Microbial Biological Control Agents Research Articles

Design of Carboxymethylcellulose/Poloxamer-Based Bioformulation Embedding Trichoderma afroharzianum for Agricultural Applications.

Microbial biological control agents are believed to be a potential alternative to classical fertilizers to increase the sustainability of agriculture. In this work, the formulation of Trichoderma afroharzianum T22 (T22) spores with carboxymethyl cellulose (CMC) and Pluronic F-127 (PF-127) solutions was investigated. Rheological and microscopical analysis were performed on T22-based systems at three different CMC/PF-127 concentrations, showing that polymer aggregates tend to surround T22 spores, without viscosity, and the viscoelastic properties of the formulations were affected. Contact angle measurements showed the ability of PF-127 to increase the wettability of the systems, and the effect of the formulations on the viability of the spores was evaluated. The viability of the spores was higher over 21 days in all the formulations, compared to the control in water, at 4 and 25 °C. Finally, the effectiveness of the formulations on sweet basil was estimated by greenhouse tests. The results revealed a beneficial effect of the CMC/PF-127 mixture, but none on the formulation with T22. The data show the potential of CMC/PF-127 mixtures for the future design of microorganism-based formulations.

Pythium oligandrum induces growth promotion in starch potato without significantly altering the rhizosphere microbiome

Plant health promoting organisms, including microbial biological control agents, are of increasing importance for the development of more sustainable agriculture. To understand the function of these microbes as biological control agents under field conditions and their overall impact on soil and plant health, we need to learn more about the impact of plant beneficial microbes on the rhizosphere microbiome of crops such as potato. The plant beneficial oomycete Pythium oligandrum has previously been reported both as a biocontrol agent and as a plant growth promoter, or biostimulant, in several crop species. To investigate the potential of P. oligandrum as a biostimulant in potato, we performed a series of controlled-environment bioassays in three cultivars. We showed that biostimulation of potato by P. oligandrum is plant genotype-specific. We confirmed the biostimulation by P. oligandrum in the starch potato cultivar Kuras under field conditions. We further investigated the effects of P. oligandrum on the potato rhizosphere microbiome, sampling individual potato plants at three time points over the growing season (representing the vegetative growth phase, flowering, and the onset of senescence). Metabarcoding using ITS and 16S amplicon sequencing revealed no significant overall effect of P. oligandrum application on the bacterial and fungal rhizosphere communities. However, some genera were significantly differentially abundant after P. oligandrum application, including some classified as plant-beneficial microbes. We conclude that P. oligandrum has a cultivar-dependent growth-promoting effect in potato and only minor effects on the rhizosphere microbiome.

Manipulating multi-level selection in a fungal entomopathogen reveals social conflicts and a method for improving biocontrol traits.

Changes in parasite virulence are commonly expected to lead to trade-offs in other life history traits that can affect fitness. Understanding these trade-offs is particularly important if we want to manipulate the virulence of microbial biological control agents. Theoretically, selection across different spatial scales, i.e. between- and within-hosts, shapes these trade-offs. However, trade-offs are also dependent on parasite biology. Despite their applied importance the evolution of virulence in fungal parasites is poorly understood: virulence can be unstable in culture and commonly fails to increase in simple passage experiments. We hypothesized that manipulating selection intensity at different scales would reveal virulence trade-offs in a fungal pathogen of aphids, Akanthomyces muscarius. Starting with a genetically diverse stock we selected for speed of kill, parasite yield or infectivity by manipulating competition within and between hosts and between-populations of hosts over 7 rounds of infection. We characterized ancestral and evolved lineages by whole genome sequencing and by measuring virulence, growth rate, sporulation and fitness. While several lineages showed increases in virulence, we saw none of the trade-offs commonly found in obligately-killing parasites. Phenotypically similar lineages within treatments often shared multiple single-nucleotide variants, indicating strong convergent evolution. The most dramatic phenotypic changes were in timing of sporulation and spore production in vitro. We found that early sporulation led to reduced competitive fitness but could increase yield of spores on media, a trade-off characteristic of social conflict. Notably, the selection regime with strongest between-population competition and lowest genetic diversity produced the most consistent shift to early sporulation, as predicted by social evolution theory. Multi-level selection therefore revealed social interactions novel to fungi and showed that these biocontrol agents have the genomic flexibility to improve multiple traits-virulence and spore production-that are often in conflict in other parasites.

