Biological control as an alternative to synthetic fungicides for the management of grey and blue mould diseases of table grapes: a review

Recent advances in biocontrol and other alternative strategies for the management of postharvest decay in table grapes

During postharvest, table grapes are often spoiled by molds. Aspergillus sp., Alternaria sp., Botrytis sp., Cladosporium sp. and Penicillium sp. are different mold genera frequently related to table grape rot. Fungal spoilage affects nutritional value and organoleptic properties while also producing health hazards, such as mycotoxins. Traditionally, synthetic fungicides have been employed to control fungal diseases. However, possible negative effects on health and the environment are a serious concern for consumers and government entities. This review summarized data on innovative strategies proposed to diminish postharvest losses and extend table grape shelf life. Among physical, chemical, and biological strategies, either alone or in combination, the integrated management of fungal diseases is a sustainable alternative to synthetic fungicides. However, to date, only a few alternative technologies have succeeded on a commercial scale. Recent research aimed at increasing the competitiveness of alternative technologies has led to the development of integrated management strategies to prevent postharvest decay and increase the safety and quality of table grapes.

Insights into the antifungal mechanism of Bacillus subtilis cyclic lipopeptide iturin A mediated by potassium ion channel

Fungal infections pose severe and potentially lethal threats to plant, animal, and human health. Ergosterol has served as the primary target for developing antifungal medications. However, many antifungal drugs remain highly toxic to humans due to similarity in cell membrane composition between fungal and animal cells. Iturin A, lipopeptide produced by Bacillus subtilis, efficiently inhibit various fungi, but demonstrated safety in oral administration, indicating the existence of targets different from ergosterol. To pinpoint the exact antifungal target of iturin A, we used homologous recombination to knock out and overexpress erg3, a key gene in ergosterol synthesis. Saccharomyces cerevisiae and Aspergillus carbonarius were transformed using the LiAc/SS-DNNPEG and Agrobacterium-mediated transformation (AMT), respectively. Surprisingly, increasing ergosterol content did not augment antifungal activity. Furthermore, iturin A's antifungal activity against S. cerevisiae was reduced while it pre-incubation with voltage-gated potassium (Kv) channel inhibitor, indicating that Kv activation was responsible for cell death. Iturin A was found to activate the Kv protein, stimulating K+ efflux from cell. In vitro tests confirmed interaction between iturin A and Kv protein. This study highlights Kv as one of the precise targets of iturin A in its antifungal activity, offering a novel target for the development of antifungal medications.

The effect of maltodextrin edible coating containing pyracantha extract and potassium nano-carbonate on secondary metabolites, antioxidant capacity and microbiological properties of grape during cold storage

This study aimed to investigate the postharvest application of edible coating of maltodextrin containing potassium nanoparticles (KNPs; 0-2%) and pyracantha extract (PE; 0-1.5 %) on the maintenance of phenolic compounds, antioxidant capacity and microbial properties of 'Rishbaba' grape during 60 days at -1 °C using response surface methodology and central composite design. The results showed that the applied coating on Rishbaba grape maintained total phenol, total flavonoids, total anthocyanin, stilbenes (resveratrol and viniferin) and catechin. That also caused higher antioxidant capacity and lower mold and yeast growth in grape during the storage time. Finally, the best cold storage conditions of 'Rishbaba' grape were determined by using the edible maltodextrin coating containing 2 % KNPs and 1.5 % of PE for 34 days with a desirability of 0.728 in terms of investigated Characteristics. The optimized sample has the amount of total phenol (5.79 mg/g), total flavonoid (8.95 mg/g), total anthocyanin (6.48 mg/g) and the greatest ability to inhibit DPPH free radical (42.56 %) and the lowest growth rate of mold and yeast (21 Cfu/g).

Revisiting the current and emerging concepts of postharvest fresh fruit and vegetable pathology for next-generation antifungal technologies

Fungal infections of fresh fruits and vegetables (FFVs) can lead to safety problems, including consumer poisoning by mycotoxins. Various strategies exist to control fungal infections of FFVs, but their effectiveness and sustainability are limited. Recently, new concepts based on the microbiome and pathobiome have emerged and offer a more holistic perspective for advancing postharvest pathogen control techniques. Understanding the role of the microbiome in FFV infections is essential for developing sustainable control strategies. This review examines current and emerging approaches to postharvest pathology. It reviews what is known about the initiation and development of infections in FFVs. As a promising concept, the pathobiome offers new insights into the basic mechanisms of microbial infections in FFVs. The underlying mechanisms uncovered by the pathobiome are being used to develop more relevant global antifungal strategies. This review will also focus on new technologies developed to target the microbiome and members of the pathobiome to control infections in FFVs and improve safety by limiting mycotoxin contamination. Specifically, this review stresses emerging technologies related to FFVs that are relevant for modifying the interaction between FFVs and the microbiome and include the use of microbial consortia, the use of genomic technology to manipulate host and microbial community genes, and the use of databases, deep learning, and artificial intelligence to identify pathobiome markers. Other approaches include programming the behavior of FFVs using synthetic biology, modifying the microbiome using sRNA technology, phages, quorum sensing, and quorum quenching strategies. Rapid adoption and commercialization of these technologies are recommended to further improve the overall safety of FFVs.

Beneficial effects of Bacillus mojavensis strain MTC-8 on plant growth, immunity and disease resistance against Magnaporthe oryzae

Rice blast, a prevalent and highly destructive rice disease that significantly impacts rice yield, is caused by the rice blast fungus. In the present study, a strain named MTC-8, identified as Bacillus mojavensis, was demonstrated has strong antagonistic activity against the rice blast fungus, Rhizoctonia solani, Ustilaginoidea virens, and Bipolaria maydis. The potential biocontrol agents were identified using ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) analysis and chromatography. Further investigations elucidated the inhibitory mechanism of the isolated compound and demonstrated its ability to suppress spore germination, alter hyphal morphology, disrupt cell membrane integrity, and induce defense-related gene expression in rice. MTC-8 promoted plant growth and may lead to the development of a biocontrol agent that meets agricultural standards. Overall, the Bacillus mojavensis MTC-8 strain exerted beneficial effects on plant growth, immunity and disease resistance against rice blast fungus. In this study, we isolated and purified a bioactive substance from fermentation broth, and the results provide a foundation for the development and application of biopesticides. Elucidation of the inhibitory mechanism against rice blast fungus provides theoretical support for the identification of molecular targets. The successful development of a biocontrol agent lays the groundwork for its practical application in agriculture.

