Alternaria Rot Research Articles

Effect of bloom sprays on Alternaria rot in California mandarins and fungicide efficacy against Colletotrichum.

This study aimed to provide new insights into the management of Alternaria rot and Colletotrichum dieback in mandarins. Field trials were conducted to evaluate the impact of bloom sprays on latent infections, disease progression, and the influence of bloom inoculations on disease development. Detached citrus leaves were used to assess the efficacy of commercial fungicides in reducing infections by Colletotrichum spp. C. karstii was more sensitive than C. gloeosporioides, as evidenced by the overall probabilities of infection. Preventative treatments containing QoI fungicides, such as Pristine, Quadris Top, and Luna Sensation, consistently reduced infections. Curative treatments with Pristine and Luna Sensation also demonstrated efficacy. Bloom inoculations with Colletotrichum species did not induce visible symptoms on flowers and twigs, nor did they lead to dieback until harvest, suggesting that bloom infections may not play a significant role in the disease cycle. For Alternaria, the frequency of latent infections in flowers increased significantly during the bloom period. Shoots inoculated with Alternaria species during bloom reduced the number of fruits per shoot at harvest. Fungicide treatments during bloom exhibited a dual effect, reducing Alternaria infections in fruitlets and influencing disease progression, ultimately reducing preharvest fruit drop. This study provides valuable insights into the role of flower infections in the development of Alternaria rot and Colletotrichum dieback in California mandarins. Furthermore, it offers insights into the efficacy of commercial fungicides in these pathosystems.

Evaluation of pre-harvest fungicide treatments against Alternaria rot in California mandarins and occurrence of mutations associated with fungicide resistance

This study aimed to investigate the management of Alternaria rot in citrus by evaluating the efficacy of late-season fungicide programs in reducing latent infections and fruit drop. Furthermore, the occurrence of mutations conferring resistance to QoI and SDHI fungicides within an Alternaria population isolated from citrus was investigated. In field trials, high frequencies of Alternaria infections were observed on the stem end and stylar end of Satsuma and Shiranui mandarins, with a higher prevalence of stem-end infections. Fungicide treatments applied towards the end of the season effectively reduced the frequency of latent infections on the stem end, indicating that such infections occur during this period under specific conditions. While some fungicide treatments demonstrated efficacy in reducing fruit drop caused by Alternaria rot, the results varied across different orchards and years. Latent infections on fruits persisted at high frequencies in the majority of trials, highlighting the complex nature of disease management. Mutations associated with resistance against QoI and SDHI fungicides were identified within the Alternaria population affecting California citrus. Our study suggests the potential need for fungicide sprays at the onset of the season to reduce the frequency of Alternaria infections on the stem end and stylar end of fruits. However, the observed non-correlation or low correlation between latent infections and fruit drop indicates that latent infections alone cannot reliably predict fruit drop. Our findings indicate that pre-harvest fungicide treatments have inconsistent efficacy and are cost-effective only during unpredictable disease outbreaks.

Inhibitory Effect and Mechanism of Carvacrol against Black Mold Disease Agent Alternaria alternata in Goji Berries.

Alternaria alternata, as a main decay fungus of goji berry, can produce mycotoxins such as alternariol (AOH), alternariol monomethyl ether (AME), and tenuazonic acid (TeA). Carvacrol (CVR) has exhibited a broad-spectrum antifungal activity in vitro. We assumed that CVR can also be applied to control Alternaria rot on goji berries and mycotoxins produced by the pathogens. To investigate whether CVR impacts the accumulation of mycotoxins and cell membrane damage of A. alternata, the antifungal activity of CVR on the fungal growth and mycotoxin production was evaluated in this study. The results showed that the minimum inhibitory concentration (MIC) of CVR against A. alternata was 0.12 µL/mL. Meanwhile, the destruction of plasma membrane integrity, cytoplasmic leakage, intracellular oxidative damage, and inhibitory effect in vivo were also observed in A. alternata treated with CVR. Moreover, CVR significantly reduced the accumulation of AOH, AME, and TeA. Transcriptomic profiling was performed by means of comparative RNA-Seq analysis to research the gene expression level of A. alternata, which attested to significant changes in nitrogen metabolism, carbon utilization, fatty acid oxidation, and antioxidant enzymes in CVR-treated A. alternata. This study suggests a new understanding of the molecular mechanism of response to CVR treatment in A. alternata, indicating that CVR is a novel antifungal agent with the potential to be applied to various fungi.

