Application Of Biocontrol Agents Research Articles

Deciphering the rhizosphere bacteriome associated with biological control of tobacco black shank disease.

The black shank disease seriously affects the health of tobacco plants. Conventional control methods have limitations in terms of effectiveness or economic aspects and cause public health concerns. Thus, biological control methods have come into the field, and microorganisms play a key role in suppressing tobacco black shank disease. In this study, we examined the impact of soil microbial community on black shank disease basing on the structural difference of bacterial communities in rhizosphere soils. We used Illumina sequencing to compare the bacterial community diversity and structure in different rhizosphere soil samples in terms of healthy tobacco, tobacco showing typical black shank symptoms, and tobacco treated with the biocontrol agent, Bacillus velezensis S719. We found that Alphaproteobacteria in the biocontrol group, accounted for 27.2% of the ASVs, was the most abundant bacterial class among three groups. Heatmap and LEfSe analyses were done to determine the distinct bacterial genera in the three sample groups. For the healthy group, Pseudomonas was the most significant genus; for the diseased group, Stenotrophomonas exhibited the strongest enrichment trend, and Sphingomonas showed the highest linear discriminant analysis score, and was even more abundant than Bacillus; for the biocontrol group, Bacillus, and Gemmatimonas were the largely distributed genus. In addition, co-occurrence network analysis confirmed the abundance of taxa, and detected a recovery trend in the network topological parameters of the biocontrol group. Further functional prediction also provided a possible explanation for the bacterial community changes with related KEGG annotation terms. These findings will improve our knowledge of plant-microbe interactions and the application of biocontrol agents to improve plant fitness, and may contribute to the selection of biocontrol strains.

Improvement of shelf-life of cherry (Prunus avium L.) by combined application of modified-atmosphere packaging and antagonistic yeast for long-distance export.

The last decade has seen a growing interest in reducing the use of chemical fungicides for postharvest decay control. In the research for new, safe alternatives, the combined application of biocontrol agents and passive modified-atmosphere packaging (MAP) has been shown to be a promising strategy to extend fruit quality. Therefore, the aim of this work was to evaluate the effect of the combined application of MAP and two antagonistic yeasts, Metschnikowia pulcherrima L672 and Pichia kudriavzevii PK18, on sweet cherry shelf life. Microbiological, physico-chemical, and quality fruit analysis from batches treated with antagonistic yeast were compared with a control batch without yeast application and a batch to which fludioxonil (Scholar®) was applied. The composition of the atmosphere and physico-chemical traits showed similar values among the different batches during cold storage. However, interestingly, the combination of MAP with the antagonistic yeasts M.pulcherrima L672 and P.kudriavzevii PK18 increases the control of microbiological spoilage with results comparable to the application of fludioxonil. In addition, these batches experienced a slight decrease in volatile compounds associated with fresh fruit aroma, whereas in the control batch an increase of altered fruit aromas was observed. The same effect of control of spoilage was observed during the shelf life period. These results showed the positive effect of the combination of antagonistic yeasts and MAP, obtaining similar results in terms of control of microbiological spoilage and physico-chemical quality compared with the application of fludioxonil. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Efficacy of preharvest application of biocontrol agents against gray mold in grapevine.

The use of biocontrol agents (BCAs) represents a promising alternative to conventional methods for the management of gray mold in vineyards during the berry ripening stage. The main advantages of BCAs are the short preharvest interval and lack of chemical fungicide residues in wine. In this study, eight commercial BCAs (based on different Bacillus or Trichoderma species and strains, Aureobasidium pullulans, Metschnikowia fructicola, and Pythium oligandrum) and a reference fungicide (boscalid) were applied to a vineyard during berry ripening over three seasons to evaluate the dynamics over time in terms of their relative efficacies in gray mold control. At 1-13 days after application of BCAs to the berry surfaces in field conditions, the berries were collected and artificially inoculated with conidia of Botrytis cinerea under controlled laboratory conditions, and gray mold severity was observed after 7 days of incubation. Significant differences were observed in gray mold severity among years, according to the number of days the BCAs grew on the berry surface before B. cinerea inoculation, and the season by day interaction (altogether accounting for >80% of the experimental variance). The variability in BCA efficacy was closely related to the environmental conditions at the time of application and in the following days. Overall, the BCA efficacy increased with the degree days accumulated between BCA application in the vineyard and B. cinerea inoculation in the dry (no rain) periods (r = 0.914, P = 0.001). Rainfall and the associated drop in temperature caused a relevant reduction of BCA efficacy. These results demonstrate that BCAs are an effective alternative to conventional chemicals for the preharvest control of gray mold in vineyards. However, environmental conditions can considerably affect the BCA efficacy.

