Signs Of Powdery Mildew Research Articles

Powdery Mildew of Xanthium strumarium Caused by Podosphaera xanthii in central China.

Xanthium strumarium, known as cocklebur, is an annual herb and has been used in traditional Chinese medicine. In October 2020, powdery mildew-like disease signs and symptoms were observed on X. strumarium grown in a crop field, Xinxiang city, Henan Province, China (35.36076° N, 113.93467° E). The specimen (PX-XS2023) was stored in Xinxiang Key Laboratory of Plant Stress Biology. White colonies in irregular or coalesced circular shaped-lesions were abundant on both ad- and abaxial surfaces of leaves and covered up to 99 % of the leaf area. Some of the infected leaves were senesced. More than 70 % of plants (n = 130) exhibited these signs and symptoms. Conidiophores were straight or slightly curved, 55 to 160 × 11 to 13 μm composed of foot-cells, shorter cells and conidia. Conidia were ellipsoid to oval, 29 to 40 × 14 to 20 μm (n = 50), with a length/width ration of 2.0 to 2.5, containing fibrosin bodies. Dark brown to black chasmothecia were found on infected leaves. The appendages were mycelium-shaped and at the base of scattered or gregarious chasmothecia (n = 50, 70 to 120 μm in diameter). Asci were 55 to 80 × 50 to 65 μm (n=30). These morphological characteristics were consistent with those of Podosphaera xanthii (Braun and Cook 2012). The internal transcribed spacer (ITS) region and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) region of the fungus (PX-XS2023) were amplified and sequenced with primers ITS1/ITS4 (White et al. 1990) and GAPDH1/GAPDH3R (Bradshaw et al. 2022) according to a previously reported method (Zhu et al. 2022). The resulting sequences were respectively deposited into GenBank (Accession No. MW300956 and PP236083). BLASTn analysis indicated that the sequences were respectively 99.82 % (564/565) and 100% (272/272) identical to P. xanthii (MT260063 and ON075658). The phylogenetic analysis indicated that the strain PX-XS2023 and P. xanthii were clustered into a same branch. Therefore, the causal agent of powdery mildew on X. strumarium was P. xanthii. To conduct pathogenicity assays, mature leaves of five healthy X. strumarium (height in 50 centimeters) were inoculated with fungal conidia by gently pressing surfaces of infested leaves onto leaves of healthy plants (Zhu et al. 2020). Five untreated plants served as controls. The controls and inoculated plants were separately maintained in greenhouses (humidity, 60%; light/dark, 16 h/8 h; temperature, 18°C). Eight days post-inoculation, signs of powdery mildew were detectable on inoculated plants, however, the controls were asymptomatic. Thus, the fungal pathogen was morphologically and molecularly identified and confirmed as P. xanthii. This powdery mildew caused by P. xanthii was previously reported on X. strumarium in Korea, Russia and India (Farr and Rossman, 2021). In addition, P. xanthii was recorded on X. strumarium in Xinjiang Province, China (Tai 1979). However, this is the first report of P. xanthii on X. strumarium in central China, where is around 3000 km away from Xinjiang Province with geographically differences. The sudden presence of powdery mildew caused by P. xanthii may adversely affect plant health and thus reduce medical value of X. strumarium. Therefore, the identification and confirmation of P. xanthii infecting X. strumarium enhance the knowledge on the hosts of this pathogen in China and will provide fundamental information for disease control in the future.

Podosphaera xanthii Causing Powdery Mildew on Salvia farinacea in Central China.

Salvia farinacea, commonly referred as mealycup sage, is a perennial herbaceous plant belonging to the Salvia genus of the Lamiaceae family. It originates from the Mediterranean region, North America, and Europe and is globally cultivated due to its appealing and captivating flowers. Moreover, mealycup sage is utilized as traditional Chinese medicinal plant for treatment of cardiovascular diseases (Li et al. 2018). In October 2023, powdery mildew-like symptoms were observed on Salvia farinacea plants cultivated in a garden located in Xinxiang City, Henan Province, China (113.93, 35.29). The leaves were covered with white and thin masses of mycelia, conidiophores and conidia of the fungus. About 100 plants were checked and 90 % were infected. There were a large number of white colonies with irregular or continuous round lesions on the adaxial and abaxial surfaces of the leaves, covering approximately 80% of the leaf area. The slightly or straight curved conidiophores (n = 30) were 46 to 145× 8 to 11 μm in size and consisted of foot cells, shorter cells and conidia. The ellipsoidal to oval conidia (n = 30), containing fibrosin bodies, were 24 to 35 × 12 to 19 μm in size and had a length/width ratio of 1.8 to 2.1. No chasmothecia were observed on leaves. These morphological features were consistent with those of Podosphaera xanthii (Braun and Cook 2012). Following the previously described method (White et al. 1990; Bradshaw et al. 2022; Zhu et al. 2022a), the sequences of ITS and Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) regions were amplified with specific primers ITS1/ITS4 (ITS1 5'-TCCGTAGGTGAACCTGCGG-3' ; ITS4 5'-TCCTCCGCTTATTGATATGC-3') and PMGAPDH1/PMGAPDH3R (PMGAPDH1 5'-GGAATGGCTATGCGTGTACC-3'; PMGAPDH3R 5'-CCCCATTCGTTGTCGTACCATG-3'), and the resulting sequences were uploaded in GenBank (Accession No. OR761885 and PP236082, respectively). BLASTn analysis showed that the sequence shared 560/565 (99%) and 272/272 (100%) homology with P. xanthii (MW301281) on Impatiens balsamina (Zhu et al. 2022b) and with P. xanthii (ON075658) on Cucumis melo (Bradshaw et al. 2022), respectively. The phylogenetic analysis clearly illustrated that the collected isolate of P. xanthii clustered in the same clade. The pathogenicity was tested according to the method previously described (Zhu et al. 2021). The fungus was inoculated onto the leaf surfaces of three healthy plants by blowing conidia from infected leaves with pressurized air. Non-inoculated plants were treated as control. Both the control and inoculated plants were separately placed in growth chambers under 60% humidity; light/dark, 16 h/8 h; and a temperature of 18°C. After a period of 12-15 days, the leaves of the inoculated plants exhibited signs of powdery mildew, whereas the control group remained unaffected. Therefore, the fungal pathogen was identified and confirmed as P. xanthii (isolate PXSF202310). Previously, P. xanthii was reported on Impatiens balsamina and S. farinacea from China and Korea (Zhu et al. 2021; Choi et al. 2022). As far as we know, this is the first documentation of P. xanthii on S. farinacea in central China. The presence of P. xanthii can lead to a deterioration in plant health and stunted growth, thereby negatively impacting both the decorative and medicinal value of S. farinacea. The recognition of P. xanthii on S. farinacea enhances our comprehension of this pathogen hosts and provides fundamental information for forthcoming disease control studies.

