Antifungal and eliciting properties of chitosan against Ceratocystis fimbriata in sweet potato

Biochemical mechanism of chlorine dioxide fumigation in inhibiting Ceratocystis fimbriata and black rot in postharvest sweetpotato

The inhibitory properties and underlying mechanism of chlorine dioxide (ClO2) fumigation on the pathogen Ceratocystis fimbriata (C. fimbriata) and resultant sweetpotato black rot were investigated in vitro and in vivo. Results revealed that the ClO2 fumigation effectively inhibited fungal growth and induced obvious morphological variation of C. fimbriata mycelia. Furthermore, the mycelial membrane suffered damage, as evidenced by a significant increase in malondialdehyde content and the leakage of protein and nucleic acid from mycelia cells, accompanied by a marked decrease in ergosterol content. Additionally, ClO2 fumigation caused spores cell membrane damage, a notable decrease in spore viability, and induced cell apoptosis as indicated by reductions in spore germination rate, two fluorescence staining observations, and flow cytometry analysis. Moreover, the decay diameter of sweetpotato black rot lesions decreased significantly after ClO2 fumigation, and the growth of C. fimbriata was also inhibited. These findings present a novel and effective technology for inhibiting the progression of sweetpotato black rot.

Physiological-Biochemical Characteristics and a Transcriptomic Profiling Analysis Reveal the Postharvest Wound Healing Mechanisms of Sweet Potatoes under Ascorbic Acid Treatment

Sweet potatoes are extremely vulnerable to mechanical wounds during harvesting and postharvest handling. It is highly necessary to take measures to accelerate wound healing. The effect of 20 g L-1 of ascorbic acid (AA) treatment on the wound healing of sweet potatoes and its mechanisms were studied. The results validated that AA treatment significantly reduced the weight loss rate and disease index. AA treatment effectively enhanced the formation speed of lignin and SPP at the wound sites, decreased the MDA content, and maintained the cell membrane integrity. AA enhanced the activities of PAL, C4H, 4CL, CAD, and POD and increased the contents of chlorogenic acid, caffeic acid, sinapic acid, ferulic acid, cinnamic acid, p-coumaryl alcohol, sinapyl alcohol, coniferyl alcohol, and lignin. Based on a transcriptomic analysis, a total of 1200 genes were differentially expressed at the sweet potato wound sites by the AA treatment, among which 700 genes were upregulated and 500 genes were downregulated. The KEGG pathway analysis showed that the differentially expressed genes were mainly involved in phenylalanine, tyrosine, and tryptophan biosynthesis; phenylpropanoid biosynthesis; and other wound healing-related pathways. As verified by a qRT-PCR, the AA treatment significantly upregulated the gene expression levels of IbSKDH, IbADT/PDT, IbPAL, and Ib4CL at the wound sties.

Preparation and characterization of Iturin A/chitosan microcapsules and their application in post-harvest grape preservation

Iturin A (IA) encapsulated in chitosan (CS) microcapsules (IA/CS) underwent thorough physicochemical characterization using thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). SEM confirmed the smooth, spherical morphology of the IA/CS microcapsules, while FTIR revealed complex intermolecular interactions between IA and CS. TGA demonstrated thermal stability within the 0-100 °C range, while particle size analysis revealed an average diameter of 553.4 nm. To evaluate IA/CS efficacy in post-harvest grape preservation, grapes were treated with sterile water (CK), 10 g/L CS, 0.1 g/L IA/CS, and 0.1 g/L chitosan empty microcapsules (CKM), then stored at 25 °C for 16 days. IA/CS significantly reduced decay and respiration intensity by 52.3 % and 23.8 %, respectively, compared to CK. IA/CS treatment also inhibited abscission rate, weight loss, firmness reduction, total soluble solids consumption, titratable acidity consumption, polyphenol oxidase, and peroxidase activities on par with CS treatment (p > 0.05), but performed better than CK (reductions of 26.9 %, 41.2 %, 25.8 %, 27.2 %, 24.2 %, 19.4 %, and 17.4 %, respectively) and CKM (p < 0.05). Sensory evaluation confirmed that IA/CS effectively suppressed decay, slowed post-harvest metabolic activity, and maintained grape quality. Therefore, IA/CS microcapsules offer a promising method for extending grape shelf life and preserving quality.

Molecular Mechanism Underlying Pathogenicity Inhibition by Chitosan in Cochliobolus heterostrophus

Chitosan, as a natural nontoxic biomaterial, has been demonstrated to inhibit fungal growth and enhance plant defense against pathogen infection. However, the antifungal pattern and mechanism of how chitosan application evokes plant defense are poorly elucidated. Herein, we provide evidence that chitosan exposure is fungicidal to C. heterostrophus. Chitosan application impairs conidia germination and appressorium formation of C. heterostrophus and has a pronounced effect on reactive oxygen species production, thereby preventing infection in maize. In addition, the toxicity of chitosan to C. heterostrophus requires Mkk1 and Mps1, two key components in the cell wall integrity pathway. The Δmkk1 and Δmps1 mutants were more tolerant to chitosan than the wild-type. To dissect chitosan-mediated plant defense response to C. heterostrophus, we conducted a metabolomic analysis, and several antifungal compounds were upregulated in maize upon chitosan treatment. Taken together, our findings provide a comprehensive understanding of the mechanism of chitosan-alleviated infection of C. heterostrophus, which would promote the application of chitosan in plant protection in agriculture.

