Report Of Powdery Mildew Research Articles

First report of Powdery Mildew Caused by Golovinomyces ambrosiae on Industrial Hemp in New Jersey.

In December 2019, New Jersey became one of the first states to have its industrial hemp (Cannabis sativa L.) plan approved by the U.S. Department of Agriculture (USDA) following enactment of the 2018 Farm Bill that authorized the production of hemp. Following this approval, hemp was legally grown for the first time in 2020. During the growing seasons of 2020 and 2021, powdery mildew-like symptoms were observed during the summer months (Jun to Aug) in greenhouse hemp research and fall months (Aug to Oct) in field production plots on Rutgers Agricultural Experiment Station farms in southern and northern New Jersey. Symptoms were observed on leaves and stems of hemp cultivars 'CB Genius', 'Cherry Wine' and 'Bay Mist'. Symptoms initially appeared as small white patches of mycelia and conidia on the adaxial surface of leaves that gradually spread to entire leaves and stems. Leaf discoloration (e.g., chlorosis) and premature leaf drop were observed. More severe symptoms and damage were observed in the greenhouse than outdoor cultivation. A voucher specimen was deposited in the U.S National Fungus Collections, USDA-ARS, Beltsville, MD (accession number 929187). Morphological examination of the white colonies from the cultivar 'Baymist' was carried out using light microscopy and further characterized by sequencing. This isolate was labelled PMH2. Hyphae were septate, conidiophores were hyaline, unbranched, measuring 130 to 240 μm in length and produced 1 to 4 conidia in chains. Conidia were hyaline, ellipsoid to ovoid in shape and measured 20 to 36 ×10 to 18 μm (n=30). Oil-like drops were present within conidia, although no distinct fibrosin bodies were observed. Chasmothecia were not observed. Morphological observations were consistent with those of Golovinomyces spp. as described by Braun and Cook (2012). Morphological observations (conidiophore and conidial measurements) were also similar to the description of G. ambrosiae on Hemp, as described in Wiseman et al, 2021. Sequencing of internal transcribed spacer (ITS), large ribosomal subunit (28S), intergenic spacer (IGS), beta- tubulin (TUB2) and chitin synthase 1(CHS1) region, were carried out with the primer sets ITS5/ITS4, LSU1/LSU2, IGS-12a/NS1R, TubF1/TubR1 and gCS1a1/gCS1b respectively, as shown by Qiu et al. (2020). Maximum-likelihood phylogenetic analysis confirmed the grouping of the PMH2 isolate within the G. ambrosiae accessions. Each individual gene alignment was treated as a separate partition. Sequences were not concatenated for maximum -likelihood phylogenetic analysis. Sequence data were deposited in GenBank under the accessions OK626453 (ITS), OK626454 (28S), OL456201 (IGS), OL415512 (TUB2) and OL415513(CHS1). To fulfill Koch's postulates, two mature, potted plants of C. sativa cv. 'Alpha Explorer' were inoculated by gently pressing symptomatic hemp leaves onto their leaf surface. They were incubated in an indoor grow room at 23°C and relative humidity of 50%. Non-inoculated healthy plants of C. sativa cv. 'Alpha Explorer' served as control. Inoculated plants developed powdery mildew symptoms within 10 to 12 days, while all control plants were asymptomatic. The powdery mildew on inoculated plants was found to be morphologically similar to the original. G. ambrosiae has been reported on C.sativa in Oregon (Wiseman et al. 2021) and G. ambrosiae (as G. spadiceus) has been reported on Cannabis in Kentucky (Szarka et al. 2019), Ohio (Farinas and Hand 2020) and New York (Weldon et al. 2020). This is the first known report of Golovinomyces ambrosiae causing powdery mildew on hemp in New Jersey. With the recent opening ( Dec15, 2021) of cultivation licensing and retailing of recreational marijuana, the acreage of Hemp production in New Jersey is expected to significantly increase, particularly for greenhouse production. It is important to document the species to develop management strategies to control this disease.

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 on Astragalus sinicus (Chinese milk vetch) caused by Erysiphe trifoliorum in China.