Morphological and molecular characterization of Neoerysiphe galeopsidis causing powdery mildew on Lagopsis supina in central China

Lagopsis supina (Xia Zhi Cao) is a widely distributed and cultivated herbal plant that has been extensively used as a traditional Chinese medicine, Tibetan medicine and Mongolian medicine for disease treatments for centuries. While the bioactive compounds of L. supina are extensively studied, the fungal pathogens of this plant are still obscure. In 2021, powdery mildew signs and symptoms were observed on leaves of L. supina in Xinxiang City, Henan Province, China. However, the causal pathogen had not been identified. Therefore, morphological characteristics and molecular analysis was applied to identify the powdery mildew pathogen. The sequence of the internal transcribed spacer (ITS) region of the fungus was obtained and showed 99.83% identity with the previously reported Neoerysiphe galeopsidis. The virulence of this phytopathogen on L. supina was confirmed by utilizing Koch’s postulates. Therefore, we identified the causal pathogen as N. galeopsidis. Based on biological and molecular characterization, this is the first comprehensive report of powdery mildew caused by N. galeopsidis on L. supina in central China. The occurrence of powdery mildew disease on L. supina may detract from the plant’s medical and ornamental value. The identification and confirmation of N. galeopsidis on L. supina expands the knowledge of this causal agent and will support efforts towards future control and management of powdery mildews.

Epidemiological etiology of Erysiphe sp. and putative viral and phytoplasma-like symptoms in Ayocote bean (Phaseolus coccineus)

Introduction/Objective. Ayocote bean (Phaseolus coccineus) has potential as a source of resistance in breeding programs because it exhibits greater tolerance to plant pathogens than P. vulgaris. However, its sanitary characterization is insipient; therefore, the purpose of this work was to carry out an etiological-epidemiological diagnosis, with emphasis on presumptive symptoms of viral and phytoplasmic organisms, and a typical fungal signs of powdery mildew. Materials and Methods. A plot (50 x 62 m) of flowering Ayocote bean was selected. It was divided into 80 (8 x 10) quadrats (6 x 6 m) and 720 subquadrats (2 x 2 m). From 25 plants with powdery-mildew-type leaf symptoms, mycelium was collected with adhesive tape for light microscopy observation and taxonomic identification. Length-width measurements were made on 60 conidia. Pure mycelium collected in situ and ex situ from 1-5 leaflets/plant was used for genomic analysis by PCR with universal primers ITS1 and ITS4. Samples were sequenced in Macrogen Inc. Korea. A total of 63 plants and 121 trifoliate leaves with viral and phytoplasmic symptoms were collected by direct sampling. In 88/121 samples, genomic analysis was performed by PCR with universal primers for Potyvirus (1), Begomovirus (2), and Phytoplasmas (1). Sequence editing and analysis were performed in SeqAssem and BLASTn/GenBank. Phylogenetic constructions were developed in Mega 11 with MUSCLE, Maximum Likelihood (ML), and HKY substitution model (1000-Bootstrap). Putative powdery mildew severity (%), flower damage (%), Macrodactylus sp. adult density, and plant vigor (%) were evaluated in 80 quadrats (3subquadrats/quadrat) with App-Monitor®v1.1 configured with a 5-class scale. In GoldenSurfer® v10, Kriging geostatistical analysis was performed to determine the spatial interrelationship between these variables. Results. Erysiphe vignae was identified as associated with powdery mildew of P. coccineus. The fungus, with hyaline, ovoid to ellipsoid conidia measuring 31.74 ± 0.3419 μm x 15.11 ± 0.1579 μm, without the presence of fibrosin bodies, had 100% genomic homology. This is the first report in Mexico. With average July-August temperature and relative humidity of 16.3 °C (±5.8) and 92.8 % (±10.7), respectively, powdery mildew leaf incidence and severity were 65.3 and 22.7 % (±16.9, range: 0 - 66.5 %), respectively. The most inductive focus (60-80 % severity) had an aggregate e 4-quadrat pattern (96 m2, lag = 4 and σ2-s = 450). Inoculum dispersal was significantly associated with dominant North-South winds and plant vigor (lag = 4 and σ2-s = 470). Flower damage was inconclusive in its spatial association with powdery mildew and Macrodactylus sp. suggesting uncorrelated events. No Potyvirus, Begomovirus, or Phytoplasmas were detected associated with yellowing, leaf distortion, mosaic, internode shortening, and other symptoms observed in situ. This confirms the relative tolerance/resistance reported for P. coccineus. Conclusion. E. vignae (Erysiphales: Erysiphaceae) associated with P. coccineus is reported for the first time in Mexico with moderate to intense epidemic level, which indicates its susceptible condition to this fungus. However, negative results for Potyvirus, Begomovirus, and Phytoplasmas, validate the apparent tolerance/resistance of P. coccineus to these organisms.

Erysiphe elevata causing powdery mildew on Eucalyptus urophylla × E. camaldulensis in China.