Preparation, characterization, antioxidant and antifungal activities of benzoic acid compounds grafted onto chitosan

The current study created three novel chitosan derivatives named BACS, PIBACS, and MHBACS by grafting benzoic acid (BA), p-isopropyl benzoic acid (PIBA), and m-hydroxybenzoic acid (MHBA) onto chitosan (CS). The structures of the derivatives were investigated using infrared spectroscopy (FT-IR) and nuclear magnetic resonance (13C NMR). The derivatives were discovered to be 45.06 %-60.49 % substituted using elemental analysis (EA). Based on the findings of in vitro antioxidant experiments (hydroxyl radical scavenging activity, superoxide anion radical scavenging activity, and DPPH radical scavenging activity), all of the derivatives had a higher hydroxyl radical scavenging activity than the chitosan raw material. MHBACS scavenged (31.02 ± 0.90)% of hydroxyl radicals at 0.5 mg/mL, 28.69 % more than chitosan raw. The derivatives scavenged more superoxide anion radicals than the chitosan feedstock at a particular concentration. For instance, at a test dose of 0.2 mg/mL, the scavenging rate of MHBACS on superoxide anion radicals was 7.75 % greater than that of chitosan raw materials. DPPH radical scavenging activity, on the other hand, was not as competent as chitosan feedstock. The growth rate approach was used to assess the potential of the three derivatives to inhibit the development of four phytopathogenic fungi. Chitosan derivatives have better antifungal efficacy than chitosan raw materials. PIBACS, MHBACS, BACS, and Wuyiencin inhibited Phytophthora capsici by (98.03 ± 1.95)%, (81.73 ± 1.63)%, (66.38 ± 1.81)%, and (93.01 ± 2.69)%, respectively, at 1.0 mg/mL. PIBACS had a higher inhibitory impact on Phytophthora capsici than the positive control. Based on the evidence presented above, it is reasonable to conclude that the addition of benzoic acid molecules increased the antioxidant and antifungal capabilities of chitosan.

Chitosan inhibits Penicillium expansum possibly by binding to DNA and triggering apoptosis

Chitosan is a natural polysaccharide that is abundant, biocompatible and exhibits effective antifungal activity against various pathogenic fungi. However, the potential intracellular targets of chitosan in pathogenic fungi and the way of activity of chitosan are far from well known. The present work demonstrated that chitosan could inhibit Penicillium expansum, the principal causal agent of postharvest blue mold decay on apple fruits, by binding to DNA and triggering apoptosis. UV-visible spectroscopy, fluorescence spectroscopy and electrophoretic mobility assay proved the interaction between chitosan and DNA, while atomic force microscope (AFM) observation revealed the binding morphology of chitosan to DNA. Chitosan could inhibit in vitro DNA replication, and cell cycle analysis employing flow cytometry demonstrated that cell cycle was retarded by chitosan treatment. Furthermore, the reactive oxygen species (ROS) assay and membrane potential analysis showed that apoptosis was induced in P. expansum cells after exposure to chitosan. In conclusion, our results confirmed that chitosan interacts with DNA and induces apoptosis. These findings are expected to provide a feasible theoretical basis and practical direction for the promoting and implementing of chitosan in plant protection and further illuminate the possible antifungal mechanisms of chitosan against fungal pathogens.

Effect of Heat Treatment on the Quality and Soft Rot Resistance of Sweet Potato during Long-Term Storage

Heat treatment is a widely applied technique in the preservation of fruits and vegetables, effectively addressing issues such as disease management, rot prevention, and browning. In this study, we investigated the impact of heat treatment at 35 °C for 24 h on the quality characteristics and disease resistance of two sweet potato varieties, P32/P (Ipomoea batatas (L.) Lam. cv 'Pushu13') and Xinxiang (Ipomoea batatas (L.) Lam. cv 'Xinxiang'). The growth in vitro and reproduction of Rhizopus stolonifer were significantly inhibited at 35 °C. However, it resumed when returned to suitable growth conditions. The heat treatment (at 35 °C for 24 h) was found to mitigate nutrient loss during storage while enhancing the structural characteristics and free radical scavenging capacity of sweet potato. Additionally, it led to increased enzyme activities for APX, PPO, and POD, alongside decreased activities for Cx and PG, thereby enhancing the disease resistance of sweet potato against soft rot. As a result, the heat treatment provided a theoretical basis for the prevention of sweet potato soft rot and had guiding significance for improving the resistance against sweet potato soft rot.

IbINV Positively Regulates Resistance to Black Rot Disease Caused by Ceratocystis fimbriata in Sweet Potato

Black rot disease, caused by Ceratocystis fimbriata Ellis & Halsted, severely affects both plant growth and post-harvest storage of sweet potatoes. Invertase (INV) enzymes play essential roles in hydrolyzing sucrose into glucose and fructose and participate in the regulation of plant defense responses. However, little is known about the functions of INV in the growth and responses to black rot disease in sweet potato. In this study, we identified and characterized an INV-like gene, named IbINV, from sweet potato. IbINV contained a pectin methylesterase-conserved domain. IbINV transcripts were most abundant in the stem and were significantly induced in response to C. fimbriata, salicylic acid, and jasmonic acid treatments. Overexpressing IbINV in sweet potato (OEV plants) led to vigorous growth and high resistance to black rot disease, while the down-regulation of IbINV by RNA interference (RiV plants) resulted in reduced plant growth and high sensitivity to black rot disease. Furthermore, OEV plants contained a decreased sucrose content and increased hexoses content, which might be responsible for the increased INV activities; not surprisingly, RiV plants showed the opposite effects. Taken together, these results indicate that IbINV positively regulates plant growth and black rot disease resistance in sweet potato, mainly by modulating sugar metabolism.

Chitosan: Properties and Its Application in Agriculture in Context of Molecular Weight

Chitosan is a naturally occurring compound that can be obtained from deacetylated chitin, which is obtained from various sources such as fungi, crustaceans, and insects. Commercially, chitosan is produced from crustaceans. Based on the range of its molecular weight, chitosan can be classified into three different types, namely, high molecular weight chitosan (HMWC, >700 kDa), medium molecular weight chitosan (MMWC, 150-700 kDa), and low molecular weight chitosan (LMWC, less than 150 kDa). Chitosan shows several properties that can be applied in horticultural crops, such as plant root growth enhancer, antimicrobial, antifungal, and antiviral activities. Nevertheless, these properties depend on its molecular weight (MW) and acetylation degree (DD). Therefore, this article seeks to extensively review the properties of chitosan applied in the agricultural sector, classifying them in relation to chitosan's MW, and its use as a material for sustainable agriculture.