Molecular characterization of apple endophytic bacteria and biological effect on Alternaria rot on apple

AbstractApple rot disease, caused by Alternaria alternata, is causing significant losses in apple production, especially in post‐harvest periods. Alternaria alternata, was isolated from rotten apple fruit of cv Amasya. Identification of the strain isolated from rotten apple fruit was made by ITS sequence and morphological analysis. In the present study, 58 different endophytic bacteria strains were isolated from apple fruit for use in apple rot disease control. Among the isolated strains, 26 endophyte strains were determined to inhibit the radial growth of mycelia of A. alternata in binary culture in PDA media. Based on 16S rRNA sequencing analysis, these antagonistic endophytic bacteria strains were identified as Bacillus ssp. Bacillus methylotrophicus (ib17) showed the highest significant inhibitory effect on the mycelial growth of A. alternata at a rate of 79.5% in PDA medium. The results of in vivo experiments showed that Bacillus licheniformis (ib20) achieved 100% biocontrol when endophyte bacterial strains were inoculated 24 h before the inoculation of A. alternata. When the three bacteria species and A. alternata were inoculated simultaneously, Bacillus myloliquefaciens (ib1), Bacillus licheniformis (ib21) and the Endophytic bacterium (ib16) showed the highest biocontrol efficacy against A. alternata at 81.8%. Furthermore, when the bacterial strains were inoculated at 24 h after inoculation of A. alternata, B. licheniformis (ib21) showed the highest biocontrol efficacy of 83.3% against the fungal pathogen compared to the controls. The endophytic bacterial strains produced fungal cell wall hydrolysing enzymes such as chitinase, cellulase, amylase and protease. According to the results of this study, apple endophytic bacteria are potential candidates to control apple decay caused by A. alternata through cell wall hydrolysing enzymes and reduce disease severity. However, the efficacy of the biological control was dependent on the applied time of epiphytic bacterial strains. Further research is needed on the biochemical mechanisms underlying the activity of these bacteria against A. alternata.

Effects of Plant Essential Oil Treatment on the Growth of Pathogenic Fungi and the Activity of Defense-Related Enzymes of Fungi-Inoculated Blueberry

Fungal decay is one of the most significant causes of postharvest losses of blueberries, with Botrytis rot caused by Botrytis cinerea and Alternaria rot caused by Alternaria alternata being the two most destructive fungal diseases. Plant essential oil has attracted the extensive attention of scholars due to its natural antifungal and anti-corrosion effects. In this study, the effects of fumigation treatment with plant essential oils on the growth of pathogenic fungi in blueberry fruits in vitro and the activity of defense-related enzymes of fungi-inoculated blueberry were evaluated. The results showed that, of the six natural plant essential oils of cinnamon, oregano, clove, tea tree, pomelo peel, and rosemary, oregano essential oil had the most efficient inhibitory effect on Botrytis cinerea and Alternaria alternata in PDA. After fumigating inoculated blueberry fruits with concentration gradients of 0, 30, 60, and 90 μL/L of oregano essential oil, it was found that the activity of defense-related enzymes such as phenylalanine ammonia lyase (PAL), polyphenol oxidase (PPO), peroxidase (POD), chitinase (CHI), and β-1,3-glucanase (GLU) in the inoculated blueberry fruits was induced and enhanced to varying degrees throughout the entire storage period, effectively enhancing the resistance of blueberry fruits to pathogenic fungi and reducing the postharvest decay caused by Botrytis cinerea and Alternaria alternata. The optimal concentration for the fumigation treatment with oregano essential oil is 60 μL/L. This study provides a theoretical basis for the postharvest application of oregano essential oil in blueberries and other fruits and vegetables.