Eucalyptus urophylla × E. camaldulensis, named Chiwei eucalypt, is a hybrid species widely used in China. Many of its clones are cultivated for afforestation due to cold tolerance, high yield, high strength and disease resistance. Clone LH1 is planted extensively for its high stability and machinability in South China. In December 2021, severe powdery mildew signs were observed on clone LH1 in Zhanjiang, Guangdong (N28°8'29"; E110°17'5"). Whitish powder principally appeared on both abaxial and adaxial leaf surfaces. All plants were infected within about a week and above 90% leaves were diseased, which resulted in abnormal growth and shrinkage of leaves. Hyphae with single, lobed appressoria were hyaline, septate, branched, 3.3-6.8 µm (ave. 4.9 µm, n>50) wide. Conidiophores with a straight to flexuous foot-cell (14.7-46.1×5.4-9.7 µm, ave. 25.8×7.9 µm, n>30) were erect, hyaline, 2-septate, unbranched, 35.4-81.8 × 5.7-10.7 (ave. 56.7×8.7 µm, n>50). Conidia were solitary, hyaline, cylindrical to elliptical, 27.7-46.6 ×11.2-19.0 (ave. 35.7×16.6 µm, n>50). Chamothecia were not found on infected trees. The further identification was confirmed by partial sequences of internal transcribed spacer (ITS), large submit rRNA gene (LSU), Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glutamine synthetase (GS), and RNA polymerase II second largest subunit (RPB2) gene. A very small amount of mycelia and spores from voucher specimens CCAS-ASBF-1 and CCAS-ASBF-2 were deposited in the herbarium of Guangdong Ocean University. Specimens were PCR amplified and sequenced with primer pairs ITS1/ITS4 (White et al 1990), LROR/LR7 (Moncalvo et al 1995), PMGAPDH1/PMGAPDH3R, GSPM2/GSPM3R and PmRpb2_4/ PMRpb2_6R (Bradshaw, et al. 2022), respectively. BLASTn results showed that ITS (OP270019 and OQ380937), LSU (OP270018 and OQ380938), GAPDH, GS and RPB2 (OQ414445- OQ414450) were above 99% identical with those of E. elevata on Catalpa bignonioides (ITS: AY587013) (Cook et al 2004), Plumeria rubra (ITS: MH985631) (Yeh et al 2019), Cerbera manghas (ITS: MZ379159; LSU: MZ379160) (Mukhtar et al 2022), and Eucalyptus camaldulensis (LSU: LC177375-6) (Meebon et al. 2017), and above 99% identical with those of Erysiphe vaccinii FH00941201 on Vaccinium corymbosum (ITS: ON073869; RPB2: ON119159; GS: ON075687) and FH00112205 on V. vacillans (ITS: ON073870; GAPDH: ON075646) (Bradshaw et al 2022). This is the first sequence data for non rDNA of E. elevata. In an ITS tree phylogenetic analysis with Maximum likelihood (ML) method showed the fungus clustered in a highly supported clade with E. elevata and E. vaccinii. In a multi-locus tree, E. elevata grouped in a sister position to E. vaccinii FH00941201. Thus, the pathogen was identified as E. elevata based on morphology, DNA BLASTn and phylogenetic analysis (Braun and Cook 2012). Pathogenicity tests were conducted on healthy leaves of 1-year-old potted plants. Ten leaves were cleaned with sterile water, inoculated by gently dusting conidia from single lesion on the naturally infected leaves, and then covered with plastic bags containing wet absorbent cotton. Non-inoculated leaves served as controls. Symptoms developed on all inoculated leaves 3 to 5 days after inoculation, and the fungus was identical to the original fungus on the infected leaves, whereas control plants remained symptomless. This is the first report of powdery mildew caused by E. elevata on Eucalyptus sp. from China. This finding is helpful for land managers to diagnose and control the disease.

First Report of Powdery Mildew Caused by Golovinomyces latisporus on Helianthus annuus in the Arizona.

Helianthus annuus, known as the common sunflower, is an annual plant indigenous to the United States. The crop is grown for its edible oil, seeds, and as an ornamental. In November 2021, powdery mildew-like signs and symptoms were observed on sunflower in a house garden located at Fortuna Foothills, Yuma County, AZ (32.6725°N, 114.4329°W). Signs of powdery mildew included white blotches of amphigenous and caulicolous mycelia. Initially, signs appeared as circular spots that expanded over the entire leaf and were also observed later on petioles and stems. Fungal hyphae were branched, septate, and with nipple-shaped appressoria. Foot cells of conidiophores were erect, cylindrical, and followed by one to three short cells bearing conidia. The conidiophores were hyaline, straight, cylindrical and produced short chains of up to four immature conidia. Conidia were ovoid to ellipsoid, seldom cylindrical, without-fibrosin bodies and measured 25 to 40 μm in length (mean= 34 μm) and 16 to 24 μm in width (mean= 18.6 μm) (n = 10), with an average length: width ratio of 1.8. The germination of conidia was Euoidium type with short germ tube. Chasmothecium formation was not detected. As the disease progressed, the infected leaves became wilted and senesced. The morphological characteristics of this fungus were in accordance with those described for G. latisporus (Braun and Cook, 2012; Qiu et al., 2020). For molecular identification, genomic DNA was isolated from fungal colonies using the DNeasy Plant kit (Qiagen). The internal transcribed spacer (ITS), large ribosomal subunit (28S), intergenic spacer (IGS), beta- tubulin (TUB2) and chitin synthase 1 (CHS1) regions were amplified using the primer sets, ITS5/ITS4 (White et al., 1990), LSU1/LSU2 (Scholin et al., 1994), IGS-12a/NS1R (Carbone and Kohn, 1999), TubF1/TubR1 and gCS1a1/gCS1b (Qiu et al., 2020). Sequences were submitted in the GenBank under accession numbers OP160535 (ITS), OP153874 (28S rDNA), OP160534 (IGS), OP168959 (TUB2) and OP168960 (CHS1). A BLAST search revealed 98.7 to 100-% identity to G. latisporus sequences (MK452603, NG_068877, MK452520, MK452476, and MK452428). Phylogenetic analysis based on the combined sequence datasets of ITS+28S rDNA+IGS+TUB2+CHS1 also grouped Yuma isolate in a monophyletic clade with G. latisporus accessions from Qiu et al. (2020). A pathogenicity test was carried out by inoculating four sunflower varieties (Velvet queen, Evening sun, Skyscraper and Mammoth). Conidia from infected leaves were dusted on the leaves of 10 individually potted, five-week-old seedlings of each variety. Four seedlings of each variety were not inoculated and served as controls. The inoculated and control plants were then kept in two separate greenhouses at 25-28°C at the Yuma Agricultural Center, Yuma, AZ. Inoculated plants started showing symptoms of powdery mildew within 7 days of inoculation, while the control plants stayed healthy and disease-free. The morphological characteristics of powdery mildew fungus on the inoculated plants were identical to the isolate collected from the garden, with the same sequence following PCR as above, thus fulfilling Koch's postulates. G. latisporus has been previously reported on common sunflower from Washington and California states (Qiu et al., 2020), however, this is a first report from Arizona. Although sunflower is not a major crop in Arizona, the wild sunflower population could serve as reservoir for the spread of the disease.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on New York Aster (Symphyotrichum novi-belgii) in Korea.

