Report Of Powdery Mildew Research Articles

First Report of powdery mildew of Quercus guyavifolia (Fagaceae) Caused by Erysiphe quercicola.

Oaks are the most abundant trees in naturally regenerated forests in China, play a crucial role in preventing soil erosion and maintaining ecological stability (Du et al. 2022). Quercus guyavifolia H. Léveillé (Fagaceae family, Subgenus Cerris, section Ilex), is endemic in China, distributed in the southeastern boundary of the Qinghai-Tibet Plateau, with elevations from 2, 000 - 4, 500 m a.s.l. (Denk et al. 2018; Sun et al. 2016). Powdery mildew is a prevalent disease of oaks with up to 60% of foliage infection, which can induce leaf necrosis or deformation and might contribute to oak decline (Marçais and Desprez-Loustau 2014). In September 2023, we found leaves of Q. guyavifolia near Yunnan Baima Snow Mountain covered with white fungal colonies. Diseased Q. guyavifolia plants were transplanted into a greenhouse at Yunnan University for pathogenicity tests. Conidia from diseased plants were blown into twenty healthy Q. guyavifolia seedlings by cold air blower and five non-inoculated healthy seedlings were used as control. The inoculated seedlings developed powdery mildew symptoms within ten days on both sides of the leaves. Trypan blue staining was used to identify the pathogen that infects Q. guyavifolia (Xiao et al. 2017). Microscopic examination revealed abundant conidia and extensive branched hyphae on leaves, similar to the characteristics of powdery mildew fungi. The mean length and width of conidia were 29.06 ± 3.96 × 9.52 ± 1.36 μm (n = 50). We collected fungi (YNBAIMAXS01) and extracted genomic DNA from five diseased plants (from the same location) using the CTAB method. We amplified and sequenced the ITS (Gardes and Bruns, 1993), MS294, and MS447 (two nuclear protein-encoding genes; Feau et al. 2011; GenBank numbers: PP079015, PP083693, PP083694). BLAST analysis revealed 100% identity of above three sequences with the ITS of Erysiphe quercicola isolate DACA010 (GenBank accession MT569439), MS294 of E. quercicola isolate GEM09_11_FRTB1 (GenBank accession KY348509), and MS447 of E. quercicola isolate A1I1.5 (GenBank accession KY466619). Therefore, the isolate YNBAIMAXS01 was identified as E. quercicola based on its morphological and molecular characteristics. Sequences from the above three regions for YNBAIMAXS01 and five Erysiphe species were used to construct a Maximum likelihood (ML) tree. In addition, we constructed a ML tree using only the ITS region of YNBAIMAXS01 and eight Erysiphe species from GenBank to better distinguish E. quercicola from these species. Both trees were constructed using MEGA X with K2 + G as best model. The ML trees confirmed the powdery mildew fungi isolated from Q. guyavifolia is closely related to E. alphitoides. To date, thirty-four powdery mildew species belonging to genus Erysiphe have been found affecting Quercus and nine oak species can be infected by E. quercicola (https://fungi.ars.usda.gov/). To our knowledge, this is the first report of powdery mildew caused by E. quercicola on Q. guyavifolia, thus the development of control strategies and disease management is urgently needed.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Acalypha indica in China.

Acalypha indica L. is an annual erect herb of the Euphorbiaceae family. This plant is found widely in the tropics and parts of Africa and Asia (Chakraborty et al. 2023). In China, A. indica is a vegetable and also used as a folk medicine due to its antipyretic and hemostatic, antibacterial and anti-inflammatory properties. In February 2022 and 2023, powdery mildew symptoms were observed on 70% of A. indica plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 66 to 150 × 10 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 31 to 59 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 20 to 33 ×12 to 20 µm (length/width ratio = 1.3 to 2.4), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMAI-23. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 575-bp sequence was deposited in GenBank (accession no. OR775733). A BLASTn search in GenBank of this sequence showed 99% similarity with the ITS sequences of P. xanthii on plants of Fabaceae, Malvaceae and Cucurbitaceae family from China (MH143485, MT242593, MK439611 and MH143483), Thailand (LC270779 and LC270778), Korea (MG754404), Vietnam (KM260704), and Puerto Rico (OP882310). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OR784547). This region shared 99% similarity with P. xanthii isolates (LC371333, LC270780, AB936277, and OP765401) as well. To confirm pathogenicity, five healthy potted plants of A. indica were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. In different countries and regions, P. xanthii has been previously reported on A. indica from Sudan and India (Amano 1986). To our knowledge, this is the first record of P. xanthii infecting A. indica in China. We are concerned that the pathogen could become a threat to the widespread planting of A. indica in the future.