Astragalus sinicus L., (Chinese milk vetch) is a traditional leguminous green manure that plays a significant role in maintaining paddy soil fertility to enhance yield and the quality of rice in China. It is also found in gardens, roadsides, farms, fields, riverbanks, open wastelands, and is often used as livestock feed. From February 2019 to 2021, severe powdery mildew infections were observed on hundreds of A. sinicus grown in gardens and at roadsides of Fuzhou city, China. The disease incidence was up to 100% on leaves and stems of A. sinicus. White superficial fungal colonies (circular to irregular patches) were present on both sides of the leaves. Hyphae were flexuous to straight, branched, 4 to 8 µm in width, and septate. Hyphal appressoria were lobulate and solitary or in opposite pairs. Conidiophores were erect and straight, hyaline, and 60 to 120 × 8 to 10 µm (n=30). Foot cell was cylindrical, straight to slightly curved, 22 to 38 × 8 to 10 µm, followed by two to three shorter cells. Conidia were cylindrical-oval to doliiform, 30 to 48 × 13.5 to 24 μm with a length/width ratio of 1.6 to 2.4 (n = 30), formed singly, and without fibrosin bodies. Conidial germ tubes were produced subterminal position. No chasmothecia were found in the collected samples. The morphological characteristics of asexual structures were consistent with the descriptions of E. trifoliorum (Wallr.) U. Braun in Braun and Cook (2012). To verify the identification of the pathogen, the ITS and the part of large subunit (LSU) rDNA gene of the isolates were amplified using ITS1/ITS4 and LSU1/ LSU2 primers (Scholin et al. 1994 and White et al. 1990, respectively) and sequences were deposited in GenBank (ITS: MZ021332, MZ021333; LSU: MZ021334, MZ021335). In BLASTn searches, the ITS and LSU sequences were 99 to 100% identical with those of E. trifoliorum parasitic on Lathyrus magellanicus (LC010015), Medicago littoralis (LC270860), Melilotus officinalis (LC009924) and Trifolium spp., (MN216308, KY660821), as well as E. baeumleri (Bradshaw et al. 2021) on Vicia nigricans (LC010014). Pathogenicity test was performed by gently pressing a diseased leaf onto 10 young leaves of three healthy potted plants, while three non-inoculated plants were used as controls. All plants were maintained in a greenhouse at 20 to 25°C, without humidity control, and natural light. Symptoms developed 7 days after inoculation, whereas the control leaves remained symptomless. The morphology of the fungus on the inoculated leaves was identical to that observed on the originally diseased leaves. Powdery mildew on A. sinicus has been reported as E. pisi and E. polygoni from Korea and China (Shin, 2000; Tai 1979), respectively. Amano (1986) listed E. pisi and Microsphaera astragali (now E. astragali) on A. sinicus from China and Japan. To our knowledge, this is the first report of powdery mildew caused by E. trifoliorum on A. sinicus in China and in general. E. astragali is the most common and widespread powdery mildew species on Astragalus spp. (Braun and Cook 2012) and would be expected on A. sinicus, but this species is genetically clearly different from E. trifoliorum (Bradshaw et al. 2021). The E. trifoliorum complex (clade) is composed of several morphologically well-distinguishable species, besides E. trifoliorum also including E. baeumleri (on Vicia spp.), E. hyperici (on Hypericum spp.), and E. euonymi (on Euonymus spp.), but based on a combination of sequence plus host identity, the collection on A. sinicus can be assigned to E. trifoliorum (Bradshaw et al. 2021). The information in this study extended the host range of E. trifoliorum as well as future studies on A. sinicus in relation to powdery mildew outbreaks in China.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Sigesbeckia orientalis in China.

Sigesbeckia orientalis L., (St Paul's wort) is an annually grown natural herb of Asteraceae with a long therapeutic history for a wide range of inflammation-related diseases in China (Zhong et al. 2019). In June 2020, typical symptoms of powdery mildew were observed on 30% of wild S. orientalis plants grown along the roadsides and gardens in Minjiang University, Fuzhou, China. Circular to irregular white powdery fungal colonies were observed on both surfaces of the leaves and young stems, causing necrosis and premature senescence. Fungal hyphae were epigenous, flexuous to straight, branched, and septate. Appressoria on the hyphae were nipple-shaped or nearly absent. Conidiophores were straight, 30 to 210× 8 to 12 μm, and produced 3 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindrical, 45 to 75 ×10 to 12 μm, followed by 1 to 2 shorter cells. Conidia were hyaline, ellipsoid-ovoid to barrel-shaped, 25 to 38 × 18 to 23 μm with distinct fibrosin bodies. Germ tubes were produced from a lateral position on the conidia. Chasmothecia were not observed on the infected leaves. Based on anamorph characteristics, fungus was identified as Podosphaera xanthii (Castagne) U. Braun & N. Shishkoff (Braun and Cook 2012). For molecular identification, total genomic DNA was extracted (Mukhtar et al. 2018) from fungal colonies on infected leaves of five collections separately. For each DNA sample, the part of LSU and ITS regions were amplified using primers LSU1/LSU2 and ITS1/ITS4 (Scholin et al. 1994; White et al. 1990), respectively. A BLAST search revealed 100 % sequences similarity with P. xanthii sequences reported on Ageratum conyzoides (KY274485), Eclipta prostrata (MT260063), Euphorbia hirta (KY388505), Sonchus asper (MN134013), and Verbena bonariensis (AB462804). Representative sequences (ITS: MZ613309; LSU: MZ614707) of an isolate were deposited in GenBank. The phylogenetic analysis also grouped the obtain sequences into P. xanthii clade. Pathogenicity was confirmed by gently pressing the infected leaves onto young leaves of five healthy one-month-old S. orientalis plants, while three non-inoculated plants were used as controls. All plants were maintained in a greenhouse at 25 ± 2°C. After, seven days, white powdery colonies were observed on inoculated plants, whereas controls remained mildew-free. On inoculated leaves, the fungus was morphologically and molecularly identical to the fungus on the original specimens. P. xanthii has been reported as a significant damaging pathogen on a wide range of plants in China (Farr and Rossman 2021). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on S. orientalis in China as well as worldwide. S. orientalis is one of the most important commercial Chinese medicinal herbs and the occurrence of powdery mildew is a threat to its production, quality, and marketability.

