Microbial-Based Plant Biostimulants

A special issue of Microorganisms (ISSN 2076-2607). This special issue belongs to the section "Plant Microbe Interactions".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 20760

Special Issue Editor

Institut de Recherche en Biologie Végétale, Département de Sciences Biologiques, Université de Montréal, Montréal, QC, Canada
Interests: environmental microbiology; plant-microbe interaction; mycorrhizal symbiosis; fungal biology; microbial genomics
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Special Issue Information

Dear Colleagues,

In recent years, major investments have been made globally to develop innovative biotechnologies that will sustain food production while reducing the environmental footprint of agriculture. Among these innovations, plant biostimulants have gained popularity. In this context, plant biostimulants are defined as microorganism-based inoculants, or substances derived from organisms, or a combination of both, that can be applied to plants to enhance nutrient uptake, protect against biotic and abiotic stress, and improve growth parameters (e.g., germination, flowering, fructification, maturity, and crop quality).

Although microbial-based plant biostimulants have been widely used in agriculture, horticulture and forestry, many scientific questions remain unanswered.  This Special Issue seeks research contributions that will advance our knowledge on the effectiveness of microbial-based plant biostimulants and their impact on indigenous microbial communities of soils, as well as on plant microbiota.

The main areas of interest in this Special Issue of Microorganisms on “Microbial-Based Plant Biostimulants” are as follows:

  • Plant growth-promoting rhizobacteria (PGPR);
  • Plant endophytes;
  • Mycorrhizal fungi;
  • Microbial biotechnology;
  • Bioinoculants and biostimulants;
  • Biocontrol.

Prof. Dr. Mohamed Hijri
Guest Editor

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Keywords

  • bioinoculants
  • biostimulants
  • PGPR
  • endophytes
  • mycorrhiza
  • plant microbiota
  • sustainable agriculture

Published Papers (8 papers)

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Editorial

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4 pages, 624 KiB  
Editorial
Microbial-Based Plant Biostimulants
Microorganisms 2023, 11(3), 686; https://doi.org/10.3390/microorganisms11030686 - 07 Mar 2023
Cited by 1 | Viewed by 2318
Abstract
Beneficial microorganisms offer essential ecological services to both natural and agricultural ecosystems [...] Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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Research