First Report of Powdery Mildew on Viburnum chinshanense Caused by Erysiphe pseudoviburni in China.

Viburnum chinshanense, a deciduous shrub in the family Caprifoliaceae, is a dominant tree distributed mainly in the North-Central and South-Central regions of China (Zhu et al. 2023). Because of its lush white flowers and vibrant red fruits, V. chinshanense is used widely as ornamental tree in China. In May 2022, severe powdery mildew symptoms were observed on V. chinshanense on the Huaxi Campus of Guizhou Normal University, Guiyang, China. The incidence was approximately 75% among 80 V. chinshanense plants observed. White mycelia were present on both adaxial and abaxial leaf sides, but not on fruits, petioles, or stems. Infected leaves showed slight chlorosis and twisting. The mycelia were amphigenous, forming small-to-large patches, often sparse on the upper leaf surface, but mostly confluent on the lower leaf surface. Hyphae were hyaline, 4-7 μm wide. Hyphal appressoria were lobed to multilobed, in opposite pairs or solitary. Conidiophores were erect, straight, or somewhat flexuous, 60-130 µm long (n = 30). Foot cells were subcylindrical to slightly curved-sinuous at the base, 20-40 × 6-10 µm (n = 30) in size, followed by 1-3 shorter cells. Conidia formed singly, occasionally two to three in a chain. Conidia were ellipsoid to ovoid, cylindrical, and 24-40 × 16-20 µm (n = 50). No fibrosin bodies were observed on the conidia. Chasmothecia were subglobose, 56-115 µm in diameter. The appendages were 35-70 µm long. Based on these morphological characteristics, the powdery mildew fungus was identified as Erysiphe pseudoviburni (Bradshaw et al. 2020). To confirm the identification, the ribosomal DNA internal transcribed spacer (ITS) and the ribosomal large subunit (LSU) region were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990) and the NL1/NL4 primer pair (Ziemiecki et al. 1990), respectively. The obtained 643-bp ITS sequence (GenBank accession no. ON729292) had 99.84% identity with E. pseudoviburni strains KUS-F27310 (MN431595) and MUMH0001 (LC009904). The obtained 593-bp LSU sequence (ON729293) had 99.83% identity with E. pseudoviburni (LC009904 and MN431595). Based on the phylogenetic analysis of the combined ITS and LSU dataset (Bradshaw et al. 2020), the isolate (GZVD-1) was grouped in a clade with the E. pseudoviburni strains KUS-F27319, KUS-F27310, and MUMH0001. To fulfill Koch's postulates, leaves of three healthy potted V. chinshanense plants were inoculated by gently pressing with diseased leaves. Non-contact plants were used as controls. All plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. Similar powdery mildew symptoms were observed on the inoculated plants 12 days after inoculation, whereas the control plants remained symptomless. The reisolated fungus from the inoculated plants was morphologically identical to that on originally diseased plants. ITS and LSU sequences of the reisolated fungus showed 100% identity with ON729292 and ON729293, respectively. E. pseudoviburni has previously been reported to infect some Viburnum species, including V. sieboldii in Japan (Takamatsu et al. 2015) and V. odoratissimum in South Korea (Bradshaw et al. 2020). To the best of our knowledge, this is the first report of powdery mildew caused by E. pseudoviburni on V. chinshanense in China. This work expands the known host range of E. pseudoviburni in the Viburnum genus.

First Report of Powdery Mildew Caused by Golovinomyces adenophorae on Adenophora triphylla var. japonica in Korea.

