Avirulent Isolates of Penicillium chrysogenum to Control the Blue Mold of Apple Caused by P. expansum

Blue mold is an economically significant postharvest disease of pome fruit that is primarily caused by Penicillium expansum. To manage this disease and sustain product quality, novel decay intervention strategies are needed that also maintain long-term efficacy. Biocontrol organisms and natural products are promising tools for managing postharvest diseases. Here, two Penicillium chrysogenum isolates, 404 and 413, were investigated as potential biocontrol agents against P. expansum in apple. Notably, 404 and 413 were non-pathogenic in apple, yet they grew vigorously in vitro when compared to the highly aggressive P. expansum R19 and Pe21 isolates. Whole-genome sequencing and species-specific barcoding identified both strains as P. chrysogenum. Each P. chrysogenum strain was inoculated in apple with the subsequent co-inoculation of R19 or Pe21 simultaneously, 3, or 7 days after prior inoculation with 404 or 413. The co-inoculation of these isolates showed reduced decay incidence and severity, with the most significant reduction from the longer establishment of P. chrysogenum. In vitro growth showed no antagonism between species, further suggesting competitive niche colonization as the mode of action for decay reduction. Both P. chrysogenum isolates had incomplete patulin gene clusters but tolerated patulin treatment. Finally, hygromycin resistance was observed for both P. chrysogenum isolates, yet they are not multiresistant to apple postharvest fungicides. Overall, we demonstrate the translative potential of P. chrysogenum to serve as an effective biocontrol agent against blue mold decay in apples, pending practical optimization and formulation.

Deep Learning in Precision Agriculture: Artificially Generated VNIR Images Segmentation for Early Postharvest Decay Prediction in Apples

Food quality control is an important task in the agricultural domain at the postharvest stage for avoiding food losses. The latest achievements in image processing with deep learning (DL) and computer vision (CV) approaches provide a number of effective tools based on the image colorization and image-to-image translation for plant quality control at the postharvest stage. In this article, we propose the approach based on Generative Adversarial Network (GAN) and Convolutional Neural Network (CNN) techniques to use synthesized and segmented VNIR imaging data for early postharvest decay and fungal zone predictions as well as the quality assessment of stored apples. The Pix2PixHD model achieved higher results in terms of VNIR images translation from RGB (SSIM = 0.972). Mask R-CNN model was selected as a CNN technique for VNIR images segmentation and achieved 58.861 for postharvest decay zones, 40.968 for fungal zones and 94.800 for both the decayed and fungal zones detection and prediction in stored apples in terms of F1-score metric. In order to verify the effectiveness of this approach, a unique paired dataset containing 1305 RGB and VNIR images of apples of four varieties was obtained. It is further utilized for a GAN model selection. Additionally, we acquired 1029 VNIR images of apples for training and testing a CNN model. We conducted validation on an embedded system equipped with a graphical processing unit. Using Pix2PixHD, 100 VNIR images from RGB images were generated at a rate of 17 frames per second (FPS). Subsequently, these images were segmented using Mask R-CNN at a rate of 0.42 FPS. The achieved results are promising for enhancing the food study and control during the postharvest stage.

Would You Like Wood or Plastic? Bin Material, Sanitation Treatments, and Bin Inoculum Levels Impact Blue Mold Decay of Stored Apple Fruit

Blue mold, caused primarily by Penicillium expansum, is a significant postharvest disease of apples. It not only causes economic losses but also produces mycotoxins that contaminate processed fruit products, which contributes to food waste and loss. Previous research has shown that packing and storage bins harbor Penicillium spores and that steam and hot water efficiently reduce spore inoculum levels. However, studies using wooden and plastic bins regarding their ability to harbor spores, the effect of chemical sanitation treatments on spore levels, and the impact of rinsate from treated bins on apple fruit decay have not been investigated for the Mid-Atlantic area (Okull et al. 2006; Rosenberger 2009). We evaluated different sanitation treatments (chemical and physical) to reduce P. expansum inoculum levels on wooden and plastic bins. We determined that wooden bins bound P. expansum spores four orders of magnitude higher than plastic. When both bin types were treated with steam (wooden) or sterile hot water (plastic), Thyme Guard, or Academy, all treatments resulted in significantly (P < 0.05) lower spore levels compared to untreated controls. Although, plastic bins retained lower numbers of spores after inoculation with contaminated spore rinsate and required much higher concentrations of P. expansum spores in rinsate to retain spores at levels that would lead to decay on apple fruit. Overall, we demonstrated that plastic bins retain fewer spores than wooden bins and that both can be sanitized by various physical or chemical treatments. We envision that our findings will be applicable in the future as the techniques implemented in this study were used to investigate industry-relevant questions. Our goal is that the research techniques and findings become feasible with advancements in technology and/or accompany other shifts in existing processes in commercial pome fruit packing and storage facilities.

Application of chitosan nanoparticles in quality and preservation of postharvest fruits and vegetables: A review

Chitosan is an interesting alternative material for packaging development due to its biodegradability. However, its poor mechanical properties and low permeability limit its actual applications. Chitosan nanoparticles (CHNPs) have emerged as a suitable solution to overcome these intrinsic limitations. In this review, all studies regarding the use of CHNPs to extend the shelf life and improve the quality of postharvest products are covered. The characteristics of CHNPs and their combinations with essential oils and metals, along with their effects on postharvest products, are compared and discussed throughout the manuscript. CHNPs enhanced postharvest antioxidant capacity, extended shelf life, increased nutritional quality, and promoted tolerance to chilling stress. Additionally, the CHNPs reduced the incidence of postharvest phytopathogens. In most instances, smaller CHNPs (<150 nm) conferred higher benefits than larger ones (>150 nm). This was likely a result of the greater plant tissue penetrability and surface area of the smaller CHNPs. The CHNPs were either applied after preparing an emulsion or incorporated into a film, with the latter often exhibiting greater antioxidant and antimicrobial activities. CHNPs were used to encapsulate essential oils, which could be released over time and may enhance the antioxidant and antimicrobial properties of the CHNPs. Even though most applications were performed after harvest, preharvest application had longer lasting effects.