Symphyotrichum novi-belgii (L.) G.L. Nesom (syn. Aster novi-belgii L.), known as New York aster, is a perennial herb used in gardens and as a potted plant. The plant is native to North America but has been developed into various horticultural varieties. In Korea, it is one of the most common plants used for autumn bloom. In September 2011, New York asters (variety unknown) showing typical signs of powdery mildew were observed in a public garden in Seoul, Korea. Since then, the disease on New York asters has been continuously found in parks and flower markets in different regions of Korea. Voucher specimens (n=3) were deposited in the Korea University Herbarium (KUS-F 30752, 31865, and 32103). On leaves, circular to irregular white patches appeared which subsequently showed abundant hyphal growth on both sides of the leaves and on young stems and inflorescences, reducing the aesthetic value and vigor of the plants affected. Hyphae were septate, branched, and 4 to 8 µm wide. Appressoria on the mycelium were nipple-shaped. Conidiophores measured 110 to 200 × 9 to 11.5 μm, were simple, and produced 2 to 5 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells of conidiophores were straight, cylindric, and 55 to 125 μm long. Conidia were hyaline, ellipsoid to barrel-shaped, measured 22 to 52 × 15 to 20 μm (length/width ratio = 1.5-2.5), lacked distinct fibrosin bodies, and produced germ tubes on the subterminal position, with reticulate wrinkling of the outer walls. No chasmothecia were observed. The structures described above were typical of the Oidium subgenus Euoidium anamorph of the genus Golovinomyces, and the fungus measurements were consistent with those of G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook (Braun and Cook 2012, Qiu et al. 2020). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS) and large subunit (LSU) regions of rDNA were amplified with primers PM10/ITS4 for ITS and PM3/TW14 for LSU (Mori et al. 2000, Bradshaw and Tobin 2020). The resulting sequences were deposited in GenBank (Accession No. OP028065-7 for ITS and OP028053-5 for LSU). A GenBank BLAST search of these sequences revealed 100% identity with sequences of G. ambrosiae on many asteraceous plants, including S. novi-belgii from China (MK452575-9 for ITS and MK452648-52 for LSU). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of five healthy potted New York aster plants. Five non-inoculated plants served as controls. Plants were maintained in an incubator at 24°C. Inoculated plants developed signs and symptoms after three weeks, whereas the control plants remained symptomless. The fungus present on the inoculated plants was morphologically identical to that observed initially on diseased plants, fulfilling Koch's postulates. The powdery mildew infections of S. novi-belgii associated with G. ambrosiae have been widely known in Europe and North America but only recently in China (Qiu et al. 2020, Farr and Rossman 2022). In Japan, Podosphaera fuliginea was known to be associated with powdery mildew of S. novi-belgii (Farr and Rossman 2022). To our knowledge, this is the first report of powdery mildew caused by G. ambrosiae on S. novi-belgii in Korea. The powdery mildew on this ornamental plant can be considered a severe threat.

First Report of Powdery Mildew on Rosa cymosa Caused by Podosphaera pannosa in Guizhou Province, China.

Rosa cymosa is a traditional Chinese medicine and an ornamental plant in China (Fan et al. 2020). In April 2022, powdery mildew symptoms were observed on R. cymosa in Guiyang, Guizhou Province, China. The incidence was approximately 5% among all observed one hundred R. cymosa plants. On average, 20% of the twig tips per diseased R. cymosa plant were affected. Powdery mildew colonies covered the adaxial and abaxial surfaces of leaves. Infected young leaves rolled up along the main vein. Stems and mature leaves occasionally had signs of powdery mildew. The hyphae were straight to flexuous, branched, septate, 3 to 6 μm in width. Conidiophores were erect, straight or somewhat flexuous, and 100 to 235 µm long. Foot cells (n = 30) were cylindrical or subcylindrical, straight or somewhat flexuous, and measured 20 to 48 µm (length) × 4.5 to 5.5 µm (width). Foot cells were followed by one to two shorter cells (n = 30) that measured 8 to 12 µm (length) × 4.5 to 5.8 µm (width). The shorter cells were followed by a chain of four to eight conidia. The conidia (n = 50) were hyaline, cylindrical to ovoid, with fibrosin bodies, and measured 20 to 28 μm (length) × 10.5 to 16.5 μm (width). No chasmothecia were observed on the surface of diseased leaves. For molecular identification, the ribosomal DNA internal transcribed spacer (ITS) was amplified and sequenced using primers ITS1/ITS4 (White et al. 1990). The obtained 508-bp ITS sequence was deposited in GenBank (Accession No. ON316871). The subsequent phylogeny grouped the ITS sequence within a clade of Podosphaera pannosa sequences. Based on both morphological and phylogenetic characteristics, the powdery mildew pathogen was identified as P. pannosa (Braun et al. 2002). The voucher specimen (Accession No. GZNU-RCPP/0804/2022) were deposited at the School of Life Sciences, Guizhou Normal University, China. Pathogenicity was assessed by gently pressing naturally diseased leaves onto young leaves of three healthy, potted 2-year-old R. cymosa plants, with three non-inoculated plants as controls. Powdery mildew symptoms were observed on all inoculated plants after incubation for 10 days at 21°C, 75% relative humidity, and 12 h/12 h light/dark cycle in a greenhouse. The control plants remained symptomless. The re-isolated powdery mildew colonies on inoculated leaves were morphologically identical to those observed on the original diseased leaves, fulfilling Koch's postulates. Podosphaera pannosa has been described as the most frequent species causing powdery mildew on the Rosaceae family, particularly on Rosa spp. and Prunus spp. (Hubert et al. 2012; Félix-Gastélum et al. 2014). The occurrence of powdery mildew on R. cymosa caused by P. pannosa could pose a potential disease threat to other Rosa crops or Prunus spp.

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.

First Report of Erysiphe magnoliicola Causing Powdery Mildew of Magnolia × soulangeana in China.

