Podosphaera Xanthii Research Articles

Induction of resistance of Podosphaera xanthii (hull-less pumpkin powdery mildew) to triazole fungicides and its resistance mechanism.

The aim of this study was to uncover the molecular mechanism through which fungicide resistance develops in Podosphaera xanthii, a fungi that causes powdery mildew in hull-less pumpkin. Treatments of inoculated P. xanthii were carried out on leaves of hull-less pumpkin and subsequently treated with kinds of triazole fungicide for seven generations. Resistant strains of P. xanthii thus obtained were evaluated for their resistance levels. The resistance levels of the fungi to four fungicides of were high except that of the propiconazole-resistant strain, which showed moderate resistance. The F7 generations of five resistant strains thus obtained were cultured continuously for five generations without fungicide induction, and their resistance level were found to be relatively stable. The DNA of the sensitive strain and the five kinds of resistant strains were extracted by the sodium dodecyl sulfate (SDS) method and its internal transcribed spacer (ITS) region was amplified by using ITS1/ITS4 primer and specific primer F/R and they were sequenced respectively. The DNA sequence comparison of resistant and sensitive strains showed that the base pairs of tebuconazole-resistant strains and flusilazole-resistant strains were mutated, with mutation rates of 4.8% and 1.6%, respectively. The base pairs of the other three resistant strains did not change.

Inhibitory Effects of Blue Light-Emitting Diode Irradiation on Podosphaera xanthii Conidial Release and Infection of Melon Seedlings

Powdery mildew fungi infect plant leaves, reducing the yield of infected melon plants. Therefore, an eco-friendly method of controlling powdery mildew in melon plants needs to be developed. A previous study described how the morphological characteristics of the conidiophores of the melon powdery mildew fungus Podosphaera xanthii Pollacci (designated KMP-6N) grown under greenhouse (natural) conditions and red light-emitting diode (LED) irradiation differed from those grown under growth chamber conditions and blue LED irradiation. In the present study, conidiophores with unconstricted conidia under blue light were collected and inoculated onto host leaves through micromanipulation; the unconstricted conidia germinated and infected the leaves, producing vigorously elongated hyphae. The number of conidia collected, the initial times of conidial release from single colonies, and the number of conidia remaining in chains on conidiophores were examined with electrostatic techniques. Under red light, the number of collected conidia gradually increased with the light irradiation period. The initial conidial release occurred between 2 to 4 h; the number of conidia remaining on the conidiophores gradually decreased and, eventually, the conidiophore lengths became shorter. In contrast, under blue light, few conidia were collected at any given time; the number of conidia on the conidiophores gradually increased and, eventually, the conidiophore lengths became longer. Next, the effects of red and blue light on the spread of powdery mildew infection by placing a KMP-6N-infected melon seedling at the centre of a tray containing healthy melon seedlings were examined. Almost all healthy seedlings caused powdery mildew symptoms at ca. 21 days after red light irradiation, whereas only healthy seedlings near the infected seedlings showed symptoms after blue light irradiation. Thus, the spread of melon powdery mildew infection clearly differed between red and blue light irradiation. This is the first report describing the effects of red and blue light on the spread of P. xanthii infection from a single infected seedling to healthy host seedlings; their results provide insight into the ecological mechanisms of powdery mildew conidial scatter from conidiophores.

First Report of Podosphaera xanthii Causing Powdery Mildew on Melothria indica in China.