Comparative Penicillium spp. Transcriptomics: Conserved Pathways and Processes Revealed in Ungerminated Conidia and during Postharvest Apple Fruit Decay

Blue mold, caused by Penicillium spp., is an impactful postharvest disease resulting in significant economic losses due to reduced pome fruit quality and mycotoxin contamination. Using two Penicillium species with different levels of aggressiveness, transcriptomics were implemented in order to identify genes expressed during apple fruit decay and loci expressed in ungerminated conidia. Total RNA was isolated from ungerminated conidia and decayed apple fruit infected with P. expansum R19 or P. polonicum RS1. There were 2442 differentially expressed genes (DEGs) between the R19 and RS1 in apple. Comparisons within species between apple and conidia revealed 4404 DEGs for R19 and 2935 for RS1, respectively. Gene ontology (GO) analysis revealed differential regulation in fungal transport and metabolism genes during decay, suggesting a flux in nutrient acquisition and detoxification strategies. In R19, the oxidoreductase GO category comprised 20% of all DEG groups in apple verses conidia. Ungerminated conidia from both species showed DEGs encoding the glyoxylate shunt and beta-oxidation, specifying the earliest metabolic requirements for germination. This is the first study to identify pre-loaded transcripts in conidia from blue mold fungi, reveal unique genes between species expressed during apple decay, and show the expression dynamics of known fungal virulence factors. These findings will enable development of targeted approaches for blue mold abatement strategies.

The secret of H2 S to keep plants young and fresh and its products

Recently, accumulating evidence has shown that hydrogen sulphide (H₂ S), a newly determined gasotransmitter, plays important roles in senescence, which is an essential biological process for plant fitness and an important agricultural trait that is critical for the yield and quality of farm produce. Here, in this review, we summarize the roles of H₂ S in senescence, both before and after the harvesting of agricultural products, and the underlying mechanism is also discussed. During the plant growth process, the function of H₂ S in the leaf senescence process has been studied extensively, and H₂ S plays roles during the whole process, including the initiation, reorganization and terminal stages. While during the postharvest stage, H₂ S can prevents farm products from deterioration resulting from over-ripening, pathogen attack and incorrect storage. The underlying H₂ S-related mechanisms during different stages of the senescence process are summarized and compared. The most prominent interaction occurs between H₂ S and reactive oxygen species, and the molecular mechanism is explored. Additionally, the conserved action mode of H₂ S in different life processes and different species is also discussed. In the future, multi-omics analyses over time will be needed to investigate the detailed mechanisms of H₂ S, and a safety attribute analysis of H₂ S is also required before it can be used in agricultural production.

Spectral pattern study of citrus black rot caused by Alternaria alternata and selecting optimal wavelengths for decay detection

Fungal decay is one of the most common diseases that affect postharvest operations and sales of citrus. Sometimes, fungal disease develops and spreads inside the fruit and in the advanced stages of the disease, it appears apparent, so the use of efficient and reliable methods for early detection of the disease is very important. In this study, early detection of citrus black rot disease caused by Alternaria genus fungus was examined using spectroscopy. Jaffa oranges were inoculated with Alternaria alternata. The samples were inspected by spectroscopy (200–1100 nm) in the 1st, 2nd, and 3rd weeks after inoculation. The classification of healthy and infected samples and selection of most important wavelengths were conducted by soft independent modeling of class analogy (SIMCA). The most important wavelengths in the detection of healthy and infected samples of the 1st week were 507, 933, 937, and 950 nm with a classification accuracy of 60%. The most important wavelengths of the 2nd week were 522 and 787 nm with a classification accuracy of 60%. Also, wavelengths of 546, 660, 691, and 839 were found to be effective in the 3rd week with a classification accuracy of 100%.

Incidence, Speciation, and Morpho-Genetic Diversity of Penicillium spp. Causing Blue Mold of Stored Pome Fruits in Serbia

Blue mold, caused by Penicillium spp., is one of the most economically important postharvest diseases of pome fruits, globally. Pome fruits, in particular apple, is the most widely grown pome fruit in Serbia, and the distribution of Penicillium spp. responsible for postharvest decay is unknown. A two-year survey was conducted in 2014 and 2015, where four pome fruits (apple, pear, quince, and medlar) with blue mold symptoms were collected from 20 storage locations throughout Serbia. Detailed morphological characterization, analysis of virulence in three apple cultivars, and multilocus phylogeny revealed three main Penicillium spp. in order of abundance: P. expansum, P. crustosum, and P. solitum. Interestingly, P. expansum split into two distinct clades with strong statistical support that coincided with several morphological observations. Findings from this study are significant and showed previously undocumented diversity in blue mold fungi responsible for postharvest decay including the first finding of P. crustosum, and P. solitum as postharvest pathogens of quince and P. crustosum of medlar fruit in the world, and P. expansum of quince in Serbia. Data from this study provide timely information regarding phenotypic, morphological and genotypic plasticity in P. expansum that will impact the design of species-specific detection tools and guide the development of blue mold management strategies.

