The application of plant-growth-promoting rhizobacteria (PGPR) at field scale has been hindered by an inadequate understanding of the mechanisms that enhance plant growth, rhizosphere incompetence and the inability of bacterial strains to thrive in different soil types and environmental conditions. Actinobacteria with their sporulation, nutrient cycling, root colonization, bio-control and other plant-growth-promoting activities could be potential field bio-inoculants. We report the isolation of five rhizospheric and two root endophytic actinobacteria from Triticum aestivum (wheat) plants. The cultures exhibited plant-growth-promoting activities, namely phosphate solubilization (1916 mg l "1 ), phytase (0.68 U ml "1 ), chitinase (6.2 U ml ) was estimated in the culture supernatant of the highest phosphate solublizer, Streptomyces mhcr0816. The mechanism of malate overproduction was studied by gene expression and assays of key glyoxalate cycle enzymes -isocitrate dehydrogenase (IDH), isocitrate lyase (ICL) and malate synthase (MS). The significant increase in gene expression (ICL fourfold, MS sixfold) and enzyme activity (ICL fourfold, MS tenfold) of ICL and MS during stationary phase resulted in malate production as indicated by lowered pH (2.9) and HPLC analysis (retention time 13.1 min). Similarly, the secondary metabolites for chitinaseindependent biocontrol activity of Streptomyces mhcr0817, as identified by GC-MS and 1 H-NMR spectra, were isoforms of pyrrole derivatives. The inoculation of actinobacterial isolate mhce0811 in T. aestivum (wheat) significantly improved plant growth, biomass (33 %) and mineral (Fe, Mn, P) content in non-axenic conditions. Thus the actinobacterial isolates reported here were efficient PGPR possessing significant antifungal activity and may have potential field applications.

Aim: To evaluate the plant growth promotion (PGP) potential and soil enzyme production under solid state fermentation (SSF) by most abundant Streptomyces spp. isolated from the wheat rhizosphere and to evaluate their effect on plant growth parameters. Methods and Results: Actinomycetes were isolated from wheat rhizosphere and screened for PGP activities. Three actinomycete isolates having significantly higher PGP activities (Streptomyces rochei IDWR19, Streptomyces carpinensis IDWR53, Streptomyces thermolilacinus IDWR81) were selected. The soil enzymes production potential of these isolates using soil extract and wheat straw under ssf was assessed. Utilization of soil extract as a fermentation medium for soil enzyme production by Actinomycetes has been reported first time in this study. Maximum chitinase (S. rochei IDWR19 12Á2 U mg À1 protein) and phytase activity (S. carpinensis IDWR53 5Á2 U mg À1 protein) was produced on 7th day of incubation, whereas maximum alkaline protease (S. rochei IDWR19 3Á2 U mg À1 protein) was produced on 6th day of incubation. For cellulase (S. rochei IDWR19 7Á4 U mg À1 protein) and invertase (S. carpinensis IDWR53 451 U mg À1 protein) maximum activity was observed on 4th as well as 5th day of incubation. On the basis of PGP activity and enzyme production, two actinomycete isolates (S. rochei IDWR19 and S. thermolilacinus IDRWR81) were selected for plant growth experiment. An increase of 12Á2 and 24Á5% in shoot length of plants inoculated with S. rochei IDWR19 and S. thermolilacinus IDWR81 was observed, respectively. A similar increase in biomass of 1Á8-and 2Á3-fold was also recorded for the two isolates, respectively. Conclusions: It could be concluded that Streptomyces sp. with high PGP activities and soil enzyme production capability significantly improved growth and development of wheat cv. Significance and Impact of the Study: The abundant Actinomycetes obtained in this study (S. rochei IDWR19 and S. thermolilacinus IDWR81) are rhizosphere competent and effective strains.

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Aseptic Lemna minor was soaked for 4 h in pond water where wild L. minor was naturally flourishing. Seven of the eight surface-colonizing bacterial strains were found capable of promoting the growth of L. minor. This high appearance of plant growth-promoting bacteria (PGPB) suggests that association of environmental bacteria is generally beneficial rather than harmful for host plants. One of the PGPB, Pseudomonas sp. Ps6, enhanced the growth of L. minor by 2-2.5-fold in 10 days. This activity was higher than that previously reported for Acinetobacter calcoaceticus P23, which enhanced growth of L. minor by 1.5-2-fold. Ps6 mostly adhered to and colonized the root rather than the frond, a leaf-like structure of duckweed where P23 preferentially adheres. It was expected that these two strains can share niches, coexist, and enhance the growth of duckweed additively upon co-inoculation. However, contrary to expectation, the growth of L. minor was enhanced by only 2.3-fold by co-inoculation of these two bacteria. P23 lowered the initial adhesion of Ps6 cells by 98.2% on the fronds and by 79.5% on the roots. However, initial adhesion of P23 cells to the roots increased dramatically, by 47.2-fold, following co-inoculation with Ps6. However, the number of P23 cells decreased dramatically to 0.7% on the root and to 3.6% on the frond after 10 days, whereas Ps6 cells increased by 12.5-fold on the frond and kept 69% on the root, thereby eventually restoring the population on the plant surfaces. Because duckweed is the fastest growing vascular plant and it is easy to grow an aseptic and axenic plant, the duckweed/bacteria co-culture system will be a model platform for studying multiple interactions among host plants and the associated bacteria.