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16 pages, 8597 KiB  
Article
Harnessing Novel Soil Bacteria for Beneficial Interactions with Soybean
Microorganisms 2023, 11(2), 300; https://doi.org/10.3390/microorganisms11020300 - 23 Jan 2023
Cited by 2 | Viewed by 2153
Abstract
It is claimed that one g of soil holds ten billion bacteria representing thousands of distinct species. These bacteria play key roles in the regulation of terrestrial carbon dynamics, nutrient cycles, and plant productivity. Despite the overwhelming diversity of bacteria, most bacterial species [...] Read more.
It is claimed that one g of soil holds ten billion bacteria representing thousands of distinct species. These bacteria play key roles in the regulation of terrestrial carbon dynamics, nutrient cycles, and plant productivity. Despite the overwhelming diversity of bacteria, most bacterial species remain largely unknown. Here, we used an oligotrophic medium to isolate novel soil bacteria for positive interaction with soybean. Strictly 22 species of bacteria from the soybean rhizosphere were selected. These isolates encompass ten genera (Kosakonia, Microbacterium, Mycobacterium, Methylobacterium, Monashia, Novosphingobium, Pandoraea, Anthrobacter, Stenotrophomonas, and Rhizobium) and have potential as novel species. Furthermore, the novel bacterial species exhibited plant growth-promoting traits in vitro and enhanced soybean growth under drought stress in a greenhouse experiment. We also reported the draft genome sequences of Kosakonia sp. strain SOY2 and Agrobacterium sp. strain SOY23. Along with our analysis of 169 publicly available genomes for the genera reported here, we demonstrated that these bacteria have a repertoire of genes encoding plant growth-promoting proteins and secondary metabolite biosynthetic gene clusters that directly affect plant growth. Taken together, our findings allow the identification novel soil bacteria, paving the way for their application in crop production. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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23 pages, 4671 KiB  
Article
Bacillus velezensis QA2 Potentially Induced Salt Stress Tolerance and Enhanced Phosphate Uptake in Quinoa Plants
Microorganisms 2022, 10(9), 1836; https://doi.org/10.3390/microorganisms10091836 - 14 Sep 2022
Cited by 7 | Viewed by 2438
Abstract
Plant Growth-Promoting Rhizobacteria (PGPR) have attracted much attention in agriculture biotechnology as biological inputs to sustain crop production. The present study describes a halotolerant phosphate solubilizing bacterium associated with quinoa plant roots. Based on a metabolic screening, one bacterial isolate, named QA2, was [...] Read more.
Plant Growth-Promoting Rhizobacteria (PGPR) have attracted much attention in agriculture biotechnology as biological inputs to sustain crop production. The present study describes a halotolerant phosphate solubilizing bacterium associated with quinoa plant roots. Based on a metabolic screening, one bacterial isolate, named QA2, was selected and screened for PGPR traits. This isolate solubilized both inorganic phosphate and zinc, produced indole-3-acetic acid, ammonia, hydrogen cyanide, cellulase, and (to be deleted) protease, and induced biofilm formation. We demonstrated that QA2 exhibited both antimicrobial and ion metabolism activities and tolerated high salt concentration at up to 11% NaCl. Genotyping analyses, using 16S rRNA and chaperonin cpn60 genes, revealed that QA2 belongs to the species of Bacillus velezensis. Using the quinoa model cultivated under a saline condition, we demonstrated that QA2 promoted plant growth and mitigated the saline irrigation effects. Analysis of harvested plants revealed that QA2 induced a significant increase of both leaf chlorophyll index by 120.86% (p < 0.05) and P uptake by 41.17% (p < 0.05), while the content of Na+ was drastically decreased. Lastly, a bibliometric data analysis highlighted the panoramic view of studies carried out so far on B. velezensis strains. Our investigation presents a holistic view of the potential application of B. velezensis as a biological inoculant to promote plant growth, control pathogen attacks, and mitigate the salinity effect of quinoa plants. Further investigations are still needed to demonstrate these effects in field conditions. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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12 pages, 571 KiB  