Phytochemical characterization of forest leaves extracts and application to control apple postharvest diseases

The study investigated the antifungal and phytochemical properties of three forest plants (Eucalyptus globulus, Pistacia lentiscus, and Juniperus phoenicea) against apple diseases caused by Colletotrichum gloeosporioides and Alternaria alternata. The determination of the total polyphenol and flavonoid contents in the three aqueous extracts of studied plants showed that E. globulus exhibited the highest contents than those of P. lentiscus and J. phoenicea. Furthermore, the three studied extracts showed very appreciable antioxidant activity with decreasing order: E. globulus, P. lentiscus, and J. phoenicea. The phytochemical analysis showed different common phenolic acids in the three studied plants namely: quinic acid, gallic acid, chlorogenic acid, and caffeoylquinic acid as well as other flavonoids mainly quercetin and catechin. The results of the current study demonstrated that the fungistatic activity of E. globulus EO (4 and 2 µl/ml) seemed to be the most effective under laboratory conditions with an inhibition zone diameter above 16 mm. However, the poisoned food technique indicated that the aqueous extract (80%) and the essential oil (4 µl/ml) of E. globulus exhibited the highest mycelial growth (> 67%) and spore germination (> 99%) inhibition. Preventive treatments with essential oils (4 µl/ml) and aqueous extracts (80%) applied to apple fruits inoculated with A. alternata and C. gloeosporioides resulted in the lowest lesion diameter (< 6.80 mm) and disease severity index (< 15%) and the most favorable inhibitory growth (> 85.45%) and protective potentials (> 84.92%). The results suggest that E. globulus has a brilliant future in the management of anthracnose and Alternaria rot of apple and provide a basis for further studies on its effects under field conditions.

Enhancement of disease resistance against Alternaria alternata in winter jujube fruit by phenyllactic acid through regulating Ca2+ signaling transduction and mitogen-activated protein kinase cascades

Alternaria rot caused by Alternaria alternata is one of destructive fungal diseases of postharvest winter jujubes. This study performed to evaluate the potential mechanisms participated in the enhancement disease resistance of winter jujubes by phenyllactic acid (PLA). Results demonstrated that PLA reduced the lesion diameter of A. alternata-inoculated winter jujubes. Additionally, PLA treatment led to an up-regulation in the transcription levels of ZjCML23/28, ZjCIPK11/12/20, ZjCDPK1/3/5, ZjMAPKKK18, ZjMAPKK6, and ZjMAPK7/19 as well as ZjNPR1 and ZjWRKY14/22/44/55/64 in fruit. Conversely, the transcription levels of ZjMAPK15 and ZjMAPKKK17 were down-regulated. Simultaneously, PLA enhanced the gene transcription levels and enzymatic activities of peroxidase, β-1,3-glucanase, and chitinase in winter jujubes, while facilitating the deposition of lignin, flavonoids, and total phenolics. Overall, these findings suggest that PLA enhances the resistance of winter jujube fruit via positively modulating the transcription of key Ca2+ receptor protein, activating the mitogen-activated protein kinase cascades, and potentially involving NPR1 and WRKY transcription factors.

Postharvest caffeic acid dipping enhances disease resistance and storage capacity of ‘Zaosu’ pear fruit via regulating phenylpropane metabolism

Caffeic acid, a naturally occurring and safe phenolic compound, acts as a precursor in lignin synthesis within the phenylpropane metabolism pathway. The aims of this study was to evaluate the impacts of postharvest caffeic acid immersion on Alternaria rot and postharvest quality of ‘Zaosu’ pear fruit, as well as elucidate the underlying mechanisms involved. Results showed that postharvest caffeic acid dipping effectively inhibited spore germination and colony diameter of Alternaria alternata, as well as lesion diameter in A. alternata-inoculated pears. Caffeic acid treatment also delayed the increase of weight loss and decline in flesh firmness, increased total soluble solids content, and reduced surface yellowing of pears. Additionally, caffeic acid treatment enhanced the enzymatic activities and gene transcription levels of phenylalanine ammonialyase, 4-coumarate/coenzyme A ligase, cinnamate 4-hydroxylase, peroxidase, cinnamyl alcohol dehydrogenase, and polyphenol oxidase in pears. Meanwhile, the transcription levels of p-coumarate-3-hydroxylase, caffeic acid O-methyltransferase, cinnamoyl CoA reductase, caffeoyl shikimate esterase, hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase, caffeoyl CoA O-methyltransferase, ferulic acid 5-hydroxylase, and laccase genes were also up-regulated by caffeic acid treatment in pears. Furthermore, caffeic acid dipping enhanced phenylalanine, flavonoids, caffeic acid, total phenolic compounds, and lignin levels in the fruit. Therefore, caffeic acid exhibits promising potential for enhancing resistance against A. alternata and maintaining the storage capacity of pears via inducing phenylpropane metabolism.

