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.

Endophytic Bacillus subtilis P10 from Prunus cerasifera as a biocontrol agent against tomato Verticillium wilt / Bacillus subtilis P10 endofítico de Prunus cerasifera como agente de biocontrole contra murcha de Verticillium de tomate

Endophytic bacteria serve key roles in the maintenance of plant health and growth. Few studies to date, however, have explored the antagonistic and plant growth-promoting (PGP) properties of Prunus cerasifera endophytes. To that end, we isolated endophytic bacteria from P. cerasifera tissue samples and used a dual culture plate assay to screen these microbes for antagonistic activity against Verticillium dahliae, Botryosphaeria dothidea, Fusarium oxysporum, F. graminearum, and F. moniliforme. Of the 36 strains of isolated bacteria, four (strains P1, P10, P16, and P20) exhibited antagonistic effects against all five model pathogens, and the P10 strain exhibited the strongest antagonistic to five pathogens. This P10 strain was then characterized in-depth via phenotypic assessments, physiological analyses, and 16s rDNA sequencing, revealing it to be a strain of Bacillus subtilis. Application of a P10 cell suspension (1×108 CFU/mL) significantly enhanced the seed germination and seedling growth of tomato in a greenhouse setting. This P10 strain further significantly suppressed tomato Verticillium wilt with much lower disease incidence and disease index scores being observed following P10 treatment relative to untreated plants in pot-based experiments. Tomato plants that had been treated with strain P10 also enhanced defense-related enzymes, peroxidase, superoxide dismutase, and catalase activity upon V. dahliae challenge relative to plants that had not been treated with this endophytic bacterium. The results revealed that the P10 bacterial strain has potential value as a biocontrol agent for use in the prevention of tomato Verticillium wilt.

As bactérias endofíticas desempenham papel fundamental na manutenção da saúde e do crescimento das plantas. Poucos estudos até o momento, no entanto, exploraram as propriedades antagônicas e promotoras de crescimento de plantas (PGP) de endófitos de Prunus cerasifera. Para esse fim, isolamos bactérias endofíticas de amostras de tecido de P. cerasifera e usamos um ensaio de placa de cultura dupla para rastrear esses micróbios quanto à atividade antagonista contra Verticillium dahliae, Botryosphaeria dothidea, Fusarium oxysporum, F. graminearum e F. moniliforme. Das 36 cepas de bactérias isoladas, quatro (cepas P1, P10, P16 e P20) exibiram efeitos antagônicos contra todos os cinco patógenos modelo, e a cepa P10 exibiu o antagonista mais forte para cinco patógenos. Essa cepa P10 foi então caracterizada em profundidade por meio de avaliações fenotípicas, análises fisiológicas e sequenciamento de rDNA 16s, revelando ser uma cepa de Bacillus subtilis. A aplicação de uma suspensão de células P10 (1 × 108 UFC / mL) aumentou significativamente a germinação das sementes e o crescimento das mudas de tomate em casa de vegetação. Essa cepa P10 suprimiu ainda mais a murcha de Verticillium do tomate com incidência de doença muito menor e pontuações de índice de doença sendo observadas após o tratamento com P10 em relação a plantas não tratadas em experimentos baseados em vasos. As plantas de tomate que foram tratadas com a cepa P10 também aumentaram as enzimas relacionadas à defesa, peroxidase, superóxido dismutase e atividade da catalase após o desafio de V. dahliae em relação às plantas que não foram tratadas com essa bactéria endofítica. Os resultados revelaram que a cepa bacteriana P10 tem valor potencial como agente de biocontrole para uso na prevenção da murcha de Verticillium em tomate.

Random forest analysis reveals taxa predictive of Prunus replant disease in peach root microbiomes.

