Factors Affecting the Infection of Sweet Cherry (Prunus avium) Fruit by Podosphaera cerasi

Powdery mildew caused by Podosphaera cerasi is the most important fungal disease of sweet cherries in the Pacific Northwest of the United States. In this study, several factors related to disease epidemiology were evaluated. The experiments were conducted to investigate flower susceptibility to P. cerasi infection by in planta and in vitro inoculation. The susceptibility of fruit at various developmental stages was investigated using defined concentrations of P. cerasi conidia. Furthermore, the threshold of conidial concentration required for fruit infection was determined. The pathogen activity during full bloom was limited and not related to fruit disease incidence and severity at harvest. Foliar infections always preceded fruit infections by an average of 42 days during the 3 years of the study. The onset of fruit infection followed, on average, 66 days after full bloom and appeared simultaneously on all susceptible cherry cultivars in the research orchard. Disease symptoms were only observed on fruit in Biologische Bundesanstalt, Bundessortenamt, and Chemical Industry scale 8 (maturity) in all cultivars examined. During this stage, a concentration of 500 conidia/ml was sufficient to cause fruit infection at harvest. Interaction between the inoculation dates and conidial concentration revealed a dependency of disease development on the host stage at the time of inoculation; the younger the fruit, the more conidia are needed to cause disease at harvest. Molecular studies showed a rapid increase in conidia viability at the transition from asymptomatic to the symptomatic disease of fruit. No evidence of ontogenic resistance of fruit to powdery mildew infection was observed.

Integration of metabolomics and existing omics data reveals new insights into phytoplasma-induced metabolic reprogramming in host plants

Phytoplasmas are cell wall-less bacteria that induce abnormal plant growth and various diseases, causing severe economic loss. Phytoplasmas are highly dependent on nutrients imported from host cells because they have lost many genes involved in essential metabolic pathways during reductive evolution. However, metabolic crosstalk between phytoplasmas and host plants and the mechanisms of phytoplasma nutrient acquisition remain poorly understood. In this study, using metabolomics approach, sweet cherry virescence (SCV) phytoplasma-induced metabolite alterations in sweet cherry trees were investigated. A total of 676 metabolites were identified in SCV phytoplasma-infected and mock inoculated leaves, of which 187 metabolites were differentially expressed, with an overwhelming majority belonging to carbohydrates, fatty acids/lipids, amino acids, and flavonoids. Available omics data of interactions between plant and phytoplasma were also deciphered and integrated into the present study. The results demonstrated that phytoplasma infection promoted glycolysis and pentose phosphate pathway activities, which provide energy and nutrients, and facilitate biosynthesis of necessary low-molecular metabolites. Our findings indicated that phytoplasma can induce reprograming of plant metabolism to obtain nutrients for its own replication and infection. The findings from this study provide new insight into interactions of host plants and phytoplasmas from a nutrient acquisition perspective.

Selection and application of antifungal VOCs-producing yeasts as biocontrol agents of grey mould in fruits

Rotting caused by grey mould (Botrytis cinerea) is a concerning disease for numerous crops both pre- and postharvest stages. Application of antagonistic yeasts is a promising strategy for controlling grey mould incidence which could mitigate undesirable consequences of using synthetic fungicides. In this work, a screening for detection of yeasts isolated from figs producers of antifungal volatile organic compounds (VOCs) were performed by confrontation in double dishes systems. Eleven out of 34 yeasts confronted reduced B. cinerea growth parameter in vitro. This reduction was correlated (p ≤ 0.050) with the production of 10 volatile compounds: two acids (acetic acid and octanoic acid), 7 esters (Ethyl propionate, n-Propyl acetate, Isobutyl acetate, 2-methylbutyl acetate, furfuryl acetate, phenylmethyl acetate, 2-phenylethyl acetate) and one ketone (Heptan-2-one). In bases on in vitro assay, Hanseniaspora uvarum 793 was applied to in vivo assays with strawberries and cherries. The reduction of incidence of B. cinerea in strawberries at 7 °C and 25 °C was 54.9 and 72.1% after 6 and 3 days, respectively. The reduction of incidence of B. cinerea in cherries at 7 °C and 25 °C was 48.9 and 45.6% after 5 and 4 days, respectively. These results showed that VOCs produced by Hanseniaspora uvarum 793 are effective in the control of incidence of Botrytis cinerea in fruits, being a potential alternative to chemical fungicide.