Melothria indica Lour. is a wild ornamental plant widely distributed in South China. In November 2020, powdery mildew symptoms with 100% (60 plants) incidence were observed on M. indica climbing on a fence in Zhanjiang (21.17N,110.18E), Guangdong, China. The symptoms were typical for powdery mildew with white colonies on leaf surfaces and stems. Conidiophores appeared in all symptomatic tissues. Chasmothecia were observed only during the late stage of disease. Hyphae were hyaline, branched, and septate. Conidiophores were erect, hyaline, smooth, and had a dimension of 61.5 to 185.6 µm × 8.5 to 14.5 µm (n=20) and a cylindrical, flexuous foot cell, followed by 1 to 5 (-6) shorter cells. Conidia were ellipsoid to ovoid and had a dimension of 24.5 to 38.5 μm×15.5 to 21.8 μm (n=50) with well-developed fibrosin bodies. Germ tubes were in the lateral position. Chasmothecia were gregarious or scattered, subglobose, (64.8-) 65.5 μm to 115.5 (-120.5) μm (n=20) in diameter. The appendages were few, and hyphoid. Ascus one per ascomas, clavate, or subglobose, 56.5 to 78.3 (-90) μm×52.5 to 60.5 (-72) (n=20) μm. Each ascus had eight ascospores that were broadly ellipsoid and sized 13.8 to 18.6 μm×12.5 to 16.5 μm (n=30). The morphological characteristics were consistent with the previous description of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012). Three voucher specimens, Ms-1, Ms-2, and Ms-3, were deposited in the fungus collection at Aquatic Organisms Museum of Guangdong Ocean University, and were used for molecular analysis. Their internal transcribed spacer (ITS) regions were amplified using primers ITS1/ITS4. Amplicons were sequenced and submitted to GenBank (accession no. MW512919, MW512920, and MW512921). The sequences were identical to each other and 100% similar to two of P. xanthii (Accession No. MT472035 and MN818563). On the basis of the morphological and molecular characteristics, the fungus was identified as P. xanthii. Pathogenicity was examined through inoculation by gently pressing the naturally infected leaves onto healthy ones of three potted M. indica plants with three leaves. Healthy leaves were leaves of three further plants which served as the control. White powdery mildew colonies with an incidence of 100% were similarly observed after 7 days at 28 °C and 80% relative humidity in a greenhouse. The fungal colonies on diseased leaves were morphologically identical to the specimen, and the control plants developed no symptoms. The Koch's postulates have completed. Golovinomyces cichoracearum is known to cause powdery mildew on M. indica in China (Liu et al. 2015). P. xanthii (synonym:P. fusca p.p.) is the cause of powdery mildew on cucurbits worldwide (Braun and Cook 2000), including M. indica (synonym:M. japonica) in Korea (Kwon et al. 2015) and Japan (Takamatsu et al. 2005), but hitherto not for China. While, the teleomorph of the fungus on cucurbits is seldom found worldwide and in China only in the north (Liu et al. 2011), chasmothecia are recorded for here southern China (21.17N,110.18E).

First Report of Powdery Mildew on Zinnia elegans Caused by Podosphaera xanthii in Northeast China.