The occurrence and management of fumonisin contamination across the food production and supply chains

BACKGROUND

Fumonisins (FUMs) are among the most common mycotoxins in plant-derived food products. FUMs contamination has considerably impacted human and animal health, while causing significant economic losses. Hence, management of FUMs contamination in food production and supply chains is needed. The toxicities of FUMs have been widely investigated. FUMs management has been reported and several available strategies have been developed successfully to mitigate FUMs contamination present in foods. However, currently available management of FUMs contamination from different phases of food chains and the mechanisms of some major strategies are not comprehensively summarized.

AIM OF REVIEW

This review comprehensively characterize the occurrence, impacts, and management of FUMs contamination across food production and supply chains. Pre- and post-harvest strategies to prevent FUMs contamination also are reviewed, with an emphasis on the potential applications and the mechanisms of major mitigation strategies. The presence of modified FUMs products and their potential toxic effects are also considered. Importantly, the potential application of biotechnological approaches and emerging technologies are enunciated.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Currently available pre- and post-harvest management of FUMs contamination primarily involves prevention and decontamination. Prevention strategies are mainly based on limiting fungal growth and FUMs biosynthesis. Decontamination strategies are implemented through alkalization, hydrolysis, thermal or chemical transformation, and enzymatic or chemical degradation of FUMs. Concerns have been raised about toxicities of modified FUMs derivatives, which presents challenges for reducing FUMs contamination in foods with conventional methodologies. Integrated prevention and decontamination protocols are recommended to control FUMs contamination across entire value chains in developed countries. In developing countries, several other approaches, including cultivating, introducing Bt maize, simple sorting/cleaning, and dehulling, are suggested. Future studies should focus on biotechnological approaches, emerging technologies, and metagenomic/genomic identification of new degradation enzymes that could allow better opportunities to manage FUMs contamination in the entire food system.

Biocontrol potential of endophytic Bacillus subtilis A9 against rot disease of Morchella esculenta

Introduction

Morchella esculenta is a popular edible fungus with high economic and nutritional value. However, the rot disease caused by Lecanicillium aphanocladii, pose a serious threat to the quality and yield of M. esculenta. Biological control is one of the effective ways to control fungal diseases.

Methods and results

In this study, an effective endophytic B. subtilis A9 for the control of M. esculenta rot disease was screened, and its biocontrol mechanism was studied by transcriptome analysis. In total, 122 strains of endophytic bacteria from M. esculenta, of which the antagonistic effect of Bacillus subtilis A9 on L. aphanocladii G1 reached 72.2% in vitro tests. Biological characteristics and genomic features of B. subtilis A9 were analyzed, and key antibiotic gene clusters were detected. Scanning electron microscope (SEM) observation showed that B. subtilis A9 affected the mycelium and spores of L. aphanocladii G1. In field experiments, the biological control effect of B. subtilis A9 reached to 62.5%. Furthermore, the transcritome profiling provides evidence of B. subtilis A9 bicontrol at the molecular level. A total of 1,246 differentially expressed genes (DEGs) were identified between the treatment and control group. Gene Ontology (GO) enrichment analysis showed that a large number of DEGs were related to antioxidant activity related. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the main pathways were Nitrogen metabolism, Pentose Phosphate Pathway (PPP) and Mitogen-Activated Protein Kinases (MAPK) signal pathway. Among them, some important genes such as carbonic anhydrase CA (H6S33_007248), catalase CAT (H6S33_001409), tRNA dihydrouridine synthase DusB (H6S33_001297) and NAD(P)-binding protein NAD(P) BP (H6S33_000823) were found. Furthermore, B. subtilis A9 considerably enhanced the M. esculenta activity of Polyphenol oxidase (POD), Superoxide dismutase (SOD), Phenylal anineammonia lyase (PAL) and Catalase (CAT).

Conclusion

This study presents the innovative utilization of B. subtilis A9, for effectively controlling M. esculenta rot disease. This will lay a foundation for biological control in Morchella, which may lead to the improvement of new biocontrol agents for production.

Biocontrol of Alternaria alternata in cold-stored table grapes using psychrotrophic yeasts and bioactive compounds of natural sources

Alternaria alternata is a common fungal pathogen causing postharvest decay in table grapes. This study addressed the potential of autochthonous yeasts and bioactive compounds of natural sources to act as biocontrol agents (BCAs) against A. alternata in cold-stored table grapes. With this purpose, 19 yeast capable of growing at 0-1 °C were isolated from the surface of Red Globe table grapes. These isolates, along with the pre-isolated strain Metschnikowia pulcherrima RCM2, were evaluated as BCAs in wounded berries. From these results, six yeast isolates were pre-selected to be combined with bioactive compounds of natural sources, like phenolic compounds (PCs) of side streams of wine industry, including bunch stem extract (BSE) (5-25 %), and cane extract (CE) (5-25 %), and functional polysaccharides from shrimp waste such as chitosan (CH) (0.5 %). Then, the biocontrol efficacy of combined treatments beyond individual ones was compared. The results revealed that 4 yeast isolates, namely M. pulcherrima RCM2 and ULA146, and Aureobasidium pullulans FUL14 and FUL18, were the most effective. However, when combined with the natural bioactive compounds, their efficacy against A. alternata did not increase significantly. Notably, ULA146 and FUL18 demonstrated a biocontrol efficacy of 36-37 %, comparable to that of the treatment with commercial doses of SO2, which only showed a 27 % reduction in the lesion diameter. These findings highlight the potential of using psychrotrophic yeasts as BCAs against A. alternata in cold-stored table grapes. Combining these yeast strains with BSE, CE and CH did not increase BCAs efficacy against this pathogen at the concentrations tested. The development of effective biocontrol strategies for A. alternata could contribute to reducing reliance on chemically synthesized fungicides, promoting sustainable practices, aiming to improve the quality and safety of cold-stored table grapes.

