Podosphaera Fusca Research Articles

Gene markers generating polygenic resistance in melon-Fusarium wilt-FOM1.2 interaction pathosystem.

Developing melon genotypes with resistance to Fusarium oxysporum f. sp. Melonis-(FOM) race1.2 is a major goal in any breeding program. In this study, we identified the role of 11 gene markers that contribute to polygenic resistance during the FOM1.2-melon interaction. qRT-PCR analysis elucidated upregulation of candidate marker genes AMT, DXPR, Fom-2, GLUC, GalS, GRF3, MLO, PRK, RuBlsCo, TLP and WRKY in resistant 'Shante-F1' and 'Khatouni', and susceptible 'Shante-T' and 'Shahabadi' at 7, 14 and 21 days post-inoculation (dpi). We also studied changes in defence-related enzyme activity: chitinase (CHI), β-1,3-glucanase (GLU) and peroxidase (POX) in melon roots. AMT, GLUC and DXPR transcripts were upregulatied in leaf and root tissues of the resistant 'Shante-F1' and 'Shahabadi'. Transcript levels for GalS and GRF3 increased 6.77- and 6.83-fold in roots of 'Shante-F1' at 7 dpi, whereas in PRK, TLP and WRKY theye increased by 7.84-, 5.15- and 12.26-fold at 14 dpi, respectively. However, transcript levels increased by 5.18-fold for Fom-2 and 8.46-fold for MLO at 21 dpi. Also, RBC transcript level peaked at 14 dpi with 4.9-fold increase in leaves of resistant genotypes, whereas AMT increased 2.94-fold at 21 dpi, and GLUC and DXPR increased 7.11- and 2.91-fold at 14 dpi in 'Shante-F', respectively. Defence-related-enzyme activity was also upregulated three-fold in resistant varieties. The dynamic shifts in the melon transcriptome induced by FOM1.2 emphasize that resistance mechanisms are predominantly regulated through signalling pathways involving CHI, GLU, and POX defence response. Surprisingly, the AMT gene, basically resistant to downy mildew, Pseudoperonospora cubensis; GLUC, MLO and PRK resistant to powdery mildew (Sphaerotheca fusca); TLP and WRKY resistant to Phytophthora blight (Phytophthora capsici); and GRF3 and RBC resistant to root knot nematodes (Meloidogyne spp.) were upregulated in resistant genotypes, indicating a dual role of these genes in resistance to more than one disease at a time.

Spinach flavonoid-rich extract: Unleashing plant defense mechanisms against cucumber powdery mildew

In response to the escalating demand for organic commodities, the exploration of non-chemical alternatives such as phytochemicals for plant disease management has gained momentum. This investigation focused on assessing the efficacy of a sustainable compound, Spinach Flavonoid-Rich Extract (SFRE), in mitigating cucumber powdery mildew (Podosphaera fusca) under controlled greenhouse conditions, and its potential in eliciting plant defense mechanisms at both biochemical and genetic levels. The application of SFRE resulted in a significant reduction in P. fusca disease severity, with a decrease of approximately 99%. High-Performance Liquid Chromatography (HPLC) analysis identified spinacetin as the dominant flavonoid in SFRE, with a concentration of 81.97 μg per 100 mg of the extract's dry weight. Furthermore, SFRE was found to induce systemic resistance in the infected seedlings, as evidenced by the upregulation of defense-related enzymes, including β-1,3-glucanase, chitinase, peroxidase, phenylalanine ammonia-lyase, and polyphenol oxidase, and the enhanced expression of β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase genes. In addition, SFRE application led to an accumulation of flavonoid/phenolic compounds and an enhancement in chlorophyll synthesis. A robust correlation was observed between phenolic compounds and the activities of defense enzymes, as well as the expression of the tested genes. This study substantiates that SFRE, as a reservoir of natural compounds, presents an effective and environmentally friendly alternative to chemical fungicides for P. fusca control, and could be incorporated into a comprehensive approach to managing cucumber powdery mildew through integrated disease management strategies.