HomePlant DiseaseVol. 106, No. 3First Report of Powdery Mildew on Zinnia elegans Caused by Podosphaera xanthii in Northeast China PreviousNext DISEASE NOTE OPENOpen Access licenseFirst Report of Powdery Mildew on Zinnia elegans Caused by Podosphaera xanthii in Northeast ChinaChao Fan, Miao Liu, Wei Li, Yongcai Lai, Lili Tang, and Yingdong BiChao Fanhttps://orcid.org/0000-0001-6307-7951Institute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, ChinaHeilongjiang Academy of Agricultural Sciences Postdoctoral Program, Harbin, Heilongjiang 150086, ChinaSearch for more papers by this author, Miao LiuInstitute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, ChinaSearch for more papers by this author, Wei LiInstitute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, ChinaSearch for more papers by this author, Yongcai LaiInstitute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, ChinaSearch for more papers by this author, Lili TangHeilongjiang Academy of Agricultural Sciences Postdoctoral Program, Harbin, Heilongjiang 150086, ChinaInstitute of Cash Crops, Heilongjiang Academy of Agricultural Sciences, Harbin, ChinaSearch for more papers by this author, and Yingdong Bi†Corresponding author: Y. D. Bi; E-mail Address: [email protected]Institute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, ChinaSearch for more papers by this authorAffiliationsAuthors and Affiliations Chao Fan1 2 Miao Liu1 Wei Li1 Yongcai Lai1 Lili Tang2 3 Yingdong Bi1 † 1Institute of Crop Cultivation and Tillage, Heilongjiang Academy of Agricultural Sciences, Heilongjiang 150086, Harbin, China 2Heilongjiang Academy of Agricultural Sciences Postdoctoral Program, Harbin, Heilongjiang 150086, China 3Institute of Cash Crops, Heilongjiang Academy of Agricultural Sciences, Harbin, China Published Online:17 Jan 2022https://doi.org/10.1094/PDIS-06-21-1218-PDNAboutSectionsView articlePDFSupplemental ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmailWechat View articleZinnia (Zinnia elegans L.) is a common garden flowering plant in China, which can also grow well in the cold regions of northeast China. In August 2020, powdery mildew on zinnia was observed in the garden of the International Agricultural Science and Technology Innovation Center of Heilongjiang Province (126°30′ N, 45°47′ E), Harbin, Heilongjiang Province, China. More than 95% of plants were affected in the garden. Powdery mildew colonies began as small white spots on the upper surface of the older leaves and then spread to entire leaves. Subsequently, younger leaves developed rapid symptoms, resulting in premature senescence of the plants. Conidia collected from infected plant tissues were ellipsoid-ovoid to barrel-shaped, with distinct fibrosin bodies visible in their cytoplasm, and measured 20 to 28 × 14 to 19 μm with a length/width ratio of 1.5 to 2.0. Conidiophores were unbranched, straight, 95 to 230 × 9 to 16 μm in size, and produced four to six immature conidia in chains. Foot cells of conidiophores were cylindrical and 35 to 70 μm long, with light constriction at the basal septum, and followed by one to three short cells. Fungal hyphae were septate, branched, flexuous to straight, and up to 5 μm wide with indistinct to slightly nipple-shaped appressoria. Chasmothecia were absent in the collected infected samples. Partial sequence of small subunit ribosomal RNA gene, internal transcribed spacer 1 (ITS1), 58S ribosomal RNA gene, internal transcribed spacer 2 (ITS2), and partial sequence of large subunit ribosomal RNA gene were amplified from conidia collected from infected leaves of four individual plants using primers ITS1/ITS4, respectively (White et al. 1990). Four ITS region sequences were deposited in GenBank (accession no. MW142496 [538 bp], MZ348457 [538 bp], MZ348458 [540 bp], and MZ348459 [540 bp]). All the amplicons exhibited more than 99% sequence identity (MW142496 [536/538], MZ348457 [536/538], MZ348458 [538/540], MZ348459 [537/540]) with those sequences of P. xanthii isolates (accessions no. MT568609 to MT568611) on Z. elegans in Taiwan (Xiao et al. 2021). Based on these morphological characteristics and molecular analysis, this pathogen was identified as P. xanthii (Braun and Cook 2012). The phylogenetic trees were constructed using the neighbor-joining method in MEGA 7.0. Based on the ITS rDNA phylogenetic tree, the sequences retrieved from the specimens clustered within a strongly supported clade with P. xanthii (MT704550, MT864007, MN818562, and MW692364), confirming the identity A pathogenicity test was performed by dusting conidia from an infected leaf onto young leaves of five healthy plants in the greenhouse with five noninoculated plants as a control. Powdery mildew symptoms were observed on inoculated leaves after 5 days of inoculation at 18/25°C (night/day) and 75% relative humidity, whereas control plants remained asymptomatic. The fungus on inoculated leaves was morphologically identified as that observed on the original diseased leaves. Powdery mildew on zinnia caused by P. xanthii has been identified in Taiwan (Xiao et al. 2021), and by Golovinomyces cichoracearum in Turkey (Soylu et al. 2011). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on Z. elegans in northeastern China.The author(s) declare no conflict of interest.

First report of powdery mildew caused by Podosphaera xanthii on Matricaria chamomilla in Korea

First report of powdery mildew caused by Podosphaera xanthii on Matricaria chamomilla in Korea

Morphological and molecular identification of new records and new host plants of powdery mildews (Erysiphaceae) from Mexico