Inhibitory effect of cinnamaldehyde on Fusarium solani and its application in postharvest preservation of sweet potato

Root rot caused by Fusarium solani is one of major postharvest diseases limiting sweet potato production. Antifungal effect and possible mode of action of cinnamaldehyde (CA) against F. solani were investigated. CA concentration of 0.075 g/L inhibited conidial viability of F. solani. CA vapor of 0.3 g/L in air completely controlled the F. solani development in sweet potatoes during storage for 10 days at 28 °C, and protected soluble sugar and starch in the flesh from depletion by the fungus. Further results demonstrated that CA induced reduction in mitochondrial membrane potential (Δψ_m), ROS accumulation, and cell apoptosis characterized by DNA fragmentation in F. solani. Moreover, CA facilitated decomposition of mitochondria-specific cardiolipin (CL) into its catabolites by the catalytic action of phospholipases. Altogether, the results revealed a specific antifungal mechanism of CA against F. solani, and suggest that CA holds promise as a preservative for postharvest preservation of sweet potato.

Antifungal Activity of Perillaldehyde on Fusarium solani and Its Control Effect on Postharvest Decay of Sweet Potatoes

Root rot caused by Fusarium solani is one of the major postharvest diseases limiting sweet potato production. Here, antifungal activity and the action mode of perillaldehyde (PAE) against F. solani were investigated. A PAE concentration of 0.15 mL/L in air (mL/L air) markedly inhibited the mycelial growth, spore reproduction and spore viability of F. solani. A PAE vapor of 0.25 mL/L in air could control the F. solani development in sweet potatoes during storage for 9 days at 28 °C. Moreover, the results of a flow cytometer demonstrated that PAE drove an increase in cell membrane permeability, reduction of mitochondrial membrane potential (MMP) and accumulation of reactive oxygen species (ROS) in F. solani spores. Subsequently, a fluorescence microscopy assay demonstrated that PAE caused serious damage to the cell nuclei in F. solani by inducing chromatin condensation. Further, the spread plate method showed that the spore survival rate was negatively correlated with the level of ROS and nuclear damage, of which the results indicated that PAE-driven ROS accumulation plays a critical role in contributing to cell death in F. solani. In all, the results revealed a specific antifungal mechanism of PAE against F. solani, and suggest that PAE could be a useful fumigant for controlling the postharvest diseases of sweet potatoes.

Deep Chemical and Physico-Chemical Characterization of Antifungal Industrial Chitosans-Biocontrol Applications

Five different chitosan samples (CHI-1 to CHI-5) from crustacean shells with high deacetylation degrees (>93%) have been deeply characterized from a chemical and physicochemical point of view in order to better understand the impact of some parameters on the bioactivity against two pathogens frequently encountered in vineyards, Plasmopara viticola and Botrytis cinerea. All the samples were analyzed by SEC-MALS, ¹H-NMR, elemental analysis, XPS, FTIR, mass spectrometry, pyrolysis, and TGA and their antioxidant activities were measured (DPPH method). Molecular weights were in the order: CHI-4 and CHI-5 (MW >50 kDa) > CHI-3 > CHI-2 and CHI-1 (MW < 20 kDa). CHI-1, CHI-2 and CHI-3 are under their hydrochloride form, CHI-4 and CHI-5 are under their NH₂ form, and CHI-3 contains a high amount of a chitosan calcium complex. CHI-2 and CHI-3 showed higher scavenging activity than others. The bioactivity against B. cinerea was molecular weight dependent with an IC50 for CHI-1 = CHI-2 (13 mg/L) ≤ CHI-3 (17 mg/L) < CHI-4 (75 mg/L) < CHI-5 (152 mg/L). The bioactivity on P. viticola zoospores was important, even at a very low concentration for all chitosans (no moving spores between 1 and 0.01 g/L). These results show that even at low concentrations and under hydrochloride form, chitosan could be a good alternative to pesticides.

Short-term effects of combined freeze–thaw and saline–alkali stresses on the physiological response in highland barley (Hordeum vulgare)

Highland barley (Hordeum vulgare L.), as the dominant crop on the Qinghai-Tibetan Plateau, is a typical representative of plants adapted to extreme environmental conditions. However, the harsh environment, severe salinisation and frequent freezing and thawing in the Qinghai-Tibetan Plateau are main limiting factor for crop growth in this region. The physiological response of highland barley to salinisation and freeze-thaw stresses was studied in this paper. Under the combined stresses of 60mmol/LNaCl·60mmol/LNaHCO3 and freeze-thaw cycles (10, -5, and 10°C), the changes in the relative moisture content, relative electrical conductivity, soluble protein, malondialdehyde (MDA) and photosynthetic indices Pn and E in seedling leaves of eight groups of treatments (CK, S, A, S-A, CK (FT), S (FT), A (FT), and S-A (FT)) were analysed. Results showed that a single stress did not cause a change in the MDA content. All of the combined stresses in S-A, CK (FT), S (FT), A (FT), and S-A (FT) treatments increased the MDA content of barley seedlings, and the MDA content of S-A (FT) reached 28.438 at T2 (-5°C) μmol/g. During the freeze-thaw cycle, the cell membrane of seedlings was damaged more seriously by alkali stress, which showed a significant increase in relative conductivity. The relative moisture content value of seedlings was more than 100% because the seedlings could absorb more moisture due to mechanical injury. The protein content of osmoregulatory substances in highland barley seedlings increased with increasing stress, indicating resistance to stress. Moreover, the effect of freeze-thaw stress on photosynthesis was more significant. The changes in indices proved that an appropriate amount of salt stress could improve the resistance of the plant cell membrane. Alkali stress had a significant effect on the growth of highland barley seedlings. Freezing and thawing can aggravate the damage of saline-alkali stress to highland barley seedlings, resulting in changes in the biological membrane permeability and photosynthesis of seedlings. The fluctuation of osmoregulation substance content confirmed that highland barley seedlings had a certain degree of stress resistance. Freeze-thaw cycles will aggravate the damage of land salinisation to highland barley seedlings. To better reduce the impact and loss of land salinisation and freeze-thaw disasters on agriculture in the Qinghai-Tibetan Plateau, priority should be given to solving freeze-thaw stress in the process of grain production.

