterial isolates were obtained from the rhizosphere of Sechium edule growing in the lower foothills of Darjeeling, India. The bacterial isolates were tested for PGPR traits in vitro such as phosphate solubilization, HCN, siderophore, IAA, chitinase, protease production as well as inhibition of pthytopathogens. Of all the bacterial isolates, one bacterium designated as BRHS/S-73 was found to possess all the tested characters which was identified on the basis of 16S rRNA gene sequence analysis as Bacillus altitudinis and was selected for in vivo studies. A significant improvement in growth measured in terms of increase in root length, shoot length, and increase in root and shoot biomass was observed when seeds of Vigna radiata, Cicer arietinum, and Glycine max were bacterized prior to sowing in field condition. Besides, the bacterium could also solubilize soil phosphate. Apart form growth promotion, root rot disease of Vigna radiata caused by Thanatephorus cucumeris was also significantly reduced by 74% when the bacterium was applied to the rhizosphere prior to pathogen challenge. The biocontrol efficacy of the bacterium was found to be 66.6% even after 30 days of pathogen inoculation. Activities of key defense related enzymes such as phenylalanine ammonia lyase, peroxidase, β-1,3-glucanase, and chitinase in both roots and leaves of treated plants were also enhanced. Results clearly suggest that B. altitudinis (BRHS/S-73) is a potential PGPR which can be used as efficient microorganism for enhancement of plant growth and suppression of fungal disease.
Polyclonal antibodies (PAbs) were raised against mycelial antigens of Macrophomina phaseolina a causal organism of root rot disease of mandarin plants. IgG was purified and further packaged into immunological formats such as immuno diffusion, Plate trapped antigen (PTA)-ELISA, dot immunobinding assay, Western blot analysis and indirect immunofluorescence for quick and accurate detection of pathogen from soil. Indirect staining of mycelia and sclerotia of M. phaseolina with homologous PAb and labeling with goat antirabbit IgG conjugated with FITC developed strong fluorescence in young hyphal tips and sclerotia of M. phaseolina. Genomic DNA prepared from mycelia of M. phaseolina was purified and PCR amplification of 18S rDNA was done using ITS region specific primer pair. The amplified DNA was sequenced and aligned against ex-type strain sequences from NCBI GenBank using BLAST and phylogenetic analysis was obtained using MEGA4 software. Amplification of ITSI region of the rDNA can be considered as a rapid technique for identifying pathogens successfully in all cases.
A total of 354 fungal isolates were obtained from soil samples collected from forests, river basins and agricultural fields of North Bengal using serial dilution, direct soil plating, serial root washing and root maceration techniques. Cultural characteristics of the isolated fungi were studied and microscopic observations were made for identification of these isolates. All the isolates were screened for their phosphate solubilizing activities in vitro. A total of 70 fungal isolates showed phosphate solubilizing activities as detected in Pikovskaya's agar medium. Quantitative evaluation of phosphate solubilization in liquid medium supplemented with two phosphate sources (tricalcium phosphate and rock phosphate) was carried out for all the isolates showing phosphate solubilizing activity. Maximum phosphate solubilizing capacity was shown by three isolates of A. niger while A. clavatus showed minimum activity. Genomic DNA was extracted from sixteen isolates showing high activity and PCR amplification of DNA from nine isolates was done.
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