First Report of Powdery Mildew Caused by Erysiphe cruciferarum on Camelina sativa in Montana.

Camelina sativa (L.) Crantz, also known as false flax, is an annual flowering plant in the family Brassicaceae and originated in Europe and Asia. In recent years, it is cultivated as an important biofuel crop in Europe, Canada, and the northwest of the United States. In June of 2021, severe powdery mildew was observed on C. sativa 'Suneson' plants under greenhouse conditions (temperature 18.3°C/22.2°C, night/day) in Bozeman, Montana (45°40'N, 111°2'W). The disease incidence was 80.67% (150 pots, one plant per pot). White ectophytic powdery mildew including mycelia and conidia were observed on the upper leaves, usually developed from bottom tissues to top parts, also present on stems and siliques. Mycelia on leaves were amphigenous and in patches, often spreading to become effused. These typical symptoms were similar to a previous report of powdery mildew on Broccoli raab (Koike and Saenz 1997). Appressoria are lobed, and foot cells are cylindrical with size 18 to 26 × 7 to 10 μm. Conidia are cylindrical and produced singly, with a size of 35 to 50 × 12 to 21 μm and a length : width ratio greater than two (Koike and Saenz 1997). No chasmothecia were observed under the greenhouse conditions. The symptoms and fungal microscopic characters are typical of Pseudoidium anamorph of Erysiphe (Braun 1995). The specific measurements and characteristics are consistent with previous records of Erysiphe cruciferarum Opiz ex L. Junell (Braun and Cook 2012; Vellios et al. 2017). To identify the pathogen, the partial internal transcribed spacer (ITS) region of rDNA of sample CPD-1 was amplified using primers ITS1 and ITS4 (White et al. 1990). The amplicons were sequenced, and the resulting 559-bp sequence was deposited in GenBank (CPD-1, Accession number: OK160719). A GenBank BLAST search of the ITS sequences showed an exact match (100% query cover, E-value 0, and 100% identity 559/559 bp) with those of E. cruciferarum on hosts Brassica sp. (KY660929.1), B. juncea from Vietnam (KM260718.1) and China (KT957424.1). A phylogenetic tree was generated with the CPD-1 ITS sequence with several of ITS sequences of close species with different hosts obtained from the GenBank. Isolate CPD-1 was grouped with pathogens from Brassica hosts rather than the holotype strain (KU672364.1) from papaveraceous hosts. To fulfill Koch's postulates, pathogenicity was confirmed through inoculation by dusting conidia onto leaves of seven healthy, potted, 14-day-old C. sativa seedlings (cv. Suneson). Seven non-inoculated plants served as a control treatment. The plants were incubated in a greenhouse with a temperature of 18°C (night) to 22°C (day). The inoculated plants developed similar symptoms after 7 days, whereas the control plants remained symptomless. The fungus on the inoculated plants was morphologically identical to that was originally observed on the diseased plants. Though many Brassica spp. have been known to be infected by E. cruciferarum throughout the world, powdery mildew of C. sativa cultivar Crantz in natural conditions by E. cruciferarum has been reported only in the province of Domokos in Central Greece (Vellios et al. 2017). To our knowledge, this is the first report of powdery mildew caused by E. cruciferarum on C. sativa in Montana. Though the powdery mildew on C. sativa was observed in the greenhouse conditions in this work, it poses a potential threat to the production of this biofuel crop in the northwest of the United States.

First report of powdery mildew caused by Golovinomyces ambrosiae on Parthenium hysterophorus in Mexico

First report of powdery mildew caused by Golovinomyces ambrosiae on Parthenium hysterophorus in Mexico

First report of powdery mildew caused by Erysiphe lonicerae on Lonicera periclymenum in Korea

First report of powdery mildew caused by Erysiphe lonicerae on Lonicera periclymenum in Korea

First Report of Erysiphe cruciferarum Causing Powdery Mildew of Alliaria petiolata in Maryland.

