Use Of Biocontrol Agents Research Articles

Role of Kairomones in The Management of Sal Borer (Hoplocerambyx Spinicornis) Population

Hoplocerambyx spinicornis is a major pest of Sal which causes extensive damage to the Sal trees. As regard to the chemical control there is any likelihood of chemical control. The grub bores very deep into the heartwood and lodges itself inside chambers and galleries. Thus the present study deals with the multidisciplinary approach like the use of biocontrol agents (natural enemies), testing of kairomones, use of olfactrometer and the use of variously designed traps to manage the borers’ population. Kairomone is the alternate chemical attractant which contain flavanoids, terpenoids and amine compounds. Such methods avoid felling of trees which are used in controlling pest population since decades. Above methods being eco friendly and environmentally sound could manage the pest population up to certain economic threshold level.

Systemic method to isolate large bacteriophages for use in biocontrol of a wide range of pathogenic bacteria

Systemic method to isolate large bacteriophages for use in biocontrol of a wide range of pathogenic bacteria

Characterization of cultural traits and fungicidal activity of strains belonging to the fungal genus Chaetomium.

Compare and characterize Chaetomium strains with special regard to their potentialities as biocontrol agents. Twelve strains of the fungal genus Chaetomium from diverse ecological niches were identified as belonging to six different species. Large differences were observed between the strains with regard to temperature requirements for mycelial growth and pigmentation of culture filtrates. Culture filtrates and ethyl acetate extracts were assayed for fungicidal effects against important phytopathogens both on agar media and in multiwell plates. The samples from Chaetomium globosum were particularly active against Botrytis cinerea, Pyrenophora graminea and Bipolaris sorokiniana, while those from C. cochliodes and C. aureum were inhibitory towards Phytophthora infestans, and P. infestans and Fusarium culmorum respectively. To narrow down the active principle, the most promising extracts were separated by preparative HPLC and the resulting fractions tested in bioassays. Chaetoglobosins were identified as active compounds produced by C. globosum. The bioassays revealed C. aureum and C. cochliodes as promising candidates for use in biocontrol. Both showed remarkably good activity against the prominent plant pathogen P.infestans. We provide the first systematic study comparing six different Chaetomium species with regard to their use as biocontrol agents.

Characterization and Genomic Analysis of Escherichia coli O157:H7 Bacteriophage FEC14, a New Member of Genus Kuttervirus.

Escherichia coli O157:H7 is an important foodborne pathogen that has become a major worldwide factor affecting the public safety of food. Bacteriophage has gradually attracted attention because of its ability to kill specific pathogens. In this study, a lytic phage of E. coli O157:H7, named FEC14, was isolated from hospital sewage. Transmission electron microscopy analysis showed that phage FEC14 had an isometric head 80 ± 5nm in diameter and a contractile tail whose terminal spikes present an umbrella-like structure. Phage FEC14 revealed 158,639bp double-stranded DNA, with the G+C content of 44.6%, 209 ORFs and four tRNAs. Genome DNA of FEC14 could not be digested by some endonucleases. Many of the features of phage FEC14 are very similar to those of the newly classified genus "Kuttervirus", including morphology, genome size and organization, etc. Phage FEC14 is proposed to be a new isolate of genus "Kuttervirus" within the family Ackermannviridae, moreover, the endonuclease resistance of phage FEC14, has priority over other genera of bacteriophages for its use in biocontrol of foodborne pathogens.

Effectiveness of Phage-Based Inhibition of Listeria monocytogenes in Food Products and Food Processing Environments.

Providing safe products and compliance of legal requirements is still a great challenge for food manufacturers regarding microbiological safety, especially in the context of Listeria monocytogenes food contamination. L. monocytogenes is a human pathogen, which, due to the ability of survival and proliferation in preservation conditions such as high salinity, acidity and refrigeration temperatures, is a significant threat to the food industry. Novel methods of elimination of the bacterial pathogen in food products and food processing environments are required. Among emerging technologies, one of the very promising solutions is using bacteriophages as natural control agents. This review focus on the major aspects of phage-based inhibition of L. monocytogenes in aspects of food safety. We describe an overview of foods and technological factors influencing the efficacy of phage use in biocontrol of L. monocytogenes. The most noteworthy are food matrix properties, phage concentration and stability, the time of phage application and product storage temperature. The combined methods, phage immobilization (active packing), pathogen resistance to phages and legislation aspects of antilisterial bacteriophage use in the food industry are also discussed.

