Screening of core microorganisms in healthy and diseased peaches and effect evaluation of biocontrol bacteria (Burkholderia sp.).

Biological antagonists serve as the most important green alternatives to chemical fungicides, a class of microorganism that inhibits the growth of pathogenic fungi to reduce fruit incidence. In this paper, healthy and diseased peach fruit was selected for amplicon sequencing of the epiphytic microbiota on their surface to obtain a comprehensive understanding. Community structure, diversity and LefSe analysis were performed to screen Acetobacter, Muribaculaceae and Burkholderia as the core bacteria, Mycosphaerella, Penicillium and Alternaria as the core fungi, they showed significant differences and were highly enriched. Two strains fungi (Penicillium K3 and N1) and one strain antagonistic bacteria (Burkholderia J2) were isolated. The in intro test results indicated the bacterial suspension, fermentation broth and volatile organic compounds of antagonistic bacteria J2 were able to significantly inhibit pathogen growth. In vivo experiments, peach was stored at 28 °C for 6 days after different treatments, and samples were taken every day. It was found that Burkholderia J2 enhanced peach resistance by increasing the activities of antioxidant-related enzymes such as SOD, POD, PAL, PPO, GR, MDHAR, and DHAR. The results improved that Burkholderia J2 has great biocontrol potential and could be used as a candidate strain for green control of blue mold.

Sodium alginate coating of Ginkgo biloba leaves extract containing phenylpropanoids as an ecofriendly preserving agent to maintain the quality of peach fruit.

Plant constituents are of great interest in the food processing industry as potential natural preservative agents for controlling foodborne pathogens. In this study, the 95% EtOH/H2 O extract of Ginkgo biloba leaves was separated using polarity extraction solvents with petroleum ether (PE), ethyl acetate (EA), n-butanol (nB), and water (W) by the principle of similarity and compatibility. Through TLC and NMR analysis of these extracts, it can be concluded that the main component of PE extract were organic acids, for EA extract were flavonoids, for nB extract were phenylpropanoids, and water extract were oligosaccharides. Twelve monomer compounds were separated from the extracts to verify the composition of each extraction stage. Results of morphological and molecular identification revealed that Monilinia fructicola and Rhizopus stolonifer were the main fungi causing peach rot. After evaluating the antifungal activity and peach quality of the four extract/sodium alginate coatings, it was found that the n-butanol extract/sodium alginate coating containing phenylpropanoids had the lowest decay index and the best preservation effect, providing a sustainable alternative to reduce the harm to the environment of synthetic preservatives. PRACTICAL APPLICATION: The abuse of synthetic preservatives poses a threat to the ecological environment and physical health. Therefore, this study developed sodium alginate coating of Ginkgo biloba leaves extract containing phenylpropanoids, which has good effects on the preservation of peaches. The agent is a promising environmentally friendly alternative for synthetic preservatives.

Stone fruit phenolic and triterpenoid compounds modulate gene expression of Monilinia spp. in culture media.

Phenolic and triterpenoid compounds are essential components in stone fruit skin and flesh tissues. They are thought to possess general antimicrobial activity. However, regarding brown rot disease, investigations were only confined to a limited number of phenolics, especially chlorogenic acid. The activity of triterpenoids against Monilinia spp., as an essential part of the peach cuticular wax, has not been studied before. In this work, the anti-fungal effect of some phenolics, triterpenoids, and fruit surface compound (FSC) extracts of peach fruit at two developmental stages were investigated on Monilinia fructicola and Monilinia laxa characteristics during in vitro growth. A new procedure for assaying anti-fungal activity of triterpenoids, which are notoriously difficult to assess in vitro because of their hydrophobicity, has been developed. Measurements of colony diameter, sporulation, and germination of second-generation conidia were recorded. Furthermore, the expression of twelve genes of M. fructicola associated with germination and/or appressorium formation and virulence-related genes was studied relative to the presence of the compounds. The study revealed that certain phenolics and triterpenoids showed modest anti-fungal activity while dramatically modulating gene expression in mycelium of M. fructicola on culture medium. MfRGAE1 gene was overexpressed by chlorogenic and ferulic acids and MfCUT1 by betulinic acid, at 4- and 7- days of mycelium incubation. The stage II FSC extract, corresponding to the period when the fruit is resistant to Monilinia spp., considerably up-regulated the MfLAE1 gene. These findings effectively contribute to the knowledge of biochemical compounds effects on fungi on in vitro conditions.

