Causal Agent Of Powdery Mildew Research Articles

Estimation of breeding value of blackcurrant genotypes for growth vigour, plant habit and their susceptibility to fungal diseases.

The study was conducted in 2012–2014 at the Experimental Orchard of the National Institute of Horticultural Research in Skierniewice, central Poland. The aim of the research was to assess the breeding value, based on the general combining abilities (GCA), specific combining abilities (SCA) and reciprocal (RE) effects, of six dessert parental forms of blackcurrant for plant growth vigour, plant habit and resistance to fungal diseases: Podosphaera mors-uvae (causal agent of powdery mildew of currant), Drepanopeziza ribis (leaf anthracnose) and Cronartium ribicola (white pine blister rust). The plant material consisted of seedlings of F1 generation obtained by crossing of six blackcurrant genotypes: ‘Bona’, ‘Ceres’, clone D13B/11, ‘Sofiivska’, ‘Vernisazh’ and ‘Big Ben’ in a diallel design according to Griffing’s Method III.It was shown that the cultivars ‘Big Ben’, ‘Sofiivska’ and ‘Vernisazh’ had significantly positive GCA effects for growth vigour and resistance of plants to powdery mildew, whereas ‘Ceres’ – for plant habit, which indicated their high breeding value for these traits. The significantly positive SCA values were estimated for the hybrid family: ‘Big Ben’ × ‘Ceres’ for low susceptibility of plants to powdery mildew and anthracnose. Statistically significant effects for reciprocal crosses (RE) were obtained only for few hybrid families.

First report of powdery mildew caused by Phyllactinia pyri-serotinae Sawada on pear (Pyrus communis L.) from India.

In August 2020 powdery mildew was observed on pear cv. Fertility at the University research field in Shalimar, Srinagar (J&K), India (34° 08' 30.5'' N and 74° 51' 42.0'' E) with a disease incidence up to 30% (100 leaves observed from ten trees). White irregularly shaped fungal colonies were observed on the abaxial leaf surface which latter covered the whole leaf surface and developed black chasmothecia. The affected leaves appeared brittle, slightly curved upwards and dropped prematurely. Mycelium was hypophyllous, septate and measured 2.0 to 5.0 μm in width. Appressoria were nipple shaped, solitary or present in opposite pairs. Conidiophores were erect, up to 440.0 µm long (n=50), mostly centrally on upper surface of mother cells. Conidiophore foot-cells were filiform, followed by 1 to 3 shorter cells, producing single conidia at the tip. Conidia were hyaline, lanceolate, with a non-papillate rounded apex, measuring55.5 to 81.4 × 14.8 to 22.5 µm (n=50) and devoid of any conspicuous fibrosin bodies. Germ tube was, filiform, twisted, arose basally and measured 2.0 to 5.0 µm in width. Chasmothecia were hypophyllous, black, scattered, globose and measured 195.0 to 255.0 µm in diameter (n=50) having 8 to 12 equatorial, acicular, up to 270.0 µm length appendages with 25.9 to 44.4 µm diameter bulbous base (n=50) and obtuse or subacute apex. Asci in a chasmothecium were clavate to saccate, 62.9 to 81.4 × 18.5 to 22.2 µm (n=50), stalked, and two- spored. Ascospores were 33.3 to 40.7 × 12.9 to 18.5 µm (n=50), pale yellowish or golden brown in color. All morphological features were consistent with Phyllactinia pyri-serotinae (Braun and Cook 2012). To confirm the fungus identity at molecular level, DNA of two isolates was extracted from chasmothecia. The internal transcribed spacer (ITS) sequence of ribosomal DNA was amplified with the primers ITS1 and ITS4 (White et al. 1990) and sequenced. The ITS sequences submitted to NCBI GenBank under Accession No. MZ505441 and MZ505442 have 97 (416/427) & 96 (424/440) per cent and 99 (424/430) & 98 (428/438) per cent base pair matching, with that of P. pyri-serotinae isolates from Japan (AB080521 and AB985507), respectively. Thus, the pathogen was identified as Phyllactinia pyri-serotinae Sawada based on morphological and molecular sequence analyses. The pathogenicity tests of both the isolates were carried out on one year old pear saplings (cv. Fertility) and repeated twice. The inoculum was prepared by collecting P. pyri-serotinae conidia in sterile distilled water from infected pear leaves. Three saplings were inoculated by spraying (15ml per sapling) the inoculum (3 x 105 spores ml-1) on leaf surfaces, while same number of saplings sprayed with sterile distilled water served as non-inoculated controls. After 15 days of incubation at 25oC in a green house, similar symptoms as observed on naturally infected plants were observed on inoculated plants and uninoculated plants remained symptomless. The pathogen of interest observed on inoculated plants was morphologically characterized and found to be similar to P. pyri-serotinae. The voucher specimen was deposited in the Herbarium Crytogamae Indiae Orientalis (HCIO), IARI, New Delhi under accession number 52213. Pear is the third most important temperate fruit grown in India (Chattopadhyay 2009) and our study reveal P. pyri-serotinae as the new causal agent of powdery mildew in addition to P. guttata (Dhar and Shah 1982) under Indian conditions.