Article
Influence on Soybean Aphid by the Tripartite Interaction between Soybean, a Rhizobium Bacterium, and an Arbuscular Mycorrhizal Fungus
Microorganisms 2022, 10(6), 1196; https://doi.org/10.3390/microorganisms10061196 - 11 Jun 2022
Cited by 6 | Viewed by 1843
Abstract
The inoculation of arbuscular mycorrhizal (AM) fungi and rhizobia in legumes has been proven to increase plant growth and yield. To date, studies of the effects of these interactions on phytophagous insects have shown them to be context-dependent depending on the inoculant strain, [...] Read more.
The inoculation of arbuscular mycorrhizal (AM) fungi and rhizobia in legumes has been proven to increase plant growth and yield. To date, studies of the effects of these interactions on phytophagous insects have shown them to be context-dependent depending on the inoculant strain, the plant, and the insect species. Here, we document how a symbiosis involving an AM fungus, Rhizophagus irregularis; a rhizobium, Bradyrhizobium japonicum; and soybean, Glycine max, influences the soybean aphid, Aphis glycines. Soybean co-inoculated with the AM fungus–rhizobium pair increased the plant’s biomass, nodulation, mycorrhizal colonization, nitrogen, and carbon concentrations, but decreased phosphorus concentration. Similar effects were observed with rhizobium alone, with the exception that root biomass was unaffected. With AM fungus alone, we only observed an increase in mycorrhizal colonization and phosphorus concentration. The aphids experienced an increased reproductive rate with the double inoculation, followed by rhizobium alone, whereas no effect was observed with the AM fungus. The size of individual aphids was not affected. Furthermore, we found positive correlation between nitrogen concentration and aphid population density. Our results confirm that co-inoculation of two symbionts can enhance both plant and phytophagous insect performance beyond what either symbiont can contribute alone. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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11 pages, 314 KiB  
Article
The Effects of an Arbuscular Mycorrhizal Fungus and Rhizobium Symbioses on Soybean Aphid Mostly Fail to Propagate to the Third Trophic Level
Microorganisms 2022, 10(6), 1158; https://doi.org/10.3390/microorganisms10061158 - 04 Jun 2022
Cited by 1 | Viewed by 1826
Abstract
The cascading effects of microbe–plant symbioses on the second trophic level, such as phytophagous insects, have been most studied. However, few studies have examined the higher third trophic level, i.e., their natural enemies. We investigated the effects of the symbiotic associations between an [...] Read more.
The cascading effects of microbe–plant symbioses on the second trophic level, such as phytophagous insects, have been most studied. However, few studies have examined the higher third trophic level, i.e., their natural enemies. We investigated the effects of the symbiotic associations between an arbuscular mycorrhizal (AM) fungus, Rhizophagus irregularis (Glomerales: Glomeraceae), a nitrogen-fixing bacterium, Bradyrhizobium japonicum (Rhizobiales: Bradyrhizobiaceae), and soybean, Glycine max (L.) Merr. (Fabaceae) on two natural enemies of the soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), the ladybird beetle Coleomegilla maculata (De Geer) (Coleoptera: Coccinellidae), and the parasitoid Aphelinus certus Yasnosh (Hymenoptera: Aphelinidae). We measured the growth and survival in the predator and parasitoid reared on aphids feeding on soybean inoculated seedlings. The rhizobium symbiosis alone was affected with a decreased rate of parasitoid emergence, presumably due to decreased host quality. However, number of mummies, sex-ratio, development time, and parasitoid size were all unaffected by inoculation. AM fungus alone or co-inoculated with the rhizobium was unaffected with any of the parameters of the parasitoid. For the predator, none of the measured parameters was affected with any inoculant. Here, it appears that whatever benefits the microbe–plant symbioses confer on the second trophic level are little transferred up to the third. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)