Effect of peach trichome removal on post-harvest brown rot and on the fruit surface microbiome.

Postharvest peaches undergo rapid soft ripening and are susceptible to fungal diseases, which often result in severe losses during storage. The peach epidermis contains trichomes that form a specific structure on the peach surface. However, the relationship between trichomes and postharvest disease and involved mechanisms has not been well studied. In this study, the removal of trichomes reduced the disease incidence of peach brown rot caused by Monilinia fructicola. Cryo-scanning electron microscope observations showed that the fungal hyphae were found attached to the surface of trichomes. The fungal and bacterial communities on the peach surface at 0 d and 6 d were obtained by amplicon sequencing technology. Fungal communities on the peach surface contained a total of 1089 amplicon sequence variants (ASVs), which were demarcated into eight fungal phyla, 25 classes, 66 orders, 137 families, and 228 genera. The bacterial communities contained 10,821 ASVs assigned to 25 phyla, 50 classes, 114 orders, 220 families, and 507 genera. Higher bacterial diversity than fungal diversity was recorded on the peach epidermis. Trichome removal changed the microbial diversity and community on the peach surface. Compared with peach epidermis samples, the peach epidermis excluded trichomes samples contained similar fungal alpha diversity but significantly lower bacterial diversity. Seventeen different fungal genera and twenty-eight different bacterial genera were identified between peach trichome and peach epidermis excluded trichomes samples. The fungal and bacterial diversity on the peach epidermis showed a decreasing trend during storage. Beta diversity analysis revealed that the microbial communities of the peach epidermis and trichomes show different change trends between 0 d and 6 d. Trichome removal decreased relative abundance of Monilinia spp. and increased relative abundance of potential yeast and bacterial biocontrol agents. This study suggested that trichomes might modulate the microbial communities on fruit surfaces, and trichome removal technology after harvest might be developed to control peach postharvest decay.

Development of natamycin-loaded zein-casein composite nanoparticles by a pH-driven method and application to postharvest fungal control on peach against Monilinia fructicola.

This work fabricated natamycin-loaded zein-casein nanoparticles (N-Z/C NPs) by a pH-driven approach and applied to control postharvest peach brown rot caused by Monilinia fructicola. When casein and phosphoric acid were used as a stabilizer and neutralizing acid, respectively, NPs with mean particle sizes < 100 nm and zeta-potentials < -30 mV could be obtained. The NPs could increase the aqueous dispersibility of natamycin and showed high stability against environmental changes, which could be attributed to both hydrophobic stacking and hydrogen bonds between natamycin and zein. Besides, the effects of N-Z/C NPs on the storage of peach were assessed in vitro and in vivo. Nanoencapsulation did not affect the antifungal activities of natamycin. The NPs with 20 and 80 µg/mL of natamycin could basically inhibit the spore germination and mycelial growth of M. fructicola, respectively. The N-Z/C NPs coatings exhibited better results than natamycin in controlling of peach brown rot.

The role of essential oils in maintaining the postharvest quality and preservation of peach and other fruits.

