Biocontrol of Pythium in the pea rhizosphere by antifungal metabolite producing and non-producing Pseudomonas strains

Abstract

Aims: Four well-described strains of Pseudomonas¯uorescens were assessed for their effect on pea growth and their antagonistic activity against large Pythium ultimum inocula. Methods and Results: The effect of Pseudomonas strains on the indigenous soil micro¯ora, soil enzyme activities and plant growth in the presence and absence of Pythium was assessed. Pythium inoculation reduced the shoot and root weights, root length, and the number of lateral roots. The effect of Pythium was reduced by the Pseudomonas strains. Strains F113, SBW25 and CHAO increased shoot weights (by 20%, 22% and 35%, respectively); strains Q2-87, SBW25 and CHAO increased root weights (14%, 14% and 52%). Strains SBW25 and CHAO increased root lengths (19% and 69%) and increased the number of lateral roots (14% and 29%). All the Pseudomonas strains reduced the number of lesions and the root and soil Pythium populations, while SBW25 and CHAO increased the number of lateral roots. Pythium inoculation increased root and soil microbial populations but the magnitude of this effect was Pseudomonas strain-speci®c. Pythium increased the activity of C, N and P cycle enzymes, while the Pseudomonas strains reduced this effect, indicating reduced plant damage. Conclusions: Strains SBW25 and CHAO had the greatest bene®cial characteristics, as these strains produced the greatest reductions in the side effects of Pythium infection (microbial populations and enzyme activities) and resulted in signi®cantly improved plant growth. Strain SBW25 does not produce antifungal metabolites, and its biocontrol activity was related to a greater colonization ability in the rhizosphere. Signi®cance and Impact of the Study: This is the ®rst critical comparison of such important strains of Ps.¯uorescens showing disease biocontrol potential.

Comparative genomic, proteomic and exoproteomic analyses of three Pseudomonas strains reveals novel insights into the phosphorus scavenging capabilities of soil bacteria

“…Various Pseudomonas strains can also degrade organic P compounds, such as phytate, phosphonates and phosphites (Ternan and Quinn, 1998; White and Metcalf, 2004, 2007). Three Pseudomonas strains , Pseudomonas putida BIRD‐1, Pseudomonas fluorescens SBW25 and Pseudomonas stutzeri DSM4166 (hereafter, BIRD‐1, SBW25 and DSM4166 respectively) are three examples of PGPR (Naseby et al ., 2001; Hass and Keel, 2003; Preston, 2004; Yu et al ., 2011; Roca et al ., 2013). SBW25 inhabits the rhizosphere of Pea plants and is antagonistic towards the pathogen Pythium ultimum (Naseby et al ., 2001), whereas DSM4166, an ‘unusual’ nitrogen‐fixing bacterium, was isolated from a cultivar of Sorghum nutans (Yu et al ., 2011).…”

“…Three Pseudomonas strains , Pseudomonas putida BIRD‐1, Pseudomonas fluorescens SBW25 and Pseudomonas stutzeri DSM4166 (hereafter, BIRD‐1, SBW25 and DSM4166 respectively) are three examples of PGPR (Naseby et al ., 2001; Hass and Keel, 2003; Preston, 2004; Yu et al ., 2011; Roca et al ., 2013). SBW25 inhabits the rhizosphere of Pea plants and is antagonistic towards the pathogen Pythium ultimum (Naseby et al ., 2001), whereas DSM4166, an ‘unusual’ nitrogen‐fixing bacterium, was isolated from a cultivar of Sorghum nutans (Yu et al ., 2011). BIRD‐1, a P‐solubilising bacterium, has been previously utilized as a bioinoculant, since it can significantly improve the germination rates, growth and yields of various agricultural crops (Roca et al ., 2013).…”

Genetic Characterization ofPseudomonas fluorescensSBW25rspGene Expression in the Phytosphere and In Vitro

“…Pathogens, such as Pythium ultimum, can hinder plant growth, whereas strains of Pseudomonas fluorescens, including P. fluorescens SBW25, can promote plant growth. The mechanism of plant growth promotion involves a combination of competition, antagonism of pathogens via the production of antimicrobial compounds, and induction of systemic resistance (15,16,31,34).To understand the interaction between P. fluorescens SBW25 and plants, SBW25 genes specifically activated in the plant environment were identified via a promoter trapping strategy (11,36). Approximately 100 rhizosphere-induced (rhi) genes have been identified and categorized into six groups: nutrient acquisition, stress response, attachment and surface colonization, antibiotic production, secretion, and unknown.…”

“…Pathogens, such as Pythium ultimum, can hinder plant growth, whereas strains of Pseudomonas fluorescens, including P. fluorescens SBW25, can promote plant growth. The mechanism of plant growth promotion involves a combination of competition, antagonism of pathogens via the production of antimicrobial compounds, and induction of systemic resistance (15,16,31,34).…”

Survival and Ecological Fitness of Pseudomonas fluorescens Genetically Engineered with Dual Biocontrol Mechanisms

“…9,10 Protection is attributed to the strong colonising ability of this organism on the roots of the plants, so successfully competitively excluding the pathogenic fungus. This bacterium with the genetic markers xylE, lacZY and KmR on its chromosome was the first free-living genetically modified bacterium to be released into the field to investigate the bio safety of genetically modified bacteria in the environment.…”