Abstract
Plant growth-promoting endophytic bacteria have been widely used during crop production for either single inoculation or co-inoculation with nitrogen-fixing bacteria. The effect of Streptomyces griseoflavus P4 on growth of various crops was studied and the effects of co-inoculation on plant growth, nodulation and nitrogen fixation by soybean was investigated. Pot experiments were conducted in an environmentally controlled room. Nitrogen fixation was evaluated based on acetylene reduction activity (ARA). Significant increases in soybean and maize growth performance were observed after inoculation with S. griseoflavus P4, although some growth parameters were not significant in some crops. S. griseoflavus P4 was co-inoculated with high nitrogen-fixing strains. Co-inoculation of Bradyrhizobium elkanii AHY3-1 with P4 into the Yezin-6 (non-Rj) soybean cultivar resulted in significantly increased root dry weight. Nitrogenase activity also increased due to co-inoculation of B. elkanii AHY3-1 with P4 when compared with single inoculation of this strain. Co-inoculation of Bradyrhizobium japonicum SAY3-7 and B. elkanii AHY3-1 with S. griseoflavus P4 into the Yezin-11 (Rj4) soybean cultivar increased nitrogen fixation significantly by 45 and 31%, respectively, when compared with single inoculation of these strains. Moreover, single or dual inoculation of bradyrhziobial strains resulted in significantly higher shoot biomass than that in the control and P4 alone. These results show that plant growth was promoted by S. griseoflavus P4 and that plant growth and nitrogen fixation were enhanced in soybean after co-inoculation of S. griseoflavus P4 with the Bradyrhizobium strains, B. japonicum SAY3-7 and B. elkanii AHY3-1. Key words: Co-inoculation, growth, nitrogenase activity, single inoculation, soybean, Streptomyces griseoflavus P4.
Highlights
Soils have been the predominant reservoir for the isolation of actinomycetes, the genus Streptomyces and soil microbes have been regarded as important sources of biologically active compounds (Balachandran et al, 2015)
These results show that plant growth was promoted by S. griseoflavus P4 and that plant growth and nitrogen fixation were enhanced in soybean after co-inoculation of S. griseoflavus P4 with the Bradyrhizobium strains, B. japonicum SAY3-7 and B. elkanii AHY3-1
Shoot length in common bean was affected significantly by inoculation with S. griseoflavus P4 (Table 2) none of the other growth parameters differed from the control
Summary
Soils have been the predominant reservoir for the isolation of actinomycetes, the genus Streptomyces and soil microbes have been regarded as important sources of biologically active compounds (Balachandran et al, 2015). Plant growth-promoting rhizobacteria have been used widely in agriculture. They promote plant growth by producing plant growth hormones, such as auxins (Tien et al, 1979), gibberellins (Bottini et al, 1989), cytokinins (Strzelczyk et al, 1994; Tien et al, 1979), ethylene (Strzelczyk et al, 1994) and indole-3-acetic acid (IAA) to improve root growth (Leong, 1996; Merckx et al, 1987; Nimnoi et al, 2010), induce plant resistance to disease and stressors (Wang et al, 2009) and enhance biological nitrogen fixation (Ashraf et al, 2011)
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