Fruits are highly susceptible to postharvest losses induced majorly by postharvest diseases. Peach are favored by consumers because of their high nutritional value and delicious taste. However, it was easy to be affected by fungal infection. The current effective method to control postharvest diseases of fruits is to use chemical fungicides, but these chemicals may cause adverse effects on human health and the residual was potentially harmful to nature and the environment. So, it is especially important to develop safe, non-toxic, and highly effective strategies for the preservation of the fruits. Essential oil, as a class of the natural bacterial inhibitor, has been proven to exhibit strong antibacterial activity, low toxicity, environmental friendliness, and induce fruit resistance to microorganism, which could be recognized as one of the alternatives to chemical fungicides. This paper reviews the research progress of essential oils (Eos) in the storage and preservation of fruits, especially the application in peach, as well as the application in active packaging such as edible coatings, microcapsules, and electrospinning loading. Electrospinning can prepare a variety of nanofibers from different viscoelastic polymer solutions, and has broad application prospects. The paper especially summarizes the application of the new Eos technology on peach. The essential oil with thymol, eugenol, and carvacrol as the main components has a better inhibitory effect on the postharvest disease of peaches, and can be further applied. PRACTICAL APPLICATIONS: As an environmentally friendly natural antibacterial agent, essential oil can be used as a substitute for chemical preservatives to keep fruits fresh. This paper summarizes the different preservation methods of essential oils for fruits, and especially summarizes the different preservation methods of essential oils for peaches after harvesting, as well as their inhibitory effects on pathogenic fungi. It could provide ideas for preservation of fruits and vegetables by essential oils.

Ppe.XapF: High throughput KASP assays to identify fruit response to Xanthomonas arboricola pv. pruni (Xap) in peach.

Bacterial spot, caused by Xanthomonas arboricola pv. pruni (Xap), is a serious peach disease with symptoms that traverse severe defoliation and black surface pitting, cracking or blemishes on peach fruit with global economic impacts. A management option for control and meeting consumer demand for chemical-free, environmentally friendly fruit production is the development of resistant or tolerant cultivars. We developed simple, accurate, and efficient DNA assays (Ppe.XapF) based on SNP genotyping with KASP technology to quickly test for bacterial spot resistance alleles in peach fruit that allows breeders to cull seedlings at the greenhouse stage. The objective of this research was to validate newly developed DNA tests that target the two major QTLs for fruit resistance in peach with diagnostic utility in predicting fruit response to bacterial spot infection. Our study confirms that with only two Ppe.XapF DNA tests, Ppe.XapF1-1 and Ppe.XapF6-2, individuals carrying susceptible alleles can be identified. Use of these efficient and accurate Ppe.XapF KASP tests resulted in 44% reduction in seedling planting rate in the Clemson University peach breeding program.

Paenibacillus caui sp. nov., a nitrogen-fixing species isolated from the rhizosphere soil of a peach tree.

A nitrogen-fixing, endospore-forming, motile, rod-shaped, facultative aerobic bacterium, designated 81-11T, was isolated from rhizosphere soil of a peach tree collected from Handan, Hebei, PR China. From the comparison of 16S rRNA gene sequence, the strain is most closely related to Paenibacillus phoenicis DSM 27463T (96.9 %) and Paenibacillus faecis DSM 23593T (96.7 %). The genome size of strain 81-11T was 4.4 Mb, comprising 4879 predicted genes with a DNA G+C content of 50.0 mol%. The average nucleotide identity values of genome sequences between the novel isolate and the type strains of related species P. phoenicis DSM 27463T and P. faecis DSM 23593T were 71.8 and 72.1 %, respectively. The major cellular fatty acids were anteiso-C15 : 0(47.8 %), iso-C16 : 0 (15.5 %) and iso-C15 : 0 (13.0 %). Menaquinone-7 was the major respiratory quinone. The polar lipids contained phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, aminophospholipid, aminoglycopid, unknown polar lipids and unidentified aminophosphoglycolipid. Based on phylogenetic, genomic and phenotypic characteristics, strain 81-11T was classified as a novel species within the genus Paenibacillus, for which the name Paenibacillus caui sp. nov. is proposed. The type strain of Paenibacillus caui is 81-11T (=JCM 34618T=CGMCC 1.18907T).