Alliaria petiolata (Bieb.) Cavara & Grande (garlic mustard) is a biennial crucifer native to Europe and invasive in North America, where it outcompetes native plants in deciduous forests. In July 2021, powdery mildew was observed on A. petiolata in Frederick County, Maryland. Signs of the disease included white, tomentose mycelium producing abundant conidia (Fig S1). A majority of plants were affected, and severity ranged from the presence of small, discrete infections to complete colonization of leaves, stems, and ripening seed pods. Conidia from field collected leaves were transferred to disease-free A. petiolata for maintenance in a growth chamber at 20°C and 80% RH with a 12 hr photoperiod. Fungal morphology was recorded 30 days after this transfer. Appressoria were irregularly lobed, and conidiophores were straight and composed of 2-3 cells. Cylindrical to oblong conidia were produced singly in pseudochains of 2-6 (x̄ = 3), measured 39-64 by 18-29 (x̄ = 52 by 24) μm, had a length to width ratio greater than two, and germinated at the ends. Fibrosin bodies were absent from conidia, and chasmothecia were not observed in the field or on inoculated plant material. Based on anamorphic characteristics, the pathogen was placed in the genus Erysiphe (Boesewinkel 1980). Species level identity was determined using DNA sequences. Conidia and mycelia were scraped from leaves and used for genomic DNA extraction with the Quick-DNA Fungal/Bacterial Miniprep Kit (Zymo Research, Irvine, CA). A portion of the internal transcribed spacer region of rDNA was amplified using the primers ITS5/ITS4 (White et al. 1990). Purified amplicons (PCR & DNA Cleanup Kit, New England BioLabs Inc., Ipswich, MA) were sequenced at Eurofins Genomics (Louisville, KY). The resulting sequence was compared to those in NCBI GenBank using the blastn algorithm (Altschul et al. 1990). The newly generated sequence (GenBank: OK157430) was identical (599/599 bp) to samples of E. cruciferarum from the United Kingdom (GenBank: KY660931.1, KY660879.1, KY660752.1). Because E. cruciferarum sensu lato is heterogeneous (Pastirčáková et al. 2016), additional sequence comparisons were made to the E. cruciferarum sensu stricto holotype (589/599 bp, GenBank: KU672364) and a vouchered E. cruciferarum s. lat. (596/599 bp, GenBank: LC009943). This supports identification of the pathogen as E. cruciferarum s. lat. and suggests the taxonomy of isolates from A. petiolata should be reassessed following any revision to E. cruciferarum. A modified Koch's postulates procedure was followed to confirm pathogenicity. Leaves colonized by E. cruciferarum were briefly pressed against the leaves of three disease-free plants grown from seed in a greenhouse. After 14 days, inoculated plants showed signs of powdery mildew similar to those observed in the field, and a control treatment using pathogen-free leaves resulted in no disease. This inoculation experiment was performed twice, and the identity of the pathogen was reconfirmed based on morphology. This is the first report of powdery mildew on A. petiolata in Maryland. Erysiphe cruciferarum s. lat. is widely distributed on other hosts and has been found on A. petiolata throughout Europe and in Ohio and Indiana (Farr and Rossman 2021; Blossey et al. 2001; Enright and Cipollini 2007; Ciola and Cipollini 2011). This pathogen has been proposed as a biological control agent (Cipollini and Enright 2009; Cipollini et al. 2020), and the presence of disease in Maryland suggests the local population of A. petiolata is susceptible to E. cruciferarum and the environment there is favorable to disease development.

First Report of Powdery Mildew Caused by Blumeria graminis on Poapratensis var. anceps 'Qinghai' in China.