Interaction and multi-objective effects of multiple non-thermal treatments of sour cherry juice: pesticide removal, microbial inactivation, and quality preservation

BACKGROUND

The consumption of pesticide-contaminated sour cherries as fruit or juice has become a major health concern, and so the search for alternative processing technologies, such as pulsed electric fields (PEF), ozone (O), and ultrasonication (US) has intensified. The objectives of this experimental study of sour cherry juice were fourfold: (1) to quantify the removal efficiency of new processing technologies (PEF, O, US), and their combinations, for the pesticides chlorpyrifos ethyl, τ-fluvalinate, cyprodinil, pyraclostrobin, and malathion; (2) to detect their impact on physical, bioactive, and sensory properties; (3) to determine their microbial inactivation levels for Escherichia coli O157:H7, Bacillus cereus, Pseudomonas syringae subs. Syringae, and Penicillum expansum; and (4) to jointly optimize multiple responses of physical, quality, and sensory properties, pesticides, and microbial inactivation.

RESULTS

Except for all the O treatments, the physical, bioactive and sensory properties of sour cherry juice were not adversely affected by the treatments. The joint optimization suggested PEF1 (24.7 kV cm^-1 for 327 μs), PEF2 (24.7 kV cm^-1 for 655 μs), PEF2 + O + US, US, and PEF2 + O as the five best treatments. PEF2 + O + US best achieved both pesticide removal and microbial inactivation.

CONCLUSION

PEF2 + O + US provided promising reductions in pesticide and microbial loads. © 2019 Society of Chemical Industry.

Ethyl pyruvate (EP) suppressed post-harvest blue mold of sweet cherry fruit by inhibiting the growth of Penicillium oxalicum

BACKGROUND

The shelf-life of fresh sweet cherry is relatively short due to fungal decay during post-harvest storage. To investigate the effect and the mechanism of action of ethyl pyruvate (EP) against blue mold of sweet cherry fruit caused by Penicillium oxalicum, the spores were treated with 25 mg L^-1 EP. The spore germination rate of P. oxalicum, the integrities of the cell wall and plasma membrane, reactive oxygen species (ROS) and malondialdehyde (MDA) were evaluated.

RESULTS

EP treatment significantly suppressed post-harvest blue mold of sweet cherry fruit. We found that the treatment of 25 mg L^-1 EP significantly suppressed blue mold of post-harvest sweet cherry fruit by directly inhibiting germination and the mycelial growth of P. oxalicum. After co-inoculation with EP for 30 min, the spore germination rate of P. oxalicum was reduced by 83.5%. In addition, the pH of the EP solution was found to affect its antimicrobial activity. After treatment with EP, the cell surface structures of the spores of P. oxalicum were much more incomplete, and higher ROS and MDA values were recorded in the spores.

CONCLUSIONS

The results suggested that EP treatment destroyed the integrities of the cell surface structures and caused oxidative damage of the spores of P. oxalicum. © 2019 Society of Chemical Industry.

Determination of Alternaria Mycotoxins in Fresh Sweet Cherries and Cherry-Based Products: Method Validation and Occurrence

Sweet cherry is susceptible to disease caused by the Alternaria species and produces various Alternaria mycotoxins. Analytical methodologies based on solid-phase extraction (SPE) and LC-MS/MS to simultaneously determine five main Alternaria mycotoxins (tenuazonic acid, 1; alternariol, 2; alternariol methyl ether, 3; altenuene, 4; and tentoxin, 5) in fresh sweet cherries and cherry products were developed and validated. The limits of quantitation (LOQ) of the analytes ranged from 0.002-0.066 μg/kg. The method was successfully applied to 83 fresh cherry and cherry-related product samples. 1 and 5 were the predominant toxins with detection frequencies >50%, followed by 3 (42%), 2 (35%), and 4 (31%). Daily intakes of Alternaria mycotoxins via fresh sweet cherries were assessed preliminarily using the measured concentrations, and consumption data were obtained from a web-based dietary questionnaire ( n = 476). The maximum exposure of 1 and 3 were 4.6 and 16.7 times the threshold of the toxicological concern (TTC) value, respectively.

