Control of citrus green and blue molds by Chinese propolis

Study on Pathogenesis of Cytospora pyri in Korla Fragrant Pear Trees (Pyrus sinkiangensis)

Pear Valsa cankers were found in various Korla fragrant pear orchards in Alaer, Xinjiang. Disease samples underwent tissue isolation, resulting in six isolates. Pathogenicity tests revealed that the XLFL-6 isolate was the most virulent, demonstrating typical Valsa canker symptoms. Research on its biological characteristics indicated that the optimal growth conditions for XLFL-6 were a temperature of 28 °C and a pH of five. Under these conditions, the colonies of XLFL-6 exhibited the largest growth diameter, and adding glucose and peptone separately to the Czapek medium was most conducive to the growth of its mycelium. Based on morphological observations and multigene sequence analyses (ITS+TEF+TUB), the pathogenic fungus was identified as C. pyri. The infection process of C. pyri was elucidated through tissue observations using both light and electron microscopy. The conidia displayed a similar germination pattern on both wounded and intact twigs. However, the infection process was delayed in the case of intact bark. By 8 h post-inoculation, the conidia achieved a germination rate of 15%. Although germination had occurred, the infection process had not yet commenced. In contrast, for wounded bark tissue, it was observed that 24 h post-inoculation, the fungal hyphae from the conidia directly invaded the wounded tissue. These hyphae penetrate the cell walls, proliferate within the host tissue, and spread throughout the phloem and xylem. After 20 d, numerous pycnidia had breached the bark surface, and yellow waxy gums filled with conidia flowed abundantly from the pycnidia ostioles, with the host tissue being nearly totally disintegrated. Regarding enzyme activity, the polygalacturonase (PG) activity, the primary cell wall-degrading enzyme in the treatment group, was seven times greater than that of the control group. The carboxymethyl cellulose (Cx) activity within the treatment group continued to increase. Xylanase activity rose swiftly to its peak between days 1 and 4, then decreased from days 5 to 10, although it remained higher than that of the control group. Overall, this study is the first to provide a detailed report on the characteristics and proliferation of C. pyri and further elucidates its modes and pathways of invasion.

Inhibitory Effects and Composition Analysis of Romanian Propolis: Applications in Organic and Sustainable Agriculture

Propolis is a sustainable and environmentally friendly agrochemical of natural origin, a resinous mixture produced by honeybees. It is used as a natural remedy in multiple pathologies., but it is also a natural defense enhancer, a phytostimulator that helps to bind, bloom, and pollinate plants. Propolis is used in organic farming as a phytoprotector and phytostimulator. The present study investigates the main physical-chemical parameters of Romanian propolis, its antifungal activity against five fungal strains (Aspergillus niger, Aspergillus flavus, Penicillium chrysogenum, Fusarium oxysporum, and Rhizopus stolonifer) and its phyto-inhibitory activity when it is applied on the layer and under the layer for different grain crops (wheat, maize, oats, and barley). Different doses were used-1, 5, and 10 g of propolis powder-and the growth of the plume was monitored for 13 days. The physical-chemical parameters investigated are volatile oils, wax, oxidation index, melting point, dry matter, ash, and resin, and maximum values were obtained for phenols (189.4 mgGAE/g), flavonoids (84.31 mgQE/g), and IC50 (0.086 µg/mL). Propolis demonstrates high antifungal activity against all fungal strains. The results showed that propolis has the best phyto-inhibition potential among the studied grain crops when it is applied on the layer, with the lowest plume growth for maize (14 mm), followed by oats, barley, and lastly wheat (24 mm). Propolis can find increasing application in sustainable and environmentally friendly agriculture and the obtaining of organic food.