Chitosan nanoparticle encapsulation of celery seed essential oil: Antifungal activity and defense mechanisms against cucumber powdery mildew

The objective of the current study was to explore the antifungal potential of celery seed essential oil (CSEO) in a nano-carrier system against Podosphaera fusca, the causal agent of cucumber powdery mildew. We assessed the physicochemical characterization of CSEO-loaded chitosan nanoparticles (CSEO-LCNPs) using dynamic light scattering, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. The successful loading of various concentrations of CSEO into chitosan nanoparticles (1:0, 1:0.25, 1:0.5, 1:0.75, and 1:1) has been verified. The particles exhibited a spherical shape, with an average diameter of 113 nm, and a negatively charged surface with a zeta potential of -31.5 mV. The Korsmeyer-Peppas model well described the release behavior of CSEO from nanoparticles. Additionally, we examined the defense mechanism, as well as biochemical/molecular responses following foliar treatment with CSEO-LCNPs. In vivo, results revealed that CSEO-LCNPs foliar application on the cucumber seedlings inoculated with P. fusca significantly reduced the disease severity of powdery mildew. Treatment with CSEO-LCNPs led to an increase in phenolic and flavonoid compounds, chlorophyll concentration, enzyme activities, and gene transcriptions in inoculated cucumber seedlings. In our study, we observed a positive correlation between antioxidant compounds and the defense-associated enzymes as well as their corresponding gene expressions. Our study underscores the potential of CSEO-LCNPs as an eco-friendly and effective solution for managing cucumber powdery mildew.

First report of powdery mildew caused by Podosphaera fusca on Coreopsis tinctoria in China.

Coreopsis tinctoria is an annual herb and commonly cultivated in gardens due to its attractive flowers, its capitula also have been used as a traditional medicine in China, Asia, North America and Europe (Shen et al. 2021). In June 2023, severe powdery mildew infection was observed on C. tinctoria in a hillside near headwork of the middle route of the South to North Water Diversion Project (32°40'55''N, 111°41'59''E). Abundant irregular white spots were found on adaxial surface of the leaves and tender stems. Approximately 75% of the observed C. tinctoria plants showed these signs and symptoms. Generative hyphae were thin-walled, smooth or almost so, and 5 to 9 μm wide. Conidiophores were unbranched, straight, 80.5 to 162.5 × 9.3 to 12.9 μm (n=25), and produced one to three immature conidia. Foot-cells of conidiophores were cylindrical, 38.5 to 62.3 μm (n=20) long. Conidia were ellipsoid to ovoid, 25.1 to 31.9 × 15.2 to 19.5 μm (n=30). The morphological characteristics of asexual structures corresponded to Podosphaera sp. (Braun and Cook 2012). For further identification, genomic DNA was extracted directly from the mycelia and conidia using Chelex 100 (Sigma Aldrich, Shanghai, China). The internal transcribed spacer (ITS) regions and 28S large subunit (LSU) of ribosomal DNA from the specimen (CT2302) were amplified using the primers ITS1/ITS4 (expected amplicon size 566 bp) (White et al. 1990) and NL1/NL4 (expected amplicon size 618 bp) (Baten et al. 2014), respectively. The sequences of ITS (GenBank accession no. OR649304) and LSU (GenBank accession no. OR649305) showed 99.63% and 100% identity values to the Podosphaera fusca isolate HMNWAFU-CF2012074 in the NCBI database (KR048109 for ITS and KR048178 for LSU), respectively. Phylogenetic analyses based on the combined ITS and LSU sequences using MEGA 7.0 software indicated that CT2302 formed a monophyletic clade together with isolates of P. fusca. Therefore, this fungus was identified as P. fusca based on the morphological and molecular characteristics. Pathogenicity tests were performed by gently pressing the infected leaves onto 15 young leaves of five healthy plants and three noninoculated plants were used as controls. All plants were maintained in a greenhouse (25℃ and 70% relative humidity). Powdery mildew symptoms similar to those of originally diseased plants were observed on all inoculated leaves after 12 days, whereas no symptoms were observed on the control leaves. Powdery mildew caused by P. fusca (previously Sphaerotheca fusca) on C. tinctoria has been reported in Russia, Poland, Korea, Romania and Ukraine (Cho and Shin 2004; Rusanov and Bulgakow 2008). To our knowledge, this is the first report of P. fusca on C. tinctoria in China. The identification of P. fusca as the causal agent on C. tinctoria is critical to the prevention and control of this disease in the future.

Defense Mechanisms Induced by Celery Seed Essential Oil against Powdery Mildew Incited by Podosphaera fusca in Cucumber.