Magnolia × soulangeana Soul.-Bod., the saucer magnolia is an important woody ornamental plant cultivated widely in China, UK and USA. In August 2021, symptoms and signs of powdery mildew appeared on leaves of M. × soulangeana at the campus of Nanjing Forestry University (NJFU). The powdery mildew mainly infected young seedlings, with an incidence of 96.8% (436/450 seedlings), and some adult trees also been infected (5/30 trees). The mycelium was amphigenous, thinly effused or conspicuous, forming circular to irregular white patches. Noticeable brown lesions and necrosis occurred in the later stage of infection. Chasmothecia started to develop in October, 2021 and fully matured in early November, 2021. Ten fresh specimens were collected and examined to identify of the pathogen. Photos were taken with a ZEISS Axio Imager A2m microscope, a Zeiss stereo microscope (SteRo Discovery v20), and a scanning electronic microscope (JSM-7600F). Conidiophores arose from the upper part of mother cells, 78.5 ± 11.2× 10.9 ± 1.7 μm (n=30). Foot cells in conidiophores are straight and cylindrical with a constricted basal septum close to hyphal mother cell, 33.6 ± 4.3 × 10.3 ± 1.2 μm (n=30). Conidia were hyaline, ellipsoid to oval, solitary or in chains of two to four, 38.5 ± 3.3 × 18.4 ± 1.0 μm (n=30). Chasmothecia were amphigenous, scattered or aggregated, blackish brown, oblate, 101.1 ± 11.4μm diam. (n=30), with 6-10 appendages. Appendages were aseptate, rarely 1-septate, 5-6 times frequently dichotomously branched; tips were noticeably recurved, brown at the base, 105.1 ± 10.7 × 8.5 ± 1.4 μm (n=30). Asci were 6 to 8 per chasmothecium (n=30), ellipsoid to obovoid or saccate with a short stalk or sessile, 64.2 ± 6.5× 46.1 ± 5.7 um (n=30) in length, 4 to 6 spored. Ascospores were oblong-ovoid, 26.2 ± 1.4 × 13.8 ± 0.7 μm (n=30). Based on the morphological characteristics, the fungus was identified as Erysiphe magnoliicola S.E. Cho, S. Takam. & H.D. Shin. To confirm the causal fungus identity, a representative voucher specimen collected and deposited in herbarium of NJFU (NF50000008) was used for a phylogenetic analysis. Mycelia and conidia were collected from diseased leaves and genomic DNA of the pathogen was extracted. The internal transcribed spacer region (ITS) and large subunit (LSU) loci were amplified with primers ITS1/ITS4 and LR0R/LR05. The resulting sequences were deposited in GenBank (OL454094 for ITS, OM758416 for LSU). BLAST results showed that the ITS sequence was highly similar with a sequence of E. magnoliicola (type) [KJ567072, 614/619 (99.2%)], while LSU sequence was highly similar with E. magnoliicola [KJ567068, 889/891 (99.8%)] and E. magnoliae [JX235969, 903/909 (99.3%)]. Phylogenetic analyses using ITS and LSU sequences with maximum likelihood and Bayesian posterior probability using IQ-TREE v. 1.6.8 and MrBayes v. 3.2.6 placed this fungus in the E. magnoliicola clade. Based on the morphology and phylogeny, the fungus was identified as E. magnoliicola. Pathogenicity tests were carried out on six potted plants of M. × soulangeana. Three seedlings were inoculated by gently pressing the naturally infected leaves onto healthy leaves. Healthy leaves from three other seedlings served as control. Inoculated and control seedlings were placed in separate growth chambers at 23 ± 2°C/16 ± 2°C, 70% relative humidity, with a 16 h/8 h light/dark period. Symptoms developed 10 days after inoculation. The powdery mildew developing on the inoculated seedlings was examined, sequenced and confirmed as E. magnoliicola. The control leaves did not develop powdery mildew. Magnolia × soulangeana is a hybrid of Magnolia denudata × Magnolia liliiflora, both species, as well as M. sieboldii were already known as host plants of E. magnoliicola. This is the first report of powdery mildew caused by E. magnoliicola on M. × soulangeana. This finding provides crucial information for developing effective strategies to monitor and manage this disease.

Powdery mildew on Coccinia grandis caused by Golovinomyces tabaci in India

In March 2021, severe signs of powdery mildew were observed on leaves and stems of Coccinia grandis in the Manchar, Pune District, Maharashtra state, India. Based on morphological examination, phylogenetic analyses, and pathogenicity test, the causal agent of powdery mildew on Coccinia grandis was identified as Golovinomyces tabaci. To our knowledge, this is the first record of G. tabaci infecting C. grandis in India. Previously, G. tabaci had only been reported on C. grandis from Taiwan and Thailand.

First report of powdery mildew caused by Erysiphe euonymicola on wintercreeper (Euonymus fortunei) in China.