Curcumin: An innovative approach for postharvest control of Alternaria alternata induced black rot in cherry tomatoes

Curcumin, a natural bioactive compound derived from Curcuma longa, has been widely recognized for its antifungal properties. In this study, we investigated the effects of curcumin on the phytopathogenic fungus Alternaria alternata and its pathogenicity in cherry tomato fruit. The results demonstrated that curcumin treatment significantly inhibited mycelial growth and spore germination of A. alternata in a dose-dependent manner. Scanning electron microscopy revealed alterations in the morphology of A. alternata mycelia treated with curcumin. Furthermore, curcumin treatment led to an increase in malondialdehyde and hydrogen peroxide contents, indicating cell membrane damage in A. alternata. Moreover, curcumin exhibited a remarkable inhibitory effect on the incidence and lesion diameters of black rot caused by A. alternata in cherry tomato fruit. Gene expression analysis revealed upregulation of defense-related genes (POD, SOD, and CAT) in tomato fruit treated with curcumin. Additionally, curcumin treatment resulted in decreased activity of exocellular pathogenic enzymes (polygalacturonase, pectin lyase, and endo-1,4-β-d-glucanase) in A. alternata. Overall, our findings highlight the potential of curcumin as an effective antifungal agent against A. alternata, providing insights into its inhibitory mechanisms on mycelial growth, spore germination, and pathogenicity in cherry tomato fruit.

Novel Pseudomonas Species Prevent the Growth of the Phytopathogenic Fungus Aspergillus flavus

In response to the escalating demand for sustainable agricultural methodologies, the utilization of microbial volatile organic compounds (VOCs) as antagonists against phytopathogens has emerged as a viable eco-friendly alternative. Microbial volatiles exhibit rapid diffusion rates, facilitating prompt chemical interactions. Moreover, microorganisms possess the capacity to emit volatiles constitutively, as well as in response to biological interactions and environmental stimuli. In addition to volatile compounds, these bacteria demonstrate the ability to produce soluble metabolites with antifungal properties, such as APE Vf, pyoverdin, and fragin. In this study, we identified two Pseudomonas strains (BJa3 and MCal1) capable of inhibiting the in vitro mycelial growth of the phytopathogenic fungus Aspergillus flavus, which serves as the causal agent of diseases in sugarcane and maize. Utilizing GC/MS analysis, we detected 47 distinct VOCs which were produced by these bacterial strains. Notably, certain volatile compounds, including 1-heptoxydecane and tridecan-2-one, emerged as primary candidates for inhibiting fungal growth. These compounds belong to essential chemical classes previously documented for their antifungal activity, while others represent novel molecules. Furthermore, examination via confocal microscopy unveiled significant morphological alterations, particularly in the cell wall, of mycelia exposed to VOCs emitted by both Pseudomonas species. These findings underscore the potential of the identified BJa3 and MCal1 Pseudomonas strains as promising agents for fungal biocontrol in agricultural crops.

Pseudomonas chlororaphis IRHB3 assemblies beneficial microbes and activates JA-mediated resistance to promote nutrient utilization and inhibit pathogen attack

Introduction

The rhizosphere microbiome is critical to plant health and resistance. PGPR are well known as plant-beneficial bacteria and generally regulate nutrient utilization as well as plant responses to environmental stimuli. In our previous work, one typical PGPR strain, Pseudomonas chlororaphis IRHB3, isolated from the soybean rhizosphere, had positive impacts on soil-borne disease suppression and growth promotion in the greenhouse, but its biocontrol mechanism and application in the field are not unclear.

Methods

In the current study, IRHB3 was introduced into field soil, and its effects on the local rhizosphere microbiome, disease resistance, and soybean growth were comprehensively analyzed through high-throughput sequencing and physiological and molecular methods.

Results and discussion

We found that IRHB3 significantly increased the richness of the bacterial community but not the structure of the soybean rhizosphere. Functional bacteria related to phosphorus solubilization and nitrogen fixation, such as Geobacter, Geomonas, Candidatus Solibacter, Occallatibacter, and Candidatus Koribacter, were recruited in rich abundance by IRHB3 to the soybean rhizosphere as compared to those without IRHB3. In addition, the IRHB3 supplement obviously maintained the homeostasis of the rhizosphere microbiome that was disturbed by F. oxysporum, resulting in a lower disease index of root rot when compared with F. oxysporum. Furthermore, JA-mediated induced resistance was rapidly activated by IRHB3 following PDF1.2 and LOX2 expression, and meanwhile, a set of nodulation genes, GmENOD40b, GmNIN-2b, and GmRIC1, were also considerably induced by IRHB3 to improve nitrogen fixation ability and promote soybean yield, even when plants were infected by F. oxysporum. Thus, IRHB3 tends to synergistically interact with local rhizosphere microbes to promote host growth and induce host resistance in the field.