Rapid Detection of Peach Shoot Blight Caused by Phomopsis amygdali Utilizing a New Target Gene Identified from Genome Sequences Within Loop-Mediated Isothermal Amplification.

Peach shoot blight (PSB), caused by Phomopsis amygdali, is a serious threat to the healthy development of the peach industry and leads to 30 to 50% damage to peach production in southern China. In this study, loop-mediated isothermal amplification (LAMP) technology was used to detect the P. amygdali target of a gene of GME6801 that was unique in the whole genome of the pathogen compared with that of Diaporthe (Phomopsis) longicolla TWH P74, Fusarium graminearum PH-1, Colletotrichum gloeosporioides SMCG1 and Magnaporthe oryzae 70-15. Blast comparison of this gene sequence in NCBI database showed that no homologous sequences were found. Therefore, the gene sequence of GME6801 was used to design two pairs of LAMP primers and one pair of PCR primers. The results showed that both primer sets were specific to the 15 strains of P. amygdali, and the other 15 fungal strains presented negative reactions, similar to the control. In addition, 50 pg of genomic DNA of P. amygdali in a 25-µl reaction system could be detected by LAMP assay, which was 100 times more sensitive than PCR. Furthermore, the GME6801 LAMP assay was used to detect artificially inoculated twigs of the pathogen, disease twigs within significantly symptomatic PSB in the fields, and healthy twigs in the same orchard, with detection rates of 100, 75, and 20.8%, respectively. However, detection rates of conventional PCR were separately 100, 62.5, and 16.7%. The results indicated that GME6801-based LAMP could be used for P. amygdali detection as its specificity, sensitivity, and simplicity. This study provides a rapid experimental basis for the identification and prediction of P. amygdali that causes PSB and is beneficial for precise prevention and control of the disease.

Copper Tolerance in Xanthomonas arboricola pv. pruni in South Carolina Peach Orchards.

Bacterial spot of peach, caused by Xanthomonas arboricola pv. pruni, causes yield loss every year in southeastern U.S. peach orchards. Management is mainly driven by season-long applications of copper-based products, site location, and choice of cultivar. Although tolerance to copper has not been reported in X. arboricola pv. pruni in the United States, adaptation of populations from frequent use is a concern. We collected X. arboricola pv. pruni from shoot cankers, leaves, and fruit of cultivar O'Henry over 2 years from three conventional farms and one organic farm in South Carolina, one orchard per farm. The four farms had been using copper extensively for years to control bacterial spot. X. arboricola pv. pruni was isolated from four canker types (bud canker, tip canker, nonconcentric canker, and concentric canker) in early spring (bud break), as well as from leaf and fruit tissues later in the season at the phenological stages of pit hardening and final swell. X. arboricola pv. pruni was most frequently isolated from cankers of the organic farm (24% of the cankers) and most isolates (45%) came from bud cankers. X. arboricola pv. pruni isolates were assessed for sensitivity to copper using minimal glucose yeast agar and nutrient agar amended with 38 µg/ml or 51 µg/ml of Cu2+. Two phenotypes of copper tolerance in X. arboricola pv. pruni were discovered: low copper tolerance (LCT; growth up to 38 µg/ml Cu2+) and high copper tolerance (HCT; growth up to 51 µg/ml Cu2+). A total of 26 (23 LCT and 3 HCT) out of 165 isolates in 2018 and 32 (20 LCT and 12 HCT) out of 133 isolates in 2019 were tolerant to copper. Peach leaves on potted trees were sprayed with copper rates typically applied at the stages of delayed dormancy (high rate; 2,397 µg/ml Cu2+), shuck split (medium rate; 599 µg/ml Cu2+), and during summer cover sprays (low rate; 120 µg/ml Cu2+), and subsequently inoculated with sensitive, LCT, and HCT strains. Results indicated that the low and medium rates of copper reduced bacterial spot incidence caused by the sensitive strain but not by the LCT and HCT strains. This study confirms existence of X. arboricola pv. pruni tolerance to copper in commercial peach orchards in the southeastern United States, and suggests its contribution to bacterial spot development under current management practices.

