Diversity and Tissue Preference of Osmotolerant Bacterial Endophytes Associated with Pearl Millet Genotypes Having Differential Drought Susceptibilities.

Genetic and functional diversity of osmotolerant bacterial endophytes colonizing the root, stem, and leaf tissues of pearl millet genotypes differing in their drought susceptibility was assessed. Two genotypes of pearl millet, viz., the drought tolerant genotype TT-1 and the drought susceptible genotype PPMI-69, were used in the present study. Diazotrophs were found to be the predominant colonizers, followed by the Gram positive bacteria in most of the tissues of both the genotypes. Higher proportion of bacterial endophytes obtained from the drought tolerant genotype was found to be osmotolerant. Results of 16S rRNA gene-ARDRA analysis grouped 50 of the highly osmotolerant isolates into 16 clusters, out of which nine clusters had only one isolate each, indicating their uniqueness. One cluster had 21 isolates and remaining clusters were represented by isolates ranging from two to four. The representative isolates from each cluster were identified, and Bacillus was found to be the most prevalent osmotolerant genera with many different species. Other endophytic bacteria belonged to Pseudomonas sp., Stenotrophomonas sp., and Macrococcus caseolyticus. High phylogenetic diversity was observed in the roots of the drought tolerant genotype while different tissues of the drought susceptible genotype showed less diversity. Isolates of Bacillus axarquiensis were present in all the tissues of both the genotypes of pearl millet. However, most of the other endophytic bacteria showed tissue/genotype specificity. With the exception of B. axarquiensis and B. thuringiensis, rest all the species of Bacillus were found colonizing only the drought-tolerant genotype; while M. caseolyticus colonized all the tissues of only the drought susceptible genotype. There was high incidence of IAA producers and low incidence of ACC deaminase producers among the isolates from the root tissues of the drought-tolerant genotype while reverse was the case for the drought-susceptible genotype. Thus, host played an important role in the selection of endophytes based on both phylogenetic and functional traits.

Effects of lindane on lindane-degrading Azotobacter chroococcum; evaluation of toxicity of possible degradation product(s) on plant and insect.

The effects of lindane on growth and plant growth-promoting traits of two lindane-degrading Azotobacter chroococcum strains (JL 15 and JL 104) were determined. The potential of both A. chroococcum strains to degrade lindane was also determined. Lower concentrations of lindane had a stimulatory effect, and higher concentrations generally had an inhibitory effect on growth and plant growth-promoting activities. A high percentage (>90%) of lindane was degraded by both strains at a lindane concentration of 10 ppm. Lindane at 1,000 ppm decreased seed germination and reduced seedling fresh weight. However, the possible degradation products for a starting lindane concentration of 10 ppm was found to be non-phytotoxic. Toxicity studies with larvae of Spilarctia obliqua resulted in an LC50 estimate of 3.41 ppm for lindane solutions into which leaf discs were dipped. No toxicity was observed for possible degradation products.

Survival of bio-inoculants on fungicides-treated seeds of wheat, pea and chickpea and subsequent effect on chickpea yield.

Survival of Mesorhizobium ciceri (SP(4)) and Azotobacter chroococcum (CBD-15 and M(4)) was tested on chickpea (Cicer arietinum) seeds treated with fungicides bavistin [methyl N-(1H-benzimidazol-2yl) carbamate] and thiram (tetramethyl-thiuram disulfide), whereas survival of phosphate solubilizing bacteria (PSB), Pseudomonas striata (27) and Bacillus polymyxa (H(5)) was examined on two cultivars (Arkel and BV) of pea (Pisum sativum) seeds treated with thiram. Viability of Azotobacter chroococcum (W(5)) was also examined on wheat (Triticum aestivum) seeds treated with bavistin, captan (cis-N-trichloromethyl thio-4 cyclohexane-1, 2-dicarboximide) and thiram under laboratory conditions using standard dilution and the plate count technique. All the tested strains of diazotrophs and PSB showed decline in their viable population on prolonged contact with fungicides. However, PSB showed variation in their viable population even with the cultivar. BV cultivar of pea seeds showed better recovery of viable P. striata (10.75 to 10.61 log no. of viable cells with in 0-24 hrs) in the presence of thiram, whereas the Arkel cultivar of pea resulted in better recovery of viable B. polymyxa. Azotobacter chroococcum (W(5)), a potential strain for wheat, showed better survival in the presence of bavistin, compared to thiram and captan. Higher viable population of Mesorhizobium ciceri (SP(4)) and Azotobacter chroococcum (M(4)) was recovered from chickpea seeds treated with bavistin compared to thiram. However, thiram-treated seeds resulted in a greater number of extractable Azotobacter chroococcum (CBD-15). Under field conditions, adverse effect of thiram was reflected on the performance of Mesorhizobium ciceri (SP(4)) and A. chroococcum (M(4)) strains, resulting in reduced root and shoot biomass and grain yield, compared to bavistin treated and culture inoculated treatment. CBD-15 showed better performance in the presence of thiram compared to bavistin.