Antifungal volatile organic compounds from Streptomyces setonii WY228 control black spot disease of sweet potato

Volatile organic compounds (VOCs) produced by microorganisms are considered as promising environmental-safety fumigants for controlling postharvest diseases. Ceratocystis fimbriata, the pathogen of black spot disease, seriously affects the quality and yield of sweet potato in the field and postharvest. This study tested the effects of VOCs produced by Streptomyces setonii WY228 on the control of C. fimbriata in vitro and in vivo. The VOCs exhibited strong antifungal activity and significantly inhibited the growth of C. fimbriata. During the 20-days storage, VOCs fumigation significantly controlled the occurrence of pathogen, increased the content of antioxidant and defense-related enzymes and flavonoids, and boosted the starch content so as to maintain the quality of sweet potato. Headspace analysis showed that volatiles 2-ethyl-5-methylpyrazine and dimethyl disulfide significantly inhibited the mycelial growth and spore germination of C. fimbriata in a dose dependent manner. Fumigation with 100 μL/L 2-ethyl-5-methylpyrazine completely controlled the pathogen in vivo after 10-days storage. Transcriptome analysis showed that volatiles mainly downregulated the ribosomal synthesis genes and activated the proteasome system of pathogen in response to VOCs stress, while the genes related to spore development, cell membrane synthesis, mitochondrial function, as well as hydrolase and toxin synthesis were also downregulated, indicating that WY228-produced VOCs act diverse modes of action for pathogen control. Our study demonstrates that fumigation of sweet potato tuberous roots with S. setonii WY228 or use of formulations based on the VOCs is a promising new strategy to control sweet potato and other food and fruit pathogens during storage and shipment. Importance Black spot disease caused by Ceratocystis fimbriata has caused huge economic losses to worldwide sweet potato production. At present, the control of C. fimbriata mainly depends on toxic fungicides, and there is a lack of effective alternative strategies. The research on biological control of sweet potato black spot disease is also very limited. The development of efficient biocontrol technique against pathogens using microbial volatile organic compounds could be an alternative method to control this disease. Our study revealed the significant biological control effect of volatile organic compounds of Streptomyces setonii WY228 on black spot disease of postharvest sweet potato and the complex antifungal mechanism against C. fimbriata. Our data demonstrated that Streptomyces setonii WY228 and its volatile 2-ethyl-5-methylpyrazine could be candidate strain and compound for the creation of fumigants, and showed the important potential of biotechnology application in the field of food and agriculture.

Antibiotic Effects of Volatiles Produced by Bacillus tequilensis XK29 against the Black Spot Disease Caused by Ceratocystis fimbriata in Postharvest Sweet Potato

Black spot disease caused by Ceratocystis fimbriata is destructive to the production, transportation, and storage of sweet potato. The antifungal effects of Bacillus tequilensis XK29 against C. fimbriata through volatile organic compounds (VOCs) were evaluated in this study. The activated carbon assay proved that XK29 could exert antibiotic effects through volatiles. By optimizing the wheat seed weight, inoculation method, concentration, volume, and time, the antifungal activity of XK29 was significantly improved. XK29 fumigation inhibited spore formation and germination and changed the cell morphology of C. fimbriata. During the storage of sweet potato tuber roots, XK29 effectively controlled black spot disease and reduced the weight loss and malondialdehyde content. Metabolomic analysis revealed that 21 volatile compounds were released from XK29. Isovaleric acid, isobutyric acid, and 2-methylbutanoic acid effectively inhibited the growth of C. fimbriata. These results indicate that B. tequilensis XK29 has a good potential to be developed as a microbial fumigation agent.

Antimicrobial Activities of Chitosan Derivatives

Considering the challenge created by the development of bacterial and fungal strains resistant to multiple therapeutic variants, new molecules and materials with specific properties against these microorganisms can be synthesized, like those synthesized from biopolymers such as chitosan with improved antimicrobial activities. Antimicrobial activities of seven obtained materials were tested on four reference strains belonging to American Type Culture Collection. The best antimicrobial activity was obtained by functionalization by impregnation of chitosan with quaternary ammonium salts, followed by that obtained by functionalization of chitosan with phosphonium. The lowest antibacterial and antifungal effects were expressed by Ch-THIO and Ch-MBT, but new materials obtained with these extractants may be precursors with a significant role in the direct control of active molecules, such as cell growth factors or cell signaling molecules.

Mode of action and efficacy of quinolinic acid for the control of Ceratocystis fimbriata on sweet potato

BACKGROUND

Ceratocystis fimbriata is a hazardous fungal pathogen able to cause black rot disease on sweet potato. The management of C. fimbriata strongly relies on the use of toxic fungicides, and there is a lack of efficient alternative strategies.

RESULTS

The antifungal properties of quinolinic acid (QA) were studied for the first time, indicating that QA shows selective antifungal activity against C. fimbriata. QA inhibited completely the mycelial growth of C. fimbriata at less than 0.8 mg mL^-1 concentration (pH 4), and was able to produce alterations in the fungal cell wall, and to impede spore agglutination and mycelium formation. QA significantly reduced the concentration of ergosterol, and was able to associate to iron (II), suggesting that QA may be a lanosterol 14-α demethylase inhibitor. In preventive applications, QA reduced the disease incidence of C. fimbriata on sweet potato by 75%, achieving higher control efficacy in comparison with commercial fungicides prochloraz and carbendazim.