Successive plantings of Prunus species produce suboptimal growth and yield in many California soils due to a poorly understood soilborne disease complex, Prunus replant disease (PRD). We explored the hypothesis that PRD is mediated by microbial taxa in roots of Nemaguard peach, a rootstock for almond and other stone fruits. In a greenhouse bioassay, portions of 10 replant soils were treated with fumigation or pasteurization or left untreated as a control before being planted with peach seedlings. Ten weeks after planting, seedlings were considered PRD-affected if their top fresh weights in the control were significantly reduced, compared to the weights in pasteurization and fumigation treatments; plants with equivalent top weights in all treatments were considered to be non-affected. The roots were washed from the soil, frozen, extracted for total DNA, and used for metabarcoding of rRNA gene amplicons from bacteria, fungi, and oomycetes. High-throughput amplicon sequencing revealed that root microbial community shifts resulted from preplant treatments, and specific taxa were associated with PRD induction among controls. Random forest (RF) analysis discriminated effectively between PRD-affected and non-affected root communities. Among the 30 RF top-ranked amplicon sequence variant (ASV) predictors, 26 were bacteria, two were oomycetes, and two were fungi. Among them, only Streptomyces scabiei, Steroidobacter denitrificans, Streptomyces bobili, and Pythium mamillatum had root abundances ≥5% that were either associated positively (former two ASVs) or negatively (latter two) with PRD. Thus, our findings were consistent with microbial mediation of PRD in roots and suggested taxa that may be involved in the mediation.

Effect of Different Sterilization Methods on the Microbial and Physicochemical Changes in Prunus mume Juice during Storage.

This study evaluated the pasteurization (P), ozone (O3), ultrasonic (US), and high-hydrostatic-pressure (HHP) sterilization approaches for processing of Prunus mume regarding browning factors and microorganisms, compared with non-sterilization (control check, CK) treatment. The microorganisms (total bacterial count and fungi and yeast count) in the juice were identified after different sterilization techniques, while the quality parameter changes (degree of browning, color measurements, total phenolic content, reducing sugar, ascorbic acid, 5-hydroxymethyl furaldehyde (5-HMF), amino acid nitrogen, total soluble solids (TSS), pH value) were investigated. The results indicate that P and HHP treatment reduced non-enzymatic browning while substantially impacting the color measurements, TSS, and pH, while the sterilization effect was remarkable, with a rate exceeding 90%. Furthermore, the Prunus mume juices treated with P and HHP sterilization were used as the objects, and the CK group was used as the control group. They were placed at 4 °C, 25 °C and 37 °C, respectively, and stored in dark for 15 d. Sampling and determination were carried out on 0, 3, 6, 9, 12, and 15 d, respectively. M-&-Y (molds and yeasts) were not detected in the late storage period, and no obvious microbial growth was observed during storage, indicating that P and HHP treatments could ensure the microbial safety of Prunus mume juice. P- and HHP- treated Prunus mume juice has better quality and low temperature storage is beneficial for maintaining the quality of Prunus mume juice. Therefore, P treatment or HHP treatment combined with low temperature storage could achieve a more ideal storage effect. Overall, this study conclusively established that P and HHP methods were suitable for sterilizing Prunus mume juice. These techniques minimally affected overall product quality while better maintaining the quality parameters than the untreated juice samples and those exposed to O3 and US treatment.

Evaluation of Dissipation Behavior, Residues, and Dietary Risk Assessment of Fludioxonil in Cherry via QuEChERS Using HPLC-MS/MS Technique.

The chemical fungicide fludioxonil is widely used to control post-harvest fungal disease in cherries. This study was implemented to investigate the dissipation behaviours and residues of fludioxonil on cherries. A reliable and efficient analytical method was established. Cherry samples from four product areas were analyzed by QuEChERS and HPLC-MS/MS methods with acceptable linearity (R2 > 0.99), accuracy (recoveries of 81-94%), and precision (relative standard deviation of 2.5-11.9%). The limits of quantification (LOQs) and limits of detection (LODs) of cherries were 0.01 mg/kg and 0.005 mg/kg. The dissipation of fludioxonil on cherries followed first order kinetics with half-lives of 33.7-44.7 days. The terminal residues of fludioxonil were all lower than 5.00 mg/kg, which is the MRL recommended by the European Commission. According to Chinese dietary patterns and terminal residue distributions, the risk quotient (RQs) of fludioxonil was 0.61%, revealing that the evaluated cherries exhibited an acceptably low dietary risk to consumers.

Rhizosphere microorganisms enhance in vitro root and plantlet development of Pyrus and Prunus rootstocks.