Powdery mildew is one of the most severe diseases affecting Cucurbitaceae. We identify the members of Erysiphaceae infecting cucurbits in three producing regions in Mexico. We determined that Golovinomyces ambrosiae (Schwein.) U. Braun & R.T.A. Cook, Neoerysiphe sechii R. Gregorio-Cipriano & D. González, and Podosphaera xanthii (Castagne) U. Braun & Shishkoff infected cultivated and wild cucurbits species or subspecies. Leaf samples showing symptoms and signs of powdery mildew were collected from the northwestern, central western, and eastern regions of Mexico between 2017 and 2020. Species associated with the disease were identified based on morphology and internal transcribed spacer rDNA sequences. All powdery mildew specimens presented only the anamorph. Podosphaera xanthii was the predominant species; it was found in 84.76% of the samples and in 13 out of 14 species or subspecies of cucurbits. Neoerysiphe sechii was found in 15.24% of the samples and in only four cucurbit species from the central western and eastern regions of Mexico. Golovinomyces ambrosiae was documented for the first time in a Cucurbitaceae species (Sicyos deppei G.Don) from central west Mexico. Three new hosts were registered for N. sechii (Cucurbita ficifolia Bouché, Echinopepon milleflorus Naudin, and Sicyos laciniatus L.) and eight for P. xanthii (Cucurbita argyrosperma C.Huber, Cucurbita argyrosperma subsp. sororia (L.H.Bailey) Merrick & D.M.Bates, C. ficifolia, Cucurbita okeechobeensis subsp. martinezii (L.H.Bailey) T.C.Andres & G.P.Nabhan ex T.W.Walte, Cucurbita radicans Naudin, Sechium edule (Jacq.) Sw., S. laciniatus, and S. deppei).

CmPMRl and CmPMrs are responsible for resistance to powdery mildew caused by Podosphaera xanthii race 1 in Melon.

Two genes for resistance to Podosphaera xanthii race 1 in melon were identified on chromosomes 10 and 12 of the Cucumis melo cultivar MR-1. Cucumis melo L. is an economically important crop, the production of which is threatened by the prevalence of melon powdery mildew (PM) infections. We herein utilized the MR-1 (P1; resistant to PM) and M4-7 (P2; susceptible to PM) accessions to assess the heritability of PM (race 1) resistance in these melon plants. PM resistance in MR-1 leaves was linked to a dominant gene (CmPMRl), whereas stem resistance was under the control of a recessive gene (CmPMrs), with the dominant gene having an epistatic effect on the recessive gene. The CmPMRl gene was mapped to a 50Kb interval on chromosome 12, while CmPMrs was mapped to an 89Kb interval on chromosome 10. The CmPMRl candidate gene MELO3C002441 and the CmPMrs candidate gene MELO3C012438 were identified through sequence alignment, functional annotation, and expression pattern analyzes of all genes within these respective intervals. MELO3C002441 and MELO3C012438 were both localized to the cellular membrane and were contained conserved NPR gene-like and MLO domains, respectively, which were linked to PM resistance. In summary, we identified patterns of PM resistance in the disease-resistant MR-1 melon cultivar and identified two putative genes linked to resistance. Our results offer new genetic resources and markers to guide future marker-assisted breeding for PM resistance in melon.

Evaluation of different fungicides and organic amendments against powdery mildew of ber

In Northern states, powdery mildew of ber (Zizyphus mauritiana Lamk.) caused by Oidium erysiphoides f. sp. zizyphi is more prevalent and has become a menace. The white powdery coating on leaves and fruits affects the photosynthesis and growth & development, respectively. This disease results in 50–60% loss in fruit yield and reduces market value of the produce. In the present investigation, fungicides and organic amendments were used as foliar spray against the powdery mildew disease of ber on the cultivars Gola and Kaithali. Among all the treatments, least per cent disease index (6.48 and 5.13) was observed in Karathane 48 EC (0.1%) treatment that supported minimum disease index, whereas, maximum per cent disease index (16.96 & 12.4) was found in mustard oil @ 0.5% on the cultivars Gola and Kaithali, respectively. Among all the treatments, Karathane 48 EC @ 0.1% showed highest reduction (73.22 and 70.45%) in disease over control followed by hexaconazole 5 EC @ 0.1%, which reduced the disease up to 65.12 and 64.08% over control with the disease index of 8.44 and 6.2% on the cultivars Gola and Kaithali, respectively. Maximum increase in fruit yield per tree i.e. 57.45 and 55.33% was recorded on ber cultivars Gola and Kaithali, respectively sprayed with Karathane 48 EC @ 0.1%

Mapping quantitative trait loci and developing first molecular marker for race 5 of Podosphera xanthii resistance in melon (Cucumis melo L.)