Wintercreeper (Euonymus fortunei) is an evergreen shrub, a semi climbing plants with very strong vitality. It can tolerate a broad range of environmental conditions varying from full sun to deep shade. So, wintercreeper is a good groundcover plants and tree species of vertical greening. It is widely used in urban greening in China. In May 2021, severe powdery mildew signs were found on wintercreeper plant in a garden of Luohe cities of Henan province, China. Approximately 40% of leaves on a plant were symptomatic, and about 60% of the plants were infected. Powdery mildew colonies appeared as white spots on the upper surface of the leaf and stem of the plants in the initial stage. Later, mycelial growth was amphigenous, thick, forming irregular white patches, effused to cover the entire leaf surface. At last, leaves turned yellow and senescence. One representative voucher specimen was deposited at the herbarium of Shangqiu Normal University (SQNU), Shangqiu, China, under the accession number of EF02. Conidiophores arising terminally from the mother cell, mostly central, erect, straight, 40.7 to 67.7µm (average 49.1µm) 6.1 to 8.5µm (average 7.5µm) (n=30) composed of 3 to 4 cells and produced conidia singly. Conidia were obovoid-ellipsoid, apex rounded, base subtruncate, ends truncate or subtruncate, long 26.1 to 36.4µm (average 30.7µm) and width 9.9 to 16.0µm (average 11.8µm) (n=30). No chasmothecia were observed. The morphological characteristics and measurements were consistent with those of Erysiphe euonymicola (Braun and Cook 2012). The internal transcribed spacer regions of EF02 were amplified using primers ITS1/ITS4, and sequences directly. The obtained sequence of 648 bp was deposited in GenBank (accession no. OM304857). The isolate (EF02) was 99.83% similarity with E. euonymicola on E. fortunei var. radicans (KM361621 from Korea) (Lee et al. 2015), 99.23% with E. euonymicola on E. fortunei (MT510003 from USA), 99.23% with E. euonymicola on E. japonicus (LC270841and LC270834 from Azerbaijan, AB250228 from Japan ). The domains D1 and D2 of the 28S rDNA obtained 619 bp sequences from the powdery mildew of isolate EF02 with primer NL1/NL4, deposited in GenBank (OM302187). A NCBI BLAST search of the EF02 isolate showed 100% similarity with 28S rDNA sequence of E. euonymicola on E. japonicus (AB250230 from Japan) (Limkaisang et al. 2006), and 28S phylogenetic tree analysis EF02 isolate is located in the same branch as E. euonymicola. The pathogenicity was confirmed by gently pressing the infected leaves onto five healthy plants. Five uninoculated plants served as controls. Ten inoculated and non-inoculated plants were placed in different growth chambers with 14-h photoperiod at 22±2°C and 60% of relative humidity. After 11 to 13 days, powdery mildew colonies developed on inoculated plants. Non-inoculated control plants did not show powdery mildew symptoms. The fungus on inoculated leaves was morphologically identical to that first observed in the field. Although E. euonymi-japonici (synonym E. euonymicola) has been recorded on E. japonicus in China (Li et al. 2011), this is the first report of powdery mildew caused by E. euonymicola on E. fortunei in China. It could become a threat to the widespread planting of wintercreeper, Similar report has been in Korea (Lee, C. K., et al. 2015).

First Report of Powdery Mildew Caused by Podosphaera xanthii on Cucurbita ficifolia in Korea.

Cucurbita ficifolia Bouché, called fig-leaf gourd, is a cucurbitaceous climbing plant native to the Americas. During summer and autumn of 2020, almost all of fig-leaf gourds planted in an experimental plot in Jeonju (35°50'54″N, 127°07'46″E), Korea, were found to be infected by a powdery mildew with a 100% disease severity. Symptoms first appeared as white, small, irregular colonies, later coalesced into abundant hyphal growth on both sides of the leaves and young stems. Subsequently premature senescence and poor growth of affected leaves was observed. A voucher specimen was housed in the Korea University herbarium (KUS-F32173). For morphological characterization of the fungus, fresh materials were used for microscopy. Conidiophores (n = 30) were straight, 90 to 190 × 10 to 12 μm and produced three to six immature conidia in chains with a crenate outline. Conidia (n = 30) were ellipsoid-ovoid to barrel-shaped, measured 28 to 38 × 18 to 24 μm with a length/width ratio of 1.3 to 2.0, and contained distinct fibrosin bodies. No chasmothecia were found over the course of the season. The morphological feature of the fungus and the host genus were compatible with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012), a well-known cucurbitaceous powdery mildew. For further confirmation, DNA was extracted from mycelium taken from above mentioned specimen. Internal transcribed spacers (ITS1 and ITS2) and large subunit (LSU) gene of the rDNA were amplified using primer pairs ITS1F/PM6 and PM3/TW14, respectively (Takamatsu and Kano 2001). Newly obtained sequences were registered to the GenBank under the accession numbers OL677355 for ITS and OL677356 for LSU. Our sequences shared 99.54~99.77% identity for ITS (MW559231 and MT250855) and 99.58% for LSU with sequences of P. xanthii (MK357445 and MK357438) in BLAST'n search. Pathogenicity tests were performed twice by pressing method of mycelial patches of the infected leaf onto the young leaves of five healthy fig-leaf gourd plants. Five non-inoculated plants were used as controls. Inoculated leaves started to develop powdery mildew signs after 5 days treatment, whereas the control plants remained symptomless. The fungus on the inoculated plants was morphologically identical to that originally observed on diseased plants, fulfilling Koch's postulates. To date three powdery mildew species have been reported on C. ficifolia (Farr and Rossman 2021). Among these reports, Golovinomyces orontii sensu lato was known from Chile, Mexico, United Kingdom, and Germany, Leveillula taurica from Korea and Podosphaera fuliginea (currently P. xanthii) was recorded Australia and India. To our knowledge, this is the first report of P. xanthii on C. ficifolia in Korea. Since this plant is used as grafting rootstock for preventing soil-borne gummy stem blight of cucumber caused by Didymella bryoniae in Korea (Choi et al. 2009), economic importance of the powdery mildew occurring on leaves of this plant is currently limited. Nevertheless, presence of a powdery mildew could be informative to breeding program of Cucurbita spp. and safe production of C. ficifolia fruits globally.

Timing of Triazole-Based Spray Schedules for Managing Mungbean Powdery Mildew in Australia: A Meta-Analysis.

Powdery mildew (PM), caused by two fungal species, Podosphaera xanthii and Erysiphe vignae, is a yield-limiting foliar disease commonly found in mungbean (Vigna radiata) cropping areas of the eastern region of Australia. Effective control of the disease relies largely on fungicide applications, mainly of the triazole group. Uncertainty in the current fungicide spray schedule recommendations, which advise commencing with a spray at the first signs of PM, prompted this study to evaluate PM severity and crop yield data obtained from fungicide trials, which also tested spray schedules starting before (early) or after (late) first signs, applied singly or combined with a follow-up spray. A meta-analytic approach was used to obtain mean differences of the PM severity and crop yield between plots sprayed with specific triazole-based spray schedules and nontreated plots. From 26 trials, 14 trials and 15 trials met the criteria for inclusion in PM severity and yield analyses, respectively. The schedule with the first spray starting at first sign, with a follow-up spray 14 days later, resulted in significantly lower disease severity compared with all other schedules. However, the yield protected was only numerically higher and not statistically different compared with single-spray at first sign, single-spray late, or two-spray starting late. PM severity and yield in the early sprayed plots did not differ from the nontreated plots. These findings support the current recommendations and provide additional evidence that yields are still protected when delaying the first spray up to a week after disease onset. They also suggest that additional sprays may not always be necessary, thus reducing direct fungicide costs, indirect costs related to fungicide insensitivity, and potential adverse effects to the environment.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Salvia farinacea in Korea.