ECONOMIC ASSESSMENT OF THE BIOLOGICAL AGENT USE IN ECOLOGICAL POTATO PRODUCTION – SYSTEM DYNAMICS SIMULATION

Aim: The aim of this study is to assess the economic viability by calculating the potential profits and expenses for farmers, and to simulate the impact of the application of a microbiological agent on the potato plant in a field trial. The field experiment aimed to identify the role of the biological agent while substituting the synthetic plant fertilization and protection. Methodology: The system dynamics method was applied to the data provided from one planting season of field experiments conducted in the framework of the PotatoMETABiome project. From eleven tested varieties on six different scenario plots, the most economically viable variety – Pasja Pomorska – was tested. The comparative approach was applied to show the results of inoculating potato plants with biological agents and using synthetic pesticides and fertilizers. Results: The results show that the application of biocontrol agents increases the quality and quantity of the potato yield compared to a variant in which no synthetic agents are used. These are, however, higher while applying the latter. It can therefore be argued that the microbiological agent could support ecological potato production, yet it does not reach the economic break-even point yet. Conclusions: Bearing in mind the limitations resulting from the experimental nature of field research, the level of economic profitability of innovative biological preparations and the importance of their use in agriculture have been demonstrated.

Basal Stem Rot of Oil Palm - The Pathogen, Disease Incidence, and Control Methods.

Basal stem rot of oil palm caused by Ganoderma boninense is the most serious disease of oil palm in Malaysia, Indonesia, and other oil palm producing countries. Economic losses caused by the disease can be up to USD500 million a year. For many years, basal stem rot was found to infect older palms of over 25 - 30 years. Only in the 1950s, the disease began to appear in much younger palms (10 to 15 years old) and in the last decade or so, palms as young as 1 year were infected by the disease. The highest incidence occurs in coastal areas of Southeast Asia but the disease has now infected oil palm in inland areas, mainly oil palm planted in peat soils. Disease incidence is also high in areas previously growing coconut or forest. Basal stem rot infection and spread occur through root-to-root contact, and basidiospores that colonize the roots also play a role. In the early stages of infection by G. boninense, the pathogen behaves as a biotroph and later as a necrotroph, secreting cell wall-degrading enzymes and triggering host defense responses. Genes, gene products and metabolic pathways involved in oil palm defense mechanisms against G. boninense have been identified, and these metabolites have the potential to be used as markers for early detection of the disease. Integrated disease management used to control basal stem rot includes cultural practices, chemical control, and application of biocontrol agents or fertilizers. Early detection tools have also been developed which could assist in management of basal stem rot infections. Development of resistant or tolerant oil palm is still at an early stage, so the existing integrated disease management practices remain the most appropriate methods for managing basal stem rot of oil palm.

Survey, identification and management of Fusarium wilt of banana in Tamirabarani tract of Southern districts of Tamil Nadu

In Tamil Nadu state, Thoothukudi district ranked second in banana production and especially the Tamirabarani tract of Thoothukudi and Tirunelveli districts are known for the production of various banana cultivars like Rasthali, Andhra Kozhi, Karpooravalli, Neypoovan, Poovan, Peyan and Chakkai. Among these varieties, cultivation of Rasthali faces 50-60% yield loss due to the incidence of Fusarium wilt disease. As the farmers have been practising ratooning for 6-7 year continuously which enhances the inoculum load of the pathogen and make the plantains succumb to Fusarium oxysporum f. sp. cubense (Foc). Studies carried out on different treatments in the management of Fusarium wilt of banana, Trichoderma sp. Tsp1(ALG) showed a maximum reduction of mycelial growth of Foc (72.18%) over control which was on par with Pseudomonas fluorescence 1(Pf1). Under pot culture conditions the combination of three treatments, Tsp1(ALG)+Pf1+ neem cake excelled and showed an 80% reduction of wilt incidence. A multifaceted approach comprising the application of biocontrol agents (Trichoderma sp.) + Pseudomonas sp. 1 (TNAU) and organic amendments was found to be the best management practice in containing the wilt.