MAIN CONCLUSION: The in vitro application of rhizosphere microorganisms led to a higher rooting percentage in Pyrus Py12 rootstocks and increased plant growth of Pyrus Py170 and Prunus RP-20. The rooting of fruit tree rootstocks is the most challenging step of the in vitro propagation process. The use of rhizosphere microorganisms to promote in vitro rooting and plant growth as an alternative to the addition of chemical hormones to culture media is proposed in the present study. Explants from two Pyrus (Py170 and Py12) rootstocks and the Prunus RP-20 rootstock were inoculated with Pseudomonas oryzihabitans PGP01, Cladosporium ramotenellum PGP02 and Phoma sp. PGP03 following two different methods to determine their effects on in vitro rooting and plantlet growth. The effects of the microorganisms on the growth of fully developed Py170 and RP-20 plantlets were also studied in vitro. All experiments were conducted using vermiculite to simulate a soil system in vitro. When applied to Py12 shoots, which is a hard-to-root plant material, both C. ramotenellum PGP02 and Phoma sp. PGP03 fungi were able to increase the rooting percentage from 56.25% to 100% following auxin indole-3-butyric acid (IBA) treatment. Thus, the presence of these microorganisms clearly improved root development, inducing a higher number of roots and causing shorter roots. Better overall growth and improved stem growth of treated plants was observed when auxin treatment was replaced by co-culture with microorganisms. A root growth-promoting effect was observed on RP-20 plantlets after inoculation with C. ramotenellum PGP02, while P. oryzihabitans PGP01 increased root numbers for both Py170 and RP-20 and increased root growth over stem growth for RP-20. It was also shown that the three microorganisms P. oryzihabitans PGP01, C. ramotenellum PGP02 and Phoma sp. PGP03 were able to naturally produce auxin, including indole-3-acetic acid (IAA), at different levels. Overall, our results demonstrate that the microorganisms P. oryzihabitans PGP01 and C. ramotenellum PGP02 had beneficial effects on in vitro rooting and plantlet growth and could be applied to in vitro tissue culture as a substitute for IBA.

Resistance analysis of cherry rootstock 'CDR-1' (Prunus mahaleb) to crown gall disease.

BACKGROUND: Crown gall disease, caused by the pathogenic bacterium Agrobacterium tumefaciens, is responsible for extensive economic losses in orchards. Cherry rootstock 'CDR-1' (Prunus mahaleb) shows high resistance but the mechanism remains unclear. Here, we examined the morphology of pathogen-infected root neck surface, determined the activity of 10 defense-related enzymes and the content of salicylic acid (SA) and jasmonic acid (JA), and also applied transcriptome analysis, transient expression and transgenic verification to explore the crown gall resistance genes in 'CDR-1' plants. RESULTS: In our study, peroxidase increased in the first 10 days, while phenylalanine ammonialyase and lipoxygenase increased in the first 15 days post-infection. Four key enzymes in the AsA-GSH cycle also responded, to a certain extent; although JA content increased significantly after the treatment, the SA content did not. In a follow-up transcriptome analysis, the differentially expressed genes Pm4CL2, PmCYP450, PmHCT1, PmHCT2, and PmCAD were up-regulated. Based on the above results, we focused on the lignin biosynthetic pathway, and further measured lignin content, and found it increased significantly. The Pm4CL2 gene was used to conduct transient expression and transgenic experiments to verify its function in crown gall disease resistance. It showed the relative expression of the treatment group was almost 14-fold that of the control group at 12 h post-treatment. After the infection treatment, clear signs of resistance were found in the transgenic lines; this indicated that under the higher expression level and earlier activation of Pm4CL2, plant resistance was enhanced. CONCLUSIONS: The crown gall resistance of 'CDR-1' is likely related to the lignin biosynthetic pathway, in which Pm4CL2 functions crucially during the plant defense response to the pathogen A. tumefaciens. The results thus offer novel insights into the defense responses and resistance mechanism of cherry rootstock 'CDR-1' against crown gall disease.

Induced resistance in nectarine fruit by Bacillus licheniformis W10 for the control of brown rot caused by Monilinia fructicola.

Brown rot caused by Monilinia fructicola has led to considerable preharvest and postharvest losses in all major nectarine fruit-growing areas. In our previous study, we successfully identified a biocontrol strain of bacteria, Bacillus licheniformis W10, that can be used to control brown rot. However, the possible mechanism of the control of brown rot by B. licheniformis W10 is still unclear. Therefore, the objectives of this study were to determine whether B. licheniformis W10 induces resistance by activating defense-related enzymes including antioxidant enzymes in nectarine. Treatment of nectarine fruit with B. licheniformis W10 reduced both M. fructicola-induced oxidative damage and reactive oxygen species (ROS) production. Furthermore, application of B. licheniformis to nectarine fruit resulted in a significant increase in the activity of antioxidant and defense-related enzymes and increase in the expression of the corresponding genes. Overall, our results verified the proposed mechanism of B. licheniformis W10 in controlling M. fructicola via regulation of ROS levels and activation of antioxidant and defense-related enzymes.