Metabolic Profiling and Molecular Mechanisms Underlying Melatonin-Induced Secondary Metabolism of Postharvest Goji Berry (Lycium barbarum L.).

Postharvest decay of goji berries, mainly caused by Alternaria alternata, results in significant economic losses. To investigate the effects of melatonin (MLT) on resistance to Alternaria rot in goji berries, the fruits were immersed in the MLT solutions with varying concentrations (0, 25, 50, and 75 μmol L-1) and then inoculated with A. alternata. The results showed that the fruits treated with 50 μmol L-1 MLT exhibited the lowest disease incidence and least lesion diameter. Meanwhile, endogenous MLT in the fruits treated with 50 μmol L-1 MLT showed higher levels than in the control fruits during storage at 4 ± 0.5 °C. Further, the enzymatic activities and expressions of genes encoding peroxidase, phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, 4-coumarate-CoA ligase, chalcone synthase, chalcone isomerase, and cinnamyl alcohol dehydrogenase were induced in the treated fruit during storage. UPLC-ESI-MS/MS revealed that secondary metabolites in the fruits on day 0, in order of highest to lowest levels, were rutin, p-coumaric acid, chlorogenic acid, ferulic acid, caffeic acid, naringenin, quercetin, kaempferol, and protocatechuic acid. MLT-treated fruits exhibited higher levels of secondary metabolites than the control. In conclusion, MLT treatment contributed to controlling the postharvest decay of goji fruit during storage by boosting endogenous MLT levels, thus activating the antioxidant system and secondary metabolism.

Biocontrol potential of lipopeptides produced by the novel Bacillus altitudinis strain TM22A against postharvest Alternaria rot of tomato

Bacillus genus exhibits antagonistic potential against a broad range of pathogenic fungi. This study presents the antifungal potential of lipopeptides (LPs) produced by a novel strain Bacillus altitudinis TM22A to suppress the infection of Alternaria rot on tomato. We investigated the antifungal effect of ten Bacillus species against Alternaria alternata, where four Bacillus strains TM22A, MCM61, S2, and CPCF54 exhibited antifungal activity. The LPs extracted from TM22A, MCM61, S2, and CPCF54 restricted mycelial growth and conidial germination of A. alternata in vitro with the highest inhibition produced by TM22A. Liquid chromatography and mass spectrometry (LC-MS) analysis revealed the presence of surfactin, fengycin, iturin, bacillibactin, and bacilysin in strain TM22A at 1036.69, 1435.76, 1085.58, 883.26, and 271.13 m/z respectively. In an In planta assay LPs from TM22A caused the lowest lesion diameter and disease incidence on tomato fruit. Furthermore, the activity of defense enzymes viz, catalase (CAT), polyphenol oxidase (PPO), peroxidase (POD), superoxide dismutase (SOD), and phenylalanine ammonia-lyase (PAL) was enhanced in Bacillus LPs treated tomato fruit with the more pronounced impact by TM22A. Postharvest quality analysis revealed little impact on ascorbic acid, fruit pH, total soluble solids (TSS), titratable acidity (TA), weight loss, and fruit firmness compared to healthy control. This is the first comprehensive study to reveal the antifungal effect of Bacillus-derived LPs against postharvest Alternaria rot of tomato and its role in defense elicitation to protect the fruit from pathogen invasion.

Characterization of Arthropeptide B, an Antifungal Cyclic Tetrapeptide from Arthrobacter humicola.

