Isolation of bacterial strains possessing nitrogen-fixation, phosphate and potassium-solubilization and their inoculation effects on sugarcane.

Inorganic nitrogen (N), phosphate (P) and potash (K) are the most influencing macro-nutrients for plant growth and microbial supplementation of these minerals through N2-fixation, P- and K-solubilization is gaining importance. In the present study, a macronutrient deficient (MD), N-free novel medium, supplemented with tri calcium phosphate (TCP as P- source) and Mica (as K- source) was used for isolation of microbes possessing nitrogen fixing, P- & K solubilizing abilities. Samples of rhizosphere and non-rhizosphere soils, roots and leaves of sugarcane varieties (viz., Co 6304, Co 86032 and CoC 671) collected from Tamil Nadu, India were used for isolation. Totally, 8 individual nitrogen-fixing, phosphate- and potash-solubilizing bacterial strains were obtained. Nitrogen-fixing abilities of these isolates were confirmed by analyzing acetylene reduction (AR) activity and the presence of nif genes. P- and K- solubilizing activities were confirmed by cultivating these isolates in solid/liquid medium supplemented with insoluble forms of P and K. These isolates which produced growth hormone IAA, were in two groups as Roseateles terrae and Burkholderia gladioli, respectively based on the morphological, physiological, biochemical and 16S rDNA gene sequence analysis. Association between diazotrophic, P- and K-solubilizing R. terrae and B. gladioli with sugarcane has not been reported earlier. These isolates were tested for their growth-promoting abilities in sugarcane cultivated in pots, and the results showed that these isolates were able to increase the leaf chlorophyll, N content and total biomass. This study may encourage farmers to use single microbe for microbial supplementation of N, P and K instead of consortium of microbes wherein the compatibility between different microbes is often compromised.

N-fertilizer saving by the inoculation of Gluconacetobacter diazotrophicus and Herbaspirillum sp. in micropropagated sugarcane plants.

Colonization of micropropagated sugarcane plants by Gluconacetobacter diazotrophicus and Herbaspirillum sp. was confirmed by a dot-immunoblot assay. In all, a 45-day short-term and 180-day long-term experiments conducted on micropropagated sugarcane plants of Co 86032, a sugar rich popular variety in South India, indicated the usefulness of these diazotrophs as plant growth promoting bacteria. Co-inoculation of these two bacteria enhanced the biomass considerably under N-limited condition in the short duration experiment. In the long-term experiment, the establishment of inoculated Herbaspirillum sp. remained stable with the age of the crop up to 180 days, while there was a reduction in population of G. diazotrophicus for the same period. The total bio-mass and leaf N were higher in plants inoculated with G. diazotrophicus and Herbaspirillum sp. without N fertilization and also in plants with 50% of the recommended N (140 kg ha(-1)) than the plants fertilized with recommended dose of inorganic N (280 kg ha(-1)). This experiment showed that inoculation with these bacteria in sugarcane variety Co 86032 could mitigate fertilizer N application considerably in sugarcane cultivation.

Natural association of Gluconacetobacter diazotrophicus and diazotrophic Acetobacter peroxydans with wetland rice.

The family Acetobacteraceae currently includes three known nitrogen-fixing species, Gluconacetobacter diazotrophicus, G. johannae and G. azotocaptans. In the present study, acetic acid-producing nitrogen-fixing bacteria were isolated from four different wetland rice varieties cultivated in the state of Tamilnadu, India. Most of these isolates were identified as G. diazotrophicus on the basis of their phenotypic characteristics and PCR assays using specific primers for that species. Based on 16S rDNA partial sequence analysis and DNA: DNA reassociation experiments the remaining isolates were identified as Acetobacter peroxydans, another species of the Acetobacteraceae family, thus far never reported as diazotrophic. The presence of nifH genes in A. peroxydans was confirmed by PCR amplification with nifH specific primers. Scope for the findings: This is the first report of the occurrence and association of N2-fixing Gluconacetobacter diazotrophicus and Acetobacter peroxydans with wetland rice varieties. This is the first report of diazotrophic nature of A. peroxydans.