Virulence of Blumeria graminis f. sp. tritici in Brazil, South Africa, Turkey, Russia, and Australia

The globally distributed causal agent of powdery mildew on wheat, Blumeria graminis f. sp. tritici (Bgt), is one of the most rapidly adapting plant pathogens and requires monitoring for shifts in virulence to wheat resistance (Pm) genes. Virulence frequencies were assessed in a total of 346 Bgt isolates from several countries that had either lately recorded increasing powdery mildew epidemics (Brazil, South Africa, and Australia) or not recently been surveyed (Turkey and Russia). The results were compared to previously published surveys of United States and Egyptian Bgt (390 isolates). Many of the Pm genes that have potentially been employed longer (Pm1a–Pm17) were shown to have lost effectiveness, and the complexity of virulence to those genes was higher among Brazilian isolates than those from any other country. Some cases of high virulence frequency could be linked to specific Pm gene deployments, such as the widespread planting of cultivar Wyalkatchem (Pm1a) in Australia. Virulence was also assessed to a set of Pm genes recently introgressed from diploid and tetraploid wheat relatives into a hexaploid winter wheat background and not yet commercially deployed. The isolate collections from Fertile Crescent countries (Egypt and Turkey) stood out for their generally moderate frequencies of virulence to both the older and newer Pm genes, consistent with that region’s status as the center of origin for both host and pathogen. It appeared that the recently introgressed Pm genes could be the useful sources of resistance in wheat breeding for other surveyed regions.

Powdery Mildew Resistance Genes in European Barley Cultivars Registered in the Czech Republic from 2016 to 2020.

Barley is an important crop grown annually on about 55 Mha and intensively cultivated in Europe. In central and north-western Europe, spring and winter barley can be grown in similar environments which creates suitable conditions for the development of barley pathogens, including Blumeria graminis f. sp. hordei, the causal agent of powdery mildew. Apart from pesticide application, it can be controlled by inexpensive and environmentally-friendly genetic resistance. In this contribution, results of the resistance gene identification in 58 barley cultivars to powdery mildew are presented. In 56 of them their resistances were postulated and in two hybrid cultivars a recently developed method of gene identification was used. In total, 18 known resistance genes were found and several unknown genes were detected. In spring barley, a gene of durable resistance mlo is still predominant. MlVe found in winter SU Celly was the only new resistance gene recorded in barley cultivars registered in the Czech Republic in this time span. Since 2001 eight new genes of specific resistance have been identified in cultivars registered in the country and their response under field conditions is discussed, including the corresponding responses of the pathogen population due to directional selection. Different strategies for breeding spring and winter barley are recommended.