Integrated Management of Pathogens and Microbes in Cannabis sativa L. (Cannabis) under Greenhouse Conditions

The increased cultivation of high THC-containing Cannabis sativa L. (cannabis), particularly in greenhouses, has resulted in a greater incidence of diseases and molds that can negatively affect the growth and quality of the crop. Among them, the most important diseases are root rots (Fusarium and Pythium spp.), bud rot (Botrytis cinerea), powdery mildew (Golovinomyces ambrosiae), cannabis stunt disease (caused by hop latent viroid), and a range of microbes that reduce post-harvest quality. An integrated management approach to reduce the impact of these diseases/microbes requires combining different approaches that target the reproduction, spread, and survival of the associated pathogens, many of which can occur on the same plant simultaneously. These approaches will be discussed in the context of developing an integrated plan to manage the important pathogens of greenhouse-grown cannabis at different stages of plant development. These stages include the maintenance of stock plants, propagation through cuttings, vegetative growth of plants, and flowering. The cultivation of cannabis genotypes with tolerance or resistance to various pathogens is a very important approach, as well as the maintenance of pathogen-free stock plants. When combined with cultural approaches (sanitation, management of irrigation, and monitoring for diseases) and environmental approaches (greenhouse climate modification), a significant reduction in pathogen development and spread can be achieved. The use of preventive applications of microbial biological control agents and reduced-risk biorational products can also reduce disease development at all stages of production in jurisdictions where they are registered for use. The combined use of promising strategies for integrated disease management in cannabis plants during greenhouse production will be reviewed. Future areas for research are identified.

Physiological Effects of Microbial Biocontrol Agents in the Maize Phyllosphere.

In a world with constant population growth, and in the context of climate change, the need to supply the demand of safe crops has stimulated an interest in ecological products that can increase agricultural productivity. This implies the use of beneficial organisms and natural products to improve crop performance and control pests and diseases, replacing chemical compounds that can affect the environment and human health. Microbial biological control agents (MBCAs) interact with pathogens directly or by inducing a physiological state of resistance in the plant. This involves several mechanisms, like interference with phytohormone pathways and priming defensive compounds. In Argentina, one of the world's main maize exporters, yield is restricted by several limitations, including foliar diseases such as common rust and northern corn leaf blight (NCLB). Here, we discuss the impact of pathogen infection on important food crops and MBCA interactions with the plant's immune system, and its biochemical indicators such as phytohormones, reactive oxygen species, phenolic compounds and lytic enzymes, focused mainly on the maize-NCLB pathosystem. MBCA could be integrated into disease management as a mechanism to improve the plant's inducible defences against foliar diseases. However, there is still much to elucidate regarding plant responses when exposed to hemibiotrophic pathogens.

Microbial Consortia for Plant Protection against Diseases: More than the Sum of Its Parts.

Biological plant protection presents a promising and exciting alternative to chemical methods for safeguarding plants against the increasing threats posed by plant diseases. This approach revolves around the utilization of biological control agents (BCAs) to suppress the activity of significant plant pathogens. Microbial BCAs have the potential to effectively manage crop disease development by interacting with pathogens or plant hosts, thereby increasing their resistance. However, the current efficacy of biological methods remains unsatisfactory, creating new research opportunities for sustainable plant cultivation management. In this context, microbial consortia, comprising multiple microorganisms with diverse mechanisms of action, hold promise in terms of augmenting the magnitude and stability of the overall antipathogen effect. Despite scientific efforts to identify or construct microbial consortia that can aid in safeguarding vital crops, only a limited number of microbial consortia-based biocontrol formulations are currently available. Therefore, this article aims to present a complex analysis of the microbial consortia-based biocontrol status and explore potential future directions for biological plant protection research with new technological advancements.

Isolation of a highly virulent Metarhizium strain targeting the tea pest, Ectropis obliqua.