Development of three duplex real-time RT-PCR assays for the sensitive and rapid detection of a phytoplasma and five viral pathogens affecting stone fruit trees.

Three duplex real-time reverse-transcription polymerase chain reaction (real-time RT-PCR) assays based on TaqMan chemistry, were developed for the simultaneous detection and specific quantification of apple chlorotic leafspot virus (ACLSV), plum pox virus (PPV), prunus necrotic ringspot virus (PNRSV), prune dwarf virus (PDV), peach latent mosaic viroid (PLMVd) and the European stone fruit yellows (ESFY) phytoplasma, which are considered among the most important pathogens affecting stone fruit trees. The quantitative RT-PCR (RT-qPCR) assays were optimized using RNA transcripts (linearized plasmid was used for the assay optimization of the ESFY phytoplasma) of known concentrations. No differences in sensitivity were recorded between the duplex and singleplex RT-qPCR assays. The amplification efficiency of the duplex assays reached 91.1-95.8%, while the linear range of quantification was from 20 to 2 × 107 RNA/linearized plasmid transcripts for PLMVd and ESFY phytoplasma, 40 to 4 × 107 RNA transcripts for ACLSV, PPV and PDV, and 102 to 108 RNA transcripts for PNRSV, respectively. The duplex RT-qPCR assays, which were validated using both characterized isolates from all pathogens and field samples from Prunus species in Northern Greece, exhibited a broad detection range. Overall, the developed methods comprise useful tools that could be applied for the simultaneous and reliable detection of graft-transmissible pathogens in certification programs of Prunus spp.

Inoculum quantification of canker-causing pathogens in prune and walnut orchards using real-time PCR.

AIMS: A real-time quantitative PCR (qPCR) assay was established to quantify the inoculum densities in the air and rainwater for six canker-causing pathogen groups in prune and walnut orchards in California. METHODS AND RESULTS: The previously published DNA primers to target six pathogen groups including Botryosphaeria dothidea, Cytospora spp., Diplodia spp., Lasiodiplodia spp., Neofusicoccum spp. and Phomopsis spp. were used in a qPCR assay. Air samples from Burkard spore traps and rain samples from special rain collector devices were collected periodically from various prune and walnut orchards. Using the qPCR approach, we were able to quantify the concentrations of these pathogen groups in rainwater and air samples and study the dynamics of pathogen inoculum in orchards showing severe canker potential. Phomopsis spp. and Diplodia spp. were not found in all rain samples in prune orchards, although they were detected in the 2016 in the walnut orchard. The other four pathogen groups were quantified at varying concentrations in the prune and walnut orchards. Cytospora spp. in some cases showed higher concentrations in the rainwater in prune orchards. CONCLUSIONS: The rainy season during winter and early spring is a highly risky period of time for infection by the pathogens when the inoculum of these pathogens can easily spread by air and rain water, thus serving as an important inoculum source for disease initiation. The different studied pathogen groups showed different concentrations during the growing season, indicating the complexity of the components of canker-causing species in various tree crops. SIGNIFICANCE AND IMPACT OF THE STUDY: This study showed the applicability of the qPCR assay in the quantification of inoculum in tree orchards to help reveal the mechanisms of canker disease epidemics and to help design disease management strategies.

Multi-scale spatial genetic structure of the vector-borne pathogen 'Candidatus Phytoplasma prunorum' in orchards and in wild habitats.

Inferring the dispersal processes of vector-borne plant pathogens is a great challenge because the plausible epidemiological scenarios often involve complex spread patterns at multiple scales. The spatial genetic structure of 'Candidatus Phytoplasma prunorum', responsible for European stone fruit yellows disease, was investigated by the application of a combination of statistical approaches to genotype data of the pathogen sampled from cultivated and wild compartments in three French Prunus-growing regions. This work revealed that the prevalence of the different genotypes is highly uneven both between regions and compartments. In addition, we identified a significant clustering of similar genotypes within a radius of 50 km or less, but not between nearby wild and cultivated Prunus. We also provide evidence that infected plants are transferred between production areas, and that both species of the Cacopsylla pruni complex can spread the pathogen. Altogether, this work supports a main epidemiological scenario where 'Ca. P. prunorum' is endemic in - and generally acquired from - wild Prunus by its immature psyllid vectors. The latter then migrate to shelter plants that epidemiologically connect sites less than 50 km apart by later providing infectious mature psyllids to their "migration basins". Such multi-scale studies could be useful for other pathosystems.