Defense responses induced by ulvan in wheat against powdery mildew caused by Blumeria graminis f. sp. tritici

Ulvan is a water-soluble sulfated heteropolysaccharide extracted from the cell walls of the green seaweeds Ulva spp. This polysaccharide is known to induce resistance and protect plants against a broad range of plant pathogenic fungi, such as Blumeria graminis f. sp. tritici (Bgt), the causal agent of powdery mildew in wheat. We aimed to study the defense mechanisms induced by ulvan against Bgt in susceptible wheat by investigating the defense-related gene expression, enzymes activity, accumulation of phenolic compounds and hydrogen peroxide (H2O2), as well as the development of Bgt infection structures in vitro and in planta. Symptoms were reduced by 42% in ulvan-treated plants. In vitro, ulvan did not inhibit conidial germination of Bgt but in planta, increased the appressorial germ tubes without haustorium. Ulvan increased the presence of fluorescent papillae and accumulation of H2O2 at the penetration sites of Bgt, as well as the content of phenolic compounds. POX, PAL and LOX activities were stimulated in ulvan-treated plants during the first 48 h after inoculation. However, few of defense-related genes studied were differentially expressed in infected plants after ulvan treatment. By contrast, in non-infected conditions, ulvan up-regulated the expression of genes involved in phenylpropanoid metabolism, i.e. PAL, CHS, COMT, ANS and FLS, genes encoding pathogenesis-related proteins, i.e. PR1, PR9, PR15, and LOX during the first 96 h after treatment. This study provides new insights about the multiple ulvan effects on wheat defense responses, and especially the elicitation of the phenylpropanoid pathway leading to phenolic compounds accumulation, which could be involved in cell wall reinforcement.

Development of Quantitative Real-Time PCR Assays to Quantify Erysiphe pisi and Erysiphe trifolii and Its Implementation for Monitoring Their Relative Prevalence in Pea Crops in Spain and Tunisia

E. pisi was thought to be the only causal agent of powdery mildew in peas, with three genes, er1, er2 and Er3, conferring resistance to this pathogen. Recently, E. trifolii has also been found to cause this disease in peas in different countries, but its relevance in pea powdery mildew disease worldwide is unknown. The objective of this study was to develop a method to identify and quantify E. pisi and E. trifolii and use it to analyze the relative prevalence of E. pisi and E. trifolii in pea fields in Spain and Tunisia. We also wanted to discern the effect of the er1, er2 and Er3 resistance genes on the relative amount of E. pisi/E. trifolii. Using the polymorphic sites present between E. pisi and E. trifolii ITS sequences, we developed a qPCR method capable of identifying and quantifying these pathogens. Our results revealed, for the first time, the occurrence of E. trifolii in Tunisia and that the presence of er1, er2 and Er3 genes have a clear effect on the ratio E. pisi/E. trifolii in both countries.

Occurrence of the Hyperparasite Ampelomyces quisqualis on Golovinomyces neosalviae (Erysiphaceae), Causal Agent of Powdery Mildew on Common Sage (Salvia officinalis)

Hamzeh, S., W. Naffaa and M.F. Azmeh. 2022. Occurrence of the Hyperparasite Ampelomyces quisqualis on Golovinomyces neosalviae (Erysiphaceae), Causal Agent of Powdery Mildew on Common Sage (Salvia officinalis). Arab Journal of Plant Protection, 40(2): 158-163. https://doi.org/10.22268/AJPP-040.2.158163 Ampelomyces quisqualis, the oldest mycoparasite of powdery mildew (PM), has been widely studied due to its potential in biocontrol. Many strains of this hyperparasite have been experimented worldwide and some of them were successfully applied for biocontrol, but others have been less efficient. No previous identification of Ampelomyces strains has been done in Syria, but some isolates were morphologically identified in the coastal region. There was no indication of Ampelomyces occurrence in any other location in Syria. During this three years survey (2019–2021), 73 plant samples were collected from five governorates, including coastal and southern regions in Syria. Ampelomyces pycnidia were detected in five samples from the coastal area and a new unpredictable finding of Ampelomyces sp. was found in southern Syria. This new occurrence of Ampelomyces isolate (S.ham82) is documented on a new mycohost; Golovinomyces neosalviae, the causal agent of PM on common sage (Salvia officinalis). Successful isolation of S.ham82 on PDA was conducted and parasitic activity was assessed by artificial inoculation using In vitro detached leaf assay. Morphological characteristics of this isolate were determined and compared with isolate Bah1 from the coastal region. Ampelomyces sp. (S.ham82) pycnidia size were 77.44 (±17.16) x 25.28 (±6.12) µm in natural host, 125.27 (±42.34) x 115.95 (±40.14) µm, 189.51 (±60.06) x 167.64 (±52.41) µm on PDA media pre and post artificial inoculation, respectively, and 88.24 (±20.05) x 27.98 (±5.68) µm on inoculated detached leaves. Conidia were also morphologically characterized and measured 8.11 (±0.87) x 3.88 (±0.51) µm in natural host, 8.86 (±1.65) x 3.18 (±0.80) µm in PDA pre and post artificial inoculation, respectively, and 7.82 (±0.69) x 3.61 (±0.37) µm in inoculated detached leaves. To our knowledge, this is the first report of the natural occurrence of Ampelomyces sp. in G. neosalviae on Saliva officinalis. Keywords: Ampelomyces sp., Common sage, Golovinomyces neosalviae, Syria.