Impact of endophytic bacteria against yellow rust (Puccinia striiformis f. sp. tritici) of wheat

Wheat is a dominant cereal crop worldwide and very important as a staple food resource. A number of pathogens cause damage to wheat crop, of which yellow rust caused by Puccinia striiformis f. sp. tritici is one of the major threats to wheat production in India. Chemical control leads to resistance development against the pathogen. Biological control, the use of natural antagonists to combat plant diseases has emerged as a promising alternative to chemical pesticides. Keeping in view the importance of the disease the present investigation was undertaken with the aim to observe the impact of endophytic bacteria Pseudomonas fluorescens and Bacillus amyloliquefaciens as biocontrol agents against yellow rust of wheat. Talc based bioformulations of two bacterial biocontrol agents, viz. Pseudomonas fluorescens and Bacillus amyloliquefaciens were used at different concentrations to observe their effectiveness against yellow rust. In addition to this, the activity of various defense related enzymes Peroxidase (PO), Polyphenol oxidase (PPO), Phenylalanine Ammonia Lyase (PAL) along with Phenols and Proteins was also observed. Our findings indicated that the yellow rust severity in P. fluorescens (T14) fermented liquid (FL) (PF) @15 g/l of water as foiler spray exhibited 43.71 per cent and it gave 50.07 per cent disease control in rabi 2015. Whereas B. amyloliquefaciens (T3) fermented liquid bacterial cell (FLBC) (FDK21) @15 g/kg of seed showed 53.25% disease severity along with 39.20% disease control in rabi 2015 and enhanced the grain yield. Both the treatments were significantly better than the untreated control. But they were less superior than the chemical control. Similar trend has been observed in rabi 2016 season. The activity of the defense related enzymes that is PO, PPO and PAL as well as phenol and protein content was observed to be elevated in P. fluorescens T4(54.35 Units min-1 g-1 F W), T10( 24.39 Units min-1 g-1 F W), T14(103.36 μg t-cinnamic acid formed hr-1 g-1), T10 (6.89 mg/g F W) and T14(111.56 mg/g F W) and B. amyloliquefaciens T3(29.01 Units min-1 g-1 F W), T3(19.54 Units min-1 g-1 F W), T3(97.98 μg t-cinnamic acid formed hr-1 g-1), T3(46.89 mg/g F W), T3 (98.08 Units min-1 g-1 F W)) treated wheat plants as compared to chemically treated (T2 19.77 Units min-1 g-1 F W, 7.41 Units min-1 g-1 F W, 97.94 μg t-cinnamic acid formed hr-1 g-1, 2.93 mg/g F W, 72.40 mg/g F W) and untreated control plants ( T1 13.61 Units min-1 g-1 F W, 1.90 Units min-1 g-1 F W, 88.73 μg t-cinnamic acid formed hr-1 g-1 , 2.74 mg/g F W, 44.90 mg/g F W). Since several strains of Pseudomonas and Bacillus can act as BCA through an induced systemic resistance response in the plant against pathogens. So these biocontrol agents played major role through an induced systemic resistance response in the plant against pathogens and also help the plant in accelerating their defense response against the pathogens. Therefore it is suggested that the novel use of biocontrol agents Pseudomonas fluorescens and Bacillus amyloliquefaciens.