Tea is one of the most widely consumed beverages around the world. Larvae of the moth, Ectropis obliqua Prout (Geometridae, Lepidoptera), are one of the most destructive insect pests of tea in China. E. obliqua is a polyphagus insect that is of increasing concern due to the development of populations resistant to certain chemical insecticides. Microbial biological control agents offer an environmentally friendly and effective means for insect control that can be compatible with "green" and organic farming practices. To identify novel E. obliqua biological control agents, soil and inset cadaver samples were collected from tea growing regions in the Fujian province, China. Isolates were analyzed morphologically and via molecular characterization to identity them at the species level. Laboratory and greenhouse insect bioassays were used to determine the effectiveness of the isolates for E. obliqua control. Eleven isolates corresponding to ten different species of Metarhizium were identified according to morphological and molecular analyses from soil and/or insect cadavers found on tea plants and/or in the surrounding soil sampled from eight different regions within the Fujian province, China. Four species of Metarhizium including M. clavatum, M. indigoticum, M. pemphigi, and M. phasmatodeae were documented for the first time in China, and the other species were identified as M. anisopliae, M. brunneum, M. lepidiotae, M. majus, M. pinghaense, and M. robertsii. Insect bioassays of the eleven isolates of Metarhizium revealed significant variation in the efficacy of each isolate to infect and kill E. obliqua. Metarhizium pingshaense (MaFZ-13) showed the highest virulence reaching a host target mortality rate of 93% in laboratory bioassays. The median lethal concentration (LC50) and median lethal time (LT50) values of M. pingshaense MaFZ-13 were 9.6 × 104 conidia/mL and 4.8 days, respectively. Greenhouse experiments and a time-dose-mortality (TDM) models were used to further evaluate and confirm the fungal pathogenic potential of M. pingshaense MaFZ-13 against E. obliqua larvae. Isolation of indigenous microbial biological control agents targeting specific pests is an effective approach for collecting resources that can be exploited for pest control with lowered obstacles to approval and commercialization. Our data show the presence of four different previously unreported Metarhizium species in China. Bioassays of the eleven different Metarhizium strains isolated revealed that each could infect and kill E. obliqua to different degrees with the newly isolated M. pingshaense MaFZ-13 strain representing a particularly highly virulent isolate potentially applicable for the control of E. obliqua larvae.

Interaction between Plants and Microorganisms: Microbial Biological Control Agents against Plant Pathogens

Plant pathogenic bacteria are a substantial and long-term danger to food supply and environmental stability across the planet. With the increase in agricultural productivity in the last few decades, farmers are getting reliant on agrochemicals as a reasonably consistent means of crop protection. But increased use of chemical inputs has various negative consequences, including disease resistance to the agents used and non-target environmental repercussions. Hence biological control is being explored as an alternative or supplement to chemical control in agriculture. This study reviews the interactions taking place between a given microorganism (fungi, bacteria, viruses) and a plant. The relation between the two organisms in the discussion can be encompassed in an elaborate manner based on the mutual gains and losses incurred by both the organisms. Microbes that interact with plants, can be manipulated and used as Biological Control Agents (BCA). BCAs are potentially seen as the alternative to using harmful chemicals in the name of fertilizers and weedicides. This study illustrates the various possible interactions between plant and other species, with specific emphasis on bacterial biocontrol and tries to answer the question: How can these interactions be articulated against a third, pathogenic and harmful species?

Best practices in the use and exchange of microorganism biological control genetic resources

The Nagoya Protocol actions the third objective of the Convention on Biological Diversity and provides a framework to effectively implement the fair and equitable sharing of benefits arising out of the use of genetic resources. This includes microorganisms used as biological control agents. Thus biological control practitioners must comply with access and benefit-sharing regulations that are implemented by countries providing microbial biological control agents. A review of best practices and guidance for the use and exchange of microorganisms used for biological control has been prepared by the IOBC Global Commission on Biological Control and Access and Benefit-Sharing to demonstrate commitment to comply with access and benefit-sharing requirements, and to reassure the international community that biological control is a very successful and environmentally safe pest management strategy that uses biological resources responsibly and sustainably. We propose that best practices include the following elements: collaboration to facilitate information exchange about the availability of microbial biological control agents and where they may be sourced; freely sharing available knowledge in databases about successes and failures; collaborative research with provider countries to develop capacity; and production technology transfer to provide economic opportunities. We recommend the use of model concept agreements for accessing microorganisms for scientific research and non-commercial release into nature where access and benefit-sharing regulations exist and where regulations are not restrictive or do not exist. We also recommend a model agreement for deposition of microbial biological control agents into culture collections.