CONCLUSIONS

The first selective antifungal agent against C. fimbriata was discovered in this work, and showed suitable antifungal properties for the management of black rot disease. © 2021 Society of Chemical Industry.

Engineered Nanomaterials Suppress the Soft Rot Disease (Rhizopus stolonifer) and Slow Down the Loss of Nutrient in Sweet Potato

About 45% of the world’s fruit and vegetables are wasted, resulting in postharvest losses and contributing to economic losses ranging from $10 billion to $100 billion worldwide. Soft rot disease caused by Rhizopus stolonifer leads to postharvest storage losses of sweet potatoes. Nanoscience stands as a new tool in our arsenal against these mounting challenges that will restrict efforts to achieve and maintain global food security. In this study, three nanomaterials (NMs) namely C₆₀, CuO, and TiO₂ were evaluated for their potential application in the restriction of Rhizopus soft rot disease in two cultivars of sweet potato (Y25, J26). CuO NM exhibited a better antifungal effect than C₆₀ and TiO₂ NMs. The contents of three important hormones, indolepropionic acid (IPA), gibberellic acid 3 (GA-3), and indole-3-acetic acid (IAA) in the infected J26 sweet potato treated with 50 mg/L CuO NM were significantly higher than those of the control by 14.5%, 10.8%, and 24.1%. CuO and C₆₀ NMs promoted antioxidants in both cultivars of sweet potato. Overall, CuO NM at 50 mg/L exhibited the best antifungal properties, followed by TiO₂ NM and C₆₀ NM, and these results were further confirmed through scanning electron microscope (SEM) analysis. The use of CuO NMs as an antifungal agent in the prevention of Rhizopus stolonifer infections in sweet potatoes could greatly reduce postharvest storage and delivery losses.

Effect of tebuconazole and trifloxystrobin on Ceratocystis fimbriata to control black rot of sweet potato: processes of reactive oxygen species generation and antioxidant defense responses

Black rot, caused by Ceratocystis fimbriata, is one of the most destructive disease of sweet potato worldwide, resulting in significant yield losses. However, a proper management system can increase resistance to this disease. Therefore, this study investigated the potential of using tebuconazole (TEB) and trifloxystrobin (TRI) to improve the antioxidant defense systems in sweet potato as well as the inhibitory effects on the growth of and antioxidant activity in C. fimbriata. Four days after inoculating cut surfaces of sweet potato disks with C. fimbriata, disease development was reduced by different concentrations of TEB + TRI. Infection by C. fimbriata increased the levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and electrolyte leakage (EL), and the activity of lipoxygenase (LOX) by 138, 152, 73, and 282%, respectively, in sweet potato disks, relative to control. In the sweet potato disks, C. fimbriata reduced the antioxidant enzyme activities as well as the contents of ascorbate (AsA) and reduced glutathione (GSH) by 82 and 91%, respectively, compared with control. However, TEB + TRI reduced the oxidative damage in the C. fimbriata-inoculated sweet potato disks by enhancing the antioxidant defense systems. On the other hand, applying TEB + TRI increased the levels of H₂O₂, MDA, and EL, and increased the activity of LOX in C. fimbriata, in which the contents of AsA and GSH decreased, and therefore, inhibited the growth of C. fimbriata. These results suggest that TEB + TRI can significantly control black rot disease in sweet potato by inhibiting the growth of C. fimbriata.

Antifungal effects of Conyza bonariensis (L.) Cronquist essential oil against pathogenic Colletotrichum musae and its incorporation in gum Arabic coating to reduce anthracnose development in banana during storage

AIM

This study evaluated the inhibitory effects on mycelial growth and damage on membrane integrity and enzymatic activity caused by Conyza bonariensis essential oil (CBEO) on distinct pathogenic Colletotrichum musae isolates, as well as the preventive and curative effects of coatings with gum Arabic (GA) and CBEO to reduce anthracnose development in banana during room temperature storage. The effects of GA-CBEO coatings on some physicochemical parameters of banana were investigated during room temperature storage.

METHOD AND RESULTS

CBEO (0.4-1 μl ml^-1 ) inhibited the mycelial growth of C. musae isolates in laboratory media. The exposure of C. musae conidia to CBEO (0.6 μl ml^-1 ) for 3 and 5 days resulted in high percentages of conidia with damaged cytoplasmic membrane and without enzymatic activity. Coatings with GA (0.1 mg ml^-1 ) and CBEO (0.4-1 μl ml^-1 ) reduced the anthracnose development in banana artificially contaminated with C. musae during storage. In most cases, the disease severity indexes found for GA-CBEO-coated banana were lower than or similar to those for banana treated with commercial fungicide. GA-CBEO-coated banana had reduced alterations in physicochemical parameters during storage, indicating more prolonged storability.

CONCLUSION

The application of GA-CBEO coatings is effective to delay the anthracnose development in banana during storage, which should help to reduce the amount of fungicides used to control postharvest diseases in this fruit.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study showing the efficacy of coatings formulated with GA and CBEO to delay the development of anthracnose in banana, as well as to decrease alterations in physicochemical parameters indicative of postharvest quality of this fruit during storage. In a practical point of view, GA-CBEO coatings could be innovative strategies to delay the anthracnose development and postharvest losses in banana.

