Abstract
Bacillus amyloliquefaciens QST713 and B. firmus I-1582 are bacterial strains which are used as active ingredients of commercially-available soil application and seed treatment products Serenade® and VOTiVO®, respectively. These bacteria colonize plant roots promoting plant growth and offering protection against pathogens/pests. The objective of this study was to develop a qPCR protocol to quantitate the dynamics of root colonization by these two strains under field conditions. Primers and TaqMan® probes were designed based on genome comparisons of the two strains with publicly-available and unpublished bacterial genomes of the same species. An optimized qPCR protocol was developed to quantify bacterial colonization of corn roots after seed treatment. Treated corn seeds were planted in non-sterile soil in the greenhouse and grown for 28 days. Specific detection of bacteria was quantified weekly, and showed stable colonization between ~104–105 CFU/g during the experimental period for both bacteria, and the protocol detected as low as 103 CFU/g bacteria on roots. In a separate experiment, streptomycin-resistant QST713 and rifampicin-resistant I-1582 strains were used to compare dilution-plating on TSA with the newly developed qPCR method. Results also indicated that the presence of natural microflora and another inoculated strain does not affect root colonization of either one of these strains. The same qPCR protocol was used to quantitate root colonization by QST713 and I-1582 in two corn and two soybean varieties grown in the field. Both bacteria were quantitated up to two weeks after seeds were planted in the field and there were no significant differences in root colonization in either bacteria strain among varieties. Results presented here confirm that the developed qPCR protocol can be successfully used to understand dynamics of root colonization by these bacteria in plants growing in growth chamber, greenhouse and the field.
Highlights
Plant growth-promoting rhizobacteria (PGPR) are a group of bacteria that colonize plant roots and provide beneficial effects on plant growth and development [1]
Two standard curves were constructed to quantify B. firmus I-1582 and B. amyloliquefaciens QST713 cells associated with corn and soybean roots
The aim of this study was to develop a qPCR-based protocol to quantitate total root colonization by two PGPR strains, B. firmus I-1582 and B. amyloliquefaciens QST713 in corn seedlings grown in natural soil
Summary
Plant growth-promoting rhizobacteria (PGPR) are a group of bacteria that colonize plant roots and provide beneficial effects on plant growth and development [1]. PGPR have direct or indirect effects on plant growth promotion and improved crop yield. Direct effects of PGPR include providing plants with fixed nitrogen and phytohormones, increasing the availability of nitrogen, soluble phosphate and minerals in the soil and control or inhibition of the activity of plant pathogens [6,7,8,9]. Most of the commercially available PGPR products contain Bacillus strains [10]. Many of these Bacillus spp. are developed as biocontrol agents of plant pests [5]. Bacillus species such as B. amyloliquefaciens, B. licheniformis, B. pumilus and B. subtilis are available in the market as biofungicide formulations [17]
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