Alterations in plant growth and in root hormone levels of lodgepole pines inoculated with rhizobacteria

Abstract

The presence of other soil microorganisms might influence the ability of rhizobacterial inoculants to promote plant growth either by reducing contact between the inoculant and the plant root or by interfering with the mechanism(s) involved in rhizobacterially mediated growth promotion. We conducted the following experiments to determine whether reductions in the extent of growth promotion of lodgepole pine mediated by Paenibacillus polymyxa occur in the presence of a forest soil isolate (Pseudomonas fluorescens M20) and whether changes in plant growth promotion mediated by P. polymyxa (i) are related to changes in P. polymyxa density in the rhizosphere or (ii) result from alterations in root hormone levels. The extent of plant growth, P. polymyxa rhizosphere density, and root hormone concentrations were determined for lodgepole pine treated with (i) a single growth-promoting rhizobacterial strain (P. polymyxa L6 or Pw-2) or (ii) a combination of bacteria: strain L6 + strain M20 or strain Pw-2 + strain M20. There was no difference in the growth of pines inoculated with strain L6 and those inoculated with strain L6 + strain M20. However, seedlings inoculated with strain Pw-2 had more lateral roots and greater root mass at 12 weeks after inoculation than plants inoculated with strain Pw-2 + strain M20. The extent of growth promotion mediated by P. polymyxa L6 and Pw-2 in each treatment was not correlated to the average population density of each strain in the rhizosphere. Bacterial species-specific effects were observed in root hormone levels: indole-3-acetic acid concentration was elevated in roots inoculated with P. polymyxa L6 or Pw-2, while dihydrozeatin riboside concentration was elevated in roots inoculated with P. fluorescens M20.

Siderophore and chitinase producing isolates from the rhizosphere of Nicotiana glauca Graham enhance growth and induce systemic resistance in Solanum lycopersicum L.

“…Nicotiana glauca was the plant species sampled since it belongs to the Solanaceae family, as tomato, and a certain degree of specificity between plant species and bacterial strains has been reported (Bent et al 2001;Ramos et al 2003). Among the species in this genera, N. glauca is the most resistant to different fungal pathogens, and due to this fact, its germoplasm is being used to identify pathogen-resistance related genes in this genera (DeBoer et al 2009).…”

Exploiting Plant Growth Promoting Rhizomicroorganisms for Enhanced Crop Productivity

“…Salamone ( 2000 ) reported the growth-promoting effect of P. fl uorescens strain G20-18 on wheat and radish plants by production of cytokinin phytohormones. As the effect of PGPR on plants was demonstrated, the concept of PGPR began to gain importance and a large number of bacterial strains have been isolated, screened (Cattelan et al 1999 ;Bertrand et al 2001 ) and evaluated for plant growth promotion (Bent et al 2001 ;Salamone 2000 ).…”

Enzyme activities and growth promotion of spinach by indole-3-acetic acid-producing rhizobacteria

“…The PGPR were tested for indole-3-acetic acid (IAA)-like auxin production using the method of Bent et al (2001). Flasks (125 ml) containing 40 ml half-strength TSB were incubated for 18 h at 27°C on a 100 rpm rotary shaker supplemented with 0, 0.1, or 25 µg tryptophan ml -1 , then each was inoculated with 1 ml of each PGPR.…”