Modelling the In Vitro Growth of Phytopathogenic Filamentous Fungi and Oomycetes: The Gompertz Parameters as Robust Indicators of Propolis Antifungal Action

Propolis is a resinous mixture produced by honeybees, mainly from plant exudates. With a rich chemical composition including many phenolic compounds, mostly responsible for its biological properties, namely antimicrobial ones, propolis may be a promising alternative to synthetic pesticides. The study of propolis from the south of Portugal and of its potential against phytopathogenic agents are still very recent and different methodological approaches hinder a comparison of efficacies. In this context, we aimed to test the value of a mathematical model for the multiparametric characterization of propolis' antifungal action on solid medium assays. An ethanol extract (EE) of a propolis sample harvested in 2016 from Alves (A16) was characterized in terms of phenolic composition and antimicrobial potential against five phytopathogenic species. A16.EE (500-2000 µg/mL) inhibited the mycelial growth of all the species, with Phytophthora cinnamomi and Biscogniauxia mediterranea being the most susceptible and Colletotrichum acutatum being the least affected. The Gompertz mathematical model proved to be a suitable tool for quantitatively describing the growth profiles of fungi and oomycetes, and its parameters exhibit a high level of discrimination. Our results reveal that propolis extracts may have potential applications beyond traditional uses, particularly within the agri-food sector, allowing beekeepers to make their businesses more profitable and diversified.

Review on Propolis Applications in Food Preservation and Active Packaging

Propolis is a natural hive product collected by honeybees from different plants and trees. The collected resins are then mixed with bee wax and secretions. Propolis has a long history of use in traditional and alternative medicine. Propolis possesses recognized antimicrobial and antioxidant properties. Both properties are characteristics of food preservatives. Moreover, most propolis components, in particular flavonoids and phenolic acids, are natural constituents of food. Several studies suggest that propolis could find use as a natural food preservative. This review is focused on the potential application of propolis in the antimicrobial and antioxidant preservation of food and its possible application as new, safe, natural, and multifunctional material in food packaging. In addition, the possible influence of propolis and its used extracts on the sensory properties of food is also discussed.

Cell-free supernatant of Bacillus velezensis suppresses mycelial growth and reduces virulence of Botrytis cinerea by inducing oxidative stress

As a notorious pathogenic fungus, Botrytis cinerea has been reported to infect more than 1400 species of plants and cause postharvest gray mold of numerous economic fruits, leading to substantial economic losses. Traditional chemical fungicides in pathogen control have potential issues regarding environmental pollution, disease resistance and human health. More safety and efficacious prevention technique of postharvest gray mold are in urgent demand. This study aims to investigate the potential function and mechanism of Bacillus velezensis to control gray mold for harvested fruits. The results showed that the cell-free supernatant (CFS) generated from B. velezensis strain A4 was able to inhibit spore germination, germ tube elongation and hyphal growth of B. cinerea in vitro, and impair the pathogenicity of B. cinerea on the four tested fruits. Further analysis demonstrated that CFS significantly reduced the expression of genes associated with growth and pathogenicity and weakened the ability of B. cinerea spores to penetrate plant cell walls in a dose-dependent manner. Moreover, the CFS destroyed the membrane of hyphae, resulting in exosmosis of cell contents and caused hyphal cells to accumulate excessive reactive oxygen species (ROS), leading to hyphal oxidative damage. Our findings indicate that B. velezensis CFS can damage B. cinerea mycelial cells by promoting excessive accumulation of ROS to realize its biological control function.

Natural Pectin-Based Edible Composite Coatings with Antifungal Properties to Control Green Mold and Reduce Losses of ‘Valencia’ Oranges

Novel pectin-based, antifungal, edible coatings (ECs) were formulated by the addition of natural extracts or essential oils (EOs), and their ability to control green mold (GM), caused by Penicillium digitatum, and preserve postharvest quality of ‘Valencia’ oranges was evaluated. Satureja montana, Cinnamomum zeylanicum (CN), Commiphora myrrha (MY) EOs, eugenol (EU), geraniol (GE), vanillin, and propolis extract were selected as the most effective antifungal agents against P. digitatum in in vitro assays. Pectin-beeswax edible coatings amended with these antifungals were applied to artificially inoculated oranges to evaluate GM control. ECs containing GE (2 g/kg), EU (4 and 8 g/kg), and MY EO (15 g/kg) reduced disease incidence by up to 58% after 8 days of incubation at 20 °C, while CN (8 g/kg) effectively reduced disease severity. Moreover, ECs formulated with EU (8 g/kg) and GE (2 g/kg) were the most effective on artificially inoculated cold-stored oranges, with GM incidence reductions of 56 and 48% after 4 weeks at 5 °C. Furthermore, ECs containing EU and MY reduced weight loss and maintained sensory and physicochemical quality after 8 weeks at 5 °C followed by 7 days at 20 °C. Overall, ECs with EU were the most promising and could be a good natural, safe, and eco-friendly commercial treatment for preserving orange postharvest quality.