Fungicide activity of milk and whey powders towards Erysiphe necator, the causal agent of powdery mildew of grapevine

Fungicide activity of milk and whey powders towards <i>Erysiphe necator</i>, the causal agent of powdery mildew of grapevine

Cucumber powdery mildew detection using hyperspectral data

This study aimed to understand the spectral changes induced by Podosphaera xanthii, the causal agent of powdery mildew, in cucumber leaves from the moment of inoculation until visible symptoms are apparent. A principal component analysis (PCA) was applied to the spectra to assess the spectral separability between healthy and infected leaves. A spectral ratio between infected and healthy leaf spectra was used to determine the best wavelengths for detecting the disease. Additionally, the spectra were used to compute two spectral variables [i.e., the red-well point (RWP) and the red-edge inflexion point (REP)]. A linear support vector machine (SVM) classifier was applied to certain spectral features to assess how well these features can separate the infected leaves from the healthy ones. The PCA showed that a good separability could be achieved from 4 days post-inoculation (DPI). The best model to fit the RWP and REP wavelengths corresponded to a linear model. The linear model had a higher adjusted R2 for the infected leaves than for the healthy leaves. The SVM trained with five first principal components scores achieved an overall accuracy of 95% at 4 DPI (i.e., two days before the visible symptoms). With the RWP and REP parameters, the SVM accuracy increased as a function of the day of inoculation, reaching 89% and 86%, respectively, when symptoms were visible at 6 DPI. Further research must consider a higher number of samples and more temporal repetitions of the experiment.

Fungal diseases of trees and shrubs growing in Siberian Square in Warsaw

A good condition of trees and shrubs growing in urban green areas is one of the key aspects of management. Plant monitoring, including recognition of symptoms of diseases caused by pathogenic fungi and prevention of their spread, is one of the ways of supporting the process of maintenance of green areas. The aim of the study was to conduct preliminary investigations of plants growing in Siberian Square in Warsaw infected by phytopathogenic fungi. The research carried out in 2017-2019 in Siberian Square in Warsaw revealed that the most common diseases observed on the trees and shrubs were caused by powdery mildew fungi infecting maples, poplars, apple trees, and barberry shrubs. Sawadaea tulasnei, Erysiphe adunca, Erysiphe berberidis , and Podosphaera leucotricha ( Erysiphales ) were identified as the causal agents of powdery mildew . Pathogens causing leaf spots and leaf lesions were identified as Venturia inaequalis on Malus x purpurea ’Ola’ and Rhytisma acerinum on Acer platanoides . Rust caused by Melampsora laricis-populina ( Pucciniales ) and basidiomata of Pleurotus ostreatus were detected on infected Populus nigra ‘Italica’ trees

Paraffin oil induces resistance against powdery mildew in grapevine through salicylic acid signaling.