First Report of Postharvest Blue Mold decay caused by Penicillium expansum on Lemon (Citrus limon) fruit in China

Lemon (Citrus limon) is one of the most important commercial (both dried and fresh) citrus fruits in China. In the spring of 2019, postharvest blue mold decay was observed at an incidence of 3-5% on lemon fruit at the local markets in Beijing, China. Fruit lesions were circular, brown, soft, and watery, and rapidly expanded at 25°C. To isolate the causal organism, small pieces (2 mm3) were cut from the lesions, surface-sterilized for 1 min in 1.5% NaOCl, rinsed three times with sterilized water, dried with sterile filter paper, placed onto potato dextrose agar (PDA) medium, and incubated at 25°C for 6 days. Eight morphologically similar single-colony fungal isolates were recovered from six lemon fruit. Colony surfaces were bluish-green on the upper surface and cream to yellow-brown one the reverse. Hyphae on colony margins were entirely subsurface and cream in color. Mycelium was highly branched, septate, and colorless, and conidiophores were 250 to 450 × 3.0 to 4.0 µm in size. Stipe of conidiophores were smooth-walled, bearing terminal penicilli, typically terverticillate or less commonly birverticillate, rami occurring singly, 16 to 23 × 3.0 to 4.0 µm, metulae in 3 to 6, measuring 12 to 15 × 3.0 to 4.0 µm. Phialides were ampulliform to almost cylindrical, in verticils of 5 to 8, measuring 8 to 11 × 2.5 to 3.2 µm with collula. Conidia were smooth-walled, ellipsoidal, measuring 3.0 to 3.5 × 2.5 to 3.0 µm. According to morphological characteristics, the fungus was identified as Penicillium expansum (Visagie et al. 2014). For molecular identification, genomic DNA of eight fungal isolates was extracted, regions of the beta-tubulin (TUB), and calmodulin (CAL) genes and ITS region, were amplified using Bt2a/Bt2b, CAL-228F/ CAL-737, and ITS1/ITS4 primers respectively. Obtained sequences of all isolates were identical to sequences of the representative isolate YC-IK12, which was submitted in the GenBank. BLAST results of YC-IK12 sequences (ITS; MT856700: TUB; MT856958: CAL; MT856959) showed 98 to 100% similarity with P. expansum accessions (NR-077154, LN896428, JX141581). For pathogenicity tests, 10 μl of conidial suspension (10 × 105 conidia/ml) from seven-day-old YC-IK12 culture was inoculated using a sterilized needle into the surface of each five asymptomatic disinfected lemons. As a control, three lemons were inoculated using sterile distilled water. All inoculated lemons were placed in plastic containers and incubated at 25°C for 7 days. Decay lesions, identical to the original observations, developed on all inoculated lemons, while control lemons remained asymptomatic. Fungus re-isolated from the inoculated lemon was identified as P. expansum on the basis morphology and Bt2a/Bt2b, CAL-228F/ CAL-737, and ITS1/ITS4 sequences. Previously, Penicillium spp. including P. expansum have been reported as post-harvest pathogens on various Citrus spp. (Louw & Korsten 2015). However, P. digitatum has been reported on lemons and P. expansum has been reported on stored Kiwifruit (Actinidia arguta), Malus, and Pyrus species in China (Tai, 1979; Wang et al. 2015). To our knowledge, this is the first report of blue mold caused by P. expansum on lemons in China. References Louw, J. P., Korsten, L. 2015. Plant Dis. 99:21-30. Tai, F.L. 1979. Sylloge Fungorum Sinicorum. Sci. Press, Acad. Sin., Peking, 1527 pages. 8097 Visagie, C.M. et al. 2014. Studies. Mycol.78: 343. Wang, C. W. et al. 2015. Plant Dis. 99:1037.

Antifungal Activity of Propyl Disulfide from Neem (Azadirachta indica) in Vapor and Agar Diffusion Assays against Anthracnose Pathogens (Colletotrichum gloeosporioides and Colletotrichum acutatum) in Mango Fruit

Microorganisms causing anthracnose diseases have a medium to a high level of resistance to the existing fungicides. This study aimed to investigate neem plant extract (propyl disulfide, PD) as an alternative to the current fungicides against mango’s anthracnose. Microorganisms were isolated from decayed mango and identified as Colletotrichum gloeosporioides and Colletotrichum acutatum. Next, a pathogenicity test was conducted and after fulfilling Koch’s postulates, fungi were reisolated from these symptomatic fruits and we thus obtained pure cultures. Then, different concentrations of PD were used against these fungi in vapor and agar diffusion assays. Ethanol and distilled water were served as control treatments. PD significantly (p ≤ 0.05) inhibited more of the mycelial growth of these fungi than both controls. The antifungal activity of PD increased with increasing concentrations. The vapor diffusion assay was more effective in inhibiting the mycelial growth of these fungi than the agar diffusion assay. A good fit (R², 0.950) of the experimental data in the Gompertz growth model and a significant difference in the model parameters, i.e., lag phase (λ), stationary phase (A) and mycelial growth rate, further showed the antifungal efficacy of PD. Therefore, PD could be the best antimicrobial compound against a wide range of microorganisms.

Microbiome approaches provide the key to biologically control postharvest pathogens and storability of fruits and vegetables

Microbes play an important role in plants and interact closely with their host starting from sprouting seeds, continuing during growth and after harvest. The discovery of their importance for plant and postharvest health initiated a biotechnological development of various antagonistic bacteria and fungi for disease control. Nevertheless, their application often showed inconsistent effects. Recently, high-throughput sequencing-based techniques including advanced microscopy reveal fruits and vegetables as holobionts. At harvest, all fruits and vegetables harbor a highly abundant and specific microbiota including beneficial, pathogenic and spoilage microorganisms. Especially, a high microbial diversity and resilient microbial networks were shown to be linked to fruit and vegetable health, while diseased products showed severe dysbiosis. Field and postharvest handling of fruits and vegetables was shown to affect the indigenous microbiome and therefore has a substantial impact on the storability of fruits and vegetables. Microbiome tracking can be implemented as a new tool to evaluate and assess all postharvest processes and contribute to fruit and vegetable health. Here, we summarize current research advancements in the emerging field of postharvest microbiomes and elaborate its importance. The generated knowledge provides profound insights into postharvest microbiome dynamics and sets a new basis for targeted, microbiome-driven and sustainable control strategies.