Sustainable Agriculture Systems in Vegetable Production Using Chitin and Chitosan as Plant Biostimulants

Chitin and chitosan are natural compounds that are biodegradable and nontoxic and have gained noticeable attention due to their effective contribution to increased yield and agro-environmental sustainability. Several effects have been reported for chitosan application in plants. Particularly, it can be used in plant defense systems against biological and environmental stress conditions and as a plant growth promoter—it can increase stomatal conductance and reduce transpiration or be applied as a coating material in seeds. Moreover, it can be effective in promoting chitinolytic microorganisms and prolonging storage life through post-harvest treatments, or benefit nutrient delivery to plants since it may prevent leaching and improve slow release of nutrients in fertilizers. Finally, it can remediate polluted soils through the removal of cationic and anionic heavy metals and the improvement of soil properties. On the other hand, chitin also has many beneficial effects such as plant growth promotion, improved plant nutrition and ability to modulate and improve plants’ resistance to abiotic and biotic stressors. The present review presents a literature overview regarding the effects of chitin, chitosan and derivatives on horticultural crops, highlighting their important role in modern sustainable crop production; the main limitations as well as the future prospects of applications of this particular biostimulant category are also presented.

Contribution of ultrasound and slightly acid electrolytic water combination on inactivating Rhizopus stolonifer in sweet potato

Effects of ultrasound (US, 300, 400, and 500 W) and slightly acidic electrolyzed water (SAEW, 10, 30, and 50 mg/L) combination on inactivating Rhizopus stolonifer in sweet potato tuberous roots (TRs) were investigated. US at 300, 400, and 500 W simultaneous SAEW with available chlorine concentration of 50 mg/L at 40 and 55 °C for 10 min significantly inhibited colony diameters (from 90.00 to 6.00-71.62 mm) and spores germination (p < 0.05). US + SAEW treatment could destroy cell membrane integrity and lead to the leakage of nucleic acids and proteins (p < 0.05). Scanning and transmission electron microscopy results showed that US + SAEW treatment could damage ultrastructure of R. stolonifer, resulted in severe cell-wall pitting, completely disrupted into debris, apparent separation of plasma wall, massive vacuoles space, and indistinct intracellular organelles. US500 + SAEW50 treatment at 40 and 55 °C increased cell membrane permeability, and decreased mitochondrial membrane potential of R. stolonifer. In addition, US500 + SAEW50 at 40 °C and US300 + SAEW50 at 55 °C controlled R. stolonifer growth in sweet potato TRs during 20 days of storage, suggesting effective inhibition on the infection of R. stolonifer. Therefore, US + SAEW treatment could be a new efficient alternative method for storing and preserving sweet potato TRs.

Antifungal effect of volatile organic compounds produced by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 on oxidative stress and mitochondrial dysfunction of Ceratocystis fimbriata

Ceratocystis fimbriata is the pathogen of black rot disease, which widely exists in sweet potato producing areas all over the world. The antifungal activity of volatile organic compounds (VOCs) released by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 against C. fimbriata was reported in our previous study. In this study, we attempted to reveal the underlying antifungal mechanism of SPS-41 volatiles. Our results showed that the VOCs released by SPS-41 caused the morphological change of hyphae, destroyed the integrity of cell membrane, reduced the content of ergosterol, and induced massive accumulation of reactive oxygen species in C. fimbriata cells. Furthermore, SPS-41 fumigation decreased the mitochondrial membrane potential, acetyl-CoA and pyruvate content of C. fimbriata cells, as well as the mitochondrial dehydrogenases activity. In addition, the VOCs generated by SPS-41 reduced the intracellular ATP content and increased the extracellular ATP content of C. fimbriata. In summary, SPS-41 fumigation exerted its antifungal activity by inducing oxidative stress and mitochondrial dysfunction in C. fimbriata.

Antifungal activity of chitosan against Phytophthora infestans, the pathogen of potato late blight

Phytophthora infestans, the pathogen of potato late blight which is a devastating disease of potatoes, causes stem and leaf rot, leading to significant economic losses. Chitosan is a naturally occurring polysaccharide with a broad spectrum of antimicrobial properties. However, the specific mechanism of chitosan on Phytophthora infestans has not been studied. In this study, we found that chitosan significantly inhibited the mycelial growth and spore germination of Phytophthora infestans in vitro, reduced the resistance of Phytophthora infestans to various adverse conditions, and it had synergistic effect with pesticides, making it a potential way to reduce the use of chemical pesticides. In addition, chitosan could induce resistance in potato pieces and leaves to Phytophthora infestans. Transcriptome analysis data showed that chitosan mainly affected cell growth of Phytophthora infestans, and most of the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways and Gene ontology (GO) terms revolved in metabolic processes, cell membrane structure and function and ribosome biogenesis. Differentially expressed genes (DEGs) related to adverse stress and virulence were also discussed. On the whole, this study provided new ideas for the development of chitosan as an eco-friendly preparation for controlling potato late blight.

Effects of Different TiO2 Nanoparticles Concentrations on the Physical and Antibacterial Activities of Chitosan-Based Coating Film

In this investigation, the effect of different concentrations of titanium dioxide (TiO₂) nanoparticles (NPs) on the structure and antimicrobial activity of chitosan-based coating films was examined. Analysis using scanning electron microscopy (SEM) and atomic force microscopy (AFM) revealed that the modified TiO₂ NPs were successfully dispersed into the chitosan matrix, and that the roughness of the chitosan-TiO₂ nanocomposites were significantly reduced. Moreover, X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses indicated that the chitosan interacted with TiO₂ NPs and possessed good compatibility, while a thermogravimetric analysis (TGA) of the thermal properties showed that the chitosan-TiO₂ nanocomposites with 0.05% TiO₂ NPs concentration had the best thermal stability. The chitosan-TiO₂ nanocomposite exhibited an inhibitory effect on the growth of Escherichia coli and Staphylococcus aureus. This antimicrobial activity of the chitosan-TiO₂ nanocomposites had an inhibition zone ranging from 9.86 ± 0.90 to 13.55 ± 0.35 (mm). These results, therefore, indicate that chitosan-based coating films incorporated with TiO₂ NPs might become a potential packaging system for prolonging the shelf-life of fruits and vegetables.