Poa pratensis, an important cool-season perennial grass, is widely cultivated for construction of grasslands and ecological management of Qinghai-Tibet Plateau (Dong et al. 2020). Poa pratensis var. anceps Gaud cv. Qinghai (PPAQ) is a variant of P. pratensis (Liu et al. 2009). In June 2016, powdery mildew was observed on PPAQ in an artificial field of PPAQ in Haiyan county of Haibei Tibetan Autonomous Prefecture, Qinghai province, China (36°59'17.76″N, 100°52'54.01″E). Approximately 30 to 50% of leaves (approximate 10 ha) were affected. Initially, irregular white mycelial colonies were observed on the adaxial surface of affected leaves. The colonies increased in number and size, and later covered a large area of leaves and stems. In advanced stages of disease, the colonies covered the whole adaxial surface and white patches appeared on the abaxial surface of affected leaves, and eventually caused leaf death. Conidiophores were unbranched, measuring 160 to 235 × 4 to 13 μm, and borne vertically on hyphae. Each conidiophore produced 4 to 11 conidia in a chain. The conidia were oval, one-celled, and hyaline, measuring 22 to 40 ×10 to 21 μm (n = 50). Chasmothecia were yellow, spherical, and 172 to 240 μm in diameter (n = 20), each of which contained 8 to 17 asci. The appendages were few, and hyphoid. Asci were oblong or ovate, measuring 79 to 115 × 31 to 45 μm (n = 20). Asci were petiolate, containing eight ascospores. Ascospores were round to oval, colorless, one-celled, measuring 17 to 33 × 8 to 14 μm (n = 50). Based on morphological characteristics, the fungal organism was identified as Blumeria graminis (DC.) Speer. To confirm the identification, the internal transcribed spacer (ITS) of 612 bp was amplified from DNA of conidia using ITS5 and P3 primers (Takamatsu et al. 2009). The ITS sequence was deposited in GenBank database (Accession No. MF429949). The ITS showed 95% sequence similarity with those of B. graminis on Poa nemoralis in USA (Accession No. AB273560) and on P. bullbosa in Iran (Accession No. AB273551) (Inuma et al. 2007). Five two-month-old healthy plants were inoculated by spraying a spore suspension (1× 105 conidia ml-1) prepared from conidia brushed from infected plants; five plants sprayed with sterile distilled water served as controls. All the plants were maintained in a growth chamber with a constant temperature of 20°C, a 12 h/12 h light/dark diurnal cycle, and 70% humidity. Two weeks after inoculation, symptoms of powdery mildew were observed on all inoculated plants, whereas the control plants remained symptomless. The same fungus was confirmed by morphological characterization and molecular assays as described above. B. graminis has been reported on P. pratensis in USA (Dugan and Newcombe 2007), Israel (Voytyuk et al. 2009), and China (Zhang et al. 2014), but has not previously been reported on PPAQ. As far as we know, this is the first report of powdery mildew caused by B. graminis on PPAQ in China. These findings indicated that the health of PPAQ was substantially threaten when infected by powdery mildew, therefore, our results also contributed some valuable information how to diagnose this disease on PPAQ in China.

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.

First Report of Sawadaea polyfida Causing Powdery Mildew of Acer palmatum in China.

Acer palmatum Thunb. is an important colorful leaf ornamental tree species widely distributed in Japan, Korea and China (Carlos et al. 2016). In October 2019, powdery mildew was observed on leaves of A. palmatum planted at Qixia Mountain Park and the campus of Nanjing Forestry University, Nanjing, Jiangsu, China. The powdery mildew infected and colonized leaves, covering both leaf surfaces with white mycelia, giving affected plants an unsightly appearance. Nearly 17.4% of the plants (87/501) exhibited these signs and symptoms. Fresh specimens were collected and examined for the identification of the pathogen. Photos were taken with a ZEISS Axio Imager A2m microscope and a scanning electronic microscope. Chasmothecia were scattered or aggregated on the upper and lower surfaces of the leaves, blackish brown, oblate, 157.5 to 238.1 × 152.3 to 217.8 μm (n=30), with numerous appendages (100 to 200). Appendages were often (1-) 2 to 3 times branched from the middle of the stalk, uncinate to circinate at the apex, hyaline, aseptate, 30.0 to 70.8 × 4.1 to 8.2 μm (n=30). Asci were 11 to 21 per chasmothecium (n=30), long oval, oval, oblong, with short stalk or sessile, 80.6 ± 8.6 × 40.3 ± 4.0 um (n=30) in length, 6 to 8 spored (n=30). Ascospores were ovoid, 18.2 ± 1.6 × 11.1 ± 1.2 μm (n=30). Microconidiophores were 25 to 50 × 4.0 to 5.5 μm, producing microconidia in chains. Microconidia were ellipsoidal, subglobose, 8.7 ± 0.6 × 7.2 ± 0.6 μm (n=30). Macroconidia were not observed. Based on the morphological characteristics, the fungus was identified as Sawadaea polyfida (C.T. Wei) R.Y. Zheng & G. Q. Chen (Zheng and Yu 1987). To confirm the causative species identity, a representative voucher specimen collected and deposited at Nanjing Forestry University was used for a molecular analysis. Mycelia and conidia were collected from diseased leaves and genomic DNA of the pathogen was extracted and the internal transcribed spacer region (ITS) was amplified with primers ITS1/ITS4 (White et al. 1990). The resulting sequence of 461 bp was deposited in GenBank (accession no. MW255383). BLAST result showed that this sequence fully agreed with a sequence of S. polyfida [AB193381.1 (ITS), identities = 461/461 (100%)]. A maximum likelihood phylogenetic analyses using IQtree v. 1.6.8 with the ITS sequence placed this fungus in the S. polyfida clade. Based on the morphology and phylogeny, the fungus was identified as S. polyfida (Hirose et al. 2005; Zheng and Yu 1987). Pathogenicity was tested through inoculation by gently pressing the naturally infected leaves onto healthy ones of three potted A. palmatum seedlings wih five leaves. Healthy leaves from three other seedlings served as control. Inoculated and control seedlings were placed in separate growth chambers maintained at 20 ± 2°C, 70% humidity, with a 16 h/8 h light/dark period. Symptoms developed 8 days after inoculation. The powdery mildew developing on the inoculated seedlings was sequenced and confirmed as S. polyfida. The control leaves did not develop powdery mildew. S. polyfida has been reported on Acer catalpifolium in China (Zheng and Chen 1980), A. amoenum, A. australe, A. japonicum, A. palmatum, A. shirasawanum, and A. sieboldianum in Japan (Hirose et al. 2005; Meeboonet al. 2015), as well as A. takesimense in Korea (Lee et al. 2011). To the best of our knowledge, this is the first report of powdery mildew caused by S. polyfida on A. palmatum in China. These results form the basis for developing effective strategies for monitoring and managing this disease.