Disease suppressive composts are known, yet little information on the potential role of specific microbial antagonist within are available. Arthrobacter humicola isolate M9-1A has been obtained from a compost prepared from marine residues and peat moss. The bacterium is a non-filamentous actinomycete with antagonistic activity against plant pathogenic fungi and oomycetes sharing its ecological niche in agri-food microecosystems. Our objective was to identify and characterize compounds with antifungal activity produced by A. humicola M9-1A. Arthrobacter humicola culture filtrates were tested for antifungal activity in vitro and in vivo and a bioassay-guided approach was used to identify potential chemical determinants of its observed activity against molds. The filtrates reduced the development of lesions of Alternaria rot on tomatoes and the ethyl acetate extract inhibited growth of Alternaria alternata. A compound, arthropeptide B [cyclo-(L-Leu, L-Phe, L-Ala, L-Tyr)], was purified from the ethyl acetate extract of the bacterium. Arthropeptide B is a new chemical structure reported for the first time and has shown antifungal activity against A. alternata spore germination and mycelial growth.

Fungicide Resistance of Alternaria alternata and A. arborescens Isolates from Mandarin Fruit and Its Influence on Control of Postharvest Alternaria Rot.

Alternaria rot, caused by Alternaria alternata and A. arborescens, is one of the common postharvest diseases affecting mandarin fruit in California. Fungicide resistance profilings of A. alternata and A. arborescens to quinone outside inhibitors (QoIs), fludioxonil, pyrimethanil, imazalil, and propiconazole were examined in this study. Of the 100 isolates of A. alternata and A. arborescens, 40 were identified as resistant to QoI fungicides according to a PCR-restriction fragment length polymorphism based on a cytochrome b partial gene. Effective concentrations of fludioxonil that caused a 50% reduction in fungal growth relative to the control (EC50) were 0.089 ± 0.020 and 0.101 ± 0.032 µg/ml for 43 A. alternata and 19 A. arborescens isolates, respectively. EC50 values of pyrimethanil, imazalil, and propiconazole for the 70 A. alternata isolates tested were 0.373 ± 0.161, 0.492 ± 0.133, and 1.135 ± 0.407 µg/ml, respectively. EC50 values of pyrimethanil, imazalil, and propiconazole for 30 A. arborescens isolates were 0.428 ± 0.190, 0.327 ± 0.180, and 0.669 ± 0.452 µg/ml, respectively. Control tests on mandarin fruit inoculated with representative isolates of both species showed that fludioxonil, pyrimethanil, imazalil and propiconazole significantly reduced disease incidence and severity. Azoxystrobin significantly reduced Alternaria rot severity and incidence on mandarin fruit inoculated with sensitive isolates but not with resistant isolates, regardless of Alternaria spp. There were no significant differences in Alternaria rot control effectiveness if treatment with any of the fungicides tested was delayed after inoculation by 6 or 12 h. These results could help in the development of postharvest fungicide programs to control Alternaria rot on mandarin fruit during storage.

Tannic acid exerts antifungal activity in vitro and in vivo against Alternaria alternata causing postharvest rot on apple fruit

Alternaria alternata is one of the main pathogens that causes black spot rot of apple fruit, mainly postharvest. Also, A. alternata can attack many other fruits and vegetables in most of the world's natural environments. In this study, the antifungal efficacy of tannic acid (TA) against A. alternata and its potential mechanisms were investigated. An in vitro bioassay suggested that 5.0 mg mL−1 TA significantly inhibited the mycelial growth and spore germination of A. alternata. The enzyme activities of hexokinase, phosphofructokinase and pyruvate kinase in glycolytic metabolism were decreased in A. alternata treated with TA. The accumulation of glucose content and the reduction of pyruvate content in A. alternata further confirmed that TA may block the glycolytic metabolism of this fungus, resulting in insufficient energy supply for cells. In addition, TA immersion treatment significantly reduced the development of lesion areas on apple fruits caused by A. alternata and delayed fruit softening during the storage period. The application of TA also increased the activity of chitinase, β-1,3-glucanase and phenylalanine ammonialyase and the contents of total phenolic compounds and flavonoids in apple fruit, indicating the activation of defense-related enzymes and phenylpropane metabolites. TA could potentially be used to prevent and control postharvest Alternaria rot by exerting antifungal activity on A. alternata and inducing resistance in apple fruit.