Genome comparison and transcriptome analysis of the invasive brown root rot pathogen, Phellinus noxius, from different geographic regions reveals potential enzymes associated with degradation of different wood substrates.

Phellinus noxius is a root-decay pathogen with a pan-tropical/subtropical distribution that attacks a wide range of tree hosts. For this study, genomic sequencing was conducted on P. noxius isolate P919-02W.7 from Federated States of Micronesia (Pohnpei), and its gene expression profile was analyzed using different host wood (Acer, Pinus, Prunus, and Salix) substrates. The assembled genome was 33.92 Mbp with 2954 contigs and 9389 predicted genes. Only small differences were observed in size and gene content in comparison with two other P. noxius genome assemblies (isolates OVT-YTM/97 from Hong Kong, China and FFPRI411160 from Japan, respectively). Genome analysis of P. noxius isolate P919-02W.7 revealed 488 genes encoding proteins related to carbohydrate and lignin metabolism, many of these enzymes are associated with degradation of plant cell wall components. Most of the transcripts expressed by P. noxius isolate P919-02W.7 were similar regardless of wood substrates. This study highlights the vast suite of decomposing enzymes produced by P. noxius, which suggests potential for degrading diverse wood substrates, even from temperate host trees. This information contributes to our understanding of pathogen ecology, mechanisms of wood decomposition, and pathogenic/saprophytic lifestyle.

Morphophylogenetic analyses revealed that Podosphaera tridactyla constitutes a species complex.

Podosphaera tridactyla (s. lat.) is a powdery mildew species occurring on a wide range of Prunus spp. almost worldwide. We have investigated the phylogeny of the Po. tridactyla complex, with special emphasis on potential aspects of cryptic speciation. The results suggested that Po. tridactyla represents a species complex consisting of at least 12 different species. Based on detailed morphological examinations and molecular sequence analyses, we propose dividing Po. tridactyla s. lat. into 10 species, encompassing 7 new species (Po. ampla, Po. pruni-avium, Po. pruni-cerasoidis, Po. prunigena, Po. pruni-lusitanicae, Po. prunina, and Po. pruni-japonicae) and 3 known species (Po. longiseta, Po. salatai, and Po. tridactyla s. str.). Oidium passerinii on Pr. laurocerasus is confirmed as a synonym of Po. tridactyla s. str. Epitypes are designated for Po. tridactyla and Oidium passerinii.

Ornithinimicrobium cerasi sp. nov., isolated from the fruit of Cerasus pseudocerasus and emended description of the genus Ornithinimicrobium.

Strain CPCC 203383T, isolated from the surface-sterilized fruit of Cerasus pseudocerasus (Lindl.) G. Don, was taxonomically characterized based on a polyphasic investigation. It had the highest 16S rRNA gene sequence similarities with Ornithinimicrobium pekingense DSM 21552 (97.2 %) and O. kibberense DSM 17687T (97.2%). Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain formed a distinct phyletic branch within the genus Ornithinimicrobium and the whole genome sequence data analyses supported that strain CPCC 203383T was phylogenetically related to the Ornithinimicrobium species. The isolate shared a range of phenotypic patterns reported for members of the genus Ornithinimicrobium, but also had a range of cultural, physiological and biochemical characteristics that separated it from related Ornithinimicrobium species. The menaquinone was MK-8(H4). The polar lipid profile consisted of diphosphatidylglycerol (DPG), phosphatidylglycerol (PG), phosphatidylinositol (PI) and unidentified lipids (ULs). The major fatty acids (>5 %) were iso-C15 : 0, anteiso-C15 : 0, iso-C16:0, 9-methyl C16 : 0, iso-C17 : 0 and anteiso-C17 : 0. The cell wall peptidoglycan contains l-ornithine as diagnostic diamino acid and an interpeptide bridge consisting of L-Orn←L-Ala←Gly←D-Asp. The combined genotypic and phenotypic data indicated that the isolate represents a novel species of the genus Ornithinimicrobium, for which the name Ornithinimicrobium cerasi sp. nov. is proposed, with CPCC 203383T(=NBRC 113522T=KCTC 49200T) as the type strain. The DNA G+C composition is 72.3 mol%. The availability of new data allows for an emended description of the genus Ornithinimicrobium.