First report of powdery mildew caused by Erysiphe russellii on Oxalis dillenii in Korea

First report of powdery mildew caused by Erysiphe russellii on Oxalis dillenii in Korea

First Record of Erysiphe cf. elevata on Cerbera manghas (Apocynaceae) in China.

Cerbera manghas L. (sea mango) is an evergreen shrub or small flowering tree up to12 m tall. It naturally occupies coastal habitats and is distributed from Seychelles in the Indian Ocean eastward to French Polynesia. In China, it is a popular ornamental urban species growing in roadside green belts, public parks, and residential areas in various coastal cities. In March 2019, powdery mildew symptoms were observed on six trees of C. manghas growing in a residential area near Minjiang University campus, in Minhou district of Fuzhou city. Approximately 60 % of leaves per plant were infected. Initial symptoms appeared as small circular to irregular white patches of superficial mycelia, conidiophores and conidia covered on both surfaces of leaves, which later coalesced and formed dense covered, resulting in discoloration and defoliation. Hyphae were septate, hyaline, smooth with simple to multilobed lobed appressoria formed singly or opposite pairs and 5 to 8 µm diam. Conidiophores were erect and 35 to 80 × 5 to 9 μm, composed of foot-cells, 20 to 35 × 5 to 9 µm, straight to usually curved or flexuous-sinuous at the base, followed by two to three shorter cells. Conidia were solitary, ellipsoid to oblong-elliptical, smooth, and 24 to 37 × 13 to 16 μm without fibrosin bodies. The teleomorph was not found on infected trees. These morphological characteristics were typical for anamorph of the genus Erysiphe (Braun and Cook 2012). To confirm fungal identification, the internal transcribed spacer (ITS) regions and the partial large subunit (LSU) rDNA were amplified using primers ITS1/ITS4 and LSU1/LSU2 (Scholin et al. 1994; White et al. 1990), respectively. The sequences were deposited in GenBank (ITS: MZ379159; LSU: MZ379160). BLAST analysis of sequences showed 99-100% similarity with Erysiphe elevata on Eucalyptus camaldulensis (LC177375), Catalpa bignonioides (MH638203), Tabernaemontana divaricata (MT802112), and Plumeria rubra (MH507182). Based on morphological and molecular analyses, the fungus was identified as E. elevata. To confirm pathogenicity, infected leaves were gently pressed onto the leaves of three healthy plants in separate pots, while three noninoculated plants were used as controls. All plants were maintained in a greenhouse at 25°C with a relative humidity of 65% to 70%. Disease symptoms were observed only on the inoculated plants after 10 days and the fungus was morphologically identical to that of the original infected leaves. Previously E. elevata has been reported on Catalpa spp. (Cook et al. 2006) from Europe, while E. camaldulensis (Meeboon and Takamatsu 2017), P. rubra (Wu et al. 2019; Yeh et al. 2019), and T. divaricata (Xu et al. 2021) have been reported as hosts from Thailand, Taiwan and China respectively. To our knowledge, this is the first report of powdery mildew caused by E. elevata on C. manghas in China and in the world. The disease would be a serious threat to ornamental plantings of C. manghas in China. References Braun, U., and Cook, R. T. A. 2012. Taxonomic Manual of the Erysiphales (Powdery Mildews). CBS Biodiversity Series No. 11. CBS, Utrecht, the Netherlands. Cook, R. T. A., et al. 2006. Mycol. Res. 110:672. Meeboon, J., and Takamatsu, S. 2017. Mycoscience 58:253. Scholin, C. A., et al. 1994. J. Phycol. 30:999. White, T. J., et al. 1990. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA. Wu, H., et al. 2019. Plant Dis. 103:1035. Xu, D., et al. 2021. Plant Dis. 105:1203. Yeh, Y. W., et al. 2019. Plant Dis. 103:371.