Biocontrol potential of lipopeptides produced by the novel Bacillus subtilis strain Y17B against postharvest Alternaria fruit rot of cherry.

The use of synthetic fungicides against postharvest Alternaria rot adversely affects human health and the environment. In this study, as a safe alternative to fungicides, Bacillus subtilis strain Y17B isolated from soil exhibited significant antifungal activity against Alternaria alternata. Y17B was identified as B. subtilis based on phenotypic identification and 16S rRNA sequence analysis. To reveal the antimicrobial activity of this strain, a PCR-based study detected the presence of antifungal lipopeptide (LP) biosynthetic genes from genomic DNA. UPLC Q TOF mass spectrometry analysis detected the LPs surfactin (m/z 994.64, 1022.68, and 1026.62), iturin (m/z 1043.56), and fengycin (m/z 1491.85) in the extracted LP crude of B. subtilis Y17B. In vitro antagonistic study demonstrated the efficiency of LPs in inhibiting A. alternata growth. Microscopy (SEM and TEM) studies showed the alteration of the morphology of A. alternata in the interaction with LPs. In vivo test results revealed the efficiency of LPs in reducing the growth of the A. alternata pathogen. The overall results highlight the biocontrol potential of LPs produced by B. subtilis Y17B as an effective biological control agent against A. alternata fruit rot of cherry.

Inhibitory effect of carvacrol against Alternaria alternata causing goji fruit rot by disrupting the integrity and composition of cell wall.

Goji (Lycium barbarum L.) is a widely planted crop in China that is easily infected by the pathogenic fungus Alternaria alternata, which causes rot after harvest. Previous studies showed that carvacrol (CVR) significantly inhibited the mycelial growth of A. alternata in vitro and reduced Alternaria rot in goji fruits in vivo. The present study aimed to explore the antifungal mechanism of CVR against A. alternata. Optical microscopy and calcofluor white (CFW) fluorescence observations showed that CVR affected the cell wall of A. alternata. CVR treatment affected the integrity of the cell wall and the content of substances in the cell wall as measured by alkaline phosphatase (AKP) activity, Fourier transform-infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Chitin and β-1,3-glucan contents in cells decreased after CVR treatment, and the activities of β-glucan synthase and chitin synthase decreased. Transcriptome analysis revealed that CVR treatment affected cell wall-related genes in A. alternata, thereby affecting cell wall growth. Cell wall resistance also decreased with CVR treatment. Collectively, these results suggest that CVR may exert antifungal activity by interfering with cell wall construction, leading to impairment of cell wall permeability and integrity.

New insights into in mycotoxins production in Alternaria infected apple during postharvest storage

As an apple fruit rot disease related fungus, Alternaria spp. could bring severe hazardous risk to apple fruits during postharvest storage. In this research, cold treatment is investigated for inhibition of Alternaria infection and related mycotoxins production during postharvest storage of apple. Morphology results show that cold treatment could inhibit Alternaria rot in inoculated apple samples. Alternariol Monomethyl Ether (AME), Alternariol (AOH), and Tenuazonic Acid (TEA) are the major mycotoxins during room storage temperature at 25 °C, while only AOH is detected after 30 d at 4 °C storage. The results revealed that room temperature could bring hazardous risk while toxic risks might still exist during cold storage. Metabolites of Alternaria mycotoxins are also identified in this work with metabolic pathways of glucose conjugation, hydrogenation reduction, oxidation, and dehydrogenation reaction. Cold storage treatment could lead to down-regulation of nature products in inoculated apples, including all five target Alternaria mycotoxins. This research proposed new insights into mycotoxins production in Alternaria infected apple during postharvest storage process, which will be benefit for better understanding of postharvest storage and safety control of fruits.