Making the best of research investment in pathogens control through biocontrol. How is research correlated with agricultural microbial biological control product availability?

While using microbial biological control products (MBCPs) to limit pathogens is one of the alternatives to the ecologically unsustainable use of synthetic pesticides that received attention, the last 2 decades have not brought the foreseen leap in developing systematic alternatives based on low-risk plant protection products (PPPs) across the globe. To explain this limited progress, we map the evolution of research on the most successful microbial biological control agents (MBCAs) worldwide. We also map the financing structure in the top funding countries and the European Union (EU) to discern the relevant trends. Available data for the European Union Member States allowed us to discover a country-level and EU-level correlation between strain-level research and biocontrol products' approval based on those strains.

Uniting the Role of Endophytic Fungi against Plant Pathogens and Their Interaction.

Endophytic fungi are used as the most common microbial biological control agents (MBCAs) against phytopathogens and are ubiquitous in all plant parts. Most of the fungal species have roles against a variety of plant pathogens. Fungal endophytes provide different services to be used as pathogen control agents, using an important aspect in the form of enhanced plant growth and induced systemic resistance, produce a variety of antifungal secondary metabolites (lipopeptides, antibiotics and enzymes) through colonization, and compete with other pathogenic microorganisms for growth factors (space and nutrients). The purpose of this review is to highlight the biological control potential of fungal species with antifungal properties against different fungal plant pathogens. We focused on the introduction, biology, isolation, identification of endophytic fungi, and their antifungal activity against fungal plant pathogens. The endosymbionts have developed specific genes that exhibited endophytic behavior and demonstrated defensive responses against pathogens such as antibiosis, parasitism, lytic enzyme and competition, siderophore production, and indirect responses by induced systemic resistance (ISR) in the host plant. Finally, different microscopic detection techniques to study microbial interactions (endophytic and pathogenic fungal interactions) in host plants are briefly discussed.

Plant growth-promoting microorganisms as biocontrol agents of plant diseases: Mechanisms, challenges and future perspectives.

Plant diseases and pests are risk factors that threaten global food security. Excessive chemical pesticide applications are commonly used to reduce the effects of plant diseases caused by bacterial and fungal pathogens. A major concern, as we strive toward more sustainable agriculture, is to increase crop yields for the increasing population. Microbial biological control agents (MBCAs) have proved their efficacy to be a green strategy to manage plant diseases, stimulate plant growth and performance, and increase yield. Besides their role in growth enhancement, plant growth-promoting rhizobacteria/fungi (PGPR/PGPF) could suppress plant diseases by producing inhibitory chemicals and inducing immune responses in plants against phytopathogens. As biofertilizers and biopesticides, PGPR and PGPF are considered as feasible, attractive economic approach for sustainable agriculture; thus, resulting in a “win-win” situation. Several PGPR and PGPF strains have been identified as effective BCAs under environmentally controlled conditions. In general, any MBCA must overcome certain challenges before it can be registered or widely utilized to control diseases/pests. Successful MBCAs offer a practical solution to improve greenhouse crop performance with reduced fertilizer inputs and chemical pesticide applications. This current review aims to fill the gap in the current knowledge of plant growth-promoting microorganisms (PGPM), provide attention about the scientific basis for policy development, and recommend further research related to the applications of PGPM used for commercial purposes.

Beauty and the pathogens: A leaf-less control presents a better image of Cymbidium orchids defense strategy.