Penicillium expansum: biology, omics, and management tools for a global postharvest pathogen causing blue mould of pome fruit

Blue mould, caused primarily by Penicillium expansum, is a major threat to the global pome fruit industry, causing multimillion-dollar losses annually. The blue mould fungus negatively affects fruit quality, thereby reducing fresh fruit consumption, and significantly contributes to food loss. P. expansum also produces an array of mycotoxins that are detrimental to human health. Management options are limited and the emergence of fungicide-resistant Penicillium spp. makes disease management difficult, therefore new approaches and tools are needed to combat blue mould in storage. This species profile comprises a comprehensive literature review of this aggressive pathogen associated with pomes (apple, pear, quince), focusing on biology, mechanisms of disease, control, genomics, and the newest developments in disease management.

TAXONOMY

Penicillium expansum Link 1809. Domain Eukaryota, Kingdom Fungi, Phylum Ascomycota, Subphylum Pezizomycotina, Class Eurotiomycetes, Subclass: Eurotiomycetidae, Order Eurotiales; Family Trichocomaceae, Genus Penicillium, Species expansum.

BIOLOGY

A wide host range necrotrophic postharvest pathogen that requires a wound (e.g., stem pull, punctures, bruises, shoulder cracks) or natural openings (e.g., lenticel, stem end, calyx sinus) to gain ingress and infect.

TOXINS

Patulin, citrinin, chaetoglobosins, communesins, roquefortine C, expansolides A and B, ochratoxin A, penitrem A, rubratoxin B, and penicillic acid.

HOST RANGE

Primarily apples, European pear, Asian pear, medlar, and quince. Blue mould has also been reported on stone fruits (cherry, plum, peach), small fruits (grape, strawberry, kiwi), and hazel nut.

DISEASE SYMPTOMS

Blue mould initially appears as light tan to dark brown circular lesions with a defined margin between the decayed and healthy tissues. The decayed tissue is soft and watery, and blue-green spore masses appear on the decayed area, starting at the infection site and radiating outward as the decayed area ages.

DISEASE CONTROL

Preharvest fungicides with postharvest activity and postharvest fungicides are primarily used to control decay. Orchard and packinghouse sanitation methods are also critical components of an integrated pest management strategy.

USEFUL WEBSITES

Penn State Tree Fruit Production Guide (https://extension.psu.edu/forage-and-food-crops/fruit), Washington State Comprehensive Tree Fruit (http://treefruit.wsu.edu/crop-protection/disease-management/blue-mold/), The Apple Rot Doctor (https://waynejurick.wixsite.com/applerotdr), penicillium expansum genome sequences and resources (https://www.ncbi.nlm.nih.gov/genome/browse/#!/eukaryotes/11336/).

Antagonistic Yeasts: A Promising Alternative to Chemical Fungicides for Controlling Postharvest Decay of Fruit

Fruit plays an important role in human diet. Whereas, fungal pathogens cause huge losses of fruit during storage and transportation, abuse of chemical fungicides leads to serious environmental pollution and endangers human health. Antagonistic yeasts (also known as biocontrol yeasts) are promising substitutes for chemical fungicides in the control of postharvest decay owing to their widespread distribution, antagonistic ability, environmentally friendly nature, and safety for humans. Over the past few decades, the biocontrol mechanisms of antagonistic yeasts have been extensively studied, such as nutrition and space competition, mycoparasitism, and induction of host resistance. Moreover, combination of antagonistic yeasts with other agents or treatments were developed to improve the biocontrol efficacy. Several antagonistic yeasts are used commercially. In this review, the application of antagonistic yeasts for postharvest decay control is summarized, including the antagonistic yeast species and sources, antagonistic mechanisms, commercial applications, and efficacy improvement. Issues requiring further study are also discussed.

Microbiome approaches provide the key to biologically control postharvest pathogens and storability of fruits and vegetables

Microbes play an important role in plants and interact closely with their host starting from sprouting seeds, continuing during growth and after harvest. The discovery of their importance for plant and postharvest health initiated a biotechnological development of various antagonistic bacteria and fungi for disease control. Nevertheless, their application often showed inconsistent effects. Recently, high-throughput sequencing-based techniques including advanced microscopy reveal fruits and vegetables as holobionts. At harvest, all fruits and vegetables harbor a highly abundant and specific microbiota including beneficial, pathogenic and spoilage microorganisms. Especially, a high microbial diversity and resilient microbial networks were shown to be linked to fruit and vegetable health, while diseased products showed severe dysbiosis. Field and postharvest handling of fruits and vegetables was shown to affect the indigenous microbiome and therefore has a substantial impact on the storability of fruits and vegetables. Microbiome tracking can be implemented as a new tool to evaluate and assess all postharvest processes and contribute to fruit and vegetable health. Here, we summarize current research advancements in the emerging field of postharvest microbiomes and elaborate its importance. The generated knowledge provides profound insights into postharvest microbiome dynamics and sets a new basis for targeted, microbiome-driven and sustainable control strategies.

Microbiome approaches provide the key to biologically control postharvest pathogens and storability of fruits and vegetables

Microbes play an important role in plants and interact closely with their host starting from sprouting seeds, continuing during growth and after harvest. The discovery of their importance for plant and postharvest health initiated a biotechnological development of various antagonistic bacteria and fungi for disease control. Nevertheless, their application often showed inconsistent effects. Recently, high-throughput sequencing-based techniques including advanced microscopy reveal fruits and vegetables as holobionts. At harvest, all fruits and vegetables harbor a highly abundant and specific microbiota including beneficial, pathogenic and spoilage microorganisms. Especially, a high microbial diversity and resilient microbial networks were shown to be linked to fruit and vegetable health, while diseased products showed severe dysbiosis. Field and postharvest handling of fruits and vegetables was shown to affect the indigenous microbiome and therefore has a substantial impact on the storability of fruits and vegetables. Microbiome tracking can be implemented as a new tool to evaluate and assess all postharvest processes and contribute to fruit and vegetable health. Here, we summarize current research advancements in the emerging field of postharvest microbiomes and elaborate its importance. The generated knowledge provides profound insights into postharvest microbiome dynamics and sets a new basis for targeted, microbiome-driven and sustainable control strategies.

