Multistrain versus single-strain plant growth promoting microbial inoculants - The compatibility issue

Abstract

Summary Plant Growth Promoting Microorganisms or Plant Probiotics (PGPMs) constitute a promising solution for agricultural sustainability. The concept that inoculation of PGPM mixtures may perform better in enhancing agricultural production than single strain application dates back to the discovery of plant growth rhizobacteria (PGPR) and is gaining ground in our days. This shift is highlighted by the increasing number of research publications dealing with the positive impact of microbial mixtures in promoting plant growth, controlling plant pathogens, as well as providing abiotic stress tolerance. The continuous deposition of patents as well as commercially available formulations concerning bioprotective and/or biostimulant multistrain mixtures also underlines this shift. A major issue in engineering an effective and consistent synthetic multistrain mixture appears to be the compatibility of its components. The present review provides a thorough literature survey supporting the view that treatment of plants with compatible multistrain mixtures generally exerts a better effect in plant growth and health than single-strain inoculation. Our study focuses on multistrain mixtures based on Pseudomonas, Bacillus and beneficial fungal strains, while commercial products are also being referred.

Microbial Interactions Within Multiple-Strain Biological Control Agents Impact Soil-Borne Plant Disease

“…The enhancement of disease inhibition by MSBCAs is widely thought to be due to the addition of different features for control ( Pierson and Weller, 1994 ; Sarma et al, 2015 ). Occupation of distinct niches in the rhizosphere may avoid competition among probiotic microorganisms, resulting in more stable rhizosphere communities ( Pierson and Weller, 1994 ; Pliego et al, 2008 ; Thomloudi et al, 2019 ). Modulation of genetic elements ( Lutz et al, 2004 ) and suppression of a broader range of phytopathogens ( Pierson and Weller, 1994 ; Thomloudi et al, 2019 ) may account for the elevated biocontrol activity in microbial communities.…”

“…Occupation of distinct niches in the rhizosphere may avoid competition among probiotic microorganisms, resulting in more stable rhizosphere communities ( Pierson and Weller, 1994 ; Pliego et al, 2008 ; Thomloudi et al, 2019 ). Modulation of genetic elements ( Lutz et al, 2004 ) and suppression of a broader range of phytopathogens ( Pierson and Weller, 1994 ; Thomloudi et al, 2019 ) may account for the elevated biocontrol activity in microbial communities. In addition, some key features related to the disease-controlling effect of BCAs, including rhizosphere colonization and suppression of pathogen growth, can be promoted in consortia via a complex network of microbe−microbe interactions.…”

“…We noted that microorganisms used for developing biocontrol consortia were often selected according to their individual disease suppressive capacity. However, except for this property, no precise selection standards have been adopted to choose microbial components ( Sarma et al, 2015 ; Thomloudi et al, 2019 ). This approach often results in equal or even lower efficacy of the multi-strain mixtures compared to the individual strains ( Sarma et al, 2015 ).…”

“…The members of a probiotic consortium are considered to be compatible when they do not inhibit growth of each other during their in vitro co-culture and/or in rhizosphere colonization competition assays ( Liu et al, 2018 ; Thomloudi et al, 2019 ). Co-inoculation with incompatible isolates might hinder one or more microbial agents from reaching the appropriate population threshold for plant disease control ( Haas and Defago, 2005 ).…”

“…In several cases, superior disease suppression exerted by MSBCAs has been reported ( Table 1 ). Diverse modes of action were proposed: (i) diversity in biocontrol mechanisms offered by each microbial component ( Pierson and Weller, 1994 ; Sarma et al, 2015 ), (ii) occupation of distinctive niches by probiotic microorganisms resulting in more stable communities ( Pierson and Weller, 1994 ; Pliego et al, 2008 ; Thomloudi et al, 2019 ), (iii) enhanced modulation of genetic elements acting in the community ( Lutz et al, 2004 ), and (iv) a broader spectrum of targeted phytopathogens ( Sarma et al, 2015 ; Thomloudi et al, 2019 ) may contribute to greater biocontrol activity in communities. However, our understanding of the mechanisms underlying the reinforcement of their disease-inhibitory effects by MSBCAs is still very limited.…”