Powdery mildew of melon caused by the Podosphaera xanthii factor is a disease that causes serious yield losses economically in all areas where melon is grown from Asia to Europe and America. The use of resistant varieties for the control of the disease is the most environmentally friendly method. However, traditional methods of melon breeding have made a noteworthy input to resistance varieties improvement, but they have been slow and incompetent in targeting complex powdery mildew disease resistance traits. To overcome these problems and to facilitate breeding programs, molecular markers closely linked to the Pm-R5 gene are needed for marker-assisted selection (MAS). The present study aimed to map quantitative trait locus for powdery mildew resistance and identify the molecular markers linked with the Pm-R gene which provides resistance to race 5 of P. xanthii for MAS breeding in melons. A total of 310 primers/combinations belonging to six marker systems including SRAP, SSR, ISSR, TRAP, CAPS, SCAR in the RIL population consisting of 136 genotypes, developed from crosses PMR-6 and susceptible inbred line were used for QTL mapping. Quantitative trait loci analysis determined one major QTL (Pm-R) on linkage group I for resistance to races 5 of powdery mildew. The SSR12202 marker is linked to the Pm-R gene QTL at 2.12 cM genetic distance, and the CMCT170b and CMMS30-3 markers are determined in the support interval of this QTL. The co-dominant markers, together with the map information reported here could be used for genotyping selection of resistance to race 5 of P. xanthii in melon breeding.

Podosphaera xanthii causing powdery mildew on Impatiens balsamina in China

Impatiens balsamina (garden balsam) is an annual herb and widely grown for ornamental and medicinal use in China. In 2020 and 2021, powdery mildew symptoms were found on I. balsamina in Xinxiang City, Henan Province, China. The pathogenic fungus was identified based on its morphological characteristics and molecular analysis. The internal transcribed spacer (ITS) region was amplified and sequenced. The sequence obtained for the fungus showed 100% identity with the previously reported Podosphaera xanthii. The virulence of the pathogen on I. balsamina was confirmed by utilizing Koch’s postulates. Therefore, we identified the causal organism of this disease as P. xanthii. This is the first report of powdery mildew caused by P. xanthii on I. balsamina in China. The identification of P. xanthii on I. balsamina will support efforts towards its future control and management.

Quantitative Trait Loci Mapping of Resistance to Powdery Mildew Race 1 in a Recombinant Inbred Line Population of Melon.

Powdery mildew, caused by the fungus Podosphaera xanthii, is one of the most important diseases of melon. Although there are several pathogenic races of P. xanthii, race 1 is the predominant race in South Carolina and in other parts of the United States. We used a densely genotyped recombinant inbred line melon population for traditional quantitative trait loci (QTL) mapping, to identify two major (qPx1-5 and qPx1-12) and two minor (qPx1-4 and qPx1-10) QTLs (named according to race - chromosome number) associated with resistance to P. xanthii race 1. QTL mapping of disease severity in multiple tissues (hypocotyl, cotyledons, true leaves, and stems) identified the same genetic basis of resistance in all tissue types. Whole-genome resequencing of the parents was used for marker development across the major QTLs and functional annotation of single nucleotide polymorphisms (SNPs) for candidate gene analysis. Kompetitive allele-specific PCR (KASP) markers were tightly linked to the QTL peaks of qPx1-5 (pm1-5_25329892, pm1-5_25461503 and pm1-5_25625375) and qPx1-12 (pm1-12_22848920 and pm1-12_22904659) in the population and will enable efficient marker-assisted introgression of powdery mildew resistance into improved germplasm. Candidate genes were identified in both major QTL intervals that encode putative R genes with missense mutations between the parents. The candidate genes provide targets for future breeding efforts and a fundamental examination of resistance to powdery mildew in melon.

Chitin Deacetylase, a Novel Target for the Design of Agricultural Fungicides.

Fungicide resistance is a serious problem for agriculture. This is particularly apparent in the case of powdery mildew fungi. Therefore, there is an urgent need to develop new agrochemicals. Chitin is a well-known elicitor of plant immunity, and fungal pathogens have evolved strategies to overcome its detection. Among these strategies, chitin deacetylase (CDA) is responsible for modifying immunogenic chitooligomers and hydrolysing the acetamido group in the N-acetylglucosamine units to avoid recognition. In this work, we tested the hypothesis that CDA can be an appropriate target for antifungals using the cucurbit powdery mildew pathogen Podosphaera xanthii. According to our hypothesis, RNAi silencing of PxCDA resulted in a dramatic reduction in fungal growth that was linked to a rapid elicitation of chitin-triggered immunity. Similar results were obtained with treatments with carboxylic acids such as EDTA, a well-known CDA inhibitor. The disease-suppression activity of EDTA was not associated with its chelating activity since other chelating agents did not suppress disease. The binding of EDTA to CDA was confirmed by molecular docking studies. Furthermore, EDTA also suppressed green and grey mould-causing pathogens applied to oranges and strawberries, respectively. Our results conclusively show that CDA is a promising target for control of phytopathogenic fungi and that EDTA could be a starting point for fungicide design.