How siderophore production can influence the biocontrol activity of Aureobasidium pullulans against Monilinia laxa on peaches

In the present study Aureobasidium pullulans strains L1 and L8 were shown both in vitro and in vivo to compete for iron with Monilinia laxa through the secretion of siderophores (1.2 and 1.4 mg ml−1, respectively) and to prevent postharvest fruit decay of peaches. The two strains reduced mycelial growth and conidial germination of M. laxa specially in presence of lower iron concentrations (5 and 10 µg l−1 FeCl3), confirming a better efficacy when nutrients are scarce. In in vivo assay, A. pullulans L1 and L8 strains inhibited pathogen virulence, reducing by 83.5% and 84.4% on average respectively the peach lesion diameter for each tested iron solutions (5, 10, 20 µg l−1 FeCl3,). The highest iron solution slowed down the antagonists’ action and conversely increase the pathogen aggressiveness. Results shows that A. pullulans L1 and L8 strains compete with M. laxa for iron, so revealing new biocontrol aspects. Both strains showed the capability to decrease the accumulation of iron competing with some fungal pathogens and reducing their virulence. These results provide new perspectives for the use of biocontrol agents in agriculture.

Genetic Response of Common Bean to the Inoculation with Indigenous Fusarium Isolates.

Fungal species from the genus Fusarium are important soil-borne pathogens worldwide, causing significant economic losses in diverse crops. The need to find sustainable solutions against this disease has led to the development of new strategies—for instance, the use of biocontrol agents. In this regard, non-pathogenic Fusarium isolates have demonstrated their ability to help other plants withstand subsequent pathogen attacks. In the present work, several Fusarium isolates were evaluated in climatic chambers to identify those presenting low or non-pathogenic behavior. The inoculation with a low-pathogenic isolate of the fungus did not affect the development of the plant, contrary to the results observed in plants inoculated with pathogenic isolates. The expression of defense-related genes was evaluated and compared between plants inoculated with pathogenic and low-pathogenic Fusarium isolates. Low-pathogenic isolates caused a general downregulation of several plant defense-related genes, while pathogenic ones produced an upregulation of these genes. This kind of response to low-pathogenic fungal isolates has been already described for other plant species and fungal pathogens, being related to enhanced tolerance to later pathogen attacks. The results here presented suggest that low-pathogenic F. oxysporum and F. solani isolates may have potential biocontrol activity against bean pathogens via induced and systemic responses in the plant.

Helper bacteria halt and disarm mushroom pathogens by linearizing structurally diverse cyclolipopeptides

The bacterial pathogen Pseudomonas tolaasii severely damages white button mushrooms by secretion of the pore-forming toxin tolaasin, the main virulence factor of brown blotch disease. Yet, fungus-associated helper bacteria of the genus Mycetocola (Mycetocola tolaasinivorans and Mycetocola lacteus) may protect their host by an unknown detoxification mechanism. By a combination of metabolic profiling, imaging mass spectrometry, structure elucidation, and bioassays, we found that the helper bacteria inactivate tolaasin by linearizing the lipocyclopeptide. Furthermore, we found that Mycetocola spp. impair the dissemination of the pathogen by cleavage of the lactone ring of pseudodesmin. The role of pseudodesmin as a major swarming factor was corroborated by identification and inactivation of the corresponding biosynthetic gene cluster. Activity-guided fractionation of the Mycetocola proteome, matrix-assisted laser desorption/ionization (MALDI) analyses, and heterologous enzyme production identified the lactonase responsible for toxin cleavage. We revealed an antivirulence strategy in the context of a tripartite interaction that has high ecological and agricultural relevance.

Biological Control of Thielaviopsis paradoxa and Colletotrichum gloeosporioides by the Extracellular Enzymes of Wickerhamomyces anomalus