Comparative genomics of Pseudomonas syringae reveals convergent gene gain and loss associated with specialization onto cherry (Prunus avium)

Genome-wide analyses of the effector- and toxin-encoding genes were used to examine the phylogenetics and evolution of pathogenicity amongst diverse strains of Pseudomonas syringae causing bacterial canker of cherry (Prunus avium), including pathovars P. syringae pv morsprunorum (Psm) races 1 and 2, P. syringae pv syringae (Pss) and P. syringae pv avii. Phylogenetic analyses revealed Psm races and P. syringae pv avii clades were distinct and were each monophyletic, whereas cherry-pathogenic strains of Pss were interspersed amongst strains from other host species. A maximum likelihood approach was used to predict effectors associated with pathogenicity on cherry. Pss possesses a smaller repertoire of type III effectors but has more toxin biosynthesis clusters than Psm and P. syringae pv avii. Evolution of cherry pathogenicity was correlated with gain of genes such as hopAR1 and hopBB1 through putative phage transfer and horizontal transfer respectively. By contrast, loss of the avrPto/hopAB redundant effector group was observed in cherry-pathogenic clades. Ectopic expression of hopAB and hopC1 triggered the hypersensitive reaction in cherry leaves, confirming computational predictions. Cherry canker provides a fascinating example of convergent evolution of pathogenicity that is explained by the mix of effector and toxin repertoires acting on a common host.

Effect of ultrasound on some chemical and microbiological properties of sour cherry juice by response surface methodology

In this study, it is aimed to determine effect of ultrasonication on some chemical and microbiological properties of sour cherry juice by response surface methodology, since ultrasound is known as an alternative method for thermal food processing. Sour cherry juice was sonicated at varying amplitude levels (50, 75, 100%); moderate temperatures (20, 30, 40 ℃); and treatment times of 2, 6, 10 min at a constant frequency of 20 kHz. Different ultrasonication amplitudes, temperatures, and times had no significant effect on pH,°Bx, and titratable acidity. A significant increase in total monomeric anthocyanins was observed as the amplitude level and temperature increased (p < 0.01). An increase in the total phenolics was also obtained as the temperature increased (p < 0.05). The effect of amplitude level on antioxidant capacity of sour cherry juice was also found significant (p < 0.05). Color parameters (L*, a*, b*, C, h) generally increased by increasing temperature, amplitude level, and treatment time. It was determined that Escherichia coli O157:H7 significantly affected by temperature and treatment time (p < 0.05).

PacMYBA, a sweet cherry R2R3-MYB transcription factor, is a positive regulator of salt stress tolerance and pathogen resistance

Plant R2R3-MYB transcription factors play crucial roles in stress responses. We previously isolated a R2R3-MYB homolog from sweet cherry cv. Hong Deng, designated PacMYBA (GenBank accession No. KF974774). To explore the role of PacMYBA in the plant stress response, we heterologously expressed PacMYBA in transgenic Arabidopsis thaliana plants. In a previous study, we demonstrated that PacMYBA is mainly localized to the nucleus and could be induced by abscisic acid (ABA). Analysis of the promoter sequence of PacMYBA revealed that it contains several stress-related cis-elements. QPCR results showed that PacMYBA is induced by salt, salicylic (SA), and jasmonic acid (JA) in sweet cherry leaves. Transgenic Arabidopsis plants heterologously expressing PacMYBA exhibited enhanced salt-tolerance and increased resistance to Pseudomonas syringe pv. tomato (Pst) DC3000 infection. Overexpression of PacMYBA decreased the osmotic potential (OP), increased the free proline content, and increased the peroxidase content in transgenic Arabidopsis plants. Furthermore, overexpression of PacMYBA also affected the expression levels of salt stress- and pathogen defense-related genes in the transgenic plants. These results indicate that PacMYBA is a positive regulator of salt stress tolerance and pathogen resistance.

Effect of phytosanitary irradiation and methyl bromide fumigation on the physical, sensory, and microbiological quality of blueberries and sweet cherries

BACKGROUND

The objective of this study was to determine whether irradiation could serve as a suitable phytosanitary treatment alternative to methyl bromide (MB) fumigation for blueberries and sweet cherry and also to determine the effect of phytosanitary irradiation treatment on survival of Salmonella spp. and Listeria monocytogenes on these fruit. 'Bluecrop' blueberries (Vaccinium corymbosum) and 'Sweetheart' cherries (Prunus avium) were irradiated at 0.4 kGy or fumigated with methyl bromide and evaluated for quality attributes during storage.

RESULTS

Irradiation caused an immediate decrease in firmness of both fruit without further significant change during storage. Fumigated fruit, in contrast, softened by 11-14% during storage. Irradiation did not adversely affect blueberry and cherry shelf-life. MB fumigation did not impact blueberry and cherry quality attributes initially; however, fumigated fruit exhibited greater damage and mold growth than the control and irradiated samples during storage. Irradiation at 400 Gy resulted in a ∼1 log CFU g(-1) reduction in Salmonella spp. and Listeria monocytogenes counts, indicating that this treatment cannot significantly enhance safety.