Combating biotic stresses in plants by synthetic microbial communities: Principles, applications and challenges.

Presently, agriculture worldwide is facing the major challenge of feeding the increasing population sustainably. The conventional practices have not only failed to meet the projected needs, but also led to tremendous environmental consequences. Hence, to ensure a food-secure and environmentally sound future, the major thrust is on sustainable alternatives. Due to challenges associated with conventional means of application of biocontrol agents in the management of biotic stresses in agroecosystems, significant transformations in this context are needed. The crucial role played by soil microbiome in efficiently and sustainably managing the agricultural production has unfolded a newer approach of rhizosphere engineering that shows immense promise in mitigating biotic stresses in an eco-friendly manner. The strategy of generating synthetic microbial communities (SynComs), by integrating omics approaches with traditional techniques of enumeration and in-depth analysis of plant-microbe interactions, is encouraging. The review discusses the significance of the rhizospheric microbiome in plant's fitness, and its manipulation for enhancing plant attributes. The focus of the review is to critically analyse the potential tools for the design and utilization of SynComsas a sustainable approach for rhizosphere engineering to ameliorate biotic stresses in plants. Furthermore, based on the synthesis of reports in the area, we have put forth possible solutions to some of the critical issues that impair the large-scale application of SynComs in agriculture.

Ulva prolifera polysaccharide enhances the root colonisation by Bacillus amyloliquefaciens strain Cas02

The application of biocontrol agent is important for the sustainable development of agriculture. Unsuccessful or limited colonisation by plant growth-promoting rhizobacteria (PGPR) has become an important constraint factor for their commercial application. Here, we report that Ulva prolifera polysaccharide (UPP) promotes root colonisation by Bacillus amyloliquefaciens strain Cas02. UPP serves as an environmental signal for bacterial biofilm formation and its glucose residue is used as a carbon source for the synthesis of the exopolysaccharides and poly-gamma-glutamate present in biofilm matrix. Greenhouse experiments demonstrated that UPP could effectively enhance the root colonisation by Cas02 in both the bacterial population and survival time under natural semiarid soil conditions. Furthermore, the microbiome analysis also indicated the promoted colonisation by Cas02, as well as the improved bacterial rhizosphere community structure, after combined treatment of UPP and Cas02. This study provides a practical approach to improve the biocontrol agent with seaweed polysaccharides.

Effects of Biocontrol Agents Application on Soil Bacterial Community and the Quality of Tobacco.

In this study, to evaluate the effect of different biocontrol agents (BCAs) on the soil bacterial community, we investigated the effects of Bacillus amyloliquefaciens, synthetic bacterial community (Aspergillus niger:Bacillus subtilis:Bacillus licheniformis:Streptomyces microflavus = 3:3:3:1, SynCom), and BCAs combined with lime-nitrogen on soil bacterial community by utilizing 16S rRNA sequencing technology. The sequencing shows that BCAs application can improve the value of Shannon and Sobs index of bacterial community during tobacco rosette and vigorous growing period. With the growth of tobacco, the effect of BCAs on the composition and difference of soil bacterial community structure becomes more and more obvious. In terms of average relative richness, the top six phyla of soil bacterial community are Proteobacteria, Actinobacteria, Chloroflexi, Acidobacteria, Gemmatimonadetes, and Bacteroidetes. Bacillus amyloliquefaciens application can increase the relative richness of Proteobacteria and Bacteroidetes. And the combination between BCAs and lime-nitrogen can increase the relative richness of Gemmatimonadetes and Bacteroidetes. The SynCom also can increase the relative richness of Bacteroidetes, whereas it decreases the relative richness of Acidobacteria. Proteobacteria, Acidobacteria, Gemmatimonadetes, and Bacteroidetes showing an extremely significant correlation with pH and exchangeable magnesium (EMg). BCAs application can improve the tobacco yield, effective leaves, and reducing sugar content that also has extremely significant positive correlation with pH and EMg. In conclusion, the results of our field experiments clearly show that BCAs application can significantly affect the soil pH and EMg by changing most of the dominant soil bacterial species. The richness of Bacteroidetes can serve as an indicator of the changes in soil pH and EMg caused by BCAs application.