Mineral oils have been widely used in the pest control of several crops. However, their mode of action is poorly understood, especially in the case of their antifungal properties. The possible direct fungicidal activity and the stress-inducing capability of paraffin oil on grapevine were examined using Vitis vinifera L. cv 'Kékfrankos' cuttings and the fungus Erysiphe necator, the causal agent of powdery mildew. Our experiments demonstrated that paraffin oil does not have fungicide activity on E. necator, but induces significant stress-related changes in grapevine physiology. Elevated H2 O2 production and the accumulation of the phytohormone salicylic acid were measured. Secondary thickening of the cell wall by lignin deposition and the accumulation of phenolic compounds were also observed. Some enzyme activities related to the detoxification of reactive oxygen species, disease response, and the synthesis of lignin were changed in accordance with the determined changes in cell wall composition and H2 O2 levels. The results suggest that paraffin oil induces stress responses on grapevine leaves through oxidative burst, and this response is systemized by salicylic acid. The accumulation of lignin and water-soluble phenolics may be directly responsible for the paraffin oil-induced resistance of grapevine against powdery mildew. © 2021 Society of Chemical Industry.

Detection of Erysiphe necator, the Causal Agent of Powdery Mildew on Grapevine, and Determination of their Mating Types in Southern Syria Using Some Molecular Markers

Powdery mildew caused by Erysiphe necator, is one of the most economically damaging diseases of grapevine throughout the world. This study aimed to identify the mating types of this pathogen in Syria using molecular markers. Three DNA extraction methods: Promega Kit, phenol chloroform isoamyl alcohol (PCI) and SDS were compared. The amount and quality of DNAs obtained by the SDS method were suitable for PCR amplification and other molecular assays. PCR amplification using specific primers (Uncin 144 and Uncin 511) was performed and the expected amplicon of 300-400 bp was obtained from 29 isolates of E. necator collected from different geographical locations and from different grapevine cultivars. Results obtained showed that E. necator may cause atypical symptoms similar to those of downy mildew, in some grapevine cultivars according to the environmental conditions and training system used. Isolates of E. necator were classified into four groups according to geographical locations and grapevine cultivar, based on the observed variation in banding pattern with E07 primer and the constructed phenogram by using UPGMA. RAPD analysis of 39 E. necator isolates using the primer E07 showed the presence of two mating types, and the frequency of each varied depending on the geographical location, with a predominance of the - mating type which did not produce a 1000 bp band using the PCR primer E07. Keywords: Powdery mildew, Erysiphe necator, RAPD, mating type, DNA extraction.

The MLO1 powdery mildew susceptibility gene in Lathyrus species: The power of high-density linkage maps in comparative mapping and synteny analysis.

Powdery mildews are major diseases for a range of crops. The loss of function of specific Mildew Locus O (MLO) genes has long been associated with pre-haustorial plant resistance to powdery mildew and has proven to be durable in several species. Erysiphe pisi is the major causal agent of powdery mildew in pea (Pisum sativum L.) and in the closely related Lathyrus sativus L. and Lathyrus cicera L. PsMLO1 has been extensively studied in pea. However, no MLO gene family members have been isolated and characterized in Lathyrus species so far. In this study, MLO1 genes were isolated and characterized in L. sativus and L. cicera genotypes with varied levels of partial resistance against powdery mildew. Phylogenetic analyses confirmed that Lathyrus MLO1 belongs to Clade V, like all dicot MLO proteins associated with powdery mildew susceptibility. A L. sativus recombinant inbred line population (RIL) was genotyped by sequencing to develop a high-density L. sativus genetic linkage map. DNA sequence polymorphisms between the analyzed genotypes allowed the location of MLO1 in the newly developed L. sativus RIL genetic linkage map. Subsequent comparative mapping between L. sativus and L. cicera genetic maps and P. sativum, Lens culinaris Medik., and Medicago truncatula Gaertn. reference genomes revealed important aspects of the conservation of the MLO1 locus position and of the overall chromosomal rearrangements occurring during legume evolution, with relevance to legume disease resistance breeding programs.

Year, Location, and Variety Impact on Grape-Associated Mycobiota of Arkansas-Grown Wine Grapes for Wine Production.

