Long Term Comparison of Talc- and Peat-Based Phytobeneficial Pseudomonas fluorescens and Pseudomonas synxantha Bioformulations for Promoting Plant Growth

Abstract

Use of plant growth promoting rhizobacteria (PGPR) is an important strategy in sustainable agriculture. Among PGPR, many Pseudomonas strains are of great interest due to their abilities to colonize and thrive in the rhizosphere, in addition to displaying mechanisms in plant growth promotion and biocontrol activities. However, as Pseudomonas strains are non-spore forming micro-organisms, their development into stable bioformulations for commercial applications can be difficult. This study examined over a long term period the effect of two different carriers, peat and talc, to prepare bioformulations using phytobeneficial Pseudomonas strains belonging to two taxonomical groups of interest: P. fluorescens and P. synxantha. Each strain has previously demonstrated plant growth promotion activity when inoculated in the rhizosphere. Each bioformulation was stored at ambient temperature and their viability was measured up to 180 days. In parallel, every 30 days (up to 180 days) each bioformulation was also applied in the rhizosphere of plantlets to validate their plant growth promotion activity, and their establishment in the rhizosphere was quantified by using strain-specific quantitative polymerase chain reaction assays. The viability of both Pseudomonas strains in the bioformulations was found to decrease after the first 15 days and remained relatively stable for up to 180 days. When applying the bioformulations to Buglossoides arvensis plantlets, the expected plant growth promotion was observed when using up to 180 day-old formulations of P. fluorescens and up to 120 day-old formulations of P. synxantha, with similar results for both carriers. Establishment of both Pseudomonas strains in the rhizosphere inoculated with the peat-based carrier bioformulations stored for up to 180 days was found to be stable. While a lower establishment of P. fluorecens in the rhizosphere was observed when talc-based bioformulations were stored for 90 days or more, rhizosphere colonization by P. synxantha talc-based bioformulations remained stable for up to 180 days. In conclusion, both peat and talc appear to be suitable carriers for Pseudomonas bioformulations, however strain-specific variability exists and therefore the viability of each Pseudomonas strain and its capacity to maintain its plant growth promotion activity should be validated in different substrates before determining which formulation to use.

Cellulose Acetate-Stabilized Pickering Emulsions: Preparation, Rheology, and Incorporation of Agricultural Active Ingredients

“…During the first 3 weeks, both the emulsion and the control show similar viability, following which the control shows a gradual loss of the cells, whereas the emulsions maintained a viability of 10 8 CFU/mL after 10 weeks of storage. These cell viability values are in the range for reported values of peat and talc-based dry carriers after 60–90 days of storage. Furthermore, our initial bacteria concentration of 10 9 CFU/mL incorporated within the emulsions is also much lower than previously reported values mostly in the range of ∼10 11 CFU/mL .…”

“…The high cell viabilities observed for Pseudomonas simiae are particularly promising since it holds potential for the development of a suitable formulation for loading other nonsporulating PGPM such as P. fluorescens 1629RS, P. syringae 724RS, P. chlororaphis 63–28 . While some Pseudomonas strains are commercially available, their current market share represents only 6% of the total biobased agriculture industry . The lack of suitable formulation platforms is a big deterrent in utilizing them to their full potential.…”

“…While prior work in the area includes reports on encapsulation of fungal conidia and sporulating bacteria such as Bacillus thuringiensis , there is a dearth of data for suitable loading platforms for Gram-negative nonsporulating bacteria due to the technical challenges associated with maintaining viability in the absence of spores . Proposed research solutions include use of dry carrier systems such as peat, talc alginate/gelatin nanocomposites, or air-dried and lyophilized dry powders with limitations including high costs for freeze-drying, high initial inoculant load to maintain viability, and nonuniform inoculant distribution . An emulsion-based formulation employing comparatively lower initial inoculant loads can potentially address these issues.…”

Optimizing Shelf-life of Pseudomonas fluorescens after Freeze Drying

“…Peat is very common used carrier material globally and has high content of organic matter, water holding capacity, and simply obtainable [19]. In previous study, it was found that peat showed good efficacy in formulation, and help colonization in plant roots when peat was used for bio formulation of P. fluorescens [20]. Nakkeeran et al also observed similar potential results of peat-based formulation for P. chlororaphis shelf-life [21].…”

Biocontrol rhizobacteria enhances growth and yield of wheat ( Triticum aestivum ) under field conditions against Fusarium oxysporum

“…40% of the 8.3 × 10 8 CFU/g BCB16 were added to the autoclaved talc powder, and the number of microbes were counted using serial dilution method every 30 days for 4 months. Novinscak and Filion [ 43 ] found that using talc powder as a carrier material for the Pseudomonas strain resulted in a stable microbe population. Tamreihao et al [ 44 ] compared corn starch and talc powder as biofertilizer formulations and concluded that the talc formulation has a higher cell count than corn starch.…”