Influence of Bacillus subtilis strain Z-14 on microbial communities of wheat rhizospheric soil infested with Gaeumannomyces graminis var. tritici.

Wheat take-all disease caused by Gaeumannomyces graminis var. tritici (Ggt) spreads rapidly and is highly destructive, causing severe reductions in wheat yield. Bacillus subtilis strain Z-14 that significantly controlled wheat take-all disease effectively colonized the roots of wheat seedlings. Z-14 increased the metabolic activity and carbon source utilization of rhizospheric microorganisms, thus elevating average well-color development (AWCD) values and functional diversity indexes of soil microbial communities. Z-14 increased the abundance of Bacillus in the rhizosphere, which was positively correlated with AWCD and functional diversity indexes. The Z-14-treated samples acquired more linkages and relative connections between bacterial communities according to co-occurrence network analyses. After the application of Ggt, the number of linkages between fungal communities increased but later decreased, whereas Z-14 increased such interactions. Whole-genome sequencing uncovered 113 functional genes related to Z-14’s colonization ability and 10 secondary metabolite gene clusters in the strain, of which nine substances have antimicrobial activity. This study clarifies how bacterial agents like Z-14 act against phytopathogenic fungi and lays a foundation for the effective application of biocontrol agents.

Advances in Soil Engineering: Sustainable Strategies for Rhizosphere and Bulk Soil Microbiome Enrichment.

The preservation of natural ecosystems, as well as the correct management of human societies, largely depends on the maintenance of critical microbial functions associated with soils. Soils are biodiversity rich pools, and rhizosphere soils can be associated with increased plant functions in addition to the regulation of nutrient cycling, litter decomposition, soil fertility and food production by agriculture systems. The application of biocontrol agents or plant growth-promoting bacteria has been tested in order to colonize roots at initial stages and offer advantages by promoting healthier and higher-yielding crops. In this review we describe the efforts to develop more sustainable systems that seek to minimize environmental disruption while maintaining plant health. Particular emphasis is given in this review to soil improvement strategies and the taxonomic groups involved in plant growth and protection against biotic stresses. It is important to define the impacts of land management and crop production practices on the structure and composition of soil bacterial communities. By promoting, monitoring and controlling the plant microbiome, and understanding the role of certain biocontrol agents within the plant throughout the lifecycle of the plant, we may substantially improve nutritional and environmental standards and reduce the negative impact of some agrochemicals. The integration of biological alternatives with traditional strategies may be critical to improve the sustainability of agriculture systems.

Crop Protection and Environment: Sustainable Control Measures of Pests and Diseases

Abstract The second Sustainable Development Goals determines to achieve zero starvation, accomplish food security and attain better-quality nutrition and encourage eco-friendly agriculture. The sustainability can be achieved by maintaining environments, improving capability for adjustment to climate change, unpredictable weather, and other natural catastrophes and enhancing land and soil quality progressively. The challenge in keeping high yield crops is pests and diseases attack. Control measures to suppress pests and diseases should also keep the ecosystems in balance. Pesticides that heavily used for plant protection besides their effectiveness in controlling pests and diseases also possess risks to non-target organisms. To diminish the harmful effect of pesticides, innovative methods to cut the amount of active ingredients applied have established, including developing new formulation of existing compounds, enhancing the bioactivity of active ingredients. In addition, there are also new development in plant protection products derived from natural ingredients, new mode of action and biochemical targets. Various cultural methods are considered eco-friendly measures, including habitat and cropping management, sanitation and fallowing. Furthermore, application of biocontrol agents and cultivation of resistant/tolerant crop varieties should be incorporate into plant protection as part of sustainable control methods of pests and diseases.

Biocontrol Approaches against Escherichia coli O157:H7 in Foods.