The effect of pulcherriminic acid produced by Metschnikowia citriensis in controlling postharvest diseases of citrus fruits

The biocontrol effectiveness of Metschnikowia citriensis relies on its production of pulcherriminic acid (PA), which forms insoluble and stable pulcherrimin pigments by chelating iron ions, this inhibits pathogen growth by preventing their utilization of chelated Fe3+. In this study, ΔM. citriensis, which did not produce PA, was used as a control to examine changes in its biocontrol effectiveness by adding tryptophan to the medium. Tryptophan was shown to have no discernible impact on the growth and PA production of ΔM. citriensis; moreover, the PA synthesis-related genes PULs, Snf2, and leucyl-tRNA synthesis-related genes A3136 and A3022 were all down-regulated in ΔM. citriensis. The PA-free ΔM. citriensis eventually showed a much poorer inhibition zone against the pathogens in vitro, and a noticeably decreased control efficiency against postharvest diseases in citrus fruit. Tryptophan was added to the medium, which had no appreciable impact on inhibitory zone of ΔM. citriensis against pathogens in vitro, but enhanced its ability to control citrus postharvest diseases. Additionally, the control effects of culture broth of M. citriensis and ΔM. citriensis on postharvest diseases in citrus fruit were assessed. It was found that both culture broth of M. citriensis and ΔM. citriensis exhibited remarkable control effects against citrus postharvest diseases, with culture broth of M. citriensis which containing PA being more effective in controlling the disease. Last but not least, we extracted and dissolved pulcherrimin to obtain PA extracts, which were then injected to citrus fruits to assess the biocontrol effectiveness. The findings demonstrated that postharvest diseases of citrus fruit can be effectively controlled by PA extracts. This research suggested a new biological strategy for the management of citrus postharvest diseases.

Biotechnological and Biocontrol Approaches for Mitigating Postharvest Diseases Caused by Fungal Pathogens and Their Mycotoxins in Fruits: A Review

Postharvest diseases caused by fungal pathogens are significant contributors to the postharvest losses of fruits. Moreover, some fungal pathogens produce mycotoxins, which further compromise the safety and quality of fruits. In this review, the potential of biotechnological and biocontrol approaches for mitigating postharvest diseases and mycotoxins in fruits is explored. The review begins by discussing the impact of postharvest diseases on fruit quality and postharvest losses. Next, it provides an overview of major postharvest diseases caused by fungal pathogens. Subsequently, it delves into the role of biotechnological approaches in controlling these diseases. The review also explored the application of biocontrol agents, such as antagonistic yeasts, bacteria, and fungi, which can suppress pathogen growth. Furthermore, future trends and challenges in these two approaches are discussed in detail. Overall, this review can provide insights into promising biotechnological and biocontrol strategies for managing postharvest diseases and mycotoxins in fruits.

Molecular Identification of Juglans Regia Endophyte LTL-G3, Its Antifungal Potential and Bioactive Substances

Background

Endophyte is one of the potential biocontrol agents for inhibiting plant pathogens. However, the mechanisms and characteristics involved in the inhibition of different phytopathogenic fungi by endophytes, especially walnut endophytes, are still largely unknown.

Objectives

The present study aimed to identify the walnut endophytic fungus LTL-G3 from a genetic point of view, assess the strain's antifungal activity, and determine the bioactivities of the substances it produces against plant pathogens.

Materials and Methods

The homologous sequence of strain LTL-G3 was examined, and typical strains of the Trichoderma virens group were used to build NJ phylogenetic trees and analyze the taxonomic position of the strain. The biocontrol agent's antagonistic potential for many plant pathogenic fungi. By using silica gel G chromatography, the active components of the strain were separated and purified. The active components were identified using GC-MS and NMR.

Results

The strain LTL-G3 was identified as Trichoderma virens. Its fermentation and secondary metabolite extracts had a broad spectrum and strong inhibitory effect on the spread of six plant pathogens (Botrytis cinerea, Fusarium graminearum, Gloeosporium fructigenum, Phytophthora capsici, Rhizoctonia solani, and Valsa mali) evaluated, of which, its inhibition rate against Valsa mali reached 76.6% (fermentation extract) and 100% (ethyl acetate and n-butanol extracts). On silica gel G chromatography, bioactive compounds were divided into 6 fractions and 7 sub-fractions. Fr.2-2 was the sub-fraction that showed the greatest inhibitory against V. mali, as an inhibition percentage of 89.36% in 1 mg. mL-1. Fifteen key inhibitory chemicals identified using GC-MS. By examining the NMR data, the chemical make-up of the precipitated white solid was identified. The inhibition rate against V. mali increased by over 95% at a dosage of 1 mg. mL-1, indicating a significant linear association between compound A and that rate.

Conclusions

The strain LTL-G3 can be applied as an efficient biological control agent against V. mali, and its highly inhibitive secondary metabolites provide the mechanism for this action.

Biocontrol Efficacy of Metschnikowia spp. Yeasts in Organic Vineyards against Major Airborne Diseases of Table Grapes in the Field and in Postharvest

The aim of this work was to evaluate the efficacy of two antagonistic yeasts, Metschnikowia pulcherrima strain MPR3 and M. fructicola strain NRRL Y-27328 (commercial product NOLI), applied in addition to the "on-farm biological treatments" (BIO) carried out during the production season, for the containment of powdery mildew and grey mould diseases on organic table grapes 'Italia'. The yeast strains were applied in the field three times, and their efficacy was evaluated during the production season and under postharvest conditions. Overall, M. pulcherrima MPR3 combined with BIO treatments reduced disease incidence caused by Erysiphe necator and disease incidence and severity caused by Botrytis cinerea with values between 67.8% and 86.2%, showing higher efficacy than BIO treatments applied alone and in combination with NOLI. Field treatments based on BIO+MPR3 maintained their performance also during fruit storage, protecting grape berries from grey mould development to a greater extent than the other treatments (disease reduction of about 98%). Thus, the presence of M. pulcherrima MPR3 seems to improve disease management both in the field and in postharvest environments, without negative impacts on grape microbial communities. These findings highlight the potential of M. pulcherrima MPR3 as a promising alternative strategy for disease control in organic vineyards and in postharvest, providing sustainable solutions to improve food quality and safety.