Wine grape berries (Vitis spp.) harbor a wide variety of yeasts and filamentous fungi that impact grapevine health and the winemaking process. Identification of these fungi could be important for controlling and improving wine production. The use of high-throughput sequencing (HTS) strategies has enabled identification and quantification of bacterial and fungal species in vineyards. The aims of this study were to identify mycobiota from Cabernet Sauvignon and Zinfandel (V. vinifera), Carlos and Noble muscadines (V. rotundifolia), Cynthiana (V. aestivalis), and Vignoles hybrid (cross of different Vitis spp.) grapes, and investigate the effect of grape variety, location, and year on grape fungal communities. Grape berries were collected in 2016 and 2017 from four vineyards located in Arkansas. The HTS of the Internal Transcribed Spacer 1 region was used to identify grape indigenous epiphytic and endophytic fungal communities. The predominant genera identified on the Arkansas wine grapes were Uwebraunia, Zymoseptoria, Papiliotrema, Meyerozyma, Filobasidium, and Curvibasidium. Overall, the data suggested that grape fungal community distribution and relative abundance were influenced by grape variety, year, and location, but each was influenced to a different extent. Not only were grape mycobiota influenced by year, variety, and location but also it appeared that communities from the previous year impacted microbial communities the following year. For example, an increase of the mycoparasite Ampelomyces quisqualis was noticed in 2017 on grapes that carried the causal agent of powdery mildew, Erysiphe necator, in 2016, thus, amplifying the importance of vineyard microbiota knowledge for disease management and winemaking.

First report of Erysiphe corylacearum, agent of powdery mildew, on hazelnut (Corylus avellana) in Romania.

Romania has an area dedicated to hazelnut (Corylus avellana L.), covering 890 hectares as of 2019. During October 2020, powdery mildew symptoms were observed on the upper side of leaves of hazelnut 'Tonda di Giffoni' in two commercial orchards in Dudeștii Vechi, Romania (Fig. 1). The disease was present on 70% of the trees in planting, with at least 5 leaves per tree having powdery mildew. Micromorphological examination revealed amphigenous, hyaline, branched, septate mycelial patches of 2.3 to 3.6 μm in diameter. Conidiophores measured 24-60 × 5-6 (average: 45 × 6) μm and consisted of erect, cylindrical to flexuous foot cells, followed by 1-2 shorter cells. Ellipsoid, ovoid to doliform conidia were produced singly and they measured 19-35 × 16-24 (average: 28 × 19) μm. Chasmothecia were spherical, 75 to 107 (average: 88) μm in diameter. Nine to thirteen straight, sometimes flexuous, appendages measured 54 to 92 (average: 66) μm in length and they had five times dichotomous branched apices with curved tips (Fig. 2). Each chasmothecium contained three to five ellipsoid, ovoid to subglobose asci measuring 41-58 × 29-55 μm (average 52 × 43) μm. The asci contained four to eight ascospores measuring 13-24 × 11-15 (average 18 × 14) μm. Morphological identification was confirmed by sequencing the ITS-region of rDNA using two isolates from leaves, stored as frozen mycelium at -20°C. PCR was performed with Erysiphales-specific primer pair PMITS1/PMITS2 (Cunnington et al. 2003). The obtained sequences were deposited in GenBank (Accession n° MW423075, MW423076). Blast analysis of both sequences had 100% identity to ITS rDNA sequences of Erysiphe corylacearum from Azerbaijan (Abasova et al. 2018; Accession n° LC270863), Turkey (Sezer et al. 2017; KY082910), Switzerland (Beenken et al. 2020; MN82272), Iran (Arzanlou et al. 2018; MH047243), Italy (Mezzalama et al. 2020; MW045425) and 99% identity from Georgia (Meparishvili et al. 2019; MK157199). The sequences had a lower percent identity (83%) to Phyllactinia guttata (Accession n° AB080558) (Fig. 3). Pathogenicity was verified on one-year-old plants of C. avellana 'Tonda di Giffoni', which were artificially inoculated with a conidial suspension from infected leaves (n = 25). Inoculated plants were incubated at 20 to 28°C with 70 to 80% relative humidity. White mycelium appeared on the upper surface of the leaves at 8 to 10 days after inoculation. No symptoms were found on control plants sprayed with sterile water. The fungus present on inoculated leaves was morphologically identical to the original isolates from diseased trees from the field. E. corylacearum is native to East Asia and was previously reported in Japan on wild species of Corylus (Takamatsu et al. 2015; Accession n° LC009928). The pathogen most likely spread into Europe from east to west of Europe (Heluta et al. 2019), through the Caucasus, starting from Turkey, Azerbaijan, Georgia, and Iran. P. guttata was considered the only causal agent of powdery mildew on hazelnut in most countries, including Romania (Brown 1995). Compared to P. guttata, which generally develops a mycelium on the underside of leaves, E. corylacearum grows with a white mycelium on the upper side of the leaves. Recently, E. corylacearum on C. avellana was reported also in Ukraine (Heluta et al. 2019), from which it could have moved to Romania. Crop protection strategies for hazelnut should be revised according to the new pathogen occurrence.