This study aimed to evaluate the effectiveness of essential oil extracted from celery (Apium graveolens) seeds (CSEO) for the control of powdery mildew of cucumber (Cucumis sativus) incited by Podosphaera fusca and to investigate the metabolic and genetic defense mechanisms triggered by the treatment with this essential oil in cucumber seedlings. The main compounds in the CSEO as determined by gas chromatography-mass spectrometry (GC-MS) analysis were d-limonene, 3-butyl phthalide, β-selinene, and mandelic acid. The treatment with CSEO led to an increase in the content of both chlorophyll and phenolic/flavonoid compounds in cucumber leaves. In greenhouse tests, the application of CSEO reduced by 60% the disease severity on leaves of cucumber plants and stimulated the activity of defense-related enzymes such as β-1,3-glucanase, chitinase, phenylalanine ammonia-lyase, peroxidase, and polyphenol oxidase. Moreover, treatment with CSEO induced overexpression of β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase genes. A highly significant correlation was found between the β-1,3-glucanase, chitinase, and phenylalanine ammonia-lyase enzymatic activities and the relative expression of the corresponding encoding genes in both inoculated and non-inoculated cucumber seedlings treated with the essential oil. Overall, this study showed that CSEO is a promising eco-friendly candidate fungicide that can be exploited to control cucumber powdery mildew.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Xanthium orientale in Korea.

Xanthium orientale L. (syn. Xanthium canadense Mill., Asteraceae), known as cocklebur, is an annual weed native to North America, which is now a neophyte distributed throughout the world. This plant was accidentally introduced to Korea in the late 1970s ( So et al. 2008) and is considered a problematic exotic weed in orchards, for which many herbicides are ineffective (Kim et al. 2020). In September 2018, powdery mildew was observed on X. orientale in Jeju, Korea. The disease incidence ranged from 40 to 60%. Voucher specimens were deposited in the Korea University Herbarium (Accession No. KUS-F30795) and Kunsan National University Herbarium (KSNUH1988). Symptoms appeared as round to irregular white patches with abundant hyphal growth on the leaf surface. Hyphal appressoria were nipple-shaped, and 3 to 6 μm diam. Conidiophores (n = 30) were 145 to 206 × 9 to 11.6 µm and produced 2 to 5 immature conidia in chains with a sinuate outline. Foot-cells of the conidiophores were straight, cylindrical, and 43 to 100.9 μm long. Conidia (n = 30) were ellipsoid-ovoid, doliiform to somewhat limoniform, 25.2 to 31.8 × 13.6 to 16.8 μm (l/w 1.6 to 2.1), and devoid of distinct fibrosin bodies. The morphological characteristics corresponded to those of Golovinomyces ambrosiae (Schwein.) U. Braun & R.T.A. Cook (Braun and Cook 2012, under Golovinomyces spadiceus (Beck. & M.A. Curtis) U. Braun; Qiu et al. 2020). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS), large subunit (LSU) (Bradshaw and Tobin 2020), the intergenic spacer (IGS) of rDNA, and the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene (Bradshaw et al. 2022) were amplified for a herbarium specimen (KUS-F30795). A BLASTn search of these sequences revealed 100% identity with reference sequences of G. ambrosiae on diverse Asteraceae plants (AB077644 for ITS, AB077643 for LSU, ON361171 for IGS, and ON075648 for GAPDH). However, there was a single nucleotide difference on both the IGS and GAPDH sequences when compared to the closely related species Golovinomyces latisporus. The sequences were deposited in GenBank (Accession No. OQ165157 (ITS), OQ165164 (LSU), OR050524 (IGS), and OR086076 (GAPDH)). Phylogenetic analyses of ITS, LSU, IGS, and GAPDH sequences revealed the Korean sample formed a well-supported group with other G. ambrosiae sequences, confirming its identity. A pathogenicity test was performed through inoculation by gently pressing diseased leaves onto the leaves of five healthy plants. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25±2°C. Powdery mildew colonies developed on the inoculated plants after ten days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that observed on the initially diseased leaves, fulfilling Koch's postulates. Powdery mildew on X. orientale has previously been reported as Golovinomyces cichoracearum (≡ Erysiphe cichoracearum) sensu lato in the USA, G. ambrosiae (= G. spadiceus) throughout all continents, and Podosphaera fusca sensu lato (now P. xanthii) in Korea (Braun and Cook 2012; Farr and Rossman 2023). To date, powdery mildew in Korea has been reported only on Xanthium strumarium as G. cichoracearum s. lat. and Podosphaera xanthii (KSPP 2022). To our knowledge, this is the first report of powdery mildew caused by G. ambrosiae on X. orientale in Korea.

β-Aminobutyric Acid and Powdery Mildew Infection Enhanced the Activation of Defense-Related Genes and Salicylic Acid in Cucumber (Cucumis sativus L.).