Effective Management of Cucumber Powdery Mildew with Essential Oils

This research evaluated the efficacy of essential oils in the management of cucumber powdery mildew. Essential oils of lemongrass, lemon, thyme, peppermint, abundance blend, purification blend, and thieves blend were tested in vitro and under greenhouse conditions in two separate experiments. The effects of essential oils were tested against powdery mildew disease at concentrations of 1.0–2.5 mL/L, and the consequent impact of the oils on plant growth was evaluated. Powdery mildew fungus, Podosphaera xanthii, was identified using sequencing of the ITS region. The essential oils significantly reduced disease incidence up to 77.3% compared with the positive control (p < 0.5). Moreover, the essential oils increased the plant length (up to 187 cm), leaf area (up to 27.5 cm2), fresh weight (up to 123 g), dry weight (up to 22.5 g), number of flowers (16.3), and metabolite content compared with the positive control (p < 0.5). Cell membrane injury decreased significantly in the oil-treated pants (p < 0.5), indicating the protective effect of essential oils. This study recommends the application of essential oils in an appropriate dose (2.5 mL/L) to protect cucumber plants against powdery mildew. Overdose of the oils (more than 2.5 mL/L) should be avoided due to adverse effects.

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.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Benincasa hispida in Korea.

Benincasa hispida (Thunb.) Cogn. (syn. B. cerifera Savi, Cucurbita hispida Thunb.), called wax gourd or ash gourd, is a cucurbitaceous vine grown for medicinal purposes and commercial values of its large fruits in Southeast Asia (Al-Snafi 2013). During the summer and autumn of 2020, leaves of wax gourd were observed to be affected by powdery mildew with 100% disease incidence in an experimental plot of Jeonbuk National University (35°50'55″N, 127°07'48″E), Korea. Fungal colonies were initially circular to irregular, forming white patches on both sides of the leaves and young stems, finally covering entire leaves and causing premature senescence of the leaves and poor growth. A representative voucher specimen was deposited in the Korea University herbarium (KUS-F32171). At least 30 measurements were taken for each asexual diagnostic features. Conidiophores arising from superficial hyphae were straight, 100 to 210 μm long, and produced 3 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindrical, 46 to 74 ×10 to 12 μm, followed by 1 to 2 shorter cells. Conidia were ellipsoid-ovoid to barrel-shaped, 30 to 40 × 18 to 23 μm with a length/width ratio of 1.4 to 2.0 and contained conspicuous fibrosin bodies. Germ tubes were produced from a lateral position on conidia. Sexual stage was not observed during the growing season. The morphological characteristics of the fungus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. DNA was extracted from mycelium, and primer sets ITS1F/PM6 and PM3/TW14 were used for amplification of ITS1-5.8S-ITS2 regions and 5´-end of 28S rDNA gene, respectively (Takamatsu and Kano 2001). Sequences determined in this study were deposited to the GenBank under the accession numbers MW559231 and MW559420, respectively. The sequences for ITS regions and 28S rDNA gene showed 99.78% and 99.07% similarity respectively with those of P. xanthii (MH465242, MH465243, MT250855 for ITS, and MK357436, MT826247 for LSU). Pathogenicity was confirmed twice by pressing a diseased leaf onto young leaves of five wax gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves developed symptoms after 5 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants. Sphaerotheca fuliginea (syn. P. xanthii) on B. hispida has been listed in Hungary, India, Japan, Singapore, and Taiwan so far (Farr and Rossman 2021). Recently, the identity of P. xanthii on B. hispida in Taiwan was confirmed with morphological examination and molecular analysis by Wu and Kirschner (2017). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on B. hispida in Korea. Since wax gourd production is only recently started on a commercial scale in the southern part of Korea, powdery mildew infections pose a serious threat to the safe production of the fruits, especially in organic farming where chemical control options are limited.