An alternative to chemical fungicides in post-harvest diseases are the use of biocontrol agents and their extracellular products against phytopathogens. Two relevant agents in post-harvest infections are Thielaviopsis paradoxa and Colletotrichum gloeosporioides, causing large economic losses in cacao, pineapple, and avocado during storage. In this work, we evaluated the effect of Wickerhamomyces anomalus, an effective biocontrol agent, against these filamentous fungi, focusing on the production of extracellular enzymes and their effect on fungal growth and germination. Moreover, we evaluated the use of inactivated fungal biomass as an inducer in complete (Potato Dextrose Agar and Yeast Peptone Dextrose) and minimal culture media. The antagonistic effect of W anomalus on the growth of both phytopathogens was also studied. The extracellular enzymes in YPD cultures, using T. paradoxa inactivated biomass as the best inducer, were capable of inhibiting the germination of both phytopathogens. In minimal media, only the production of a 30 kDa glucanase with activity against laminarin was observed. The enzyme was effective against the spore germination of T. paradoxa. In post-harvest crop protection tests, growth inhibition of T. paradoxa was observed using the cell-free enzyme extract, which is a promising system to protect cocoa fruits from T. paradoxa during post-harvest.

Beneficial Effects of Arbuscular Mycorrhizal Fungi and Trichoderma on Diseased Shallot

Purple blotch and fusarium basal rot are important shallot diseases which have caused significant yield loss. An alternative control method for these diseases is the use of biocontrol agents, such as arbuscular mycorrhizal fungi (AMF) and Trichoderma. The objectives of this study were to determine the effects of AMF and Trichoderma sp. on shallot growth and disease suppression. The experiment was set as a Complete Randomized Block Design with three treatments and three replications. The treatments were AMF, Trichoderma sp., and control. Each treatment was applied to a row and 15 shallot plants were taken as samples for observation. Disease severity of purple blotch and fusarium basal rot, plant height, number of leaves and shallot resistances to Fusarium solani were observed during this study. Results demonstrated that at seven weeks after planting, the application of AMF and Trichoderma sp. tended to suppress fusarium basal rot to 0.89% and 1.78% respectively, but only the application of AMF that suppressed purple blotch disease to 0.44%. The application of AMF and Trichoderma sp. also tended to increase plant height, number of leaves, leaf fresh weight and dry weight, root length, and bulb weight. In addition, AMF and Trichoderma sp. application increased shallot resistances against Fusarium solani.

Effect of Substrate Characteristics on the Growth and Sporulation of Two Biocontrol Microorganisms during Solid State Cultivation

Biocontrol agents are a group of naturally occurring organisms capable of interrupting the lifespan and suppressing the propagation of disease organisms. The use of biocontrol agents offers an environment-friendly and sustainable solution to the synthetic agrochemicals. In this study, we investigated parboiled rice and millets as substrates for spore production of two model biocontrol microorganisms (Bacillus pumilus and Streptomyces griseus) under solid state cultivation (SSC) conditions. The effects of cultivation parameters such as initial moisture content, water activity, and cultivation time on microbial growth and spore production were studied. Furthermore, texture profile analysis was performed to test the stress and strain curve and the hardness and stickiness of the substrates. The greatest spore production occurred at 50% moisture content with millets as a substrate, yielding a count of 1.34 × 108 spores/g-wet-substrate enumerated with plate count analysis and 1.70 × 108 events/g-wet-substrate using flow cytometry analysis. Substrate texture profile was highly correlative to the initial moisture content and substrate type and all proved to be essential process variables in controlling the bacterial growth and sporulation during SSC processes.

Evaluation of rhizospheric Trichoderma species strains for producing cell wall-degrading and defense related enzymes in response to Fusarium oxysporum f. sp. lentis