Powdery mildew disease, caused by Sphaerotheca fusca, is a major disease affecting cucumbers cultivated in greenhouses. This study was conducted to find defense genes induced by β-aminobutyric acid (BABA) and powdery mildew in cucumber. Disease severities of 25% and 5% were exhibited by the 2000 and 5000 mg/L BABA-treated cucumber, respectively. BABA did not affect the spore germination of the powdery mildew pathogen, showing that BABA is not an antifungal agent against the pathogen. In quantitative real-time PCR analysis, BABA-treated cucumber upregulated the transcriptional levels of the defense genes CsPAL, CsPR3, CsPR1, CsLOX1, CsLOX23, Cs LecRK6.1, CsWRKY20, and Cupi4 in cucumber to maximum levels at 48 h, whereas CsLecRK6.1 reached maximum expression after 24 h, and further, salicylic acid (SA) levels were significantly increased in BABA-treated cucumber plants. In addition, the cucumber infected with powdery mildew underwent a 1.6- to 47.3-fold enhancement in the defense genes PAL, PR3, PR1, Lox1, Lox 23, LecRK6.1, WRKY20, and Cupi4 compared to heathy cucumber. These results suggest that the BABA-induced defense response is associated with SA signaling pathway-dependent systemic acquired resistance (SAR) in cucumber, which is involved in plant resistance mechanisms.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Leucanthemum vulgare in Korea.

Leucanthemum vulgare Lam. (Asteraceae), known as ox-eye daisy, is a perennial herb native to Europe and western Asia (Clements et al. 2004, McDougall et al. 2018). In Korea, this plant was introduced for ornamental purposes but has been naturalized as a widespread invasive species. In June 2015, symptoms of a powdery mildew disease were observed on L. vulgare in a public garden in Goseong (38°14'18"N, 128°32'56"E), Korea. Since then, its findings have continued throughout the country, including Mokpo and Seogwipo (in 2018), Hongcheon and Seoul (in 2020), Boeun, Gunsan, and Namwon (in 2022), where the disease incidence was often higher than 80%. Symptoms first appeared as circular to irregular white powdery patches covering leaves and stems. Affected plants became distorted, eventually losing their aesthetic and ornamental value. A total of sixteen samples were deposited in the herbarium of Korea University (KUS-F), Korea. Microscopic observations showed that hyphal appressoria were nipple-shaped. Conidiophores were cylindrical, 98 to 157 × 9 to 12 μm, and produced 2 to 5 immature conidia in chains with a sinuate outline. Foot cells were cylindrical, straight, and 37 to 65 μm long. Conidia were ellipsoid to barrel-shaped, 23 to 39 × 12 to 19 μm, with a length/width ratio of 1.4 to 2.3 and devoid of fibrosin bodies. Germ tubes were produced in the perihilar position of the conidia. Primary conidia were apically rounded and basally subtruncated. No chasmothecia were found until the plants died in winter. The morphological characteristics were typical for anamorph of the genus Golovinomyces. To identify the fungus, genomic DNA was extracted from the four herbarium specimens (KUS-F 28650, 30839, 31728, and 31787). PCR products were amplified using the primer sets PM10/ITS4 for internal transcribed spacer (ITS) and PM3/TW14 for the large subunit (LSU) of the rDNA (Mori et al. 2000, Bradshaw and Tobin 2020). Sequences obtained in the present study were deposited at GenBank (accession numbers ON834488-91 for ITS and ON834494-7 for LSU). A BLASTn search of the Korean specimens showed 100% identity with reference sequences of G. ambrosiae in GenBank (KX98730, MK452580, and MK452588 for ITS and MF612182, MK452653, and MK452661 for LSU). In phylogenetic trees of a concatenated dataset of the ITS and LSU sequences, the Korean specimens formed a well-supported clade with the reference sequences of G. ambrosiae. Pathogenicity tests were carried out by touching and dusting an infected leaf (KUS-F 31787) onto the upper leaf surface of five healthy plants. Five non-inoculated plants served as controls. After two weeks, all inoculated plants formed white patches on the surface of leaves and stems, whereas the control plants remained symptomless. The fungus on the inoculated plants was identical to that observed on the initially diseased plant, fulfilling Koch's postulates. As a result, the causal agent of the powdery mildew on L. vulgare was confirmed as G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook, based on the current taxonomy and nomenclature of this species by Qiu et al. (2020).. Previously powdery mildew collections on L. vulgare have been reported as Golovinomyces cichoracearum (≡ Erysiphe cichoracearum) s. lat. in Estonia, Finland, Germany, and Switzerland, Golovinomyces biocellatus in Spain, and Podosphaera fusca (probably P. xanthii according to the current taxonomy) in the former Soviet Union (now Russia and adjacent countries) (Farr and Rossman 2022). This study is the first report of powdery mildew disease caused by G. ambrosiae on L. vulgare in Korea. Qiu et al. (2020) confirmed the occurrence of G. ambrosiae on L. maximum, another species of the genus Leucanthemum. As powdery mildew causes damage to the cultivation of L. vulgare by loss of ornamental value, appropriate control measures should be developed.