The complete genome sequence of Rahnella aquatilis ZF7 reveals potential beneficial properties and stress tolerance capabilities.

Rahnella aquatilis ZF7 is a plant beneficial strain isolated from Sakura tree soil with potential for biocontrol. Here, we present the complete genome sequence of R. aquatilis ZF7, which consists of one 4.49 Mb circular chromosome and a 54-kb plasmid named pRAZF7. Phylogenetic analyses revealed that R. aquatilis ZF7 is much similar to the strains Rahnella sp. Y9602 and R. aquatilis HX2 than others evaluated. In this study, multiple genes encoding functions that likely contribute to plant growth promotion, biocontrol and stress tolerance were identified by comparative genome analyses, including IAA production, phosphate solubilization, antibiotic resistance and formation of Se nanoparticles (SeNPs). In addition, these functions were also confirmed by in vitro experiments. Considering its ability to form SeNPs, strain R. aquatilis ZF7 will contribute to nano-agriculture. Overall, the features of R. aquatilis ZF7 make it a high potential and competitive strain in biocontrol, and the genome data will help further studies on the mechanisms of plant growth promotion and biocontrol.

Labeling of Monilinia fructicola with GFP and Its Validation for Studies on Host-Pathogen Interactions in Stone and Pome Fruit.

To compare in vivo the infection process of Monilinia fructicola on nectarines and apples using confocal microscopy it is necessary to transform a pathogenic strain with a construct expressing a fluorescent chromophore such as GFP. Thus, germinated conidia of the pathogen were transformed with Agrobacterium tumefaciens carrying the plasmid pPK2-hphgfp that allowed the expression of a fluorescent Hph-GFP chimera. The transformants were selected according to their resistance to hygromycin B, provided by the constitutive expression of the hph-gfp gene driven by the glyceraldehyde 3P dehydrogenase promoter of Aspergillus nidulans. The presence of T-DNA construct in the genomic DNA was confirmed by PCR using a range of specific primers. Subsequent PCR-mediated analyses proved integration of the transgene at a different genomic location in each transformant and the existence of structural reorganizations at these insertion points. The expression of Hph-GFP in three independent M. fructicola transformants was monitored by immunodetection and epifluorescence and confocal microscopy. The Atd9-M. fructicola transformant displayed no morphological defects and showed growth and pathogenic characteristics similar to the wild type. Microscopy analysis of the Atd9 transformant evidenced that nectarine infection by M. fructicola was at least three times faster than on apples.

Induction of Antiphytopathogenic Metabolite and Squalene Production and Phytotoxin Elimination by Adjustment of the Mode of Fermentation in Cocultures of Phytopathogenic Nigrospora oryzae and Irpex lacteus.

The investigation of the metabolites from different cocultures of Nigrospora oryzae and Irpex lacteus in solid medium revealed two new squalenes (1 and 2); one new azaphilone (3); two new tremulane sesquiterpenes (4 and 5); and three known compounds, conocenol B (6), conocenol C (7), and 4-(4-dihydroxymethylphenoxy)benzaldehyde (8). The antagonistic relationship was examined by studying metabolite production. The production of compounds 6 and 8 by I. lacteus after the induction of coculture indicated significant selectivity for antifungal activity against phytopathogenic N. oryzae, with MICs of 16 µg/mL; compounds 6 and 8 also exhibited antifungal activities in vivo against Cerasus cerasoides infected by N. oryzae at concentrations of 100 µg/mL. New compounds 2 and 4 showed antifungal activities against Colletotrichum gloeosporioides, with MICs of 8 µg/mL, and compound 4 showed antifungal activity against Didymella glomerata with an MIC of 1 µg/mL. These results indicate that the mutually antagonistic relationship in the coculture of the phytopathogen and the endophyte can result in antibiotics that inhibit the phytopathogen and downregulate the production of phytotoxins by phytopathogenic N. oryzae. New compound 5 from I. lacteus showed weak activity against acetylcholinesterase (AChE), with an inhibition ratio of 16% at a concentration of 50 µM.

Immuno-detection and differentiation of Listeria monocytogenes and Listeria ivanovii in stone fruits.