Nutrient Status of Cucumber Plants Affects Powdery Mildew (Podosphaera xanthii).

We examined the effects of applications of N, P, K, Mg, and Ca through an irrigation solution and spraying K, Ca, and Mg salts on cucumber powdery mildew (CPM, Podosphaera xanthii) in potted plants and under commercial-like conditions. Spraying CaCl2 and MgCl2, or KCl and K2SO4, decreased CPM. There were significant negative correlations between the anion-related molar concentrations of the salts and disease severity. Among the sprayed treatments, NaCl provided significantly less CPM control when applied at a low (0.05 M) concentration, as compared with CaCl2 and MgCl2. When sprayed applications of Mg and K salts were analyzed separately from the untreated control, the Cl− salts were found to be more effective than the SO4−2 salts. High N and Mg concentrations in the irrigation water delivered to young, fruit-less cucumber plants reduced CPM, whereas more CPM was observed when the irrigation solution contained a medium amount of P and a high amount of K. In contrast, mature, fruit-bearing plants had less severe CPM at higher N, lower P, and higher K levels. Spraying mature plants with monopotassium phosphate, polyhalite (K2Ca2Mg(SO4)4·2H2O), and the salts mentioned above over an entire growing season suppressed CPM. CPM severity was also reduced by spray applications of Ca, Mg, and KSO4−2 and Cl− salts. Spray applications provided better CPM control than fertigation treatments. Induced resistance is probably involved in the effects of nutrients on CPM.

Powdery Mildew oftall verbenaCaused byPodosphaera xanthiiin China.

Tall verbena (Verbena bonariensis) is widely used in landscape layout in sparse forests, botanical gardens and villa areas, and it is also a kind of Chinese herbal medicine. The flower and bud use as Chinese herbal medicine causing heat-clearing and detoxification. In August 2019, observed on tall verbena in Shangqiu, Henan Province, China. Symptoms white fungal growth observed on both sides of fresh and mature leaves of tall verbena grown on campus at Shangqiu Normal University. More than 60% plants were infected by this fungus and infected plants were observed to shed leaves early. One representative voucher specimen was deposited at the herbarium of Shangqiu Normal University (SQNU), Shangqiu, China, under the accession number of Vb01. Conidiophores of the fungus contained 5-6cells and measured 102.0-142.9μm (mean 126.2μm, n = 30) long, with foot-cells of conidiophores measured 36.5-46.9μm (mean 42.9μm, n = 30). Conidia produced in chains were variable in shape, ellipsoid to ovoid, and measured 24.8-30.7×12.0-17.9 μm (mean 27.35×15.08μm, n = 50), with a length/width ratio of 1.4 to 2.3. Fibrosin bodies were observed in the conidia. No chasmothecia were found. The morphological characteristics were consistent with the genus Podosphaera. To identify above powdery mildew fungus at species level using molecular markers, the complete ITS region of rDNA from the representative specimen was amplified with universal primer pair ITS1/ITS4 and directly sequenced. The resulting sequence of 567 bp was deposited in GenBank (Accession No. MT864007). A BLAST search of this sequence showed more than 99% sequence identity with P. xanthii isolates (AB046985, AB462804, AB936277 and KM260741) on various hosts (Hirata T, 2000; Meeboon, J., and Takamatsu, S. 2015; Tam L. T. T. 2016). Phylogenetic analysis revealed that ITS sequence from Vb01 isolate was grouped into a clade with P. xanthii s. lat.. A pathogenicity test was conducted through inoculation by gently pressing a diseased leaf onto five healthy leaves of a potted tall verbena. Five non-inoculated seedlings were used as controls. The plants were maintained in a greenhouse at 26 to 28 ℃, and relative humidity of 60 to 65%. Inoculated leaves developed symptoms after nine days, whereas the control plants remained symptomless. The fungus presented on the inoculated plant was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. P. xanthii s. lat. has been reported on several hosts in China (Braun & Cook, 2012). This is the first report of P. xanthii s. lat. on Verbena bonariensis outside of Japan (Meboon, 2015).