First report of Podosphaera fusca Causing Powdery Mildew on Coreopsis lanceolata in China.

Coreopsis lanceolata, known as lance-leaf coreopsis, is a perennial plant with high ornamental value. It is widely grown in many public parks and home gardens in China due to its showy flowers. From May to June 2020, typical powdery mildew-signs and symptoms were seen on leaves of C. lanceolata cultivated in the east campus of Henan Normal University, Henan Province, China. Abundant white powder-like masses in spot- or coalesced-lesions were on ad- and abaxial surfaces of plant leaves and covered up to 50 % of the leaf area. The infected leaves were deformed and eventually prematurely senescent. Approximately 80 % of observed C. lanceolata plants showed these signs and symptoms. Unbranched conidiophores (n = 25) were 90 to 200 × 12 to 20 μm and showed a foot cell, followed by 1 to 3 short cells and conidia. Ellipsoid-ovoid shaped conidia (n = 30) were 22 to 36 × 15 to 23 μm, with a length/width ratio of 1.4 to 2.4. No chasmothecia were detected. The powdery mildew fungus was initially identified as Podosphaera fusca based on the morphological characteristics. Total genomic DNA of the pathogen was extracted and the rDNA internal transcribed spacer (ITS) region was amplified and sequenced using the primers ITS1/ITS4 (White et al. 1990; Zhu et al. 2019). The obtained sequence was deposited into GenBank under Accession No. MT899186 and was 100 % identical to P. fusca (JX546297) from Herba eupatorii (Ding et al. 2013). To perform pathogenicity assays, leaf surface of three healthy plants was inoculated with fungal conidia according to a previously described method (Zhu et al. 2021). As a control, three non-inoculated plants were used. The control and inoculated plants were placed separately in two growth chambers (light/dark, 16 h/8 h; humidity, 65 %; temperature, 20 ℃). Fourteen- to sixteen-days post inoculation, powdery mildew signs were noticed on inoculated plants, whereas control remained asymptomatic. Similar results were found by performing two repeated pathogenicity assays. Therefore, based on the morphological and molecular analysis, the pathogen was identified and confirmed as P. fusca. This fungus has been reported on C. lanceolata in Korea (Park et al. 2010) and Italy (Garibaldi et al. 2007). This is, to the best of our knowledge, the first report of P. fusca on C. lanceolata in China. The sudden occurrence of this powdery mildew disease on C. lanceolata may adversely affect the health of valuable ornamentals in China. The precise identification of the causal agent of this powdery mildew of C. lanceolata is a preliminary step in developing effective disease management strategies.

Plant physiology, microbial community, and risks of multiple fungal diseases along a soil nitrogen gradient

Nitrogen (N) is an essential element for plant growth and development. N levels in soil may also impact plant disease occurrence. However, the physiological and microbial mechanisms between N levels in soil and plant disease occurrence are not quite clear at present. In this study, we examined the impact of seven urea levels (0 to 800 mg kg−1 soil) on the physiology of tomato (Lycopersicon esculentum) and fungal disease occurrence. Our results showed that the disease incidence and index caused by a tomato early blight pathogen (Alternaria alternata) increased with increasing N levels. The disease index and percentage of disease incidence were positively correlated with N content, indole-3-acetic acid (IAA) and salicylic acid (SA) in plants, but negatively correlated with fungal community diversity. In addition to pathogens (A. alternata) that cause known early blight, 39 other fungal taxa were also identified as plant pathogens in tomato roots, leaves, and soil, the dominant putative pathogens included Ceratobasidiaceae sp., Fusarium oxysporum, Macrophomina phaseolina, Nectriaceae sp., Podosphaera fusca and Trichoderma viride. N levels affected the distribution and dynamics of the fungal pathogen community, such as the abundance of Fusarium oxysporum increased by 33% on roots from days 25 to 35. Our results demonstrated that plants undergo complex disease risk from different pathogens under different N levels, highlighting a need for proper N management, and integration of nutrient management as a disease control approach for sustainable agricultural production.