Active compound identification by screening 33 essential oil monomers against Botryosphaeria dothidea from postharvest kiwifruit and its potential action mode

The antifungal activity of postharvest kiwifruit against the pathogen Botryosphaeria dothidea was evaluated for 33 essential oil monomers. The possible mechanism for the known active compounds were further assessed in this study. The results show all the EO components exhibit inhibitory effects on the pathogen to different degrees except for Farnesol. Carbon chain length and C₂-C₃ double bonds had a great effect on the antifungal activities of aldehydes. Of all of these, carvacrol had the strongest antifungal activity with EC₅₀ of 12.58 μL/L and EC₉₀ of 22.08 μL/L. Carvacrol also exhibits significant inhibitory effects on the pathogen, both in vivo and in vitro. Carvacrol evidently alters the hyphal morphology of B. dothidea and severely damages cell membrane and inhibits the formation of lipid components on the membrane. As cell membrane permeability increases, intracellular homeostasis including ion and biomacromolecules were destroyed by carvacrol. Furthermore, carvacrol appears to significantly inhibit mitochondrial activity and respiration rates, resulting in cell death of B. dothidea. Our results provide evidence that carvacrol could be a very useful compound for controlling postharvest rot soft in kiwifruit.

CsMYB96 enhances citrus fruit resistance against fungal pathogen by activating salicylic acid biosynthesis and facilitating defense metabolite accumulation

Citrus fruit are generally confronted with various fungal diseases that cause fruit deterioration and economic loss. Salicylic acid (SA), a plant hormone, is an important signal molecule required for stimulating the disease resistance of plants. However, there has been limited information about the molecular mechanism of SA biosynthesis involving biotic stress response in citrus fruit. In the present study, an R2R3 MYB transcription factor (CsMYB96) was identified to mediate SA signaling in response to fungal diseases. The transient overexpression assay revealed that CsMYB96 contributed to the strong tolerance of citrus fruit to Penicillium italicum along with an increase in SA content; meanwhile, CsMYB96 conferred resistance to Botrytis cinerea in Arabidopsis plants. Further metabolomic profiling of stable transgenic Arabidopsis revealed that CsMYB96 participated in the regulation of various metabolism pathways and enhanced the accumulation of phenolic acids. RNA-seq analysis confirmed that overexpression of CsMYB96 activated the expression of genes involved in plant-pathogen interaction, phenylpropanoid biosynthesis, and SA signaling. Besides, CsMBY96 directly activated the transcription of calmodulin binding protein 60g (CsCBP60g), a predominant transcription factor required for the activation of SA signaling. In summary, our results reveal that CsMYB96 promotes SA biosynthesis and the accumulation of defense metabolites to enhance the fungal pathogen resistance of citrus fruit and Arabidopsis and provide new insights into the regulation of disease response.

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

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

Potential Application of Propolis Extracts to Control the Growth of Stemphylium vesicarium in “Rocha” Pear

Stemphylium vesicarium (Wallr.) E. G. Simmons is the pathogen responsible of brown spot disease in pear and has become one of the main concerns for European pear producers. In Portugal, S. vesicarium is responsible for significant yield reduction and economic losses in “Rocha” pear (Pyrus communis L. cv Rocha) production. Considering the antimicrobial potential of propolis, the high incidence of brown spot in pears and the emergence of fungicides resistance in S. vesicarium, this study aimed to evaluate the potential of Portuguese propolis as an alternative strategy to control brown spot disease in “Rocha” pear. In vitro assays showed that propolis extracts were able to inhibit up to 90% the S. vesicarium mycelial growth. In vivo assays in artificially wounded and inoculated “Rocha” pears showed that, compared to the control, the disease incidence decreased up to 25% and the lesions diameter up to 57%, in fruits treated with propolis. Moreover, propolis seems to be more efficient in reducing the disease incidence when applied after pathogen inoculation (curative assay) than when applied before pathogen inoculation (prophylactic assay). Thus, the results suggest that propolis extracts have potential to be applied as part of an integrated approach for the control of brown spot of pear.