Shiga-toxin-producing Escherichia coli O157:H7 is a well-known water- and food-borne zoonotic pathogen that can cause gastroenteritis in humans. It threatens the health of millions of people each year; several outbreaks of E. coli O157:H7 infections have been linked to the consumption of contaminated plant foods (e.g., lettuce, spinach, tomato, and fresh fruits) and beef-based products. To control E. coli O157:H7 in foods, several physical (e.g., irradiation, pasteurization, pulsed electric field, and high-pressure processing) and chemical (e.g., using peroxyacetic acid; chlorine dioxide; sodium hypochlorite; and organic acids, such as acetic, lactic, and citric) methods have been widely used. Although the methods are quite effective, they are not applicable to all foods and carry intrinsic disadvantages (alteration of sensory properties, toxicity, etc.). Therefore, the development of safe and effective alternative methods has gained increased attention recently. Biocontrol agents, including bacteriophages, probiotics, antagonistic bacteria, plant-derived natural compounds, bacteriocins, endolysins, and enzymes, are rapidly emerging as effective, selective, relatively safe for human consumption, and environmentally friendly alternatives. This paper summarizes advances in the application of biocontrol agents for E. coli O157:H7 control in foods.

Alternative Management Approaches of Citrus Diseases Caused by Penicillium digitatum (Green Mold) and Penicillium italicum (Blue Mold).

Green mold (Penicillium digitatum) and blue mold (Penicillium italicum) are among the most economically impactful post-harvest diseases of citrus fruit worldwide. Post-harvest citrus diseases are largely controlled with synthetic fungicides such as pyrimethanil, imazalil, fludioxonil, and thiabendazole. Due to their toxic effects, prolonged and excessive application of these fungicides is gradually restricted in favor of safe and more eco-friendly alternatives. This review comprehensively describes alternative methods for the control of P. digitatum and P. italicum: (a) antagonistic micro-organisms, (b) plant extracts and essential oils, (c) biofungicides, (d) chitosan and chitosan-based citrus coatings, (e) heat treatments, (f) ionizing and non-ionizing irradiations, (g) food additives, and (h) synthetic elicitors. Integrating multiple approaches such as the application of biocontrol agents with food additives or heat treatments have overcome some drawbacks to single treatments. In addition, integrating treatment approaches could produce an additive or synergistic effect on controlling both molds for a satisfactory level of disease reduction in post-harvest citrus. Further research is warranted on plant resistance and fruit-pathogen interactions to develop safer strategies for the sustainable control of P. digitatum and P. italicum in citrus.

A Meta-Analysis to Determine the State of Biological Control of Aphanomyces Root Rot.

The increasing incidence and prevalence of the pathogen Aphanomyces euteiches in various pulse-growing regions worldwide necessitates the development of effective management strategies, including biological control agents. Numerous labs have undertaken research examining biological control methods to evaluate aphanomyces root rot suppression in multistep processes that include isolation of inhibitory organisms, lab assays, growth chamber assays, and field trials. Given the emergence of various biocontrol agents and the need to mitigate aphanomyces yield losses, we have undertaken a meta-analysis approach to analyze the effectiveness of biocontrol agents in relation to application method, biocontrol agent richness, biocontrol agent type, the type of study, and reporting system-oriented moderator variables. An effect size, calculated as a natural log response ratio, resulted in a summary weighted mean of −0.411, suggesting the overall effectiveness of biocontrol agents (p < .001). Aphanomyces root rot suppression using biological treatments showed significant heterogeneity for all moderator variables, confirming that the studies do not share a common effect size and the use of a random effect model was appropriate. Across studies, meta-analyses revealed that soil amendments, biocontrol agent application as a seed coating and suspension, bacterial and fungal biocontrol agents, mixed applications, growth chamber and field studies, and qualitative and quantitative reporting systems were all associated with significantly positive outcomes for aphanomyces root rot suppression. Our findings suggest that there is potential promise for biological control of aphanomyces root rot, and more field trials need to be conducted to demonstrate the efficacy level observed under growth chamber conditions. Moreover, we identified a lack of detailed understanding of the mechanism(s) of biological control of aphanomyces root rot as a research priority.