First report of Podosphaera fusca causing powdery mildew on asparagus bean in Taiwan

First report of Podosphaera fusca causing powdery mildew on asparagus bean in Taiwan

English

The powdery mildew caused by air borne pathogen (Podosphaera fusca) is an important disease of cucurbits including melon (Cucumis melo L.) plants. Three antagonistic bacterial strains (M4, M10 and M11); isolated from the melon plants were tested for antagonistic activity against P. fusca and soil-borne pathogens of melon plants (Monosporascus cannonballus, Fusarium oxysporum f. spp. melonis, F. solani and Phomopsis spp.). All the three strains were identified as Bacillus velezensis based on sequence analysis of gyrase subunit A (gyrA) gene sequence. The bacterial strains showed significant antagonistic activity against soil and air borne pathogenic fungi. Among all strains, M10 showed a broad spectrum of mycelial growth inhibition against phytopathogenic fungi. The tested culture broth did not affect the pollen fertilization, flowering, fruit rot occurrence and fruit set development during blooming and cultivation season of the melon plants. The M10 culture broth stored for 3 and 6 months displayed biocontrol efficiency of 73.2 and 72.3%, respectively. Application of mixed solution of M10 culture broth + paraffin oil strongly suppressed the incidence and spread of powdery mildew. These results suggested that the combination of paraffin oil and B. velezensis M10 culture broth is an ecofriendly approach and possess strong biocontrol potential against melon powdery mildew and can also be used as antifungal agents for several plant pathogens. © 2021 Friends Science Publishers

A cohort study of cucumber greenhouse workers’ exposure to microorganisms as measured using NGS and MALDI-TOF MS and biomarkers of systemic inflammation

Work in greenhouses entails exposure to airborne fungi and bacteria. The aims of this study are to obtain knowledge about whether exposure to fungal and bacterial genera and species during work in a cucumber greenhouse is affected by work tasks, and whether a cohort of greenhouse workers' serum levels of serum amyloid A (SAA) and C-reactive protein (CRP), biomarkers of systemic inflammation, are associated with this. Data on personal exposure to airborne fungal and bacterial species measured over 4 years as well as serum levels of SAA and CRP sampled over two years were analyzed. For data analysis, the main work tasks were grouped into three different groups, called ‘grouped work task’. Microorganisms were identified using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF MS) and next-generation sequencing (NGS). The ‘daily exposure’ of greenhouse workers' were as follows: 4.8 × 104 CFU bacteria/m3, 1.4 × 106 CFU fungi/m3, and 392 EU/m3 of endotoxin. Workers were exposed to many different microbial species including several species within the genera Acinetobacter, Bacillus, Microbacterium, Pseudomonas, Staphylococcus, and Streptomyces. The genera Ralstonia and Cladosporium were found in most samples. The exposure levels as well as the microbial composition were associated significantly with grouped work task and season with high exposures during tasks in close contact with mature and old plants and in the autumn. CRP and SAA levels were also associated with exposure level and grouped work tasks. The Shannon-Wiener indices were not different in the 3 ‘grouped work tasks’. Several specific species including e.g. Halomonas elongata, Stenotrophomonas maltophilia, Podosphaera fusca, and Wallemia spp. were found frequently or in high concentrations in the exposures associated with the highest levels of CRP and SAA. The microorganisms S. maltophilia, P. fusca, and Wallemia spp. were also found on the cucumber plant leaves. In conclusion, both exposure level and the species composition seem to have an effect on the serum levels of CRP and SAA of exposed workers. The greenhouse workers were exposed to only a few species characterized as human pathogens.

First Report of Powdery Mildew Caused by Podosphaera fusca on Helianthus tuberosus in China.