Bioefficacy of fungal chitin oligomers in the control of postharvest decay in tomato fruit

Tomato is one of the most commercialised and consumed fruits worldwide. However, tomatoes are highly susceptible to Alternaria rot. Among the safe strategies proposed to control Alternaria rot is the induction of defence mechanisms through biological elicitors, such as chitin. Chitin and its oligosaccharides are an activate plant defence mechanisms, but studies of fruits exposed to fungal chitin fragments are scarce. Therefore, the present work aimed to obtain and partially characterise chitin oligomers of Alternaria alternata, and evaluate their effect on the defence mechanism of tomato fruits and their tolerance to Alternaria rot. The chitin oligomers obtained had a molecular weight of ≤ 1 kDa, 12% N-acetyl-glucosamine, 0.2% residual protein, and were 94% acetylated. These oligomers markedly increased the enzymatic activity of chitinase and β-1,3-glucanase in tomato fruits, and the development of Alternaria rot was inhibited by 78%. Chitin oligomers of A. alternata represent a promising alternative to attenuate Alternaria rot in tomato fruits through an enzymatic defence mechanism.

Antagonist Effect of Bacillus Species against Alternaria Rot of Tomato

The PGPR possesses antifungal activity against a broad range of pathogens. In this research study, the LPs of Bacillus strain B1 and B2 against Alternaria alternata were assessed. In vitro and in Planta assay on tomato fruit was made to check the post-harvest quality of fruits. The lipopeptides produced by both strains suppress the growth of the fungal pathogen Alternaria alternata and lessen the disease severity of the Alternaria rot on tomato fruits. The result revealed the quality of the Bacillus-treated fruits was also maintained and satisfactory. The lipopeptides of bacillus strain B1 and B2 represent a new innovative method to lessen the use of fungicides and chemical approaches to reduce the post-harvest loss caused by Alternaria alternata.

Utilization of the antagonistic yeast, Wickerhamomyces anomalus, combined with UV-C to manage postharvest rot of potato tubers caused by Alternaria tenuissima

Postharvest rot of potato tubers caused by fungal pathogens is the main cause of significant economic losses, while also raising potential food safety issues. Integrated disease management, utilizing bio-safe and eco-friendly methods, represents a sustainable strategy for reducing postharvest losses in crops, including potato. In the current study, the application of the antagonistic yeast, Wickerhamomyces anomalus, combined with a UV-C treatment was evaluated for the management of postharvest Alternaria rot of potato tubers, caused by Alternaria tenuissima. Both W. anomalus and UV-C as individual treatments reduced the size of A. tenuissima infections on potato tubers, relative to the control, while the combined treatment of W. anomalus and UV-C exhibited the highest level of inhibition. W. anomalus or UV-C alone, and especially when used in combination, induced the expression of defense-related genes, including polyphenol oxidase, peroxidase, and β-1,3-glucanase, and also increased the level of flavonoids and lignin in potato tubers. Our findings indicate that the mechanism of action by which UV-C enhances the biocontrol effect of W. anomalus against postharvest Alternaria rot includes the activation of defense-related response in potato tubers. The integration of biocontrol agents and physical treatments (e.g., UV-C) represents an effective, eco-friendly hurdle technology for managing postharvest rot in potato.

Native Cultivable Bacteria from the Blueberry Microbiome as Novel Potential Biocontrol Agents.

Blueberry production is affected by fungal postharvest pathogens, including Botrytis cinerea and Alternaria alternata, the causative agents of gray mold disease and Alternaria rot, respectively. Biocontrol agents adapted to blueberries and local environments are not known to date. Here, we report on the search for and the identification of cultivable blueberry epiphytic bacteria with the potential to combat the aforementioned fungi. Native, blueberry-borne bacterial strains were isolated from a plantation in Tucumán, Argentina and classified based on 16S rRNA gene sequences. Antagonistic activities directed at B. cinerea and A. alternata were studied in vitro and in vivo. The 22 bacterial strains obtained could be attributed to eleven different genera: Rosenbergiella, Fictibacillus, Bacillus, Pseudomonas, Microbacterium, Asaia, Acinetobacter, Curtobacterium, Serratia, Sphingomonas and Xylophilus. Three strains displaying antagonistic impacts on the fungal pathogens were identified as Bacillus velezensis (BA3 and BA4) and Asaia spathodeae (BMEF1). These strains are candidates for biological control agents of local blueberry production and might provide a basis for the development of eco-friendly, sustainable alternatives to synthetic pesticides.