Effective and Promising Strategy in Management of Tomato Root-Knot Nematodes by Trichoderma harzianum and Arbuscular Mycorrhizae

The ecosystem is considerably affected due to the extensive use of chemical pesticides and fertilizers. As an alternative strategy, this study aimed to assess the biocontrol potential of the bioagents arbuscular mycorrhizal fungi and plant growth-promoting Trichoderma harzianum MZ025966 against tomato root-knot nematodes (Meloidogyne javanica). T. harzianum showed a great potentiality to produce indole acetic acid (IAA) (12.11 ± 2.12 μg/mL) and exhibited a noticeable activity of ammonification. Furthermore, T. harzianum revealed protease and lipase enzymatic activity of 28.36 ± 2.82 U/mL and 12.30 ± 0.31 U/mL, respectively, which may illustrate the control mechanism of nematode eggs and juveniles. As in mycorrhizal and/or T. harzianum inoculated tomato plants, the penetration rates of nematodes, as well as the number of juveniles, females, egg mass, and galls were significantly reduced. The lowest number of juveniles was observed in the case of either single mycorrhizal inoculation (45%) or in combination with T. harzianum (55%). The enzymatic activity of glutathione peroxidase and catalase was enhanced in tomato plants inoculated with the bioagents to overcome the negative impact of nematode parasitism. Our results proved that the application of biocontrol agents not only reduced the nematode population and penetration rate but also improved the plant growth, increased the nutritional elemental content and stimulated the plant’s systematic resistance.

Effect of Pythium aphanidermatum (root rot pathogen) on the physiology of Luffa cylindrica (Sponge gourd) and its management by microbial antagonists

Effect of Pythium aphanidermatum (damping off/root rot pathogen) on the physiology of Luffa cylindrica (sponge gourd) and its management by microbial antagonists were studied. In this regard, plants were exposed to P. aphanidermatum suspension (@1 × 10−3cfu/ml) to initiate disease. Later, suspension of three biocontrol agents, i.e., Paecilomyces variotii (3 × 10−1cfu/ml), Bacillus subtilis (0.65×10−1cfu/ml), and Trichoderma harzianum (2 × 10−1cfu/ml) were employed for disease control and management. Non-destructive chlorophyll “a'' fluorescence assay was used to assess photosynthetic performance of the infected plants. The study reveals that biocontrol agent enhanced photosynthetic performance due to better chlorophyll quantum yields (ΦPSII and Fv/Fm), photochemical quenching (qP), electron supply (rETR) for PSII systems in infected plants. Biocontrol has greatly reduced energy loss in terms of heat dissipation and increased quantum efficiency, electron transport rate, and OJIP values in diseased plants. The study demonstrates that the application of biocontrol agents in the infected plants also covered up the root colonization of P. aphanidermatum suppressing disease intensity. T. harzianum greatly suppressed pathogen invasion due to more root colonization as compared to P. variotii and B. subtilis. Moreover, the biocontrol application decreased H2O2 and MDA concentrations in the infected plants due to adequate CAT and SOD activities during disease management. The role of biocontrol agents in disease management were varied and are discussed in detail.

Bioeffector Pseudomonas fluorescens ZX Elicits Biosynthesis and Accumulation of Functional Ingredients in Citrus Fruit Peel: A Promising Strategy for a More Sustainable Crop

Preharvest application of biocontrol agents is a promising strategy for promoting biosynthesis and accumulation of functional ingredients in fruit crops. In this study, we sought to evaluate the potential of Pseudomonas fluorescens ZX in stimulating the primary and secondary metabolism of citrus fruit peel. Pretreatment with P. fluorescens ZX was found to significantly affect the concentrations and profiles of both primary and secondary metabolites. More importantly, using P. fluorescens ZX suspension to increase inoculation numbers during fruit development typically elicited stronger stimulus effects, and multiple applications of P. fluorescens ZX significantly improved the biosynthesis process of beneficial compounds, resulting in their abundant accumulation in the peel. In fruit pretreated four times with P. fluorescens ZX, hesperidin, sinensetin, nobiletin, synephrine, and pectin were increased by approximately 26.0, 31.3, 44.8, 19.7, and 23.1%, respectively, compared to the untreated control. Collectively, these results indicated that, as a biostimulant, preharvest application of P. fluorescens ZX is an effective, affordable, ecological, and ecofriendly alternative agricultural technique for exploiting citrus crops. This approach is also promising for increasing the value of citrus fruit peel (currently regarded primarily as processing waste), thereby allowing industrial agricultural practices to move one step closer toward a circular economy.