A Hybrid Genome Assembly Resource for Podosphaera xanthii, the Main Causal Agent of Powdery Mildew Disease in Cucurbits.

Podosphaera xanthii is the main causal agent of powdery mildew in cucurbits and, arguably, the most important fungal pathogen of cucurbit crops. Here, we present the first reference genome assembly for P. xanthii. We performed a hybrid genome assembly, using reads from Illumina NextSeq550 and PacBio Sequel S3. The short and long reads were assembled into 1,727 scaffolds with an N50 size of 163,173 bp, resulting in a 142-Mb genome size. The combination of homology-based and ab initio predictions allowed the prediction of 14,911 complete genes. Repetitive sequences comprised 76.2% of the genome. Our P. xanthii genome assembly improves considerably the molecular resources for research on P. xanthii-cucurbit interactions and provides new opportunities for further genomics, transcriptomics, and evolutionary studies in powdery mildew fungi.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

First Report of Podosphaera xanthii Causing Powdery Mildew on Zinnia elegans in Taiwan.

Zinnia elegans L., known as common zinnia, is an annual flowering plant belonging to the Asteraceae family and native to North America. The plant has colorful flowers and is one of the popular ornamental bedding plants for gardening. In March 2020, powdery mildew symptoms were observed in a zinnia floral field with an incidence of >70% in Dacun Township, Changhua County, Taiwan. The symptoms were spotted on the stems, flower petals and leaves which appeared as irregular colonies and white patches on the surfaces. When disease progressed, most of the plant surfaces were covered by the white fungal colonies and became yellowish. Under microscopic examination, hyphal appressoria of the fungus were indistinct or slightly nipple-shaped. The conidiophores were unbranched, erect, straight, smooth to slightly rough, 75.0 to 200.0 × 10.0 to 15.0 µm (n=10), composed of a cylindrical, flexuous foot cell, 40.0 to 100.0 × 8.8 to 15.0 µm (n=10), and following 1 to 5 shorter cells. The conidia were ellipsoid to ovoid, 25.0 to 37.5 × 15.0 to 23.8 µm (n=60), with an average length-to-width ratio of 1.8 and contained fibrosin bodies. No chasmothecia were found. Three voucher specimens (TNM Nos. F0033680, F0033681, and F0033682) were deposited in the National Museum of Natural Science, Taichung City, Taiwan. To confirm the identification, the internal transcribed spacer (ITS) regions of the three specimens were amplified using primer pairs ITS1/PM6 and PM5/ITS4 (Shen et al. 2015) and sequenced from both ends. The resulting sequences were deposited in GenBank under Accession Nos. MT568609, MT568610, and MT568611. The sequences were identical to each other and shared a 100% identity with that of Podosphaera xanthii MUMH 338 on Z. elegans from Japan (Accession No. AB040355) (Ito and Takamatsu 2010) over a 475 bp alignment. Accordingly, the fungus was identified as P. xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012) based on its morphological and molecular characters. Pathogenicity was demonstrated through inoculation by gently pressing naturally infected leaves onto leaves of three healthy potted common zinnia that had been sprayed with 0.02% Tween 20. Additional three non-inoculated plants treated in the same way without inoculating the powdery mildew served as the controls. Powdery mildew colonies were observed on inoculated leaves after 10 days at room temperature, later the diseased leaves became yellowish and deteriorated. The morphological traits of the fungus on the inoculated leaves were similar to those of the first observed. In addition, the ITS sequence from a colony on the inoculated leaves was 100% identical to MT568609-MT568611, fulfilling the Koch's postulates. All the controls remained symptomless. Z. elegans is known to be a host for different species of powdery mildew in the genus Erysiphe, Golovinomyces, and Podosphaera (Farr and Rossman 2020). In Taiwan, powdery mildew has been briefly reported on zinnia without detailed descriptions (Hsieh 1983). This study confirmed P. xanthii as a causal agent of powdery mildew in Taiwan and the awareness of the disease may benefit the floral industry. To our knowledge, this is the first confirmed report of P. xanthii on Z. elegans in Taiwan.