Biocontrol strategies have been mainly focused on proposing the use of biocontrol agents (BCAs) isolated from the rhizospheric region of the plant for protection against phytopathogens. In the present study six isolates of Trichoderma sp. were isolated and identified. Among them, two isolates were identified as Trichoderma harzianum, two as T. asperellum, one as T. virens, and the rest one identified as T. hamatum. These isolates were identified molecularly by using Internal Transcribed Spacer (ITS) primers amplification by polymerase chain reaction and submitted to National Center for Biotechnology Information (NCBI). All identified isolates along with isolate ITCC-5593 were screened for their antagonistic activity using dual culture method. Trichoderma harzianum isolates (ThL-1, ThL-4 and 5593) were found more potent antagonists against Fusarium oxysporum f. sp. lentis (Fol) NFLRJ-3. Selected isolates of Trichoderma sp. after dual culture assay were further studied for the production of cell wall-degrading enzymes (chitinase and β-1,3 glucanase) against NFLRJ-3 along with production of phyto-hormones i.e. Indole Acetic Acid (IAA) and Gibberllic Acid (GA3) two isolates namely ThL-4 and 5593 gave maximum production of hormones. The elicitation of the defense related enzymes in the plants were analysed using biochemical assays for important enzymes, i.e. Peroxidase (PO), Polyphenol oxidase (PPO) and Super oxide dismutes (SOD) level in challenged plants over untreated and unchallenged control plants. It was found that T. harzianum secretes two major cell wall-degrading enzymes, i.e., chitinase and β-1,3 glucanase. Optimum production of both the enzymes were found at 96 h of incubation and maximum activity was showed by isolate 5593 i.e. 9.16 and 2.86 U/mg protein, respectively. The role of T. harzianum isolates in inducing defense enzymes (PO, PPO and SOD) in lentil when exposed to Fol was also observed. It was found that T. harzianum (ThL-4 and 5595) induced higher levels of enzymes. This study proposes the use of rhizospheric Trichoderma sp. isolates for better and all around protection of plants against soil and seed borne phytopathogens.

Combined application of antagonistic Wickerhamomyces anomalus BS91 strain and Cynara cardunculus L. leaf extracts for the control of postharvest decay of citrus fruit

Combined use of biocontrol agents and plant extracts can be considered a viable and promising strategy for protecting plant tissues with different synergistic mechanisms of action that improve the antimicrobial activity of the mixtures. Treatments of citrus fruits with Wickerhamomyces anomalus BS91 have been previously reported as effective measures to reduce the incidence of green mold caused by Penicillium digitatum. On the opposite, the knowledge of the antifungal activity of cultivated cardoon (Cynara cardunculus L. var. altilis DC.) leaf extract, vegetable widespread in some Mediterranean areas, is still very limited. In this study, experimental trials were conducted to evaluate the effectiveness in vitro of leaf aqueous, methanolic and ethanolic extracts of C. cardunculus against seven fungal pathogens responsible for considerable food losses in the postharvest stage. In addition, biocontrol yeast W. anomalus BS91 and the three C. cardunculus extracts were tested in vivo both as a single treatment and in mixture, against Penicillium digitatum on ‘Tarocco’ oranges and ‘Femminello’ lemons. The combination of W. anomalus BS91 and leaf ethanolic extract reduced with the highest efficacy the incidence and severity of green mold on orange and lemon fruits with respect to the control, and was more effective than treatment with antagonistic yeast or leaf extracts applied alone. Incidence and severity of citrus decay were more consistently reduced when mixtures were applied 24 h before the inoculation of the pathogen, thus suggesting the relevance of preventive treatments. The mixtures of antagonistic W. anomalus BS91 and ethanolic leaf extract were more effective in controlling green mold decay on oranges than on lemons. These results indicate that biocontrol agents and leaf extracts, used in appropriate combination, can provide a stronger protection than when used singularly. However, compatibility between microbial antagonist and antimicrobial extract should be preliminary verified.

Bioactive Excreted/Secreted Products of Entomopathogenic Nematode Heterorhabditis bacteriophora Inhibit the Phenoloxidase Activity during the Infection.

Entomopathogenic nematodes (EPNs) are efficient insect parasites, that are known for their mutualistic relationship with entomopathogenic bacteria and their use in biocontrol. EPNs produce bioactive molecules referred to as excreted/secreted products (ESPs), which have come to the forefront in recent years because of their role in the process of host invasion and the modulation of its immune response. In the present study, we confirmed the production of ESPs in the EPN Heterorhabditis bacteriophora, and investigated their role in the modulation of the phenoloxidase cascade, one of the key components of the insect immune system. ESPs were isolated from 14- and 21-day-old infective juveniles of H. bacteriophora, which were found to be more virulent than newly emerged nematodes, as was confirmed by mortality assays using Galleria mellonella larvae. The isolated ESPs were further purified and screened for the phenoloxidase-inhibiting activity. In these products, a 38 kDa fraction of peptides was identified as the main candidate source of phenoloxidase-inhibiting compounds. This fraction was further analyzed by mass spectrometry and the de novo sequencing approach. Six peptide sequences were identified in this active ESP fraction, including proteins involved in ubiquitination and the regulation of a Toll pathway, for which a role in the regulation of insect immune response has been proposed in previous studies.