The interaction effects of pesticides with Saccharomyces cerevisiae and their fate during wine-making process

Pesticide residues in grapes could be transferred to fermentation system during the wine-making process, which may interfere the normal proliferation of Saccharomyces cerevisiae and subsequently affect the safety and quality of wine products. However, the interaction between pesticides and Saccharomyces cerevisiae is still poorly understood. Herein, the fate, distribution and interaction effect with Saccharomyces cerevisiae of five commonly-used pesticides during the wine-making process were evaluated. The five pesticides exerted varied inhibition on the proliferation of Saccharomyces cerevisiae, and the order of inhibition intensity was difenoconazole > tebuconazole > pyraclostrobin > azoxystrobin > thiamethoxam. Compared with the other three pesticides, triazole fungicides difenoconazole and tebuconazole showed stronger inhibition and played a major role in binary exposure. The mode of action, lipophilicity and exposure concentration were important factors in the inhibition of pesticides. Saccharomyces cerevisiae had no obvious impacts on the degradation of target pesticides in the simulated fermentation experiment. However, the levels of target pesticides and their metabolite were significantly reduced during the wine-making process, with the processing factors ranged from 0.030 to 0.236 (or 0.032 to 0.257) during spontaneous (or inoculated) wine-making process. As a result, these pesticides were significantly enriched in the pomace and lees, and showed a positive correlation (R² ≥ 0.536, n = 12, P < 0.05) between the hydrophobicity of pesticides and distribution coefficients in the solid-liquid distribution system. The findings provide important information for rational selection of pesticides on wine grapes and facilitate more accurate risk assessments of pesticides for grape processing products.

Indigenous Yeasts for the Biocontrol of Botrytis cinerea on Table Grapes in Chile

One hundred twenty-five yeast strains isolated from table grapes and apples were evaluated for the control Botrytis cinerea of in vitro and in vivo. Ten strains were selected for their ability to inhibit mycelial growth of B. cinerea in vitro. In the in vivo assays, these yeasts were tested at 20 °C on 'Thompson Seedless' berries for 7 days; only three were selected (m11, me99 and ca80) because they significantly reduced the incidence of gray mold. These three yeast strains were then evaluated at different concentrations (1 × 10⁷, 1 × 10⁸ and 1 × 10⁹ cells mL^-1) on 'Thompson Seedless' grape berries at 20 °C. The strains m11, me99 and ca80 reduced the incidence of B. cinerea to 11.9, 26.1 and 32.1%, respectively, when the berries were submerged in a yeast suspension at a concentration of 1 × 10⁹ cells mL^-1 24 h before inoculation with B. cinerea. The most favorable pH for antifungal activity was 4.6 in the three isolates. The three yeast strains secreted the hydrolytic enzymes chitinase and β-1-glucanase, and two strains (me99 and ca80) produced siderophores. The three yeast strains exhibited low oxidative stress tolerance and only strain m11 had the ability to produce biofilms. The strains were identified using 5.8S-ITS rDNA PCR-RFLP and correspond to the Meyerozyma guilliermondii (m11) and Aureobasidium pullulans (me99 and ca80) species.

Screening of antagonistic yeast strains for postharvest control of Penicillium expansum causing blue mold decay in table grape

Blue mold decay caused by Penicillium expansum is one of the most important postharvest diseases of grapes, leading to considerable economic losses. Regarding the increasing demand for pesticide-free foods, this study aimed to find potential yeast strains for biological control of blue mold on table grapes. A total of 50 yeast strains were screened for antagonistic activity against P. expansum using the dual culture method and six strains significantly inhibited the fungal growth. All six yeast strains (Coniochaeta euphorbiae, Auerobasidium mangrovei, Tranzscheliella sp., Geotrichum candidum, Basidioascus persicus, and Cryptococcus podzolicus) reduced the fungal growth (29.6-85.0%) and the decay degree of wounded grape berries inoculated with P. expansum while G. candidum was found to be the most efficient biocontrol agent. On the basis of antagonistic activity, the strains were further characterized by in vitro assays involving inhibition of conidial germination, production of volatile compounds, iron competition, production of hydrolytic enzymes, biofilm-forming capacity, and exhibited three or more putative mechanisms. To our knowledge, the yeasts are reported for the first time as potential biocontrol agents against the blue mold of grapes but more study is required to evaluate their efficiency related to field application.

Screening of endophytic fungi from Cremastra appendiculata and their potential for plant growth promotion and biological control

Biocontrol fungi are widely used to promote plant growth and pest control. Four fungi were isolated from Cremastra appendiculata tubers and screened for plant growth-promoting and antagonistic effects. Based on the morphological characterization and ITS, 18S rRNA and 28S rRNA gene sequencing analysis, the fungi were identified to be related to Colletotrichum gloeosporioides (DJL-6), Trichoderma tomentosum (DJL-9), Colletotrichum godetiae (DJL-10) and Talaromyces amestolkiae (DJL-15). The growth inhibition tests showed that the four isolates had different inhibitory effects on Colletotrichum fructicola, Alternaria alternata and Alternaria longipes, among which DJL-9 showed the highest inhibitory activity. Their culture filtrates (especially that of DJL-15) can also inhibit pathogens. Four isolates were positive for the production of indole-3-acid (IAA) and β-1,3-glucanase and possessed proteolytic activity but were negative for the production of iron siderophore complexes. The four fungi showed strong nitrogen fixation and potassium dissolution abilities. In addition to DJL-9 being able to solubilize phosphate, DJL-10 was able to produce chitinase and cellulase. Pot experiments indicated that the four fungi increased the germination rate of C. appendiculata and soybean seeds and increased soybean radicle growth and plant biomass. Among them, DJL-6 had a better growth-promoting effect. Therefore, we successfully screened the biocontrol potential of endophytes from C. appendiculata, with a focus on preventing fungal diseases and promoting plant growth, and selected strains that could provide nutrients and hormones for plant growth.