Use of α -Lactalbumin, β -Lactoglobulin and Lactoferrin for Controlling Cucumber Powdery Mildew Disease under Plastic House Conditions استخدام α-lactalbumin و β-lactoglobulin و lactoferrin في مکافحة مرض البياض الدقيقي للخيار تحت ظروف الصوب البلاستيکية

The effect of native cow’s whey and whey proteins α-lactalbumin, β-lactoglobulin, and lactoferrin was studied under the plastic house conditions for controlling the cucumber powdery mildew disease caused by Sphaerotheca fuliginea (Schlecht.) Pollaci, prophylactically and curatively sprays application during 2019 and 2020 growing seasons with improvement the total cucumber product (yield/plant). Disease severity percentages, area under disease progressive curve (AUDPC), final disease severity, efficacy percentage, microscopic observations, growth parameters, yield components and enzyme activities were investigated. Obtained results of prophylactically application indicated that the disease severity was decreased significantly (P ≤ 0.05) by the application of whey 40% dilution which scored 10 and 6%, followed by a mixture of β-lactoglobulin + α-lactalbumin + lactoferrin (10.4 and 6.4%), and lactoferrin (20.3 and 16.4%), compared to Topas 100 (9.3 and 4.3%) and control treatment (62.3 and 59.1%) during 2019 and 2020 growing seasons respectively. Furthermore, disease severity percentages were higher through curatively application than prophylactically. Consequently, the final disease severity, AUDPC values were decreased, while efficacy percentage, growth parameters, yield components and enzyme activities were increased during the experiment period with the selected treatments either under prophylactically or curatively application during the two successive growing seasons. Photography of light and scanning electron microscopy showed that the selected treatments affected the fungal hyphae, conidiophores and conidia at 24 hr after the application of selected treatments

Morphological characterization and epidemiological studies of summer squash (Cucurbita pepo) powdery mildew

Samples of powdery mildew of summer squash (Cucurbita pepo L.) collected from Solan, Shimla, Hamirpur and Kinnaur districts of Himachal Pradesh during 2017-18 revealed the presence of anamorphs, whereas the cool and dry temperate region of district Kinnaur showed the occurrence of both teleomorphic and anamorphic stages of powdery mildew on summer squash. Present studies constitute the first report of cleistothecial occurrence on summer squash under Indian conditions. Based on anamorphic characters like ellipsoidal conidia, presence of fibrosin bodies and germinating conidia produced both simple and forked germ tubes without appressorium and teleomorphic characters like cleistothecia with myceloid appendages, single ascus with eight ascospores the associated pathogen was identified as Sphaerotheca fuliginea (Schlecht.) Pollaci. Maximum conidial germination was observed at 25° temperature and 100% relative humidity. The development of powdery mildew disease was significantly favored at moderate temperature coupled with high relative humidity and cumulative rainfall.

Gene Mining for Conserved, Non-Annotated Proteins of Podosphaera xanthii Identifies Novel Target Candidates for Controlling Powdery Mildews by Spray-Induced Gene Silencing

The powdery mildew fungus Podosphaera xanthii is one of the most important limiting factors for cucurbit production worldwide. Despite the significant efforts made by breeding and chemical companies, effective control of this pathogen remains elusive to growers. In this work, we examined the suitability of RNAi technology called spray-induced gene silencing (SIGS) for controlling cucurbit powdery mildew. Using leaf disc and cotyledon infiltration assays, we tested the efficacy of dsRNA applications to induce gene silencing in P. xanthii. Furthermore, to identify new target candidate genes, we analyzed sixty conserved and non-annotated proteins (CNAPs) deduced from the P. xanthii transcriptome in silico. Six proteins presumably involved in essential functions, specifically respiration (CNAP8878, CNAP9066, CNAP10905 and CNAP30520), glycosylation (CNAP1048) and efflux transport (CNAP948), were identified. Functional analysis of these CNAP coding genes by dsRNA-induced gene silencing resulted in strong silencing phenotypes with large reductions in fungal growth and disease symptoms. Due to their important contributions to fungal development, the CNAP1048, CNAP10905 and CNAP30520 genes were selected as targets to conduct SIGS assays under plant growth chamber conditions. The spray application of these dsRNAs induced high levels of disease control, supporting that SIGS could be a sustainable approach to combat powdery mildew diseases.