Bioactive Secondary Metabolites from Trichoderma spp. against Phytopathogenic Fungi.

Phytopathogenic fungi, causing significant economic and production losses, are becoming a serious threat to global food security. Due to an increase in fungal resistance and the hazardous effects of chemical fungicides to human and environmental health, scientists are now engaged to explore alternate non-chemical and ecofriendly management strategies. The use of biocontrol agents and their secondary metabolites (SMs) is one of the potential approaches used today. Trichoderma spp. are well known biocontrol agents used globally. Many Trichoderma species are the most prominent producers of SMs with antimicrobial activity against phytopathogenic fungi. Detailed information about these secondary metabolites, when grouped together, enhances the understanding of their efficient utilization and further exploration of new bioactive compounds for the management of plant pathogenic fungi. The current literature provides the information about SMs of Trichoderma spp. in a different context. In this review, we summarize and group different antifungal SMs of Trichoderma spp. against phytopathogenic fungi along with a comprehensive overview of some aspects related to their chemistry and biosynthesis. Moreover, a brief overview of the biosynthesis pathway, action mechanism, and different approaches for the analysis of SMs and the factors affecting the regulation of SMs in Trichoderma is also discussed.

Population-specific effect of Wolbachia on the cost of fungal infection in spider mites.

Many studies have revealed the ability of the endosymbiotic bacterium Wolbachia to protect its arthropod hosts against diverse pathogens. However, as Wolbachia may also increase the susceptibility of its host to infection, predicting the outcome of a particular Wolbachia‐host–pathogen interaction remains elusive. Yet, understanding such interactions and their eco‐evolutionary consequences is crucial for disease and pest control strategies. Moreover, how natural Wolbachia infections affect artificially introduced pathogens for biocontrol has never been studied. Tetranychus urticae spider mites are herbivorous crop pests, causing severe damage on numerous economically important crops. Due to the rapid evolution of pesticide resistance, biological control strategies using entomopathogenic fungi are being developed. However, although spider mites are infected with various Wolbachia strains worldwide, whether this endosymbiont protects them from fungi is as yet unknown. Here, we compared the survival of two populations, treated with antibiotics or naturally harboring different Wolbachia strains, after exposure to the fungal biocontrol agents Metarhizium brunneum and Beauveria bassiana. To control for potential effects of the bacterial community of spider mites, we also compared the susceptibility of two populations naturally uninfected by Wolbachia, treated with antibiotics or not. In one population, Wolbachia‐infected mites had a better survival than uninfected ones in absence of fungi but not in their presence, whereas in the other population Wolbachia increased the mortality induced by B. bassiana. In one naturally Wolbachia‐uninfected population, the antibiotic treatment increased the susceptibility of spider mites to M. brunneum, but it had no effect in the other treatments. These results suggest that natural Wolbachia infections may not hamper and may even improve the success of biological control using entomopathogenic fungi. However, they also draw caution on the generalization of such effects, given the complexity of within‐host–pathogens interaction and the potential eco‐evolutionary consequences of the use of biocontrol agents for Wolbachia‐host associations.

Bioactive Secondary Metabolites from Trichoderma spp. against Phytopathogenic Bacteria and Root-Knot Nematode.