CONCLUSION

This study indicates that irradiation at a target dose of 0.4 kGy for phytosanitary treatment does not negatively impact blueberry and cherry quality and can serve as an alternative to methyl bromide fumigation. © 2016 Society of Chemical Industry.

Characterization of community structure of culturable endophytic fungi in sweet cherry composite trees and their growth-retarding effect against pathogens

Endophytic fungi have the potential to protect their host plants in stress situations. Characterizing the ecology and complex interaction between these endophytes and their host plants is therefore of great practical importance, particularly in horticultural plants. Among horticultural plants, fruit trees form a special category because of their longevity and because they are composites of rootstock and scion, which often belong to different plant species. Here we present the first characterization of culturable endophytic fungal community of sweet cherry. Samples from the Hungarian cultivar 'Petrus' grafted on 11 different rootstocks were collected in autumn and in spring in a bearing orchard and the dependence of colonization rate and endophyte diversity on rootstock, organ and season was analysed. On the basis of their ITS sequences 26 fungal operational taxonomic units were identified at least down to the genus level. The dominant genus, comprising more than 50% of all isolates, was Alternaria, followed by different Fusarium and Epicoccum species. We observed some organ-specificity amongst endophytes, and organs showed more sizeable differences in colonization rates and endophyte diversity than rootstocks. Most dynamic endophyte populations, strongly influenced by environmental conditions and crop management, were observed in leaves. The potential of selected endophytes to confer protection against Monilinia laxa was also analysed and 7 isolates were found to inhibit the growth of this pathogen in vitro.

A unique ecological niche fosters hybridization of oak-tree and vineyard isolates of Saccharomyces cerevisiae

Differential adaptation to distinct niches can restrict gene flow and promote population differentiation within a species. However, in some cases the distinction between niches can collapse, forming a hybrid niche with features of both environments. We previously reported that distinctions between vineyards and oak soil present an ecological barrier that restricts gene flow between lineages of Saccharomyces cerevisiae. Vineyard isolates are tolerant to stresses associated with grapes while North American oak strains are particularly tolerant to freeze-thaw cycles. Here, we report the isolation of S. cerevisiae strains from Wisconsin cherry trees, which display features common to vineyards (e.g. high sugar concentrations) and frequent freeze-thaw cycles. Genome sequencing revealed that the isolated strains are highly heterozygous and represent recent hybrids of the oak × vineyard lineages. We found that the hybrid strains are phenotypically similar to vineyard strains for some traits, but are more similar to oak strains for other traits. The cherry strains were exceptionally good at growing in cherry juice, raising the possibility that they have adapted to this niche. We performed transcriptome profiling in cherry, oak and vineyard strains and show that the cherry-tree hybrids display vineyard-like or oak-like expression, depending on the gene sets, and in some cases, the expression patterns linked back to shared stress tolerances. Allele-specific expression in these natural hybrids suggested concerted cis-regulatory evolution at sets of functionally regulated genes. Our results raise the possibility that hybridization of the two lineages provides a genetic solution to the thriving in this unique niche.

Freshness maintenance of cherries ready for consumption using convenient, microperforated, bio-based packaging

BACKGROUND

Current consumer demand for high-quality ready-to-eat fresh fruit in convenient bio-based packaging was met utilizing sanitized stem-free sweet cherries and a polylactic acid (PLA) cup with a PLA peelable microperforated lid. The newly developed packaging system was compared with the petroleum-based macroperforated bag currently used for retail.

RESULTS

After 27 days of storage at 1 °C, the PLA package maintained the cherry firmness, compared with a 50% reduction of the controls. No fungal decay was detected in the cherries stored in PLA, while the controls were non-marketable after 21 days. The PLA package allowed minimal weight loss (0.8%), compared with a weight loss of approximately 16% in the controls. Differences in the cherry aroma, color, acidity, soluble solids content, pH and quality index were also caused by the packaging type. A consumer sensory evaluation showed that cherries stored in PLA packages were more acceptable than those of the controls for appearance, texture, flavor and overall acceptability.

CONCLUSION

The new package matched both the consumer demand for high-quality fresh fruit ready for consumption in convenient bio-based packaging and the extended fruit marketability and consumer satisfaction desired by industry.