Production of Alternaria Toxins in Yellow Peach (Amygdalus persica) upon Artificial Inoculation with Alternaria alternate.

The yellow peach (Amygdalus persica), an important fruit in China, is highly susceptible to infection by Alternaria sp., leading to potential health risks and economic losses. In the current study, firstly, yellow peaches were artificially inoculated with Alternariaalternate. Then, the fruits were stored at 4 °C and 28 °C to simulate the current storage conditions that consumers use, and the Alternaria toxins (ATs) contents from different parts of the fruits were analyzed via ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS). The results showed that the growth of A. alternate and the ATs production were dramatically affected by the storage temperature. At 28 °C, the fungi grew rapidly and the lesion diameter reached about 4.0 cm within 15 days of inoculation, while, at 4 °C, the fungal growth was noticeably inhibited, with no significant change in the lesion diameter. To our surprise, high contents of ATs were produced under both storage conditions even though the fungal growth was suppressed. With an increase in the incubation time, the amounts of ATs showed a steady tendency to increase in most cases. Remarkably, alternariol monomethyl ether (AME), alternariol (AOH), and tenuazonic acid (TeA) were detected in the rotten tissue and also in the surrounding tissue, while a large amount of TeA could also be found in the healthy tissue. To the best of our knowledge, this is the first report regarding the production of ATs by the infection of Alternaria sp. in yellow peach fruits via artificial inoculation under regulated conditions, and, based on the evidence herein, it is recommended that ATs be included in monitoring and control programs of yellow peach management and food safety administration.

Specialized 16SrX phytoplasmas induce diverse morphological and physiological changes in their respective fruit crops.

The host-pathogen combinations-Malus domestica (apple)/`Candidatus Phytoplasma mali´, Prunus persica (peach)/`Ca. P. prunorum´ and Pyrus communis (pear)/`Ca. P. pyri´ show different courses of diseases although the phytoplasma strains belong to the same 16SrX group. While infected apple trees can survive for decades, peach and pear trees die within weeks to few years. To this date, neither morphological nor physiological differences caused by phytoplasmas have been studied in these host plants. In this study, phytoplasma-induced morphological changes of the vascular system as well as physiological changes of the phloem sap and leaf phytohormones were analysed and compared with non-infected plants. Unlike peach and pear, infected apple trees showed substantial reductions in leaf and vascular area, affecting phloem mass flow. In contrast, in infected pear mass flow and physicochemical characteristics of phloem sap increased. Additionally, an increased callose deposition was detected in pear and peach leaves but not in apple trees in response to phytoplasma infection. The phytohormone levels in pear were not affected by an infection, while in apple and peach trees concentrations of defence- and stress-related phytohormones were increased. Compared with peach and pear trees, data from apple suggest that the long-lasting morphological adaptations in the vascular system, which likely cause reduced sap flow, triggers the ability of apple trees to survive phytoplasma infection. Some phytohormone-mediated defences might support the tolerance.

Efficacy of commercial overhead washing and waxing systems on the microbiological quality of fresh peaches.

Overhead spray washing and waxing systems (WWS) are used commercially to reduce the risk of microbial contamination and improve the quality of fresh produce during packing. This study evaluated the microbiological quality of overhead spray water and spent peach wash water, as well as fresh peaches before and after they pass the WWS. Pre- and post-washed/waxed peach samples (n = 192) and overhead spray water and spent peach wash water samples (n = 54) were collected several times over the course of a processing day in three packing facilities located in the state of Georgia. Populations of total aerobes (TA), yeasts and molds (YM), and coliforms (TC) and the presence of thermotolerant coliforms (TTC) and enterococci (EC) were measured in collected samples. The average TA and TC counts and the incidences of TTC and EC were significantly higher (P < 0.05) on peach samples collected after the WWS compared to those collected before the WWS. Counts and incidences of TA, YM, and TC in spent peach wash water were significantly higher than in the overhead spray water where neither TTC nor EC was detected. Results suggest that the commercial washing and waxing systems had little effect in improving the microbiological quality of fresh peaches.