Antifungal activity of propyl disulphide from neem against Lasiodiplodia theobromae and Neofusicoccum parvum causing stem end rot in mango

AIM

To investigate the antifungal effect of the neem extract volatile propyl disulphide against the fungal plant pathogens.

METHODS AND RESULTS

Postharvest pathogens were isolated and identified as Lasiodiplodia theobromae and Neofusicoccum parvum causing the stem end rot of mango fruit. Antifungal activity of propyl disulphide at different concentrations was determined in comparison with ethanol and distilled water. Both diffusion assays were effective in controlling the mycelial growth of the tested fungi. The high coefficient of determination (R² , 0·970-0·997) of the growth curves indicated the good fit of the experimental data to the Gompertz growth model. Propyl disulphide significantly (P ≤ 0·05) decreased the mycelial growth during the stationary phase (A) and increased the lag phase (λ) than both control (ethanol and distilled water).

CONCLUSION

This compound can potentially be applied to other tropical and subtropical fruits for the successful control of postharvest losses of fresh produce.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of propyl disulphide from neem extract against plant pathogens and could be beneficial for effective microbial decay prevention in food industries.

Phenylalanine: A Promising Inducer of Fruit Resistance to Postharvest Pathogens

More than 40% of harvested fruit is lost, largely due to decay. In parallel, restrictions on postharvest fungicides call for eco-friendly alternatives. Fruit's natural resistance depends mainly on flavonoids and anthocyanins-which have antioxidant and antifungal activity-synthesized from the phenylpropanoid pathway with phenylalanine as a precursor. We hypothesized that phenylalanine could induce fruit's natural defense response and tolerance to fungal pathogens. The postharvest application of phenylalanine to mango and avocado fruit reduced anthracnose and stem-end rot caused by Colletotrichum gloeosporioides and Lasiodiplodia theobromae, respectively. The postharvest application of phenylalanine to citrus fruit reduced green mold caused by Penicillium digitatum. The optimal phenylalanine concentrations for postharvest application were 6 mM for citrus fruits and 8 mM for mangoes and avocadoes. The preharvest application of phenylalanine to strawberries, mangoes, and citrus fruits also reduced postharvest decay. Interestingly, citrus fruit resistance to P. digitatum inoculated immediately after phenylalanine application was not improved, whereas inoculation performed 2 days after phenylalanine treatment induced the defense response. Five hours after the treatment, no phenylalanine residue was detected on/in the fruit, probably due to rapid phenylalanine metabolism. Additionally, in vitro testing showed no inhibitory effect of phenylalanine on conidial germination. Altogether, we characterized a new inducer of the fruit defense response-phenylalanine. Preharvest or postharvest application to fruit led to the inhibition of fungal pathogen-induced postharvest decay, suggesting that the application of phenylalanine could become an eco-friendly and healthy alternative to fungicides.

Fungal Gene Mutation Analysis Elucidating Photoselective Enhancement of UV-C Disinfection Efficiency Toward Spoilage Agents on Fruit Surface

Short-wave ultraviolet (UV-C) treatment represents a potent, clean and safe substitute to chemical sanitizers for fresh fruit preservation. However, the dosage requirement for microbial disinfection may have negative effects on fruit quality. In this study, UV-C was found to be more efficient in killing spores of Botrytis cinerea in dark and red light conditions when compared to white and blue light. Loss of the blue light receptor gene Bcwcl1, a homolog of wc-1 in Neurospora crassa, led to hypersensitivity to UV-C in all light conditions tested. The expression of Bcuve1 and Bcphr1, which encode UV-damage endonuclease and photolyase, respectively, were strongly induced by white and blue light in a Bcwcl1-dependent manner. Gene mutation analyses of Bcuve1 and Bcphr1 indicated that they synergistically contribute to survival after UV-C treatment. In vivo assays showed that UV-C (1.0 kJ/m²) abolished decay in drop-inoculated fruit only if the UV-C treatment was followed by a dark period or red light, while in contrast, typical decay appeared on UV-C irradiated fruits exposed to white or blue light. In summary, blue light enhances UV-C resistance in B. cinerea by inducing expression of the UV damage repair-related enzymes, while the efficiency of UV-C application for fruit surface disinfection can be enhanced in dark or red light conditions; these principles seem to be well conserved among postharvest fungal pathogens.

Hot air treatment reduces postharvest decay and delays softening of cherry tomato by regulating gene expression and activities of cell wall-degrading enzymes

BACKGROUND

Fruit softening facilitates pathogen infection and postharvest decay, leading to the reduction of shelf-life. Hot air (HA) treatment at 38 °C for 12 h is effective in reducing postharvest disease and chilling injury of tomato fruit. To explore the effect and mechanism of HA treatment on reducing postharvest decay and softening of cherry tomato, fruit at the mature green stage were treated with HA and then stored at 20 °C for 15 days. Changes in natural decay incidence, firmness, cell wall compositions, activities and gene expression of cell wall-degrading enzymes of cherry tomatoes were assessed.

RESULTS

HA treatment reduced natural decay incidence, postponed the firmness decline, inhibited the respiration rate and ethylene production, and retarded pectin solubilisation and cellulose degradation of cherry tomatoes. Enzymatic activities and gene expression of pectin methylesterase, polygalacturonase, cellulase and β-galactosidase were inhibited by HA treatment. In addition, the gene expression of LeEXP1 was reduced, while LeEXT was up-regulated after HA treatment.

CONCLUSIONS

Our findings suggested that HA treatment could inhibit cell wall degradation and postpone softening of cherry tomatoes by regulating gene expression and activities of cell wall-degrading enzymes, resulting in the reduction of postharvest decay. © 2017 Society of Chemical Industry.