AIMS: The aim of this study was to develop a rapid detection and differentiation method for pathogenic Listeria species in stone fruits. METHODS AND RESULTS: We utilized activated charcoal enrichment media (ACM) to induce overexpression and hypersecretion of pathogenic Listeria virulence proteins which can subsequently be detected via immunoblot analysis. Plum and nectarine slices spiked with either L. monocytogenes or L. ivanovii were incubated in pre-enrichment broth followed by enrichment in ACM. Secreted proteins were precipitated and subjected to SDS-PAGE and immunoblot analysis using a combination of L. monocytogenes-specific antibody (α-listeriolysin O) and antibody specific for both L. monocytogenes and L. ivanovii (α-Internalin C). As low as 1 CFU per gram of L. monocytogenes in plum and nectarine was detected, whereas a detection limit of 10 CFU per gram was achieved for L. ivanovii in each food tested following a 20-h enrichment period. Nonpathogenic Listeria species and non-Listeria bacterial pathogens tested were negative. CONCLUSIONS: These results demonstrate the highly sensitive and specific nature of the detection method for pathogenic Listeria in stone fruits using activated charcoal enrichment as well as the capability to discriminate between L. monocytogenes and L. ivanovii. SIGNIFICANCE AND IMPACT OF THE STUDY: This method is the first to identify and differentiate L. monocytogenes and L. ivanovii in select stone fruit enrichments within 24 h using immunological techniques. The rapidity and sensitivity of the method could aid in the reduction of exposure to the public in the event of an outbreak and expedite the administration of appropriate antibiotics to infected individuals.

Exploitation of Prunus mahaleb fruit by fermentation with selected strains of Lactobacillus plantarum and Saccharomyces cerevisiae.

The organoleptic attributes of Prunus mahaleb, a fruit representing a new source of bioactive compounds, are so pronounced that it can be consider non-edible. This study was designed to evaluate the acceptance of P. mahaleb fruits after fermentation with different Saccharomyces cerevisiae and Lactobacillus plantarum protechnological strains. Four different bacterial and one yeast strains, as single or mixed starter formulation, were used to inoculate an aqueous suspension of P. mahaleb fruits. The fermented fruits and fermentation broths were subjected to physico-chemical characterization and the organoleptic properties of both samples were also assessed by a hedonic panel. The obtained results indicated that all the employed strains were able to grow and to ferment the matrix. However, the mixed starter FG69 + Li180-7 (L. plantarum/S. cerevisiae) had the best impact on sensory characteristics of P. mahaleb fruit and fermented medium. The adopted protocol allowed us to attain edible fruits and a new fermented non-dairy drink with valuable probiotic health-promoting properties. In our knowledge, this is the first study concerning the exploitation of P. mahaleb fruits. This investigation confirmed the potential of yeasts and lactic acid bacteria co-inoculation in the design of starter tailored for this kind of food applications.

Phylogeny and taxonomy of Podosphaera cerasi, sp. nov., and Podosphaera prunicola sensu lato.

Powdery mildew of Prunus spp. is a significant disease in most cherry growing regions of Washington, USA. Powdery mildews on Prunus virginiana and Pr. avium were previously assigned to Podosphaera clandestina s. lat. (= Po. oxyacanthae) or Po. prunicola. In this report, we confirm the presence of two distinct Podosphaera species on these hosts. Phylogenetic analyses of nuc rDNA sequences from the internal transcribed spacer region (ITS1-5.8S-ITS2 = ITS) and 28S subunit confirmed the presence of two distinct species. A morphological comparison with type material of Po. prunicola and additional collections demonstrated that the powdery mildew on Pr. virginiana (including var. demissa and var. melanocarpa) is in fact Po. prunicola. The powdery mildew on Pr. avium is genetically, morphologically, and biologically distinct from Po. prunicola and is described here as the new species Po. cerasi. Cross-inoculation experiments confirmed that these two species are host specific. Podosphaera prunicola was unable to colonize Pr. avium, whereas Po. cerasi was unable to colonize Pr. virginiana. Morphological reexamination of numerous specimens identified as Po. prunicola on a broad range of Prunus species suggests that Po. prunicola is probably confined to species in Prunus subgen.Padus (= Prunus subgen. Cerasus sect. Laurocerasus, including sect. Padus), with Pr. virginiana as the principal host. Podosphaera cerasi occurs on hosts in Prunus subgen. Cerasus, and our work confirms a newly described species of powdery mildew on Pr. avium. This work also includes the first documented and genetically proven European record of Po. prunicola on Pr. serotina and its widespread occurrence in the United States.