Transcriptome profiling reveals the underlying mechanism of grape post-harvest pathogen Penicillium olsonii against the metabolites of Bacillus velezensis

Introduction

Pathogen infection influences the post-harvest shelf life of grape berries. In a preliminary study, metabolites produced by Bacillus velezensis significantly inhibited the growth of the grape postharvest pathogen Penicillium olsonii.

Methods

To investigate the mechanism of interaction between B. velezensis and P. olsonii, a draft genome was generated for P. olsonii WHG5 using the Illumina NovaSeq platform, and the transcriptomic changes in WHG5 were analyzed in response to the exposure to B. velezensis metabolites (10% v/v).

Results

The expression levels of genes associated with sporulation, including GCY1, brlA, and abaA, were down-regulated compared with those of the control. In addition, spore deformation and abnormal swelling of the conidiophore were observed. The expression of crucial enzymes, including fructose 2,6-bisphosphate and mannitol-2-dehydrogenase, was down-regulated, indicating that the glycolytic pathway of WHG5 was adversely affected by B. velezensis metabolites. The KEGG pathway enrichment analysis revealed that glutathione metabolism and the antioxidant enzyme system were involved in the response to B. velezensis metabolites. The down-regulation of the pathogenesis-related genes, PG1 and POT1, suggested that B. velezensis metabolites decreased the pathogenicity of P. olsonii. B. velezensis metabolites disrupted the homeostasis of reactive oxygen species in P. olsonii by affecting glucose metabolism, resulting in spore deformation and disruption of growth. In addition, the expression of key pathogenesis-related genes was down-regulated, thereby reducing the pathogenicity of P. olsonii.

Disscusion

This study provides insights into the responses of P. olsonii to B. velezensis metabolites and identifies potential target genes that may be useful in biocontrol strategies for the suppression of post-harvest spoilage in grapes.

Biocontrol potential of wine yeasts against four grape phytopathogenic fungi disclosed by time-course monitoring of inhibitory activities

Grapes' infection by phytopathogenic fungi may often lead to rot and impair the quality and safety of the final product. Due to the concerns associated with the extensive use of chemicals to control these fungi, including their toxicity for environment and human health, bio-based products are being highly preferred, as eco-friendlier and safer alternatives. Specifically, yeasts have shown to possess antagonistic activity against fungi, being promising for the formulation of new biocontrol products.In this work 397 wine yeasts, isolated from Portuguese wine regions, were studied for their biocontrol potential against common grapes phytopathogenic fungal genera: Aspergillus, Botrytis, Mucor and Penicillium. This set comprised strains affiliated to 32 species distributed among 20 genera. Time-course monitoring of mold growth was performed to assess the inhibitory activity resulting from either diffusible or volatile compounds produced by each yeast strain. All yeasts displayed antagonistic activity against at least one of the mold targets. Mucor was the most affected being strongly inhibited by 68% of the tested strains, followed by Botrytis (20%), Aspergillus (19%) and Penicillium (7%). More notably, the approach used allowed the detection of a wide array of yeast-induced mold response profiles encompassing, besides the decrease of mold growth, the inhibition or delay of spore germination and the complete arrest of mycelial extension, and even its stimulation at different phases. Each factor considered (taxonomic affiliation, mode of action and fungal target) as well as their interactions significantly affected the antagonistic activity of the yeast isolates. The highest inhibitions were mediated by volatile compounds. Total inhibition of Penicillium was achieved by a strain of Metschnikowia pulcherrima, while the best performing yeasts against Mucor, Aspergillus and Botrytis, belong to Lachancea thermotolerans, Hanseniaspora uvarum and Starmerella bacillaris, respectively. Notwithstanding the wide diversity of yeasts tested, only three strains were found to possess a broad spectrum of antagonistic activity, displaying strong or very strong inhibition against the four fungal targets tested. Our results confirm the potential of wine yeasts as biocontrol agents, while highlighting the need for the establishment of fit-for-purpose selection programs depending on the mold target, the timing, and the mode of application.

Microbial volatile organic compounds: Antifungal mechanisms, applications, and challenges

The fungal decay of fresh fruits and vegetables annually generates substantial global economic losses. The utilization of conventional synthetic fungicides is damaging to the environment and human health. Recently, the biological control of post-harvest fruit and vegetable diseases via antagonistic microorganisms has become an attractive possible substitution for synthetic fungicides. Numerous studies have confirmed the potential of volatile organic compounds (VOCs) for post-harvest disease management. Moreover, VOC emission is a predominant antifungal mechanism of antagonistic microorganisms. As such, it is of great significance to discuss and explore the antifungal mechanisms of microbial VOCs for commercial application. This review summarizes the main sources of microbial VOCs in the post-harvest treatment and control of fruit and vegetable diseases. Recent advances in the elucidation of antifungal VOC mechanisms are emphasized, and the applications of VOCs produced from antagonistic microorganisms are described. Finally, the current prospects and challenges associated with microbial VOCs are considered.

Eco-friendly 'ochratoxin A' control in stored licorice roots - quality assurance perspective

According to toxicity data, ochratoxin A (OTA) is the second most important mycotoxin and is produced by Aspergillus and Penicillium. As a natural antifungal agent, clove essential oil (CEO) is a substance generally recognised as safe (GRAS) and shows strong activity against fungal pathogens. Here, we aimed to investigate the control efficacy of CEO in nano-emulsions (CEN) against OTA production in licorice roots and rhizomes during storage. The experiments were performed under simulated conditions of all four seasons (i.e. Spring, Summer, Autumn and Winter). Relative humidity (RH) and temperature were simulated in desiccators along with various salt solutions in incubators. Fresh licorice roots were immersed in CEN at various concentrations (150, 300, 600, 1200 and 2400 µl/l). Before utilising the nano-emulsions, we measured their polydispersity index and mean droplet size by the dynamic light scattering (DLS) technique. Also, the chemical composition of the CEO was determined using GC and GC-MS analyses. Sampling was carried out to monitor OTA once every five days. The samples were dried immediately and analysed by high-performance liquid chromatography (HPLC). Results showed that various concentrations of CEN inhibited the growth of fungi and OTA production. The most effective CEN concentrations were 1200 and 2400 µl/l, which reduced OTA production to 19 and 20 ppb under Winter and Autumn conditions, respectively. These results suggest an effective eco-friendly method for the storage of licorice to reduce postharvest fungal decay.