Proteomic Analysis of Kiwifruit in Response to the Postharvest Pathogen, Botrytis cinerea

Gray mold, caused by the fungus Botrytis cinerea, is the most significant postharvest disease of kiwifruit. In the present study, iTRAQ with LC-ESI-MS/MS was used to identify the kiwifruit proteins associated with the response to B. cinerea. A total of 2,487 proteins in kiwifruit were identified. Among them, 292 represented differentially accumulated proteins (DAPs), with 196 DAPs having increased, and 96 DAPs having decreased in accumulation in B. cinerea-inoculated vs. water-inoculated, control kiwifruits. DAPs were associated with penetration site reorganization, cell wall degradation, MAPK cascades, ROS signaling, and PR proteins. In order to examine the corresponding transcriptional levels of the DAPs, RT-qPCR was conducted on a subset of 9 DAPs. In addition, virus-induced gene silencing was used to examine the role of myosin 10 in kiwifruit, a gene modulating host penetration resistance to fungal infection, in response to B. cinerea infection. The present study provides new insight on the understanding of the interaction between kiwifruit and B. cinerea.

Calmodulin Gene Expression in Response to Mechanical Wounding and Botrytis cinerea Infection in Tomato Fruit

Calmodulin, a ubiquitous calcium sensor, plays an important role in decoding stress-triggered intracellular calcium changes and regulates the functions of numerous target proteins involved in various plant physiological responses. To determine the functions of calmodulin in fleshy fruit, expression studies were performed on a family of six calmodulin genes (SlCaMs) in mature-green stage tomato fruit in response to mechanical injury and Botrytis cinerea infection. Both wounding and pathogen inoculation triggered expression of all those genes, with SlCaM2 being the most responsive one to both treatments. Furthermore, all calmodulin genes were upregulated by salicylic acid and methyl jasmonate, two signaling molecules involved in plant immunity. In addition to SlCaM2, SlCaM1 was highly responsive to salicylic acid and methyl jasmonate. However, SlCaM2 exhibited a more rapid and stronger response than SlCaM1. Overexpression of SlCaM2 in tomato fruit enhanced resistance to Botrytis-induced decay, whereas reducing its expression resulted in increased lesion development. These results indicate that calmodulin is a positive regulator of plant defense in fruit by activating defense pathways including salicylate- and jasmonate-signaling pathways, and SlCaM2 is the major calmodulin gene responsible for this event.

Effect of alternative postharvest control treatments on the storability of 'Golden Delicious' apples

BACKGROUND

Apples are subject to a high degree of fungal diseases, but the use of synthetic fungicides has been questioned because of public safety concerns, social rejection, and the development of resistance in pathogens. Thus, development of new postharvest treatments against apple fungal pathogens is necessary. Most studies have reported their effectiveness, but not all report the effects on the quality and storability of the fruit. In this study, the effects of physical (hot water), chemical (quercetin) and biological (yeast antagonist) microfungal control on the quality of 'Golden Delicious' apple during storage at 2 ± 0.5 °C, and 90 ± 2% of relative humidity, for 2 months were investigated and compared.

RESULTS

Heat-treated apples exhibited peel fruit damage (surface browning and internal breakdown disorders) and promoted ripening in the fruit. The quercetin caustic spray caused the development of peel chemical burn in all treated fruit. Both yeast antagonist and quercetin treatments did not affect the apple ripening process but stimulated an increase in ethylene production and in respiratory activity.

CONCLUSION

The data indicated that the effects on quality and storability were dependent on the method of treatment used, and antagonistic yeast was the best microfungal control because of it did not cause any disorders or negative effects on apple quality during storage.

Effects of chitin and its derivative chitosan on postharvest decay of fruits: a review

Considerable economic losses to harvested fruits are caused by postharvest fungal decay during transportation and storage, which can be significantly controlled by synthetic fungicides. However, considering public concern over pesticide residues in food and the environment, there is a need for safer alternatives for the control of postharvest decay to substitute synthetic fungicides. As the second most abundant biopolymer renewable source in nature, chitin and its derivative chitosan are widely used in controlling postharvest decay of fruits. This review aims to introduce the effect of chitin and chitosan on postharvest decay in fruits and the possible modes of action involved. We found most of the actions discussed in these researches rest on physiological mechanisms. All of the mechanisms are summarized to lay the groundwork for further studies which should focus on the molecular mechanisms of chitin and chitosan in controlling postharvest decay of fruits.

A Postharvest Fruit Rot in Apple Caused by Phacidiopycnis washingtonensis

During a survey of postharvest diseases in Red Delicious apples (Malus domestica) conducted in 2003, a previously undescribed postharvest fruit rot was discovered in Washington State. The causal agent has been described as a new species, Phacidiopycnis washingtonensis. In this study, we described the symptomatology of this disease, determined its occurrence and prevalence in Washington State, tested pathogenicity, and determined infection courts on fruit of three apple varieties. Decayed fruit were sampled from 26, 72, and 81 grower lots during March to August in 2003, 2004, and 2005, respectively, during packing operations from commercial packinghouses. Symptoms of decayed fruit were recorded and isolations were made from decayed fruit to correlate causal agents with the disease symptoms observed. Fruit of Red Delicious, Golden Delicious, and Fuji apples were inoculated in the orchards with conidial suspensions of the fungus at 1 and 2 weeks before harvest. All fruit were harvested and stored at 0°C, and decay development on the fruit was monitored monthly for up to 9 months. The symptoms were primarily stem-end rot and calyx-end rot. Infection also occurred at lenticels on fruit skin, particularly on Golden Delicious. The decayed area was spongy to firm and appeared light brown to brown. On Red Delicious, brown to black specks at lenticels often appeared at the decayed area as the disease advanced. This disease occurred in 23, 26, and 17% of the total grower lots, accounting for approximately 1, 4, and 3% of the total decay in 2003, 2004, and 2005, respectively. In 2004 and 2005, severe losses of fruit were observed in three grower lots of Red Delicious, and their losses were as high as 24%. After 9 months in storage, 48, 48, and 24% of Red Delicious, Golden Delicious, and Fuji that were inoculated in the orchards, respectively, developed symptoms of this disease, and the fungus was reisolated from decayed fruit. Stem-end rot was common on Red Delicious and Golden Delicious, whereas calyx-end rot was common on Fuji. We propose "speck rot" as the name of this disease.