Chitosan-triggered immunity to Fusarium in chickpea is associated with changes in the plant extracellular matrix architecture, stomatal closure and remodeling of the plant metabolome and proteome

Pathogen-/microbe-associated molecular patterns (PAMPs/MAMPs) initiate complex defense responses by reorganizing the biomolecular dynamics of the host cellular machinery. The extracellular matrix (ECM) acts as a physical scaffold that prevents recognition and entry of phytopathogens, while guard cells perceive and integrate signals metabolically. Although chitosan is a known MAMP implicated in plant defense, the precise mechanism of chitosan-triggered immunity (CTI) remains unknown. Here, we show how chitosan imparts immunity against fungal disease. Morpho-histological examination revealed stomatal closure accompanied by reductions in stomatal conductance and transpiration rate as early responses in chitosan-treated seedlings upon vascular fusariosis. Electron microscopy and Raman spectroscopy showed ECM fortification leading to oligosaccharide signaling, as documented by increased galactose, pectin and associated secondary metabolites. Multiomics approach using quantitative ECM proteomics and metabolomics identified 325 chitosan-triggered immune-responsive proteins (CTIRPs), notably novel ECM structural proteins, LYM2 and receptor-like kinases, and 65 chitosan-triggered immune-responsive metabolites (CTIRMs), including sugars, sugar alcohols, fatty alcohols, organic and amino acids. Identified proteins and metabolites are linked to reactive oxygen species (ROS) production, stomatal movement, root nodule development and root architecture coupled with oligosaccharide signaling that leads to Fusarium resistance. The cumulative data demonstrate that ROS, NO and eATP govern CTI, in addition to induction of PR proteins, CAZymes and PAL activities, besides accumulation of phenolic compounds downstream of CTI. The immune-related correlation network identified functional hubs in the CTI pathway. Altogether, these shifts led to the discovery of chitosan-responsive networks that cause significant ECM and guard cell remodeling, and translate ECM cues into cell fate decisions during fusariosis.

Novel antifungal mechanism of oligochitosan by triggering apoptosis through a metacaspase-dependent mitochondrial pathway in Ceratocystis fimbriata

The antifungal effects of oligochitosan (OCS) against Ceratocystis fimbriata that causes black rot disease in sweet potato and its apoptosis mechanism were evaluated. OCS restrained the mycelial growth and spores germination of C. fimbriata, and decreased the ergosterol content of cell membrane. Transmission electron microscopy observation and flow cytometry analysis revealed that OCS induced morphology changes with smaller size and increased granularity of C. fimbriata, which was the typical feature of apoptosis. To clarify the apoptosis mechanism induced by OCS, a series of apoptosis-related parameters were analyzed. Results showed that OCS induced reactive oxygen species accumulation, Ca²⁺ homeostasis dysregulation, mitochondrial dysfunction and metacaspase activation, coupled with hallmarks of apoptosis including phosphatidylserine externalization, DNA fragmentation, and nuclear condensation. In summary, OCS triggered apoptosis through a metacaspase-dependent mitochondrial pathway in C. fimbriata. These findings have important implications for the application of OCS to control pathogens in food and agriculture.

Postharvest benzothiazole treatment enhances healing in mechanically damaged sweet potato by activating the phenylpropanoid metabolism

BACKGROUND

Sweet potato often suffers mechanical damage during harvest, handling, and transportation. Infections, water loss, and quality changes of sweet potato caused by mechanical damage pose great financial losses. Wound healing is an effective method to alleviate such problems. In this study, the effects of postharvest treatment with benzothiazole (BTH) on wound healing of sweet potato was investigated.

RESULTS

Postharvest BTH treatment of sweet potatoes promoted lignin accumulation in wounded tissues, and 100 mg L^-1 BTH exhibited better effects than 50 mg L^-1 or 150 mg L^-1 BTH. The biosynthesis of lignin in wounded tissues significantly decreased the weight loss of sweet potatoes. An increase in respiration intensity after BTH treatment was observed. The total phenolic and flavonoid contents and the activity of phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase were increased in BTH-treated sweet potatoes. This suggests that BTH increases phenylpropanoid metabolism.

CONCLUSION

Postharvest 100 mg L^-1 BTH treatment could promote wound healing in mechanically damaged sweet potatoes. The activation of the phenylpropanoid metabolism might be the mechanism of action of BTH in wound healing. © 2020 Society of Chemical Industry.

Antifungal activity of chitosan against Aspergillus ochraceus and its possible mechanisms of action

Chitosan is a polysaccharide with a wide-range antimicrobial spectrum and has been shown to be effective in control postharvest diseases of various fruit, but the possible mode of action is far from well known. In this study the antifungal activity of chitosan was tested on A. ochraceus and its possible mechanisms involved were also investigated both at microstructure and transcriptome level. Here, we found that chitosan could significantly inhibited spore germination and mycelia growth of A. ochraceus. Scan electron microscopy (SEM) and transmission electron microscopy (TEM) observations showed that chitosan induced remarkable changes in morphology and microstructure of hyphae, such as shriveling, abnormal branching and vacuolation. Changes in expression profiles of A. ochraceus upon chitosan treatment were analyzed by RNA sequencing and a total of 435 differentially expressed genes (DEGs) were identified. Further KEGG analysis revealed that DEGs involved in ribosome biogenesis were down-regulated, while DEGs related to membrane homeostasis, such as glycerophospholipid metabolism, ether lipid metabolism and steroid biosynthesis, were up-regulated. Chitosan may affect the growth and development of A. ochraceus by impairing the integrity of cell surface architecture and protein biosynthesis. These findings have practical implications with respect to the use of chitosan as an alternative way for controlling fungal pathogens.

Identification of Rhizospheric Actinomycete Streptomyces lavendulae SPS-33 and the Inhibitory Effect of its Volatile Organic Compounds against Ceratocystis Fimbriata in Postharvest Sweet Potato (Ipomoea Batatas (L.) Lam.)