Using essential oils to control diseases in strawberries and peaches.

Strawberry and peach crops are of great economic and social importance, mainly due to the added value and income generation for small and medium producers in different regions of Brazil. Some fungal diseases can compromise the final profitability of production, such as those caused by Colletotrichum sp., Botrytis cinerea and Monilinia fructicola fungi. The control of these pathogens mainly occurs through fungicides, which has been generating concern for consumers, as well as biological imbalance and environmental contamination. The need for new alternatives for disease control has been leading to more research being conducted on essential oils. Our scientific questions were based on a compilation of experiments which revealed the efficiency of essential oils in disease control. With the purpose of evaluating the fungicidal activity of Aloysia citriodora, Cymbopogon winterianus, Lippia alba and Ocimum americanum essential oils on the control of fungi, such as Colletotrichum sp., Botrytis cinerea and Monilinia fructicola in vitro and in the post-harvest of fruits, this work was developed at the Federal University of Santa Maria, Frederico Westphalen county (Rio Grande do Sul state), Brazil, from 2016 to 2018. The following evaluations were done: (i) characterization of essential oil doses in vitro for controlling Colletotrichum sp., Botrytis cinerea and Monilinia fructicola fungi, and (ii) determination of the minimum inhibitory concentration (Ω, mL/L) of essential oils in post-harvest of strawberries and peaches. All essential oils have high fungicidal activity in vitro experiments. The A. citriodora, L. alba and O. americanum essential oils had a satisfactory effect for post-harvest controlling of Colletotrichum sp. C. winterianus and O. americanum. The essential oils promoted satisfactory post-harvest control of Botrytis cinerea in strawberries. All essential oils have high fungitoxicity against Monilinia fructicola in vitro and post-harvest, highlighting the greater efficiency of A. citriodora essential oil in peaches. The essential oils present high fungitoxicity for controlling diseases in strawberries and peaches, presenting high potential performance for formulating commercial fungicide.

Antifungal activity screening for mint and thyme essential oils against Rhizopus stolonifer and their application in postharvest preservation of strawberry and peach fruits.

AIMS: With a goal to identify specific essential oils that can control postharvest Rhizopus rot on strawberry and peach fruits, we performed screening for 26 essential oils based on their antifungal activity against Rhizopus stolonifer in vitro and investigated the underlying mechanism. METHODS AND RESULTS: Mentha spicata (Ms), Mentha piperita (Mp), Thymus vulgaris CT carvacrol (Tc) and Thymus vulgaris CT thymol (Tt) exhibited strong inhibition on R. stolonifer growth in the screening. These essential oils increased plasma membrane permeability of R. stolonifer and resulted in the outflow of intercellular electrolyte, nucleic acid, protein and soluble sugar. Morphology of R. stolonifer mycelia was greatly altered by these essential oils. Hyphae treated by these essential oils exhibited high accumulation of superoxide anion and malonaldehyde. Combination of these essential oils in commercial package reduced Rhizopus rot on strawberry and peach fruits, with Mp showing the strongest efficiency. CONCLUSION: Ms, Mp, Tc and Tt essential oils inhibited R. stolonifer growth by targeting its plasma membrane and reduced Rhizopus rot on strawberry and peach fruits. SIGNIFICANCE AND IMPACT OF THE STUDY: This study provides potential applications of natural plant extract, as alternatives to tradition fungicides, to control postharvest decay on fruits and vegetables.