Distribution of Potebniamyces pyri in the U.S. Pacific Northwest and Its Association with a Canker and Twig Dieback Disease of Pear Trees

Winter pears (Pyrus communis) in the United States are produced primarily in the Pacific Northwest. Potebniamyces pyri (anamorph Phacidiopycnis piri) is the causal agent of Phacidiopycnis rot, a recently reported postharvest disease on pears in the United States. Infection of fruit by P. pyri occurs in the orchard, and symptoms develop during storage. P. pyri was observed to be associated with cankers, dead bark, and twig dieback of pear trees. P. pyri was isolated from 40 to 50% of the twig samples exhibiting dieback symptoms from three commercial d'Anjou pear orchards, and 35% of dying bark samples from one orchard. However, little information is available regarding pathogenicity of P. pyri on pear trees. To determine the distribution of P. pyri, dying and dead bark samples were collected from pear orchards in various pear-producing areas in Oregon and Washington, and examined for presence of fruiting bodies (pycnidia or apothecia) of P. pyri. In the orchard, 2-year-old twigs were wounded using a sterile cork borer with or without spraying with a commercial aerosol tissue-freezing product at the wound sites. Wounds were then inoculated with either mycelial plugs from an agar medium or conidial suspensions of P. pyri. In a separate experiment, freshly made pruning wounds were inoculated with conidial suspensions of P. pyri. Canker development was monitored approximately monthly for up to 6 months after inoculation, at which time reisolation of P. pyri was attempted. P. pyri was found to be widespread in the Pacific Northwest. Incidence of trees infected by P. pyri based on presence of viable pycnidia in pear orchards ranged from 0 to 100%. Monthly tree inoculations in the orchard indicated that P. pyri in general did not cause cankers on non-cold-injured, wound-inoculated twigs, but apparently became established on cold-injured, wound-inoculated twigs and caused small cankers. Minor dieback developed on twigs inoculated at pruning wounds. At 6 months after inoculation, P. pyri was recovered from the majority of inoculated twigs. Thus, P. pyri appears to be a weak canker-causing pathogen on pear trees.

Prevalence and Incidence of Phacidiopycnis Rot in d'Anjou Pears in Washington State

Phacidiopycnis rot, caused by Phacidiopycnis piri, is a newly recognized postharvest disease in pear fruit (Pyrus communis cv. d'Anjou) in the United States. To determine the prevalence and incidence of this disease, decayed fruit were sampled during packing and repacking operations from four packinghouses in 2001 and 2002. During March to May (repacking) in 2001, Phacidiopycnis rot was found in packed fruit that were stored in cardboard boxes from 22 of 26 grower lots (orchards), and accounted for 5 to 71% of the total decay. Phacidiopycnis rot, gray mold caused by Botrytis cinerea, and blue mold caused by Penicillium spp. accounted for an average of 34.1, 10.3, and 33.6% of decayed fruit from conventional orchards, respectively; and 22.8, 35.7, and 23.5% of decayed fruit from organic orchards, respectively. During November 2001 to January 2002 (packing), Phacidiopycnis rot was observed in fruit that were stored in field bins before packing from 30 of 33 grower lots, accounting for 18.4% of decayed fruit sampled. During March to May in 2002, Phacidiopycnis rot was responsible for 2 to 68% of decayed fruit sampled from 36 of 39 grower lots. Phacidiopycnis rot, gray mold, and blue mold accounted for an average of 19.6, 26.8, and 37.4% of decayed fruit from conventional orchards, respectively; and 42.2, 25.7, and 8.2% of decayed fruit from organic orchards, respectively. Most Phacidiopycnis rot that occurred in field bins before packing appeared to originate from wound infections; whereas after packing, approximately 60 and 30% of Phacidiopycnis rot originated from stem and calyx infections, respectively. This study indicates that Phacidiopycnis rot should be considered one of the targets for control of postharvest diseases in d'Anjou pears in the region.

A Postharvest Fruit Rot in d'Anjou Pears Caused by Sphaeropsis pyriputrescens sp. nov

During a survey of postharvest diseases in stored pears conducted in the 2001-02 storage season, a new postharvest fruit rot in d'Anjou pears was discovered in Washington State. Symptoms of this disease were stem-end rot, calyx-end rot, and wound-associated rot, which presumably originated from infections of stem, calyx, and wounds on the fruit surfaces, respectively. The decayed area on the fruit was firm or spongy and appeared brown. During the late storage period from March to May 2002, this disease was observed in 19 of 39 lots and accounted for 2 to 21% of all decayed fruit. The causal agent, Sphaeropsis sp., was consistently recovered from decayed fruit with the symptoms described above. Two isolates of the fungus were used for pathogenicity tests on pear fruit. Decay symptoms developed on fruit inoculated with spore suspensions of the fungus on the stem, calyx, and wounds on the fruit surface. The fungus was reisolated from these decayed fruit. The fungus, Sphaeropsis pyriputrescens sp. nov., was characterized and described. On potato dextrose agar (PDA), oatmeal agar, and pear juice agar at 20°C, the fungus grew at mean rates of 21, 15, and 24 mm day^-1 in colony diameter, respectively. On PDA, the fungus formed a circular colony with dense, hyaline hyphae and a few or some aerial mycelia. Colonies appeared light yellow to yellow on 2-week-old PDA cultures. The fungus grew at temperatures from 0 to 25°C, with optimum growth between 15 and 20°C, little or no growth at 30°C, and no growth at 35°C. This is a low-temperature species.