Adenophora triphylla var. japonica (Campanulaceae), known as Japanese lady bell, is native to East Asia. It has been used as a medicinal plant but is widely cultivated in Korea as an indigenous vegetable (Park et al. 2011). In the summer of 2020, about 100 plants in an experimental plot at the National Institute of Forest Science, Seoul, Korea, showed powdery mildew symptoms with a 100% disease incidence. Signs first appeared as white colonies, subsequently expanding over the leaves, stems, and inflorescences. Infected young shoots were elongated and became slender. Chasmothecia were found in late October. Voucher specimens were deposited in the Korea University Herbarium (KUS-F). Conidiophores arising from the lateral part of the hyphae were upright, 100 to 220 × 10 to 12 µm, and produced 2 to 5 immature conidia in chains with sinuate edge lines. Basal parts of foot-cells in conidiophores were curved. Conidia were barrel-shaped to ellipsoid, 26 to 40 × 14 to 20 µm, and produced germ tubes on the perihilar position of the conidia. Chasmothecia with short mycelioid appendages were gregarious, 144 to176 µm in diam., and contained 8 to 22 asci. Asci were clavate-saccate with short stalks, 60 to 82 × 28 to 42 µm, and contained two spores. Ascospores were broadly ellipsoid, cytoplasm-dense without vacuoles, colorless, and 22 to 28 × 12 to 18 µm. The structures and measurements were consistent with those of Golovinomyces adenophorae (R.Y. Zheng & G.Q. Chen) Heluta (Braun & Cook, 2012). To confirm the morphology-based identification, two herbarium specimens (KUS-F29252 and F31898) were sequenced for the internal transcribed spacer (ITS) and large subunit (LSU) regions with PM10/ITS4 and PM3/TW14 primers, respectively (Bradshaw and Tobin, 2020). A Blastn search revealed high similarities in the ITS and LSU sequences, with 99.81% (538/539 bp) and 99.86% (697/698 bp) to G. adenophorae sequences (AB077633 and AB077632), respectively. All resulting sequences were deposited in GenBank under accession numbers OR841069-70 for ITS and OR841071 for LSU. A pathogenicity test was performed through inoculation by gently dusting the conidia from a detached symptomatic leaf onto the leaves of five healthy plants. Five non-inoculated plants served as controls. Following inoculation, plants were covered with plastic film and maintained in a greenhouse (24 to 32°C) until symptoms developed. Powdery mildew colonies developed on the inoculated plants after twelve days, whereas the control plants remained symptomless. The inoculated pathogen was confirmed morphologically and molecularly by the sequence comparison aforementioned, fulfilling Koch's postulates. Based on morphological characteristics and the sequencing data, the powdery mildew was identified as G. adenophorae. The association of G. adenophorae and Adenophora spp. has been known in China, Japan, Kazakhstan, and the Far East of Russia (Farr and Rossman, 2023). This is the first report of powdery mildew caused by G. adenophorae on A. triphylla var. japonica in Korea. Since the commercial cultivation of this plant aims to harvest young shoots as one of the most popular vegetables in Korea, appropriate control measures for the powdery mildew should be considered.

First Report of Powdery Mildew on Berchemia floribunda Caused by Erysiphe berchemiae in China.

The genus Berchemia (family Rhamnaceae), a group of climbing plants, is mainly distributed in Asia, Africa, and South America. Berchemia plants are widely used in traditional medicine in some Asian countries (Inoshiri et al. 1987). For example, in Japan, B. racemosa (synonym B. floribunda) is used for the treatment of gallstones, liver diseases, neuralgia, and stomach cramps, and in China, B. floribunda is used for the treatment of rheumatism and lumbago. In August 2022, typical powdery mildew symptoms were observed on wild B. floribunda plants in Huaxi District, Guiyang, Guizhou Province, China. The incidence was approximately 60% among 100 B. floribunda plants observed outdoors. White colonies almost entirely covered on both adaxial and abaxial surfaces of all leaves on symptomatic plants. Infected leaves appeared curled or chlorotic, infection occasionally leading to defoliation. To describe the pathogen morphologically, fungal samples were collected from two individual B. floribunda plants and microscopically characterized. In these samples, hyphae were flexuous to straight, branched, septate, 3-6 μm wide, with lobed hyphal appressoria. Conidiophores were erect, flexuous to straight, and 50-160 µm long (n = 30). Foot cells were subcylindrical to slightly curved-sinuous at the base, 20-40 µm long (n = 30), followed by 2-3 shorter cells. Conidia formed singly, occasionally 2-3 in a chain. Conidia were ellipsoid to ovoid, 20-42 × 12-18 µm (n = 50), without fibrosin bodies. Chasmothecia were not found. For molecular identification, the ribosomal DNA internal transcribed spacers (ITSs) of the two fungal samples were amplified and sequenced using the ITS1/ITS4 primer pair (White et al. 1990). The obtained 649-bp ITS sequences (GenBank accession nos. OR414364 and OR414365, respectively) shared 100% identity, and they showed 99.52% identity with the ITS sequence (GenBank accession no. LC009934) of Erysiphe berchemiae. Phylogenetic analysis grouped OR414364 and OR414365 in a clade with LC009934. Based on morphological and molecular characteristics, the powdery mildew fungus from B. floribunda was identified as E. berchemiae (Braun and Cook 2012). The voucher specimen (accession no. GZNU-BFEE/0820/2022) were deposited at the School of Life Sciences, Guizhou Normal University. Pathogenicity was assessed by gently pressing naturally diseased leaves of B. floribunda onto leaves of three healthy potted 1-year-old B. floribunda plants. Three non-inoculated healthy plants were used as controls. The plants were incubated in a greenhouse at 25 ± 2°C, 80% relative humidity. Similar powdery mildew symptoms were observed on the inoculated plants 9 days after inoculation, whereas the control plants remained symptomless. The reisolated fungus from inoculated leaves was morphologically identical to that observed on the original diseased leaves, and the ITS sequence of the reisolated fungus shared 100% identity with OR414364 and OR414365, fulfilling Koch's postulates. E. berchemiae has previously been described as a powdery mildew pathogen on B. yunnanensis (Chen et al. 1987) and B. kulingensis (Chen 1993) in China and B. racemosa (synonym B. floribunda) in Japan (Braun and Cook 2012; Takamatsu et al. 2015), but this is the first report of E. berchemiae causing disease of B. floribunda in China. This work suggests that E. berchemiae is an important pathogen of Berchemia plants, at least for some species in the genus Berchemia.