Black spot disease, which is caused by the pathogenic fungal Ceratocystis fimbriata, seriously affects the production of sweet potato and its quality during postharvest storage. In this study, the preliminary identification of the rhizosphere actinomycete strain SPS-33, and its antifungal activity of volatiles in vitro and in vivo was investigated. Based on morphological identification and phylogenetic analysis of the 16S rRNA gene sequence, strain SPS-33 was identified as Streptomyces lavendulae. Volatile organic compounds (VOCs) emitted by SPS-33 inhibited mycelial growth and sporulation of C. fimbriatain vitro and also induced a series of observable hyphae morphological changes. In an in vivo pathogenicity assay, exposure to SPS-33 significantly decreased the lesion diameter and water loss rate in sweet potato tuberous roots (TRs) inoculated with C. fimbriata. It increased the antioxidant enzymes’ activities of peroxidase, catalase, and superoxide dismutase as well as decreased malondialdehyde and increased total soluble sugar. In the VOC profile of SPS-33 detected by a headspace solid-phase micro extraction (HS-SPME) and gas chromatography-mass spectrometry (GC-MS), heptadecane, tetradecane, and 3-methyl-1-butanol were the most abundant compounds. 2-Methyl-1-butanol, 3-methyl-1-butanol, pyridine, and phenylethyl alcohol showed strong antifungal effects against C. fimbriata. These findings suggest that VOCs from S. lavendulae SPS-33 have the potential for pathogen C. fimbriata control in sweet potato postharvest storage by fumigant action.

Application of Pullulan and Chitosan Multilayer Coatings in Fresh Papayas

In this work, some multilayer coatings (two-layer, four-layer or six-layer) based on pullulan and chitosan for protecting papayas were prepared by the layer-by-layer technique. The papayas were coated by immersion and stored at 25 °C, 50% relative humidity or up to 14 days. Uncoated and monolayer-coated papayas were used as controls. The pullulan/chitosan coatings decreased the papaya weight loss, softening, color change (b*, ΔE), and pH, retarded the fall of titratable acidity and vitamin C, and maintained respiratory rate and soluble solid contents. Sensory quality evaluation demonstrated that pullulan/chitosan coatings effectively preserved papaya flavor and overall acceptance. In general, the four-layer coatings provided the best fruit preservation. In conclusion, multilayer pullulan/chitosan coatings are efficient in maintaining the post-harvest quality and prolonging the shelf life of fresh papaya.

Effects of chitosan treatment on the storability and quality properties of longan fruit during storage

Effects of various concentrations of Kadozan (chitosan) treatment on storability and quality properties of harvested 'Fuyan' longans were investigated. Compared to the control samples, Kadozan treated-longans displayed lower fruit respiration rate, lower pericarp cell membrane permeability, pericarp browning index, pulp breakdown index, fruit disease index, and weight loss, but higher rate of commercially acceptable fruit, higher levels of pericarp chlorophyll, carotenoid, anthocyanin, flavonoid and total phenolics, higher amounts of pulp total soluble sugar, sucrose, total soluble solids, and vitamin C. These results revealed Kadozan treatment could increase storability and retain better quality of harvested longan fruit. Among different concentrations of Kadozan, the dilution of 1:500 (V_Kadozan: V_{Kadozan + Water}) showed the best results in storability and maintained the best quality of longans during storage. These findings demonstrated that Kadozan could be a facile and eco-friendly postharvest handling approach for increasing storability and lengthening shelf-life of harvested 'Fuyan' longan fruit.

Volatile Organic Compounds Produced by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 as Biological Fumigants To Control Ceratocystis fimbriata in Postharvest Sweet Potatoes

The biocontrol activity and chemical composition of the volatile organic compounds (VOCs) produced by Pseudomonas chlororaphis subsp. aureofaciens SPS-41 were investigated. The VOCs inhibited mycelial growth and spore germination in Ceratocystis fimbriata, which causes black rot disease in sweet potato tuber roots (TRs) and showed wide-spectrum antifungal activity against several plant pathogenic fungi. A microscopic examination of C. fimbriata cells suggested morphological changes and a loss of cellular contents. Different inoculation strategies significantly affected the antifungal activity of the VOCs. In the volatile profile of SPS-41, the most abundant compound, 3-methyl-1-butanol, followed by phenylethyl alcohol and 2-methyl-1-butanol showed strong inhibition toward C. fimbriata. The weight loss rate and disease severity of the TRs were significantly reduced in response to the VOCs emitted by SPS-41. The results suggest that the VOCs produced by P. chlororaphis subsp. aureofaciens SPS-41 might constitute an attractive biological fumigant for controlling black rot disease in sweet potato TRs.

Molecular Mechanisms of Chitosan Interactions with Fungi and Plants

Chitosan is a versatile compound with multiple biotechnological applications. This polymer inhibits clinically important human fungal pathogens under the same carbon and nitrogen status as in blood. Chitosan permeabilises their high-fluidity plasma membrane and increases production of intracellular oxygen species (ROS). Conversely, chitosan is compatible with mammalian cell lines as well as with biocontrol fungi (BCF). BCF resistant to chitosan have low-fluidity membranes and high glucan/chitin ratios in their cell walls. Recent studies illustrate molecular and physiological basis of chitosan-root interactions. Chitosan induces auxin accumulation in Arabidopsis roots. This polymer causes overexpression of tryptophan-dependent auxin biosynthesis pathway. It also blocks auxin translocation in roots. Chitosan is a plant defense modulator. Endophytes and fungal pathogens evade plant immunity converting chitin into chitosan. LysM effectors shield chitin and protect fungal cell walls from plant chitinases. These enzymes together with fungal chitin deacetylases, chitosanases and effectors play determinant roles during fungal colonization of plants. This review describes chitosan mode of action (cell and gene targets) in fungi and plants. This knowledge will help to develop chitosan for agrobiotechnological and medical applications.