Helianthus tuberosus L. (Jerusalem artichoke) is an herbaceous perennial plant in the Asteraceae that is native to North America but introduced to China in the 17th century. The tubers of H. tuberosus are used as a vegetable, for the pharmaceutical production of inulin and as a source of ethanol biofuel, several B vitamins and minerals。From June to September 2009, severe powdery mildew infection was observed on H. tuberosus in a vegetable garden at Shangqiu Normal University, Shangqiu, China. Approximately 60% of leaves on individual plants were symptomatic, and almost 70% of the plants were infected. Initially, discrete powdery mildew colonies appeared on the upper surface of the leaves and on stems of the plants. Later, mycelial growth was amphigenous, thick, forming irregular white patches, covering the whole leaf surface. Eventually, leaves turned yellow, withered, and abscissed. Microscopic observations showed that conidia on infected leaves were ellipsoid-ovoid to barrel-shaped, with distinct fibrosin bodies visible in their cytoplasm, measuring 28 to 38 × 15 to 22 μm (n = 40). Conidiophores were unbranched, straight, 80 to 210 × 8 to 14 µm (n = 40) in size, and produced two to six immature conidia in chains with intercellular diaphragms. Foot cells of conidiophores were cylindrical and 45 to 65 μm × 8 to 14 µm (n = 40), with slight constrictions at basal septa, and followed by one to three short cells. Fungal hyphae were septate, branched, and flexuous to straight and 5 to 8 µm wide with indistinct to slightly nipple-shaped appressoria. These structures are typical of the genus Podosphaera, although chasmothecia were not observed. The sequence of ITS1-5.8s-ITS2 region of rDNA were amplified from conidia collected from infected leaves with universal primers ITS1F and ITS4 (White et al. 1990), sequenced and analyzed using the BLASTn search of GenBank. Amplicons were 603 bp (GQ927254) and exhibited 99.83% sequence identity with sequence of P. fusca from Cucurbita pepo (KJ698669) in Italy (Pirondi et al. 2015). The fungal species was identified as P. fusca (synonym P. xanthii ) by morphological characteristics and molecular analysis (Braun and Takamatsu 2000; Braun and Cook 2012). Pathogenicity tests were conducted by gently pressing the infected leaves onto leaves of six healthy H. tuberosus plants while six noninoculated plants served as controls. Plants were maintained in a greenhouse at 25 ± 2°C. Eight days after inoculation, symptoms similar to those observed under natural conditions developed on the inoculated leaves of H. tuberosus plants, whereas the control plants remained symptomless. The fungus on inoculated leaves was morphologically identical to that first observed in the field. P. fusca parasitizes a large number of asteraceous species including Euryops pectinatus (Saenz et al. 2000), Coreopsis lanceolata (Garibaldi et al. 2007), Cosmos caudatus (Siddiqui et al. 2011), Herba eupatorii (Ding et al. 2013) and etc. Powdery mildew caused by P. fusca has been reported on H. tuberosus in Russia (Farr and Rossman 2019). Golovinomyces ambrosiae was previously recorded on H. tuberosus in China (Huang et al. 2017; Radisek et al. 2018). This is the first report to our knowledge of powdery mildew P. fusca on H. tuberosus in China. It could cause significant yield losses and become a threat to production of H. tuberosus .

Fungal diversity in tomato (Solanum lycopersicum) leaves and fruits in Russia

Sequencing of cloned PCR-amplified species-specific rDNA fragments and isolation of axenic cultures from tomato fruits was carried out to study the mycobiota of tomato leaves and fruits in European part of Russia. DNA was extracted from the leaves, and library of ITS region fragments was constructed in E. coli by cloning of PCR products. This survey revealed fourteen species associated with disease-affected leaves: Septoria lycopersici, Fulvia fulva (=Cladosporium fulvum), Didymella glomerata (=Phoma glomerata), Cladosporium herbarum, Podosphaera fusca, Neocamarosporium goegapense (=Phoma betae), Rhizoctonia solani, Candida albicans, Dioszegia hungarica, Cladosporium cladosporioides, Didymella lycopersici, Alternaria infectoria, Alternaria alternata, Cryptococcus tephrensis. In the leaves from healthy plants without any visible symptoms DNA of three species was found: Aspergillus versicolor, Alternaria alternata, Aureobasidium pullulans. Analysis of axenic cultures isolated from green diseased tomato fruits revealed fungal species: Alternaria alternata, Alternaria solani, Phomopsis phaseoli, Fusarium equiseti, Chaetomium cochliodes, Clonostachys sp., Irpex lacteus, Colletotrichum coccodes. This research provides new information on the mycobiota of tomato in Southern Russia, the main tomato producing region of the country.