Review

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22 pages, 1270 KiB  
Review
The Potential Applications of Commercial Arbuscular Mycorrhizal Fungal Inoculants and Their Ecological Consequences
Microorganisms 2022, 10(10), 1897; https://doi.org/10.3390/microorganisms10101897 - 23 Sep 2022
Cited by 13 | Viewed by 2660
Abstract
Arbuscular mycorrhizal fungal (AMF) inoculants are sustainable biological materials that can provide several benefits to plants, especially in disturbed agroecosystems and in the context of phytomanagement interventions. However, it is difficult to predict the effectiveness of AMF inoculants and their impacts on indigenous [...] Read more.
Arbuscular mycorrhizal fungal (AMF) inoculants are sustainable biological materials that can provide several benefits to plants, especially in disturbed agroecosystems and in the context of phytomanagement interventions. However, it is difficult to predict the effectiveness of AMF inoculants and their impacts on indigenous AMF communities under field conditions. In this review, we examined the literature on the possible outcomes following the introduction of AMF-based inoculants in the field, including their establishment in soil and plant roots, persistence, and effects on the indigenous AMF community. Most studies indicate that introduced AMF can persist in the target field from a few months to several years but with declining abundance (60%) or complete exclusion (30%). Further analysis shows that AMF inoculation exerts both positive and negative impacts on native AMF species, including suppression (33%), stimulation (38%), exclusion (19%), and neutral impacts (10% of examined cases). The factors influencing the ecological fates of AMF inoculants, such as the inherent properties of the inoculum, dosage and frequency of inoculation, and soil physical and biological factors, are further discussed. While it is important to monitor the success and downstream impacts of commercial inoculants in the field, the sampling method and the molecular tools employed to resolve and quantify AMF taxa need to be improved and standardized to eliminate bias towards certain AMF strains and reduce discrepancies among studies. Lastly, inoculant producers must focus on selecting strains with a higher chance of success in the field, and having little or negligible downstream impacts. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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22 pages, 731 KiB  
Review
Diversity of Phosphate Chemical Forms in Soils and Their Contributions on Soil Microbial Community Structure Changes
Microorganisms 2022, 10(3), 609; https://doi.org/10.3390/microorganisms10030609 - 13 Mar 2022
Cited by 29 | Viewed by 4199
Abstract
In many soils, the bioavailability of Phosphorus (P), an essential macronutrient is a limiting factor for crop production. Among the mechanisms developed to facilitate the absorption of phosphorus, the plant, as a holobiont, can rely on its rhizospheric microbial partners. Therefore, microbial P-solubilizing [...] Read more.
In many soils, the bioavailability of Phosphorus (P), an essential macronutrient is a limiting factor for crop production. Among the mechanisms developed to facilitate the absorption of phosphorus, the plant, as a holobiont, can rely on its rhizospheric microbial partners. Therefore, microbial P-solubilizing inoculants are proposed to improve soil P fertility in agriculture. However, a better understanding of the interactions of the soil-plant-microorganism continuum with the phosphorus cycle is needed to propose efficient inoculants. Before proposing further methods of research, we carried out a critical review of the literature in two parts. First, we focused on the diversity of P-chemical forms. After a review of P forms in soils, we describe multiple factors that shape these forms in soil and their turnover. Second, we provide an analysis of P as a driver of microbial community diversity in soil. Even if no rule enabling to explain the changes in the composition of microbial communities according to phosphorus has been shown, this element has been perfectly targeted as linked to the presence/absence and/or abundance of particular bacterial taxa. In conclusion, we point out the need to link soil phosphorus chemistry with soil microbiology in order to understand the variations in the composition of microbial communities as a function of P bioavailability. This knowledge will make it possible to propose advanced microbial-based inoculant engineering for the improvement of bioavailable P for plants in sustainable agriculture. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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Other

8 pages, 254 KiB  
Perspective
Does Commercial Inoculation Promote Arbuscular Mycorrhizal Fungi Invasion?
Microorganisms 2022, 10(2), 404; https://doi.org/10.3390/microorganisms10020404 - 09 Feb 2022
Cited by 10 | Viewed by 2305
Abstract
Interventions with commercial inoculants have the potential to reduce the environmental footprint of agriculture, but their indiscriminate deployment has raised questions on the unintended consequences of microbial invasion. In the absence of explicit empirical reports on arbuscular mycorrhizal fungi (AMF) invasion, we examine [...] Read more.
Interventions with commercial inoculants have the potential to reduce the environmental footprint of agriculture, but their indiscriminate deployment has raised questions on the unintended consequences of microbial invasion. In the absence of explicit empirical reports on arbuscular mycorrhizal fungi (AMF) invasion, we examine the present framework used to define AMF invasion and offer perspectives on the steps needed to avoid the negative impacts of AMF invasion. Although commercial AMF isolates are potential invaders, invasions do not always constitute negative impacts on native community diversity and functions. Instead, the fates of the invading and resident communities are determined by ecological processes such as selection, drift, dispersal, and speciation. Nevertheless, we recommend strategies that reduce overdependence on introduced inoculants, such as adoption management practices that promote the diversity and richness of indigenous AMF communities, and the development of native propagules as a supplement to commercial AMF in applicable areas. Policies and regulations that monitor inoculant value chains from production to application must be put in place to check inoculant quality and composition, as well as the transport of inoculants between geographically distant regions. Full article
(This article belongs to the Special Issue Microbial-Based Plant Biostimulants)
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