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

First report of powdery mildew caused by Erysiphe buhrii on Dianthus caryophyllus in Italy

First report of powdery mildew caused by Erysiphe buhrii on Dianthus caryophyllus in Italy

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Bidens pilosa in China.

Bidens pilosa L., (spanish needle), is a wild, flowering plant of Asteraceae, that is grown in gardens, fields, roadsides, and riverbanks in Fuzhou, China. It is also used in traditional folk medicine for a broad range of ailments in China. In March 2019 and 2020, hundreds of B. pilosa growing along the roadsides, and gardens in the districts of Minhou and Jinshan were observed to be severely affected by a powdery mildew with approximately 80% disease incidence. Symptoms appeared as circular to irregular small white, powdery patches, typically on the adaxial sides of leaves and progressed to coalescent colonies on the leaves. As the disease developed, the infected leaves became wilted and senesced. Mycelia on leaves were superficial and solitary appressoria were slightly to distinctly nipple-shaped. Conidiophores were erect, 120 to 230 × 10 to 12 µm, and produced two to five conidia in chains with a sinuate outline. Foot-cells were erect, cylindrical, and 60 to 110 μm long. Conidia were hyaline, ellipsoid to barrel-shaped, 26 to 40 × 18 to 24 μm, and devoid of distinct fibrosin bodies. Germ tubes were long and produced at the perihilar position of the conidia. No chasmothecia were observed. Morphological characteristics overlapped with Golovinomyces ambrosiae, G. cichoracearum, and G. spadiceus (Braun and Cook 2012) on hosts within the Asteraceae tribe Heliantheae (Takamatsu et al. 2013). For molecular identification, ITS and IGS regions as well as partial LSU of two representative collections (MJU-IM019- MJU-IM020), were amplified using ITS1/ITS4, IGS-12a/ NS1R and LSU1/LSU2 primers (Carbone & Kohn, 1999; Scholin et al. 1994; White et al. 1990), respectively. The resulting sequences were deposited in GenBank (ITS: MW965777, MW965778; LSU: MW965787, MW965788; IGS: MW981256, MW981257). A BLAST search revealed 99 to 100 % sequence similarity to G. ambrosiae sequences (KX987303, AB769421, AB077689, AB769426, AB077643, and AB769425). Phylogenetic analysis of ITS, LSU and IGS also grouped obtained sequences within the G. ambrosiae complex (Qiu et al. 2020). Pathogenicity was confirmed through inoculation by gently pressing infected leaves onto leaves of five healthy, potted, young B. pilosa plants, while five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 25 ± 2°C. Inoculated plants developed symptoms after 7 to 10 days, whereas the control plants remained symptomless. The morphology of the resulting fungus on inoculated plants was identical to that originally observed on diseased plants. Podosphaera spp., have been reported on B. pilosa (Farr & Rossman 2021) from North America, Africa, and Asia. To our knowledge, this is the first report of powdery mildew caused by G. ambrosiae on B. pilosa in China and Asia. Wild populations of B. pilosa may be the primary source of powdery mildew inoculum for commercial Asteraceae members and may warrant consideration in the control of this disease.

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.

First report of powdery mildew caused by Golovinomyces magnicellulatus on Phlox maculata in Italy

First report of powdery mildew caused by Golovinomyces magnicellulatus on Phlox maculata in Italy

Occurrence of Powdery Mildew Caused by Erysiphe buhrii on Dianthus chinensis in Inner Mongolia, China.

