0635-B4
Dilfuza Egamberdiyeva 1 and Kielo Haahtela 2
In pot experiments with sandy clay soil the effect of plant-growth-promoting bacteria on seedling growth of Scots pine and silver birch were investigated. Inoculation resulted in statistically significant seedling biomass increases after 12 weeks of pine and birch growth. The bacterial strains Bacillus megaterium KMNL1A and B. longisporus KNOL6 significantly increased the shoot growth of pine and birch. Growth promoting bacteria produced the phytohormon auxin, celulase and pectinase enzymes.
Soil microorganisms are integral components of forest ecosystems, many of which have the potential to influence plant growth significantly (Chanway, 1997). These bacteria are now commonly called plant growth promoting rhizobacteria (PGPR) (Kloepper et al., 1991). PGPR can help the improvement of plant growth, plant nutrition, root growth pattern, and responses to external stress factors, include the production of growth-promoting chemical substances (Kloepper et al., 1988; Muller et al., 1989; Haahtela, et al., 1990; Bothe et al., 1992, Sarwar, 1992; Höflich et al., 1994). Different plant-growth promoting rhizosphere bacteria, including associative bacteria such as Azospirillum, Bacillus, Pseudomonas, Enterobacter group have being used for their beneficial effects on plant growth (Kloepper et al., 1992; Höflich et al. 1994). Rhizosphere bacteria Pseudomonas fluorescens, Rhizobium trifolii and Agrobacterium rghizogenes stimulated seedling growth of pine on forest and arable soils (Hoflich et al, 2001). Inoculation of lodgepole pine seed with Bacillus polymyxa strain L6 increased seedling biomass accumulation relative to uninoculated controls (Chanway et al. 1991a; Chanway and Holl, 1994). The objectives of our study were to investigate the effect of plat growth promoting bacteria on seedling growth of Scots pine and silver birch in sandy clay soil.
The soil (sandy clay) was collected for pot experiment from field site near Helsinki, Finland. The soil chemical and physical properties are presented in Table1.
Table 1. Soil chemical properties, and soil particle distribution at 0-30 cm soil layer.
Type |
Ct Ntot mg . (100g) -1 |
pH |
Soil particle distribution, % | |||
Sand |
Fine sand |
Loam |
Clay | |||
Sandy clay |
410 23 |
5.7 |
24 |
22 |
17 |
37 |
Soil texture was determined by a pipette method according to Elonen. Total C and N concentrations were determined by using an autoanalyzer (leco CHN-900).
Scots pine (Pinus sylvestris) and silver birch (Betula pendula) was employed as the inoculation experiments.
The bacterial strains Paenibacillus borealis KK19, P. pabuli HNNM3, Bacillus megaterium KMNL1A, Bacillus longisporus KNOL6, P. fluorescens KKCK11 from humus spuce stands isolated and identifyed by Elo, et al., (2000). Pectinase activity was detected by the method of Chatterjee and Starr (1972). Cellulase activity was detected according to Andro et al., (1984). All plates for hydrolytic tests were incubated at 28 o C for 3 d. Auxin production was detected by a rapid in situ assay (Bric et al., 1991).
The study of the effect of bacterial strains on seedling growth was carried out in pot experiment with sandy clay soil. The inoculation treatments were set-up in a complete randomised design with four replicates. The day before sowing, pots were filled with 350 g soil. Eight seeds of Scots pine and silver birch were sown per pot. After germination, plants were thinned to two per pot. The bacteria were grown in Luria medium, Pseudomonas strains in King B and Paenibacillus borealis KK19 in Nutrient medium. Tubes were secured on a rotary shaker (120 rpm; 28°C) and agitated for three days. Seedlings of these plants were inoculated with 1 ml of the bacterial suspension that resulted in an inoculum's density of ca. 10 6 x 10 7 cfu/ml. Control seeds received 1 ml medium. Plants were grown in pots for twelve weeks under natural weather conditions with a temperature of 18 to 20°C during the day and 12 to 14°C at night. Twelve weeks after germination, shoots were separated and dried overnight at 80°C before determining the shoot dry weight.
The data were analysed with a single factor ANOVA test for testing the significant differences (p<0.05) of main effects.
Bacterial inoculation affected the seedling growth of pine and birch. The inoculation of pine with effective bacteria significantly (p<0.05) increased the shoot dry weights from 26 to 64% as compared to the control (Fig.1).
Fig.1 The Influence of plant growth promoting bacteria strains on shoot dry matter of Scots pine (Pinus sylvestris) (pot experiment, control=100, Paenibacillus pabuli HNNM3, Pseudomonas fluorescens HNNK14, Bacillus longisporus KNOL6, Bacillus megaterium KMNL1A), *Significantly different from the control for P < 0.05
The most effective shoot and root dry weight-promoting isolate was Bacillus megaterium KMNL1A which generated a 64% increase over the control (Fig.1).
The inoculation of silver birch seedlings with plant growth promoting bacteria increased the shoot dry weight (Fig.2).
Fig.2 The Influence of plant growth promoting bacteria strains on shoot dry matter of silver birch (pot experiment, control=100; Paenibacillus pabuli HNNM3, Pseudomonas fluorescens HNNK14, Pseudomonas fluorescens KKCK11, Paenibacillus borealis KK19), *Significantly different from the control for P < 0.05
The bacterial strains Paenibacillus borealis KK19, Pseudomonas fluorescens KKCK 11 significantly (P<0.05) increased shoot dry weight of silver birch (Fig.2).
Plant growth promoting bacterial strains Bacillus longisporus KNOL6, Pseudomonas fluorescens KKCK11, P. fluorescens HNNK 14 produced phytohormon auxin, and all bacterial strains produced cellulase, pectinase enzymes. They were not antagonistic against plant pathogenic fungi Fusarium culmorum.
This work demonstrated that selected growth-stimulating bacteria isolates are able to increase the growth of Scots pine and silver birch in sandy clay soil. Inoculation with bacterial strains Pseudomonas spp., Arthrobacter spp., and Agrobacterium spp. stimulated pine seedling biomass by up to 35% compared with uninoculated controls after 8 weeks of growth (Holl and Chanway, 1991; Leyval and Berthelin, 1993; Hoflich et al., 2001).
The production of plant growth-promoting substances has been postulated as responsible for the increased plant growth (Kloepper et al., 1991; Höfte et al., 1991; Haahtela et al, 1990). Our effective bacteria isolates Bacillus longisporus KNOL6, Pseudomonas fluorescens KKCK11, P. fluorescens HNNK14 produced auxin and stimulated seedling growth of pine and birch. Hoflich et al., (2001) reported that plant growth-promoting bacteria isolated from mycorrhizosphere of pine produced phytohormone auxin, cellulase and pectinase enzymes and increased seedling growth of pine. Also several workers have demonstrated the production of phytohormones by plant growth promoting bacteria (Holl et al., 1988; Zimmer et al., 1995; Turjanista et al., 1995; Haahtela, 1990).
From the final results we concluded that plant growth promoting bacteria can play an essential role in helping the plant establish and grow of pine and birch. They may belong to different genera and origin.
We thank Seja Elo for providing the bacterial cultures. Prof. Helina Hartikainen is thanked for help in analyzing soil samples. This work was financially supported by the Center of International Mobility Foundation (CIMO).
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1 Institute of Microbiology, Uzbek Academy of Sciences, Abdulla Qadiry 7 B, Tashkent 700128, Uzbekistan
2 Department of Biosciences Division of General Microbiology, Viikinkaari 9 C, University of Helsinki, 00014, Finland
e-mail: [email protected]