Functional roles of LaeA, polyketide synthase, and glucose oxidase in the regulation of ochratoxin A biosynthesis and virulence in Aspergillus carbonarius.

Aspergillus carbonarius is the major producer of ochratoxin A (OTA) among Aspergillus species, but the contribution of this secondary metabolite to fungal virulence has not been assessed. We characterized the functions and addressed the roles of three factors in the regulation of OTA synthesis and pathogenicity in A. carbonarius: LaeA, a transcriptional factor regulating the production of secondary metabolites; polyketide synthase, required for OTA biosynthesis; and glucose oxidase (GOX), regulating gluconic acid (GLA) accumulation and acidification of the host tissue during fungal growth. Deletion of laeA in A. carbonarius resulted in significantly reduced OTA production in colonized nectarines and grapes. The ∆laeA mutant was unable to efficiently acidify the colonized tissue, as a direct result of diminished GLA production, leading to attenuated virulence in infected fruit compared to the wild type (WT). The designed Acpks-knockout mutant resulted in complete inhibition of OTA production in vitro and in colonized fruit. Interestingly, physiological analysis revealed that the colonization pattern of the ∆Acpks mutant was similar to that of the WT strain, with high production of GLA in the colonized tissue, suggesting that OTA accumulation does not contribute to A. carbonarius pathogenicity. Disruption of the Acgox gene inactivated GLA production in A. carbonarius, and this mutant showed attenuated virulence in infected fruit compared to the WT strain. These data identify the global regulator LaeA and GOX as critical factors modulating A. carbonarius pathogenicity by controlling transcription of genes important for fungal secondary metabolism and infection.

Scrutinising the relationship between major physiological and compositional changes during 'Merrill O'Henry' peach growth with brown rot susceptibility.

In the present work, the major physiological and compositional changes occurring during 'Merrill O'Henry' peach growth and its relationship with susceptibility to three strains of Monilinia spp. at 49, 77, 126 and 160 days after full bloom were explored. Results of disease incidence indicated wide differences among phenological stages, being 49 and 126 days after full bloom the moment when peaches showed significantly lower susceptibility to brown rot (40 and 23% of rotten fruit, respectively, for strain ML8L). Variation in brown rot susceptibility among different growth stages was also strain-dependent. Lower fruit susceptibility to ML8L at 49 and 126 was accompanied by noticeable changes in the fruit ethylene and respiration patterns, and also in sugars and organic acids content. By employing a partial least squares regression model, a strong negative relationship between citric acid, and a positive association of ethylene with peach susceptibility to Monilinia spp. at diverse phenological stages were observed. The results obtained herein highlight that the content of certain compounds such as citrate, malate and sucrose; the respiratory activity and the fruit ethylene production may mediate in a coordinated manner the fruit resistance to Monilinia spp. at different phenological stages of peach fruit.

Ethylene biosynthesis and response factors are differentially modulated during the interaction of peach petals with Monilinia laxa or Monilinia fructicola.

Monilinia spp. may infect stone fruit at any growth stage, although susceptibility to brown rot depends on both host properties and climatological conditions. This said, no studies deciphering the host response in the interaction between peach blossoms and Monilinia spp. are yet available. This study presents an in-depth characterization of the role of ethylene in the interaction of 'Merrill O'Henry' peach petals (Prunus persica (L.) Batch) with Monilinia laxa and M. fructicola. We investigated the physiological responses of the host and the fungi to the application of ethylene and 1-methylcyclopropene (1-MCP) as well as the molecular patterns associated with the biosynthetic and ethylene-dependent responses during the interaction of both Monilinia species with the host. The incidence of both species was differentially affected by 1-MCP and ethylene; M. laxa was favoured by the enhanced host ethylene production associated with the treatments whereas M. fructicola reduced its infection capacity. Such differences were host-dependent as treatments did not affect growth or colony morphology of Monilinia spp. Besides, host ethylene production was altered in M. laxa inoculated petals, either by the fungus or the host itself. Molecular analysis revealed some important ERFs that could be involved in the different ability of both species to activate a cascade response of peach petals against these pathogens.