Dianthus chinensis is widely cultivated for ornamental and medicinal use in China (Guo et al. 2017). The plant has been used in traditional Chinese medicine for the treatment of urinary problems such as strangury and diuresis (Han et al. 2015). In June and July 2020, powdery mildew-like signs and symptoms were seen on leaves of D. chinensis cultivated on the campus of Inner Mongolia Agricultural University, Hohhot city, Inner Mongolia Province, China. White powder-like masses occurred in irregular shaped lesions on both leaf surfaces and covered up to 50% of leaf area. Some infected leaves were deformed on their edges and some leaf senescence occurred. More than 40 % of plants (n = 180) exhibited these signs and symptoms. Conidiophores (n = 50) of the suspect fungus were unbranched and measured 70 to 140 µm long × 6 to 10 µm wide and had foot cells that were 25 to 48 µm long. Conidia (n = 50) were produced singly, elliptical to cylindrical shaped, 30 to 45 µm long × 12 to 19 µm wide, with length/width ratio of 2.0 to 3.2, and lacked fibrosin bodies. No chasmothecia were found. Based on these morphological characteristics, the fungus was tentatively identified as an Erysiphe sp. (Braun and Cook 2012). Fungal structures were isolated from diseased leaves and genomic DNA of the pathogen extracted utilizing the method described by Zhu et al. (2019). The internal transcribed spacer (ITS) region was amplified by PCR employing the primers PMITS1/PMITS2 (Cunnington et al. 2003) and the amplicon sequenced by Invitrogen (Shanghai, China). The sequence for the powdery mildew fungus (deposited into GenBank under Accession No. MW144997) showed 100 % identity (558/558 bp) with E. buhrii (Accession No. LC009898) that was reported on Dianthus sp. in Japan (Takamatsu et al. 2015). Pathogenicity tests were done by collecting fungal conidia from infected D. chinensis leaves and brushing them onto leaves of four healthy plants. Four uninoculated plants served as controls. Inoculated and uninoculated plants were placed in separate growth chambers maintained at 19 ℃, 65 % humidity, with a 16 h/8 h light/dark period. Nine-days post-inoculation, powdery mildew disease signs appeared on inoculated plants, whereas control plants remained asymptomatic. The same results were obtained for two repeated pathogenicity experiments. The powdery mildew fungus was identified and confirmed as E. buhrii based on morphological and molecular analysis. An Oidium sp. causing powdery mildew on D. chinensis previously was reported in Xinjiang Province, China (Zheng and Yu 1987). This, to the best of our knowledge, is the first report of powdery mildew caused by E. buhrii on D. chinensis in China (Farr and Rossman 2020). The sudden occurrence of this destructive powdery mildew disease on D. chinensis may adversely affect the health, ornamental value and medicinal uses of the plant in China. Identifying the cause of the disease will support efforts for its future control and management.

First Report of Powdery Mildew Caused by Golovinomyces ambrosiae on Verbena bonariensis in Korea.

Verbena bonariensis L., named as purple-top vervain or Argentinian vervain, is native to tropical South America. It is cultivated worldwide as an ornamental plant. During summer and autumn of 2020, over 50% of the leaves of V. bonariensis were found infected with powdery mildew in a flower garden in Seoul (37°35'19"N 127°01'07"E), Korea. White, superficial mycelia developed initially on the leaves and subsequently covered surfaces of leaves and stems, are resulting in leaf discoloration, early defoliation, and shoots distortion. Heavily infected plants lost ornamental value. A representative voucher specimen was deposited in the Korea University herbarium (KUS-F32168). Morphological characterization and measurements of conidiophores and conidia were carried out using fresh samples. Microscopic observation showed that aAppressoria on the superficial hypha were nipple-shaped, but rarely found or nearly absent. Conidiophores (n = 30) were cylindrical, 110 to 220 × 10 to 12 µm, and produced 2 to 5 immature conidia in chains with a sinuate outline, followed by 2 to 3 short cells. Foot-cells of conidiophores were straight, cylindrical, and 46 to 90 μm long. Conidia (n = 30) were hyaline, ellipsoid to doliiform, 28 to 40 × 18 to 24 μm with a length/width ratio of 1.3 to 2.0, and contained small be like oil-like drops, but without distinct fibrosin bodies. Primary conidia were apically rounded and sub-truncate at the base. Germ tubes were produced at perihilar position of the conidia. Chasmothecia were not observed. These morphological characteristics were typical of the conidial stage of the genus Golovinomyces (Braun and Cook 2012, Qiu et al. 2020). To identify the fungus, rDNA was extracted from the voucher sample. PCR products were amplified 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). The resulting sequences were registered to GenBank (MW599742 for ITS, and MW599743 for LSU). Using Blast'n search of GenBank, sequences showed 100% identity for ITS and LSU with G. ambrosiae (MT355557, KX987303, MH078047 for ITS, and AB769427, AB769426 for LSU), respectively. Thus, based on morphology and molecular analysis, the isolate on V. bonariensis in Korea was identified as G. ambrosiae (Schwein.) U. Braun & R.T.A. Cook. Pathogenicity tests were carried out by touching an infected leaf onto healthy leaves of disease-free pot-grown plants using a replication of five plants, with five non-inoculated plants used as controls. After 7 days, typical powdery mildew colonies started to appear on the inoculated leaves. The fungus on inoculated leaves was morphologically identical to that originally observed in the field. All non-inoculated control leaves remained symptomless. On different global Verbena species, tThere have been many reports of Golovinomyces powdery mildews including G. cichoracearum s.lat., G. longipes, G. monardae, G. orontii s.lat., and G. verbenae (Farr and Rossman 2021). In China, G. verbenae was recorded on V.erbena phlogiflora (Liu et al. 2006). Golovinomyces powdery mildew has not been reported on Verbena spp. in Korea. Powdery mildew has been reported on V. bonariensis in California, but identity of the causal agent had not been reported. To our knowledge, this is the first report on the identity of the powdery mildew caused by G. ambrosiae on V. bonariensis in Korea. Since heavily infected plants lost ornamental value, appropriate control measures should be developed.