Biological control is a safe way of combating plant diseases using the living organisms. For the precise use of microbial biological control agents, the genetic information on the hypersensitive response (HR), and defense-related gene induction pathways of plants are necessary. Orchids are the most prominent stakeholders of floriculture industry, and owing to their long-awaited flowering pattern, disease control is imperative to allow healthy vegetative growth that spans more than 2 years in most of the orchids. We observed leaf-less flowering in three orchid species (Cymbidium ensifolium, C. goeringii and C. sinense). Using these materials as reference, we performed transcriptome profiling for healthy leaves from non-infected plants to identify genes specifically involved in plant-pathogen interaction pathway. For this pathway, a total of 253 differentially expressed genes (DEGs) were identified in C. ensifolium, 189 DEGs were identified in C. goeringii and 119 DEGs were found in C. sinense. These DEGs were mainly related to bacterial secretion systems, FLS2, CNGCs and EFR, regulating HR, stomatal closure and defense-related gene induction. FLS2 (LRR receptor-like serine/threonine kinase) contained the highest number of DEGs among three orchid species, followed by calmodulin. Highly upregulated gene sets were found in C. sinense as compared to other species. The great deal of DEGs, mainly the FLS2 and EFR families, related to defense and immunity responses can effectively direct the future of biological control of diseases for orchids.

Systematic stepwise screening of new microbial antagonists for biological control of European canker

Neonectria ditissima is the causal agent of European canker. This pathogen causes cankers on apple branches and the main stem, which may lead to the loss of the whole tree. Chemical control is the essential component in disease management and no suitable biocontrol products are commercially available. This study aimed at selecting potential microbial antagonists against N. ditissima through a systematic stepwise screening program for the development of a new biocontrol product. A total of 520 potential candidates were isolated from apple branches showing canker symptoms. Important characteristics for application of Microbial Biological Control Agents were tested per each candidate: spore production, spore survival during storage, cold tolerance, drought tolerance and UV-B resistance. Isolates able to germinate and grow at human body temperature were excluded. A total of 252 candidates fulfilled the stablished criteria. All 520 candidates belonged to 44 different taxonomic groups, being the most abundant Alternaria spp. (22.2 %), Aureobasidium pullulans (16.1 %), Cladosporium spp. (9.5 %) and Fusarium spp. (9.0 %). Information on possible pathogenicity and toxicity for humans, animals, plants and the environment and on patents in biocontrol use was collected per each identified species. A total of 158 candidates belonging to species that did not show potential risks or patent conflicts were assessed by their antagonistic behaviour against N. ditissima in bioassays in planta. Each candidate was inoculated in ‘Elstar’ apple branches inoculated with N. ditissima 24 h before. Inoculated branches were incubated at 17 °C, 16 h light per day and RH > 90 %. After four weeks, canker symptom expression was visually assessed. The capacity of the candidates to reduce colonisation of N. ditissima in the branches was evaluated by quantifying N. ditissima DNA concentration using qPCR. Four candidates of Clonostachys rosea showed antagonistic properties; after four weeks of treatment, no canker symptoms or small bark cracks were observed in the inoculated branches and N. ditissima DNA was reduced by 90–99 %. Following them, the branches inoculated with one candidate of Akanthomyces muscarius, A. pullulans and Cladosporium europaeum showed small bark cracks and small swollen bark and N. ditissima DNA was reduced by more than 90 %. The systematic stepwise screening approach was a powerful strategy to find new MBCAs against N. ditissima with antagonistic properties that also fulfilled major criteria with regards to commercial production and safety, as well as ecological needs.

Comparison of Antifungal Activity of Bacillus Strains against Fusarium graminearum In Vitro and In Planta

Fusarium graminearum (Fg) causes Fusarium head blight (FHB) disease in wheat and barley. This pathogen produces mycotoxins including deoxynivalenol (DON), the T-2 and fumorisin B1. Translocation of the mycotoxins in grains causes important losses in yields and contributes to serious health problems in humans and livestock. We tested the Bacillus strains, two commercial, QST713 (Serenade®) and FZB24 (TAEGRO®) and one non-commercial strain EU07 as microbial biological control agents against the F. graminearum strain Fg-K1-4 both in vitro and in planta. The EU07 strain showed better performance in suppressing the growth of Fg-K1-4. Cell-free bacterial cultures displayed significant antagonistic activity on Fg-K1-4. Remarkably, heat and proteinase K treatment of bacterial broths did not reduce the antagonistic activity of Bacillus cultures. DON assays showed that Bacillus strain was not affected by the presence of DON in the media. Leaf and head infection assays using Brachypodium distachyon (Bd-21) indicated that EU07 inhibits Fg-K1-4 growth in vivo and promotes plant growth. Overall, the EU07 strain performed better, indicating that it could be explored for the molecular investigations and protection of cereal crops against FHB disease.