Redox status regulates subcelluar localization of PpTGA1 associated with a BABA-induced priming defence against Rhizopus rot in peach fruit.

This study attempted to characterize the involvement of a change in the redox status and subcellular localization in the BABA-induced priming resistance of peach fruit against Rhizopus rot. Specifically, 50 mM BABA primed the peaches for the enhanced disease resistance against R. stolonifer, as demonstrated by suppression of the disease development upon pathogen challenge accompanied by the clearly elevated level of TGA transcription factor (PpTGA1) and NPR1 gene (PpNPR1). In addition, the BABA elicitation enhanced the activities of a series of critical enzymes in the PPP and AsA-GSH cycle, and eventually promoted the NADPH and GSH pools, which altered the intracellular redox state towards a highly reductive condition. Additionally, PpTGA1-GFP was localized in the cytoplasm in the absence of BABA treatment or R. stolonifer inoculation, while BABA elicitation plus R. stolonifer inoculation caused PpTGA1-GFP to specifically translocate to the nucleus, where it interacted with PpNPR1 and regulated the positive expression of PR genes. Therefore, the observations implied that BABA could promote the reduction of the redox state, resulting in the translocation of PpTGA1 to the nucleus, which was a prerequisite for the induction of a priming defence against Rhizopus rot in peach.

Survival of a serotype 4b strain and a serotype 1/2a strain of Listeria monocytogenes, isolated from a stone fruit outbreak investigation, on whole stone fruit at 4 °C.

In the summer of 2014, a multistate outbreak of listeriosis associated with contaminated stone fruit (peach and nectarine) was reported. A serotype 4b variant Listeria monocytogenes (Lm) strain of singleton Sequence Type (ST) 382 was isolated from clinical samples and stone fruit associated with the outbreak. A serotype 1/2b Lm strain of ST5, Clonal Complex 5 was isolated only from outbreak-associated stone fruit, not from clinical samples. Here we investigated the fate of the serotype 4b and 1/2b strains, at two inoculation levels (high level at 3.7 logCFU/fruit and low level at 2.7 logCFU/fruit), on the surfaces of white peach, yellow peach and yellow nectarine stored at 4 °C for 26 days. After rinsing the fruits, we determined the Lm levels in the rinsates and on the peels. We enumerated Lm using a direct plating method and compared two chromogenic agars. The Lm populations rapidly declined in the first 3 days and then declined more slowly until Day 19/21. The maximum decline was 1.6 logCFU/fruit on yellow peach inoculated with serotype 4b at high level. For fruits inoculated with high-level Lm, the lowest level of Lm (1.7 logCFU/fruit) was observed on for white peach inoculated with serotype 1/2b, and the highest level of Lm (2.6 logCFU/fruit) on Day 19/21 was observed on yellow peach inoculated with the serotype 1/2b strain. For fruits inoculated with low-level Lm, the lowest level of Lm (1.3 logCFU/fruit) was observed on yellow nectarine inoculated with either the serotype 4b or 1/2b strain, and the highest level of Lm (1.7 logCFU/fruit) on Day 19/21 was observed on yellow peach inoculated with ST382. The D-values ranged from 15 days to 28 days. Lm remained viable until the end of storage (Day 26), but the levels were not significantly different from those on Day 19/21. The types of stone fruit and Lm strain did not significantly affect the survival of Lm. These results demonstrate that contaminated stone fruit can carry a potential risk for causing listeriosis in susceptible populations. Comparison of direct plating results using two chromogenic agars showed that RAPID' L. mono and Agar Listeria Ottavani & Agosti performed equivalently for enumerating Lm on stone fruit. The fruit rinsing recovered 80% to 84% of Lm from fruit surfaces.