Losses in crops caused by plant pathogenic bacteria and parasitic nematode are increasing because of a decrease in efficacy of traditional management measures. There is an urgent need to develop nonchemical and ecofriendly based management to control plant diseases. A potential approach of controlling plant disease in the crops is the use of biocontrol agents and their secondary metabolites (SMs). Luckily fungi and especially the genus Trichoderma comprise a great number of fungal strains that are the potential producer of bioactive secondary metabolites. In this study secondary metabolites from ten Trichoderma spp. were evaluated for their antibacterial and nematicidal potential against phytopathogenic bacteria Ralstonia solanacearum, Xanthomonas compestris and plant parasitic nematode Meloidogyne incognita. Five different growth media were evaluated for the production of SMs. It was shown that SMs of different Trichoderma spp. obtained on different growth media were different in the degree of their bioactivity. Comparison of five growth media showed that SMs produced on solid wheat and STP media gave higher antibacterial activity. SMs of T. pseudoharzianum (T113) obtained on solid wheat media were more effective against the studied bacteria followed by SMs from T. asperelloides (T136), T. pseudoharzianum (T129) and T. pseudoharzianum (T160). Scanning electron microscopy (SEM) was further conducted to observe the effect of SMs on bacterial cell morphology. As evident from the SEM, SMs produced severe morphological changes, such as rupturing of the bacterial cell walls, disintegration of cell membrane and cell content leaking out. SMs from T. viridae obtained on liquid STP and solid wheat media showed the highest percent of M. incognita juveniles (J2s) mortality and inhibition in egg hatching of M. incognita. The results of our study suggest that T. pseudoharzianum (T113) and T. viridae could be selected as an effective candidate for SMs source against phytopathogenic bacteria and M. incognita respectively.

The effect of aggregation of pathogen and biocontrol microbe propagules on biocontrol potential: a simple modelling study

Effective use of biocontrol agents (BCAs) is a potentially important component of sustainable agriculture. The ecological processes determining the success of biocontrol are complex, which may partly explain the limited success of biocontrol against plant diseases in field crops. Understanding the ecological characteristics of BCAs in addition to biocontrol mechanisms and direct biocontrol efficacy, including their survival and dispersal under heterogeneous conditions, is critically important to improve biocontrol efficacy. In this simulation study, we focused on the effects of the spatial aggregation of initial pathogen and biocontrol propagules (inocula) under spatially homogeneous and heterogeneous conditions on biocontrol potential. The simulation showed that, as expected, increasing the biocontrol propagule density led to increased biocontrol potential. Under a given inoculum density, increasing spatial aggregation of BCAs is not only likely to reduce biocontrol potential but also to increase variabilities in biocontrol outcomes. A spatially random distribution of BCA propagules is most likely to result in best biocontrol outcomes. Spatial aggregation of BCAs is more important than spatial heterogeneity in influencing biocontrol potential. Thus, the present simulation study illustrates the importance of ensuring a close-to-homogeneous distribution of BCA propagules for maximising biocontrol potential. By the same reasoning, a faster host growth rate will reduce biocontrol potential if BCA cannot keep up with host growth in terms of coverage: increasing BCA aggregation essentially leads to decreased effective coverage.

A Generic Model Accounting for the Interactions among Pathogens, Host Plants, Biocontrol Agents, and the Environment, with Parametrization for Botrytis cinerea on Grapevines

Although the use of biocontrol agents (BCAs) to manage plant pathogens has emerged as a sustainable means for disease control, global reliance on their use remains relatively insignificant and the factors influencing their efficacy remain unclear. In this work, we further developed an existing generic model for biocontrol of foliar diseases, and we parametrized the model for the Botrytis cinerea–grapevine pathosystem. The model was operated under three climate types to study the combined effects on BCA efficacy of four factors: (i) BCA mechanism of action, (ii) timing of BCA application with respect to timing of pathogen infection (preventative vs. curative), (iii) temperature and moisture requirements for BCA growth, and (iv) BCA survival capability. All four factors affected biocontrol efficacy, but factors iii and iv accounted for > 90% of the variation in model simulations. In other words, the most important factors affecting BCA efficacy were those related to environmental conditions. These findings indicate that the environmental responses of BCAs should be considered during their selection, BCA survival capability should be considered during both selection and formulation, and weather conditions and forecasts should be considered at the time of BCA application in the field.