Improving the Authorization of Microbial Biological Control Products (MBCP) in the European Union within the EU Green Deal Framework

Developing sustainable agriculture by identifying non-chemical alternative Plant Protection Products (PPP) is a cornerstone in achieving long-sought environmental friendliness. Despite significant legislative and political efforts to promote biocontrol solutions and Integrated Pest Management (IPM), the literature points out the disadvantages posed by European Union’s (EU) two-tier system for Microbial Biological Control Agents (MBCA) approval and subsequent Microbial Biological Control Products (MBCP) authorization by each EU Member State (MS). Despite the disadvantages, in a recent article, we showed that the EU had outcompeted the US and other countries in approved MBCA in the last decades; however, MBCP approval at the national level lags. Achieving the EU Green Deal’s aim set out in the ‘Farm to Fork Strategy’ to reduce the use and risk of pesticides by 50% by 2030 is difficult without developing viable alternatives. Why do we not have higher MBCP availability and usage in the EU? Is it the current legislation, its poor application, or some other factors? The current legislative framework stimulated MBCA approval. Thus, we compare MBCA approval and MBCP authorization procedure to evaluate if MBCP authorization is more difficult and thus causes a bottleneck. We find that requirements for MBCP authorization are unnecessarily more complex. We recommend simplifying the MBCP dossier requirements and making them as similar to MBCA as possible to accelerate the MBCP authorization in more EU MS to increase their availability and integration in agronomic crops’ pest management plans.

Multi-Trait Wheat Rhizobacteria from Calcareous Soil with Biocontrol Activity Promote Plant Growth and Mitigate Salinity Stress.

Plant growth promoting rhizobacteria (PGPR) can be functional microbial fertilizers and/or biological control agents, contributing to an eco-spirit and safe solution for chemical replacement. Therefore, we have isolated rhizospheric arylsulfatase (ARS)-producing bacteria, belonging to Pseudomonas and Bacillus genus, from durum wheat crop grown on calcareous soil. These isolates harbouring plant growth promoting (PGP) traits were further evaluated in vitro for additional PGP traits, including indole compounds production and biocontrol activity against phytopathogens, limiting the group of multi-trait strains to eight. The selected bacterial strains were further evaluated for PGP attributes associated with biofilm formation, compatibility, salt tolerance ability and effect on plant growth. In vitro studies demonstrated that the multi-trait isolates, Bacillus (1.SG.7, 5.SG.3) and Pseudomonas (2.SG.20, 2.C.19) strains, enhanced the lateral roots abundance and shoots biomass, mitigated salinity stress, suggesting the utility of beneficial ARS-producing bacteria as potential microbial fertilizers. Furthermore, in vitro studies demonstrated that compatible combinations of multi-trait isolates, Bacillus sp. 1.SG.7 in a mixture coupled with 5.SG.3, and 2.C.19 with 5.SG.3 belonging to Bacillus and Pseudomonas, respectively, may enhance plant growth as compared to single inoculants.

Unravelling the fruit microbiome: The key for developing effective biological control strategies for postharvest diseases.

Fruit-based diets are recognized for their benefits to human health. The safety of fruit is a global concern for scientists. Fruit microbiome represents the whole microorganisms that are associated with a fruit. These microbes are either found on the surfaces (epiphytes) or in the tissues of the fruit (endophytes). The recent knowledge gained from these microbial communities is considered relevant to the field of biological control in prevention of postharvest fruit pathology. In this study, the importance of the microbiome of certain fruits and how it holds promise for solving the problems inherent in biocontrol and postharvest crop protection are summarized. Research needs on the fruit microbiome are highlighted. Data from DNA sequencing and "meta-omics" technologies very recently applied to the study of microbial communities of fruits in the postharvest context are also discussed. Various fruit parameters, management practices, and environmental conditions are the main determinants of the microbiome. Microbial communities can be classified according to their structure and function in fruit tissues. A critical mechanism of microbial biological control agents is to reshape and interact with the microbiome of the fruit. The ability to control the microbiome of any fruit is a great potential in postharvest management of fruits. Research on the fruit microbiome offers important opportunities to develop postharvest biocontrol strategies and products, as well as the health profile of the fruit.