Deciphering the modes of action of Golubevia sp., an antagonist against the causal agent of powdery mildew in wheat, using an mRNA-based systems approach

Biocontrol agents are living organisms with the potential to suppress populations of plant pathogens or pests in a cropping system. The complex interplay between the different players and the changing environment, results in a combination of different modes of action. Here, we applied an mRNA-based systems approach to gain insight into the antagonist-pathogen-host interaction of Golubevia sp. isolates BC0812 and BC0850 with the causal agent of wheat powdery mildew, Blumeria graminis f. sp. tritici, in planta over time. Bioassays were performed on potted wheat plants (water-treated control, antagonist, pathogen, antagonist+pathogen) under controlled conditions. A significantly higher percentage of mildew conidia were parasitized after treatment with Golubevia sp. BC0812 with 26% and BC0850 with 16% compared to the water control with 1%. Differential gene expression analysis of antagonists, pathogen and host 5, 6, 7, and 11 days after inoculation (dai) with the antagonist pointed to a combination of different modes of action: An interplay of modulating plant defense responses, impairing conidiogenesis of the pathogen by scavenging H2O2, facultative hyperparasitism and nitrogen competition. Microscopic observations supported the suggested hyperparasitism as thin mycelium could be observed on Bgt conidia at 6 dai and later.Taken together the results allowed the formulation of new hypothesis regarding modes of action and the interplay between antagonist, pathogen and host. It showed that a solid molecular understanding of the antagonist-pathogen relationship over time is essential for less biased mode of action studies. Understanding this complex interplay is the basis for targeted optimization strategies and allows discovery of new potential targets and markers for future biocontrol development.

First report of powdery mildew caused by Golovinomyces bolayi on okra (Abelmoschus esculentus)

Powdery mildew collected from Abelmoschus esculentus (Malvaceae) in Karaj (Iran) was identified as Golovinomyces bolayi, a species that was recently delimited from the G. orontii species complex. The fungus was identified based on morphological characteristics of its asexual and sexual morphs, and rDNA ITS sequence analyses. This is the first identification of Golovinomyces bolayi as the causal agent of powdery mildew on Abelmoschus esculentus globally. Earlier, closely related taxa from the G. orontii species complex were reported from okra from different parts of the world.

Collection of conidia of Podosphaera xanthii by honey bee workers

Honey bees, Apis mellifera, actively collect a range of materials including pollen and fungal spores. However, the interaction between honey bees and fungal spores is largely unexplored. Therefore, this study aimed to assess the corbicular contents of workers foraging on zucchini leaves severely affected by powdery mildew. The dimensions (length and width) of conidia removed from the corbiculae of honey bee workers and from the zucchini leaves were similar and conidia matched the description of Podosphaera xanthii, the causal agent of powdery mildew of cucurbits. Our findings that corbicular loads comprised only conidia of P. xanthii confirm that honey bees exhibited constancy, just as they almost always forage on a single species of flower per foraging trip, and highlight the importance of understanding the behaviour of honey bee workers in regards to the collection of fungal spores.