Powdery Mildew of Pterocypsela indica Caused by Podosphaera xanthii in China

Pterocypsela indica L. Shih (synonym Lactuca indica L.) is an annual or biennial herbaceous plant in the Asteraceae that has a worldwide distribution. In China, it is often used as a component for traditional Chinese medicine or as a leafy edible foraged from the wild. In September 2018 in Qianxi county (27.24 N, 106.01 E) of China, where a 2-ha field of P. indica was being planted, severe powdery mildew was observed on the leaves of P. indica. Approximately 35% of leaves on a plant were symptomatic, and about 40% of the plants were infected. Colonies were circular or irregular. White patches on the adaxial surface of the leaves appeared from June to September, and necrotic symptoms were observed in the autumn. To identify the pathogen, a voucher specimen (isolate CG) was examined for morphological characters using a microscope under 40× magnification. Each unbranched conidiophore was composed of a cylindrical foot cell followed by one to three short cells, ranging in size from 90 to 270 × 8 to 14 μm (n = 40). Conidia of the pathogen were ellipsoid-ovoid to barrel-shaped and measured 25 to 34 × 17 to 22 μm (n = 40). Fibrosin bodies were absent. Fungal hyphae were septate, branched, flexuous to straight, and up to 7 μm wide. These structures were identical with those of the anamorph of Podosphaera xanthii U. Braun & N. Shishkoff (Braun and Cook 2012), previously known as Podosphaera fusca (Cho et al. 2013). The pathogen was identified as P. xanthii on the basis of morphology and the sequence of ITS1-5.8s-ITS2 region of rDNA amplified by polymerase chain reaction with universal primers ITS-1 (5′-TCCGTAGGTGAACCTGCGGaaawf-3′) and ITS-4 (5′-TCCTCCGCTTATTGATATGC-3′) (White et al. 1990). The sequence submitted on December 6, 2017 (GenBank accession MG647826.1) of the ITS region exactly matched the sequences of P. xanthii accessions (e.g., GenBank accession nos. KX369541.1 and MG754404.1). Pathogenicity of the fungus was confirmed by performing Koch’s postulate as follows. Six healthy P. indica plants at the eight-leaf stage were selected for the test in the greenhouse. They were inoculated with conidia from an infected plant. Another six plants not inoculated were regarded as controls. After the inoculation, all plants were incubated in the greenhouse for symptom development. They were kept at room temperature, >70% relative humidity, 80 Lux, and 8 h light/day. The experiments were conducted twice. Fourteen days after incubation, powdery mildew symptoms appeared on the leaves of inoculated plants, and the pathogen morphology was similar to that of the original voucher, whereas control plants were still asymptomatic. Powdery mildew caused by P. xanthii has been reported on cucurbits, composites, and solanaceous crops in China (Fan et al. 2019) and on papaya in Korea (Joa et al. 2013). However, to the best of our knowledge, this is the first report of P. xanthii causing powdery mildew on P. indica in China. Owing to abundant dissemination of conidia of P. xanthii, the disease could be a threat to P. indica in Qianxi county of China, and this geography is right for P. xanthii to possibly spread to Lactuca sativa.

First report of powdery mildew caused by Podosphaera fusca on Euphorbia hirta in Odisha state, India

First report of powdery mildew caused by Podosphaera fusca on Euphorbia hirta in Odisha state, India

Importance of prumycin produced by Bacillus amyloliquefaciens SD-32 in biocontrol against cucumber powdery mildew disease.

Powdery mildew disease of cucurbits is caused mainly by Podosphaera fusca, which is one of the most important limiting factors in cucurbit production worldwide. Previously we reported that Bacillus amyloliquefaciens biocontrol strain SD-32 produces C17 bacillomycin D and [Ile 2002]surfactin, and that these metabolites play important roles in SD-32's biocontrol over cucumber gray mold disease. Our further investigation demonstrated that the culture broth and its supernatant suppressed cucumber powdery mildew disease in greenhouse experiments. However, the active principle(s) remained unknown. The active compound was isolated from the culture supernatant after anti-powdery mildew disease activity-guided purification and identified as prumycin. Prumycin significantly suppressed the disease, whereas bacillomycin D and [Ile 2002]surfactin did not. Prumycin did not induce the expression of plant defense genes (PR1a and VSP1), suggesting that it does not act via plant defense response. Light microscopic observations of prumycin-treated cucumber cotyledon suggested that prumycin inhibits the conidial germination of P. fusca. This study demonstrates that prumycin is a major factor in SD-32's suppression of cucumber powdery mildew disease. Our findings shed light for the first time on prumycin's role in biocontrol by Bacillus against this disease. © 2017 Society of Chemical Industry.

Use of multicolour fluorescence imaging for diagnosis of bacterial and fungal infection on zucchini by implementing machine learning.

Zucchini (Cucurbita pepo L.) is a cucurbitaceous plant ranking high in economic importance among vegetable crops worldwide. Pathogen infections cause alterations in plants primary and secondary metabolism that lead to a significant decrease in crop quality and yield. Such changes can be monitored by remote and proximal sensing, providing spatial and temporal information about the infection process. Remote sensing can also provide specific signatures of disease that could be used in phenotyping and to detect a pest, forecast its evolution and predict crop yield. In this work, metabolic changes triggered by soft rot (caused by Dickeya dadantii) and powdery mildew (caused by Podosphaera fusca) on zucchini leaves have been studied by multicolour fluorescence imaging and by thermography. The fluorescence parameter F520/F680 showed statistically significant differences between infected (with D. dadantii or P. fusca) and mock-control leaves during the whole period of study. Artificial neural networks, logistic regression analyses and support vector machines trained with a set of features characterising the histograms of F520/F680 images could be used as classifiers, discriminating between healthy and infected leaves. These results show the applicability of multicolour fluorescence imaging on plant phenotyping.

First Report of Powdery Mildew Caused by Podosphaera fusca on Potentilla supina in China

First Report of Powdery Mildew Caused by <i>Podosphaera fusca</i> on <i>Potentilla supina</i> in China