Induction of Wheat Resistance to STB by the Endophytic Fungus serendipita Indica and pseudomonas Protegens.

Background:Septoria tritici blotch (STB) caused by fungus Zymoseptoria tritici, is one of the important wheat (Triticum aestivum L.) diseases difficult to control because of the lack of wheat resistant cultivars. The use of biological control agents is one possible way for triggering host plant resistance to biotic and abiotic stressesObjective: In this study, we examined the ability of Serendipita indica and Pseudomonas protegens CHA0-mCherry in inducing the local wheat cultivar Tajan resistance to STB.Materials and Methods: The interaction between biological control agents and the roots of wheat was evaluated. The experiment was conducted in a completely randomized design by three replicates. Spore suspension was supplied at concentrations of 107 and 109 for S. indica and bacteria isolate (CHA0-mCherry) respectively. Five treatments were applied including S. indica, CHA0-mCherry, S. indica and CHA0-mCherry co-inoculation, positive and negative control. Twenty-one days after inoculation, the interaction between biological agents and plant roots were evaluated through morphological traits and qPCR. The plant resistance, disease severity, and the correlation between resistance and disease severity were assessed. Pycnidial variation and agronomic traits were also evaluated.Results: Twenty-one days after inoculation, both biological agents clearly colonized all treated roots of all treatments except in control plants as demonstrated by qPCR analysis. Chlamydospores were observed in the S. indica-treated hosts with the CHA0-mCherry colonizing assessment showing 5×109 CFU g-1 in the root. The asexual phase of the fungal pathogen, pycnidial diameter, was reduced in S. indica treated plants more considerably than in the other treatments. There was a positive correlation between resistance and disease severity mean when calculated by Pearson’s correlation. There was a significant difference between the root length, fresh, and dry weight of root. Spore density was inversely correlated to resistance and disease severity, when compared with control, with CHA0-mCherry being the most effective in reducing the spore density. S. indica was the most effective in promoting root growth and stem biomass, when compared with control.Conclusions:Serendipita indica and Pseudomonas protegens CHA0-mCherry colonies showed a potential biological control activity and efficiently enhanced the plant resistance to Z. tritici in the treated wheat roots. The microbial biological control agents are very practical in crop protection against plant disease and can be very useful in sustainable agriculture.Abbreviations: PLSN: percentage of leave surface necrosis, DPI: day past inoculation, PLACL: percentage of leaf area covered by lesions, PPMLA: pycnidia per millimeter in leaf area.

Role of Bacillus tequilensis EA-CB0015 cells and lipopeptides in the biological control of black Sigatoka disease

Black Sigatoka disease is a devastating fungal pathogen that affects banana crops worldwide and is caused by the ascomycete fungus Pseudocercospora fijiensis. In an effort to mitigate the environmental impacts of chemical fungicides, microbial biological control agents (MBCA) have been developed. However, a comprehensive understanding of the modes of action of these products are needed to enhance their efficacy under field conditions. Consequently, the functional role of different components of a Bacillus tequilensis EA-CB0015-based product was studied to understand their role in conferring protection to banana plants against the infection of P. fijiensis. Under this perspective, we evaluated the effect of B. tequilensis EA-CB0015 lipopetides on the severity of black Sigatoka disease, as well as the ability of the bacterial cells to colonize and produce lipopeptides on the leaf surface of banana plants (Musa AAA cv. Williams). Our work provides evidence that lipopetides significantly reduce the disease severity and that the bacterial cells colonize the leaf surface of banana plants inoculated with P. fijiensis during the first 48 h of incubation. Furthermore, we were able to detect an increased production of surfactins during colonization using mass spectrometry analysis. Altogether, our results suggest that the biological control strategies implemented by the MBCA product against P. fijiensis involves a direct interaction via antibiosis, as well as an indirect interaction via competition of nutrients and space.