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

Amy Novinscak,Martin Filion

doi:10.3389/fsufs.2020.602911

Abstract

Use of plant growth promoting rhizobacteria (PGPR) is an important strategy in sustainable agriculture. Among PGPR, manyPseudomonasstrains 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, asPseudomonasstrains 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 phytobeneficialPseudomonasstrains belonging to two taxonomical groups of interest:P. fluorescensandP. 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 bothPseudomonasstrains 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 toBuglossoides arvensisplantlets, the expected plant growth promotion was observed when using up to 180 day-old formulations ofP. fluorescensand up to 120 day-old formulations ofP. synxantha, with similar results for both carriers. Establishment of bothPseudomonasstrains 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 ofP. fluorecensin the rhizosphere was observed when talc-based bioformulations were stored for 90 days or more, rhizosphere colonization byP. synxanthatalc-based bioformulations remained stable for up to 180 days. In conclusion, both peat and talc appear to be suitable carriers forPseudomonasbioformulations, however strain-specific variability exists and therefore the viability of eachPseudomonasstrain and its capacity to maintain its plant growth promotion activity should be validated in different substrates before determining which formulation to use.

Highlights

The world population is increasing at an alarming rate and is set to reach 9 billion by the year 2050, while the land available for agriculture has been decreasing due to industrialization (Aamir et al, 2020)
The overall results of this study show that bioformulations stable up to 180 days at room temperature were successfully developed for two distinct Pseudomonas species
When trying to determine if peat or talc would be a better carrier in general for Pseudomonas strains, our results indicated that both carriers yielded similar results at most time-points for both bacteria and demonstrated a shelf-life up to 180 days

Summary

Introduction

The world population is increasing at an alarming rate and is set to reach 9 billion by the year 2050, while the land available for agriculture has been decreasing due to industrialization (Aamir et al, 2020). Food production has increased through advances in agriculture such as the use of chemical pesticides and fertilizers, as well as breeding efforts to develop plant cultivars that are more productive and more stress tolerant (Aamir et al, 2020). Studies show that most chemical pesticides used in conventional agriculture can have detrimental effects on human health (Moses et al, 1993; Reigart and Roberts, 2013). In addition to their negative effects on human health, chemical pesticides can negatively affect aquatic systems, the wildlife and the richness of soil microorganisms (Dorigo et al, 2009). The use of chemical fertilizers has been beneficial to achieve greater crop productivity, long-term experiments on the effects of fertilizers on soil fertility have shown that continual use can decrease soil quality (Kumar and Yadav, 2001; Yang, 2006)

Methods

Results

Conclusion