Pathogen-Mediated Assembly of Plant-Beneficial Bacteria to Alleviate Fusarium Wilt in Pseudostellaria heterophylla

Fusarium wilt (FW) is a primary replant disease that affects Pseudostellaria heterophylla (Taizishen) and is caused by Fusarium oxysporum, which occurs widely in China under the continuous monocropping regime. However, the ternary interactions among the soil microbiota, P. heterophylla, and F. oxysporum remain unknown. We investigated the potential interaction relationship by which the pathogen-mediated P. heterophylla regulates the soil and the tuberous root microbiota via high-throughput sequencing. Plant-pathogen interaction assays were conducted to measure the arrival of F. oxysporum and Pseudomonas poae at the tuberous root via qPCR and subsequent seedling disease incidence. A growth assay was used to determine the effect of the tuberous root crude exudate inoculated with the pathogen on P. poae. We observed that pathogen-mediated P. heterophylla altered the diversity and the composition of the microbial communities in its rhizosphere soil and tuberous root. Beneficial microbe P. poae and pathogen F. oxysporum were significantly enriched in rhizosphere soil and within the tuberous root in the FW group with high severity. Correlation analysis showed that, accompanied with FW incidence, P. poae co-occurred with F. oxysporum. The aqueous extract of P. heterophylla tuberous root infected by F. oxysporum substantially promoted the growth of P. poae isolates (H1-3-A7, H2-3-B7, H4-3-C1, and N3-3-C4). These results indicated that the extracts from the tuberous root of P. heterophylla inoculated with F. oxysporum might attract P. poae and promote its growth. Furthermore, the colonization assay found that the gene copies of sucD in the P. poae and F. oxysporum treatment (up to 6.57 × 10¹⁰) group was significantly higher than those in the P. poae treatment group (3.29 × 10¹⁰), and a pathogen-induced attraction assay found that the relative copies of sucD of P. poae in the F. oxysporum treatment were significantly higher than in the H₂O treatment. These results showed that F. oxysporum promoted the colonization of P. poae on the tuberous root via F. oxysporum mediation. In addition, the colonization assay found that the disease severity index in the P. poae and F. oxysporum treatment group was significantly lower than that in the F. oxysporum treatment group, and a pathogen-induced attraction assay found that the disease severity index in the F. oxysporum treatment group was significantly higher than that in the H₂O treatment group. Together, these results suggest that pathogen-mediated P. heterophylla promoted and assembled plant-beneficial microbes against plant disease. Therefore, deciphering the beneficial associations between pathogen-mediated P. heterophylla and microbes can provide novel insights into the implementation and design of disease management strategies.

Identification of Volatile Organic Compounds in Extremophilic Bacteria and Their Effective Use in Biocontrol of Postharvest Fungal Phytopathogens

Phytopathogenic fungal growth in postharvest fruits and vegetables is responsible for 20-25% of production losses. Volatile organic compounds (VOCs) have been gaining importance in the food industry as a safe and ecofriendly alternative to pesticides for combating these phytopathogenic fungi. In this study, we analysed the ability of some VOCs produced by strains of the genera Bacillus, Peribacillus, Pseudomonas, Psychrobacillus and Staphylococcus to inhibit the growth of Alternaria alternata, Botrytis cinerea, Fusarium oxysporum, Fusarium solani, Monilinia fructicola, Monilinia laxa and Sclerotinia sclerotiorum, in vitro and in vivo. We analysed bacterial VOCs by using GC/MS and 87 volatile compounds were identified, in particular acetoin, acetic acid, 2,3-butanediol, isopentanol, dimethyl disulphide and isopentyl isobutanoate. In vitro growth inhibition assays and in vivo experiments using cherry fruits showed that the best producers of VOCs, Bacillus atrophaeus L193, Bacillus velezensis XT1 and Psychrobacillus vulpis Z8, exhibited the highest antifungal activity against B. cinerea, M. fructicola and M. laxa, which highlights the potential of these strains to control postharvest diseases. Transmission electron microscopy micrographs of bacterial VOC-treated fungi clearly showed antifungal activity which led to an intense degeneration of cellular components of mycelium and cell death.

Aspergillus carbonarius-derived ochratoxins are inhibited by Amazonian Bacillus spp. used as a biocontrol agent in grapes

Bacillus spp. have been used as a biocontrol strategy to eliminate/reduce toxic fungicides in viticulture. Furthermore, the presence of fungi that are resistant to commonly used products is frequent, highlighting the need for new biocontrol strains. Aspergillus carbonarius can produce ochratoxins, including ochratoxin A (OTA), which has a regulatory maximum allowable limit for grape products. The purpose of this study was to assess the ability of four Amazonian strains of Bacillus (P1, P7, P11, and P45) to biocontrol A. carbonarius and various forms of ochratoxins in grapes. Berries treated with strain P1 presented no fungal colonies (100% reduction), while P7, P11 and P45 strains caused a reduction of 95, 95 and 61% on fungal counts, respectively. Six forms of ochratoxin were found in the grapes inoculated with A. carbonarius, including ochratoxin α, ochratoxin β, ochratoxin α methyl-ester, ochratoxin α amide, N-formyl-ochratoxin α amide, and OTA. Four of these ochratoxin forms (ochratoxin β, ochratoxin α methyl-ester, ochratoxin α amide, N-formyl-ochratoxin α amide) are reported for the first time in grapes. These ochratoxins were identified using liquid chromatography coupled to quadrupole time-of-flight mass spectrometry (LC-QToF-MS). All Bacillus strains inhibited the synthesis of OTA, which is the most toxic form of ochratoxin. No ochratoxin form was found when P1 and P7 were used. Although some forms of ochratoxin were detected in grapes treated with Bacillus spp. P11 and P45, the levels decreased by 97%. To our knowledge, this is the first report on the inhibition of Aspergillus carbonarius-derived ochratoxin by Bacillus species. P1 strain, identified as Bacillus velezensis, was found to be the most promising for completely inhibiting fungal growth and production of all ochratoxins.