Salvia farinacea Benth. (Lamiaceae) is an herbaceous perennial plant, native to Mexico and southern parts of the United States. This plant is cultivated worldwide for its ornamental value. In November 2019, hundreds of S. farinacea 'Blue Bedder" grown in a flower garden in Jeju (33°30'57"N 126°32'50"E), Korea have been found to be infected with a powdery mildew fungus. The disease severity was estimated to be 100%. Likewise in October 2020, a similar situation with this plant was also observed in a flower garden in Seoul (37°35'19"N 127°01'07"E), Korea. Leaves, stems and inflorescence of plants were covered by white, thin mycelial felt, bearing an abundance of conidiophores and conidia. Eventually, infected plants lose their ornamental value. Two voucher specimens have been deposited in the Korea University Herbarium (KUS-F31478 and F32164). Fresh materials were examined. Hyphal appressoria were nipple-shaped, but rarely found. Conidiophores (n = 30) were straight, 95 to 160 × 10 to 12 μm and produced 2 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindric and 36 to 60 μm long. Conidia (n = 30) were ellipsoid-ovoid to barrel-shaped, 32 to 38 × 18 to 24 μm, and contained conspicuous fibrosin bodies. Dark brown chasmothecia were found partly embedded in the mycelial felt on leaves, mostly hypophyllous, spherical, and 82 to 100 µm diameter, with a single ascus in each. Appendages were few, mycelioid, 1- to 4-septate, brown near the base when mature, but paler above. Asci were broadly ellipsoid to subglobose, 56 to 68 × 50 to 62 μm, sessile and 8-spored. Ascospores were colorless, oval to subglobose, and 14 to 18 × 12 to 15 µm. These characteristics were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012). For further confirmation, genomic DNA was extracted from chasmothecia from KUS-F31478 and F32164. PCR amplification was performed using the primer pair ITS1F/PM6 for internal transcribed spacer (ITS) and PM3/TW14 for the large subunit (LSU) of the rDNA (Takamatsu and Kano 2001). Obtained sequences were deposited to the GenBank under the accession numbers MZ359847 and MZ359859 for ITS, MZ359858 and MZ359861 for LSU. For ITS regions 99.80-100% similarity was found with sequences MT131256 (Salvia farinacea), MT131254 (Mazus pumilus) and MT131252 (Erigeron bellioides) of P. xanthii, whereas it was 99.90% with sequences of this fungus on Echinacea purpurea (MT826247 and MT826245) for 28S rDNA gene. Pathogenicity tests were carried out by touching an infected leaf onto healthy leaves of disease-free 30 days old potted 'Blue Bedder' using replication of five plants, with five non-inoculated plants used as controls. The typical signs of powdery mildew started to develop on the inoculated leaves in 7 to 10 days, and microscopic examination revealed the morphological identity with the fungus observed from the field. All non-inoculated control plants remained symptomless. Hitherto Golovinomyces powdery mildews on Salvia spp. were reported globally (Farr and Rossman 2021). However, Podosphaera elsholtziae on Salvia sp. and P. xanthii on S. farinacea were reported from China and Taiwan (Zheng and Yu 1987, Yeh et al. 2021). To our knowledge, this is the first report of P. xanthii on S. farinacea in Korea. The occurrence of Podosphaera powdery mildew on S. farinacea could pose a serious threat to the beauty of this plant, causing premature senescence of young leaves and gray to purplish discoloration of the leaves.

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).

First Report of Golovinomyces sonchicola Causing Powdery Mildew on Sonchus oleraceus in Mexico.

Sonchus oleraceus, common sow thistle, is native to Europe, Northern Africa, and Western Asia. This plant has become a common weed throughout the world. In Mexico, this weed has become widely naturalized by replacing indigenous plants and invading many agricultural areas. During the spring of 2018 and 2019, common sow thistle plants showing typical symptoms and signs of powdery mildew, were collected from agricultural fields in Ahome, Sinaloa, Mexico. As much as 30% of plants were diseased and 60 to 95% of the foliage was affected. Mycelium was conspicuous and white-gray, and on stems and both surfaces of leaves. Appressoria were nipple-shaped to crenulate. Conidiophores (n= 30) were hyaline, cylindrical, erect, and up to 150 μm long. Foot-cells (n= 30) were distinctly curved, 47 to 75 × 10 to 13 μm, slightly constricted, followed by 1-3 shorter cells and formed conidia in chains. Conidia (n= 100) were ellipsoid to doliiform to subcylindrical, 28 to 37 × 14 to 19 μm, lacked fibrosin bodies, and germinated from the apex. Chasmothecia were not observed. The morphological characters were consistent with those of the anamorphic state of Golovinomyces sonchicola (Braun and Cook 2012, Jakše et al. 2019). A voucher specimen (accession no. FAVF215) was deposited in the Herbarium of the Faculty of Agriculture of El Fuerte Valley at the Autonomous University of Sinaloa (Juan Jose Rios, Sinaloa, Mexico). To confirm the morphological identification, genomic DNA was extracted from mycelium and conidia, and the internal transcribed spacer (ITS) region and part of the 28S gene were amplified by PCR and sequenced. The ITS region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). For amplification of the 28S rRNA partial gene, a nested PCR was performed using the primer sets PM3 (Takamatsu and Kano 2001)/TW14 (Mori et al. 2000) and NL1/TW14 (Mori et al. 2000) for the first and second reactions, respectively. Phylogenetic analyses using the maximum parsimony and maximum likelihood methods (Braun et al. 2019), including ITS and 28S sequences of isolates of Golovinomyces spp. were performed and confirmed the results obtained from the morphological analysis. Isolate FAVF215 grouped in a clade with the other isolates of G. sonchicola. The ITS and 28S sequences were deposited in GenBank under accession numbers MW425872 and MW442972, respectively. Pathogenicity was demonstrated by gently dusting conidia from infected leaves onto leaves of 20 healthy plants and covered with plastic bags for 24 h. Ten non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25 to 35ºC. All inoculated plants developed similar symptoms to those observed in the field from natural infections after 12 days, whereas powdery mildew symptoms and signs were not observed on control plants. The morphology asexual structures of fungus on inoculated plants were identical to those on naturally infected plants, fulfilling Koch's postulates. Inoculation tests were repeated twice with identical results. Based on the morphological data and phylogenetic analysis, the fungus was identified as G. sonchicola. This fungus has been reported causing powdery mildew on S. oleraceus in Germany, The Netherlands, Slovenia, and The United Kingdom (Farr and Rossman 2021). To the best of our knowledge, this is the first report of G. sonchicola causing powdery mildew on S. oleraceus in Mexico. This powdery mildew pathogen may represent an option for the biological control of common sow thistle.