Elucidation of the Initial Growth Process and the Infection Mechanism of Penicillium digitatum on Postharvest Citrus (Citrus reticulata Blanco)

Green mold disease, a common citrus post-harvest disease caused by Penicillium digitatum, has an unresolved initial infection mechanism. Understanding the infection mechanism leads to the development of potential controls and preventive measures against the disease. The present study aimed to delineate the infection mechanism by investigating spore germination, changes of organic molecules and enzyme activity, and differential expression of genes in the P. digitatum infection. P. digitatum spore germination was observed by a pathology section scanner and it was found that in vivo germination was 3 h behind the in vitro germination. In addition, cell wall degrading enzymes and soluble sugar and titratable acid content during the infection process measured dynamically. The level of pectinase reached its maximum of 6067 U/g before 48 hpi, while cellulase increased rapidly after 48 hpi. The soluble sugar and organic acid content increased considerably with the progression of the infection. The transcriptomic profile of P. digitatum before and after infection was analyzed by RNA-seq. The genes related to cell wall degrading enzymes were significantly up-regulated and annotated to participate in two major carbon source synthesis pathways. The study delineated the initial infection mechanism of P. digitatum which eventually opened the gate way for the development of new control strategies in the future.

Inhibition of Key Citrus Postharvest Fungal Strains by Plant Extracts In Vitro and In Vivo: A Review

Citrus fruits are subjected to a diversity of postharvest diseases caused by various pathogens during picking, packing, storage and transportation. Green and blue molds, caused by Penicillium digitatum and Penicillium italicum, respectively, are two major postharvest citrus diseases and cause significant economic losses during the commercialization phase. Currently, the control of postharvest citrus diseases relies mainly on the use of synthetic fungicides, which usually result in the resistance against fungal attack, environment pollution and health hazards. In recent years, much attention has been given to the preservation of citrus by naturally isolated edible plant extracts, medicinal plant extracts, Citrus extracts and volatiles, et al. Scientists worldwide devote their time and energy to discover the high effect, low toxicity, safety and inexpensive plant-derived fungicides. The current review will highlight plant-derived fungicides and chemical constituents that aim to inhibit P. digitatum and P. italicum in vitro and in vivo. Coatings enriched with plant extracts could be good alternative methods for Citrus fruits preservation. Problems and prospects of the research and development of plant-derived natural fungicides will also be discussed in this article.

Effects of poplar buds as an alternative to propolis on postharvest diseases control of strawberry fruits

BACKGROUND

Botrytis cinerea and Rhizopus stolonifer, two main postharvest pathogens, cause great loss of strawberry fruits. Here, the effects of poplar buds extracts, a main plant source for Chinese propolis, on disease control were investigated in vitro and in vivo.

RESULTS

The HPLC profile of poplar buds ethanol extract (PBEE) was almost identical to that of propolis ethanol extract (PEE), with the active flavonoids identified as pinocembrin, chrysin and galangin. PBEE exhibited similar inhibitory activities on spore germination of both pathogens compared with PEE, and PBEE also strongly inhibited the mycelial growth of the pathogens. In vivo, PBEE could effectively reduce decay of strawberry fruits stored at 13 °C. Although the weight loss was slightly increased, the contents of total soluble solid, titritable acid, vitamin C and total anthocyanins were significantly higher in PBEE treated fruits than those of the control.

CONCLUSION

PBEE had the similar antifungal activity with propolis and had great potential as an alternative to propolis to control strawberry fruits diseases.

Use of active extracts of poplar buds against Penicillium italicum and possible modes of action

Antifungal components, from poplar buds active fraction (PBAF) against Penicillium italicum, the causal agent of blue mold in citrus fruits, were identified and possible action modes were investigated. Pinocembrin, chrysin and galangin were determined as active components in PBAF, using HPLC and HPLC-MS analysis. The antifungal activity is stable at temperatures ranging from 4 °C to 100 °C and pH levels ranging from 4 to 8. In the presence of PBAF, the hyphae become shriveled, wrinkled and the cell membrane became seriously disrupted. Further investigation on cell permeability, nucleic acid content and alkaline phosphatase suggest that the cell membrane might be the target. Mycelial oxygen consumption and the respiration-related enzymatic activity of succinate dehydrogenase, malate dehydrogenase and ATPase were all inhibited by PBAF. We propose that PBAF is a potentially useful alternative for blue mold control and may act against P. italicum by interfering with respiration and disrupting the cell membrane.