Changes in the Fungal Community Assembly of Apple Fruit Following Postharvest Application of the Yeast Biocontrol Agent Metschnikowia fructicola

Recently, increasing focus has been placed on exploring fruit microbiomes and their association with their hosts. Investigation of the fruit surface microbiome of apple has revealed variations in the composition and structure depending on management practices, phenological stages, and spatial distribution on the fruit itself. However, the fate of the fruit surface microbiome assembly and dynamics in apple following interventions such as the application of biocontrol agents remains unknown. The objective of the study was to explore the effect of a postharvest application of a yeast biocontrol agent, Metschnikowia fructicola, on the composition of the epiphytic fungal microbiota on apples during cold storage. Our results demonstrated that the applied biocontrol agent, M. fructicola, persisted in high abundance (>28% relative abundance) on the fruit surface throughout the storage period. The biocontrol application significantly decreased the richness and caused a significant shift in the overall composition and structure of the fungal microbiome relative to untreated or water-treated controls. The yeast application reduced the abundance of several apple fungal pathogens, namely, Alternaria, Aspergillus, Comoclatris, Stemphylium, Nigrospora, Penicillium, and Podosphaera, throughout the cold storage period.

The use of previous crops as sustainable and eco-friendly management to fight Fusarium oxysporum in sesame plants

Sesame (Sesamum indicum L.), the “Queen of oil seeds” is being infected with pathogens, i.e., fungi, bacteria, virus and nematodes. Fusarium oxysporum sp. sesami (Zap.), is one of the fiercest pathogens causing severe economic losses on sesame. This work aimed to evaluate the impact of the cultivation of some preceding crops and seed inoculation with antagonistic predominant rhizospheric bacteria and actinomycetes on the incidence and development of Fusarium damping-off and wilt disease. Results showed that the lowest pre and/or post-emergence damping-off and wilt of sesame were recorded after onion and garlic, followed by wheat compared to clover in both the 2019 and 2020 seasons. In vitro, soil extracts from plots where onion and garlic have been cultivated slightly decreased the conidia germination and mycelium radial growth of F. oxysporum. The numbers of sesame rhizospheric F. oxysporum and fungi were lower after the cultivation of onion and garlic than those after wheat and clover. However, the numbers of actinomycetes and bacteria were higher in the onion, garlic, and clover rhizosphere than wheat. Among all isolated bacteria and actinomycetes associated with sesame roots cultivated after preceding plants, the Tricoderma viride and Bacillus subtilis (isolate No.3) profoundly reduce F. oxysporum mycelial growth in vitro. When sesame seeds were inoculated with Tricoderma viride, Bacillus subtilis, Streptomyces rochei and Pseudomonas fluorescens, the disease incidence of damping-off and wilt significantly decreased in the greenhouse and field trials conducted in both tested growing seasons, also had highly significant on plant health and growth parameters. Therefore, the current study suggested that using the preceding onion and garlic plants could be used for eco-friendly reduction of damping-off and wilt disease of sesame.

Diversity of Mycobiota in Spanish Grape Berries and Selection of Hanseniaspora uvarum U1 to Prevent Mycotoxin Contamination

The occurrence of mycotoxins on grapes poses a high risk for food safety; thus, it is necessary to implement effective prevention methods. In this work, a metagenomic approach revealed the presence of important mycotoxigenic fungi in grape berries, including Aspergillus flavus, Aspergillus niger aggregate species, or Aspergillus section Circumdati. However, A. carbonarius was not detected in any sample. One of the samples was not contaminated by any mycotoxigenic species, and, therefore, it was selected for the isolation of potential biocontrol agents. In this context, Hanseniaspora uvarum U1 was selected for biocontrol in vitro assays. The results showed that this yeast is able to reduce the growth rate of the main ochratoxigenic and aflatoxigenic Aspergillus spp. occurring on grapes. Moreover, H. uvarum U1 seems to be an effective detoxifying agent for aflatoxin B₁ and ochratoxin A, probably mediated by the mechanisms of adsorption to the cell wall and other active mechanisms. Therefore, H. uvarum U1 should be considered in an integrated approach to preventing AFB₁ and OTA in grapes due to its potential as a biocontrol and detoxifying agent.

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.

Inhibitory Effect of Moriniafungin Produced by Setosphaeria rostrata F3736 on the Development of Rhizopus Rot

Rhizopus rot is a serious postharvest disease of various crops caused by Rhizopus spp. and controlled mainly by synthetic fungicides. We detected the antifungal activity of a culture extract of Setosphaeria rostrata F3736 against Rhizopus oryzae. The active ingredient was identified as moriniafungin, a known sordarin derivative, which showed minimum inhibitory concentrations of 1-8 μg/ml against Colletotrichum spp. and 0.03-0.13 μg/ml against Rhizopus spp. in vitro. Moriniafungin showed protective control efficacies against Rhizopus rot on apple and peach fruits. Treatment with 25 μg/ml moriniafungin delimited the lesion diameter significantly by 100% on R. oryzae-inoculated apple fruits compared with the non-treated control. Treatment with 0.04 μg/ml of moriniafungin reduced the lesion diameter significantly by 56.45%, and treatment with higher concentrations of 0.2-25 μg/ml reduced the lesion diameter by 70-90% on Rhizopus stolonifer var. stolonifer-inoculated peach fruit. These results suggest moriniafungin has potential as a control agent of postharvest diseases caused by Rhizopus spp.