First Report of Golovinomyces cichoracearum Causing Powdery Mildew on Zinnia elegans in China.

Zinnia elegans, common zinnia, is an annual plant with highly ornamental values. It is widely planted in many nurseries, city parks, universities and home gardens in China. From August to October 2020, powdery mildew-like signs and symptoms were observed on leaves of Z. elegans growing on the campus of Henan Normal University, Henan Province, China. White powdery colonies in circular- or irregularly shaped-lesions were abundant on both surfaces of leaves and covered up to 95 % of the leaf area. Any infected leaves were chlorotic, deformed or senescence. More than 70 % of the monitored Z. elegans plants showed these signs and symptoms. Conidiophores (n = 20) were 100 to 200 × 9 to 13 μm and composed of foot cells, followed by straight cells and conidia. Mycelial appressoria were single and nipple-shaped. The oval-shaped conidia (n = 30) were 22 to 36 × 12 to 18 μm, with a length/width ratio of 1.4 to 2.7, and produced germ tubes from the polar ends of the spore. No chasmothecia were found. Based on these morphological characteristics, the pathogen was initially identified morphologically as Golovinomyces cichoracearum (Braun and Cook 2012). Structures of the pathogen were scraped from infected leaves and total genomic DNA was isolated using the method previously described by Zhu et al. (2019). The internal transcribed spacer (ITS) region of rDNA was amplified by PCR using the primers ITS1/ITS4 (White et al. 1990) and the amplicon was sequenced by Invitrogen (Shanghai, China). The sequence for the fungus was deposited into GenBank under Accession No. MW029904 and was 99.83 % identical (595/596 bp) to G. cichoracearum on Symphyotrichum novi-belgii (HM769725)(Mørk et al. 2011). To perform pathogenicity analysis, leaf surfaces of five healthy plants were fixed in a settling tower and then inoculated by blowing fungal conidia from mildew-infested leaves using pressurized air. Five non-inoculated plants served as a control. The inoculated and non-inoculated plants were separately maintained in two growth chambers (humidity, 60 %; light/dark, 16 h/8 h; temperature, 18 ℃). Eleven- to twelve-days post-inoculation, powdery mildew signs were conspicuous on inoculated plants, while control plants remained healthy. Similar results were obtained by conducting two repeated pathogenicity assays. Thus, based on the morphological characteristics and molecular analysis, the pathogen was identified and confirmed as G. cichoracearum. This pathogen has been reported on Z. elegans in India, Israel, Jordan, Korea, Nepal, Sri Lanka, Switzerland, and Turkey (Farr and Rossman 2020). To our best knowledge, this is the first report of G. cichoracearum on Z. elegans in China. The sudden outbreak of powdery mildew caused by G. cichoracearum on Z. elegans may adversely impact the plant health and ornamental value in China. Therefore, the confirmation of G. cichoracearum infecting Z. elegans expands the understanding of this pathogen and provides the fundamental knowledge for future powdery mildew control.

Controlling Cucumber Powdery Mildew using Cow Milk and Whey under Greenhouse Conditions

The role of raw cow's milk and whey (40 and 50% dilution in water) and number of sprays against cucumber powdery mildew caused by Sphaerotheca fuliginea was studied in greenhouse experiments during 2017/18 and 2018/19. As a result of number of sprays, the disease severity percentage and area under the disease progress curve (AUDPC) were affected by the number of sprays with raw milk and whey. The number of sprays played an important role in controlling powdery mildew, and significant differences have occurred among all applied sprays. Four sprays with intervals of one week was the effective treatment in reducing disease severity, AUDPC values, compared to other treatments, i.e., two and three sprays in comparison to the fungicide as well as a control treatment. Additionally, treated plants showed a significant increase in plant growth and yield parameters in case of spraying four times. Also, the activity of defense-related enzymes (catalase, peroxidase, and polyphenoloxidase) and amino acid proline was high in response to increasing the number of sprays at four times compared with untreated plants. Light and scanning electron microscopic observations showed a clear change in the morphology of S. fuliginea spores, in addition to hyphae degradation and loss the vitality of conidia as well as rupturing the content of conidia. The results obtained also indicated that cow's milk and whey dilution effectively reduced the powdery mildew signs and symptoms on infected cucumber plants at 50% with the four sprays treatment being the most effective treatment.

Powdery mildew caused by Golovinomyces spadiceus on wild sunflower in Sinaloa, Mexico

Wild sunflower is a common weed that grows among agricultural crops in many parts of the world, where it is both highly invasive and competitive and can serve as a reservoir for plant pathogens. Recently, signs of powdery mildew (PM) were observed on wild sunflower plants in Sinaloa, Mexico. The aim of this study was to identify the causal agent based on morphology and molecular techniques, and to determine pathogenicity on sunflower plants. Phylogenetic analysis of the ITS region grouped the sequences within lineage III of the genus Golovinomyces, which comprises pathogenic species of the plant tribe Heliantheae of Asteraceae. However, within this lineage, the three species belonging to this group: G. circumfusus, G. ambrosiae and G. spadiceus, cannot be differentiated based on the ITS region due to their close phylogenetic relationship. Morphometric analyses, particularly conidium size and germ tube morphology, confirmed the identity of the fungus infecting wild sunflowers as G. spadiceus. Inoculation tests under greenhouse conditions confirmed the pathogenicity of G. spadiceus in wild sunflower and in the commercial sunflower hybrid SYN3950HO. Signs of powdery mildew displayed on sunflower were similar to those observed under field conditions and in two independent inoculation tests. Our results confirm that wild sunflower is a potential source of G. spadiceus inoculum for commercial sunflower during the autumn–winter growing season.