Isolation and Evaluation of Rhizosphere Actinomycetes With Potential Application for Biocontrolling Fusarium Wilt of Banana Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4.

Fusarium wilt of banana caused by Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) is globally one of the most destructive soil-borne fungal diseases. Biological control using environmental microorganisms is considered as an alternative and sustainable strategy. Actinomycetes have the potential to explore biocontrol agents due to their production of diverse metabolites. The isolation and identification of high-efficiency and broad-spectrum antagonistic actinomycetes are the key for the application of biocontrol agents. In the present study, 60 actinomycetes were obtained from the rhizosphere soil of Machilus pingii in the primitive ecological natural reserve of Hainan province, China. Seventeen isolates and their extracts exhibited significant antifungal activity against F. oxysporum TR4. Particularly, strain BITDG-11 with the strongest inhibition ability had a broad-spectrum antifungal activity. The assay of its physiological and biochemical profiles showed that strain BITDG-11 had the ability to produce IAA and siderophores and had a positive response to gelatin liquefaction and nitrate reduction. Enzyme activities of chitinase, β-1,3-glucanase, lipase, and urease were also detected. Average nucleotide identity calculated by comparison with the standard strain genome of Streptomyces albospinus JCM3399 was 86.55% below the novel species threshold, suggesting that the strain could be a novel species. In addition, Streptomyces BITDG-11 obviously reduced the disease index of banana plantlets and promoted plant growth at 45 days post inoculation. The higher and lasting expression levels of defense genes and activities of antioxidant enzymes were induced in the roots of banana. Genome sequencing revealed that the Streptomyces BITDG-11 chromosome contained large numbers of conserved biosynthesis gene clusters encoding terpenes, non-ribosomal peptides, polyketides, siderophores, and ectoines. Fifteen bioactive secondary metabolites were further identified from Streptomyces BITDG-11 extract by gas chromatography–mass spectrometry. Dibutyl phthalate demonstrating a strong antifungal activity was the major compound with the highest peak area. Hence, Streptomyces sp. BITDG-11 has a great potential to become an essential constituent of modern agricultural practice as biofertilizers and biocontrol agents.

Effectiveness of fungal, bacterial and yeast antagonists for management of mango anthracnose (Colletotrichum gloeosporioides)

BackgroundMango anthracnose, caused by Colletotrichum gloeosporioides, is one of the most important diseases of mango crop. It mainly attacks leaves, flowers, young fruits and twigs and also appears as a post-harvest disease of ripened fruits. Application of bio-control agents has huge potential in plant disease management. The goal of the present research was to establish the potential of individual and combined bio-control agents for the management of mango anthracnose under in vitro and under field conditions.ResultsThe antagonistic reaction of six fungi, six bacteria and nine yeasts against C. gloeosporioides on potato dextrose agar medium and malt extract agar medium was observed among which Trichoderma harzianum was found to be the most efficient with 89.26% mycelial growth inhibition. Evaluation of bio-control agents against anthracnose disease development on mango fruit revealed that dip treatment of mango fruits in spore suspension (1.2 × 104 cfu/ml) of T. harzianum for 5 min was the most effective and provided disease control to the tune of 81.67%. Combined application of effective bio-control agents as a post-harvest fruit dip treatment was also evaluated against the mango anthracnose on mango fruits, where the treatment of T. harzianum + Pichia anomala was very effective with 93.39% disease control. Under field conditions, three consecutive sprays of T. harzianum, starting with the initiation of disease on leaves, followed by other two sprays at an interval of 15 days during 2015 and 2016 were found the best for the management of mango anthracnose disease both on leaves and on fruits at two locations.ConclusionsThe combined and individual applications of bio-control agents, viz.T. harzianum, Bacillus subtilis and P. anomala, through foliar spray or by fruit dip had the potential to control mango anthracnose. The bio-formulations of these bio-control agents had the potential to replace chemical fungicides and also protect the natural environment, thus playing a significant role in integrated disease management.