Chlorine Concentration and the Inoculation of Tomato Fruit in Packinghouse Dump Tanks

Chlorine concentrations (pH 6 to 7 and 22 to 27°C) that killed arthrospores (spores) of Geotrichum candidum or sporangioles (spores) of Rhizopus stolonifer, causal agents of sour rot and Rhizopus rot, respectively, in moving water within 30 to 45 s did not prevent these pathogens from inoculating wounded tomatoes (Lycopersicon esculentum) in a water flume containing chlorine and spores. Free chlorine concentrations of 20 or 25 mg/liter were lethal to spores of G. candidum within 30 s in most in vitro tests, whereas spores of R. stolonifer were slightly less sensitive. Wounded tomatoes placed in a flume with free chlorine at 30 mg/liter and then exposed to spores for 1 min developed about 50% less decay incidence during storage at 24°C for 6 days than did fruit exposed to spores and water alone. In the absence of chlorine, incidence averaged 57% (range, 15 to 95%) for R. stolonifer and 38% (range, 17 to 58%) for G. candidum. Sporadic sour rot lesions were observed among fruit that had been treated with free chlorine at 75 mg/liter, whereas chlorine at up to 180 mg/liter failed to completely protect fruit from Rhizopus rot. A water-soluble dye rapidly penetrated wounds on tomato fruit. The dye framed the outlines of cells at the wound surface and appeared to penetrate into a few intercel-lular spaces. Application of 1% sodium hypochlorite decolorized the dye on the wound surface, whereas deposits located below the wound surface remained blue. Thus, spores suspended in moving water can escape the action of chlorine if carried into intercellular spaces by diffusion or by capillary movement of cell sap and water.

Effect of Gaseous Ozone Exposure on the Development of Green and Blue Molds on Cold Stored Citrus Fruit

The effects of gaseous ozone exposure on in vitro growth of Penicillium digitatum and Penicillium italicum and development of postharvest green and blue molds on artificially inoculated citrus fruit were evaluated. Valencia oranges were continuously exposed to 0.3 ± 0.05 ppm(vol/vol) ozone at 5°C for 4 weeks. Eureka lemons were exposed to an intermittent day-night ozone cycle (0.3 ± 0.01 ppm ozone only at night) in a commercial cold storage room at 4.5°C for 9 weeks. Both oranges and lemons were continuously exposed to 1.0 ± 0.05 ppm ozone at 10°C in an export container for 2 weeks. Exposure to ozone did not reduce final incidence of green or blue mold, although incidence of both diseases was delayed about 1 week and infections developed more slowly under ozone. Sporulation was prevented or reduced by gaseous ozone without noticeable ozone phytotoxicity to the fruit. A synergistic effect between ozone exposure and low temperature was observed for prevention of sporulation. The proliferation of spores of fungicide-resistant strains of these pathogens, which often develop during storage, may be delayed, presumably prolonging the useful life of postharvest fungicides. In vitro radial growth of P. italicum, but not of P. digitatum, during a 5-day incubation period at 20°C was significantly reduced by a previous 0.3 ± 0.05 ppm ozone exposure at 5°C for 4 days. Inoculum density did not influence the effect of gaseous ozone on decay incidence or severity on oranges exposed to 0.3 ± 0.05 ppm ozone at 20°C for 1 week. Susceptibility of oranges to decay was not affected by a previous continuous exposure to 0.3 ± 0.05 ppm ozone at 20°C for 1 week. A corona discharge ozone generator was effective in abating ethylene in an empty export container.

Control of Postharvest Blue and Green Molds of Oranges by Hot Water, Sodium Carbonate, and Sodium Bicarbonate

Control of citrus blue mold, caused by Penicillium italicum, was evaluated on artificially inoculated oranges immersed in water at up to 75°C for 150 s; in 2 to 4% sodium carbonate (wt/vol) at 20 or 45°C for 60 or 150 s; or in 1 to 4% sodium bicarbonate at room temperature for 150 s, followed by storage at 20°C for 7 days. Hot water controlled blue mold at 50 to 55°C, temperatures near those that injured fruit, and its effectiveness declined after 14 days of storage. Sodium carbonate and sodium bicarbonate were superior to hot water. Temperature of sodium carbonate solutions influenced effectiveness more than concentration or immersion period. Sodium carbonate applied for 150 s at 45°C at 3 or 4% reduced decay more than 90%. Sodium bicarbonate applied at room temperature at 2 to 4% reduced blue mold by more than 50%, while 1% was ineffective. In another set of experiments, treatments of sodium bicarbonate at room temperature, sodium carbonate at 45°C, and hot water at 45°C reduced blue mold incidence on artificially inoculated oranges to 6, 14, and 27%, respectively, after 3 weeks of storage at 3°C. These treatments reduced green mold incidence to 6, 1, and 12%, respectively, while incidence among controls of both molds was about 100%. When reexamined 5 weeks later, the effectiveness of all, particularly hot water, declined. In conclusion, efficacy of hot water, sodium carbonate, and sodium bicarbonate treatments against blue mold compared to that against green mold was similar after storage at 20°C but proved inferior during long-term cold storage.

Peracetic Acid and Chlorine Dioxide for Postharvest Control of Monilinia laxa in Stone Fruits

The effects of different concentrations of peracetic acid (PAA; 62.5, 125, 250, 500, and 1,000 μg/ml)and chlorine dioxide (ClO₂; 12.5, 25, 50, 100, and 200 μg/ml) on germination of Monilinia laxa conidia were tested. Conidia germination was related to the concentration of chemical product used, as well as duration of treatment. Complete inhibition of germination was observed with PAA at 500 μg/ml after 5 min of contact with conidia and with ClO₂ at 50 μg/ml after 1 min of contact with conidia. The results of in vitro tests were confirmed by inoculation of fruits with treated conidia. The PAA treatment also was effective 1 h after pathogen inoculation but only on plums, for which a 1,000 μg/ml treatment significantly reduced decay incidence by 50%. In a semi-commercial test, pathogen conidia dipped for 20 min in PAA at 250 μg/ml or ClO₂ at 10 μg/ml or for 5 min in PAA at 250 μg/ml were completely inhibited, and no brown rot was observed in inoculated wounded nectarines and plums.