First Report of Powdery Mildew caused by Erysiphe astragali on Sphaerophysa salsula.

Sphaerophysa salsula (Pall.) DC., also known as Yang Liao Pao, belongs to the Leguminosae family and is the only existing species in the Sphaerophysa genus. S. salsula is tolerance to cold, high salt, and alkaline soil, it is widely cultivated in China as a forage crop, and used as a Chinese folk medicine to treat hypertension (Ma et al., 2002). In 2023, signs and symptoms similar to powdery mildew were found on S. salsula planted in Tumd left (40.515°N, 110.424°E), Baotou City, Inner Mongolia Autonomous Region, China. The white powdery substance covered 90% of the leaf area, and the infected plants showed weak growth and senescence. More than 80% of plants (n=200) had these powdery mildew-like symptoms. Hyphal appressoria are solitary, conidiophores have few branches and septa. Conidia are cylindrical to clavate, 25-32 μm long and 8-15 μm wide (n=30), conidia form single subapical germ tubes, straight to curved-sinuous, with swollen apex or distinctly lobed conidial appressorium. Based on these morphological characteristics, the fungus was tentatively identified as an Erysiphe sp. (Schmidt and Braun 2020). Fungal structures were isolated from diseased leaves, and genomic DNA of the pathogen was extracted using the method described by Zhu et al. (2022). The internal transcribed spacer (ITS) region was amplified by PCR using the primers PMITS1/PMITS2 (Cunnington et al. 2003) and the amplicon sequenced by Invitrogen (Shanghai, China). The powdery mildew strain, named as KMD (GenBank accession no.: PP267067), showed an identity of 100% (645/645bp) with Erysiphe astragali, a powdery mildew reported on Astragalus glycyphyllos in Golestan, Iran (GenBank: OP806834) and identity of 99.6% (643/645bp) with Erysiphe astragali (GenBank: MW142495), a powdery mildew reported on A. scaberrimus in Inner Mongolia, China (Sun et al. 2023). Pathogenicity tests were conducted by brushing the conidia from infected S. salsula leaves onto leaves of four healthy plants, while four control plants were brushed in the same manner. All the treated plants were placed in separate growth chambers maintained at 19°C and 65% humidity, with a 16 h light/8 h dark photoperiod. Nine days after inoculation, the treated plants showed powdery mildew symptoms, while the control plants remained asymptomatic. The same results were obtained for two repeated pathogenicity experiments. The powdery mildew fungus was reisolated and identified as E. astragali based on morphological and molecular analysis, thereby fulfilling Koch's postulates. No report on the occurrence of powdery mildew on S. salsula plants has been found previously. The occurrence of this destructive powdery mildew may adversely affect the cultivation of S. salsula. Identifying the pathogen of powdery mildew will support future efforts to control and manage powdery mildew on S. salsula.

First report of Powdery Mildew Caused by Podosphaera xanthii on Siraitia grosvenorii in Guizhou, China.

Swingle (Siraitia grosvenorii), a member of the Cucurbitaceae family, stands out as a distinctive plant with both economic and medicinal significance. In October 2023, severe powdery mildew were observed on S. grosvenorii in Guiyang City (26.50°N; 106.66°E), Guizhou Province, China. About 80 % of the plants in the greenhouse showed powdery mildew symptoms. Three infected plant samples were selected for morphological and molecular analysis (GZAAS 23-0801, GZAAS 23-0802 and GZAAS 23-0803). The voucher specimens are deposited in the Key Laboratory of Agricultural Biotechnology of Guizhou Province. The symptoms initially manifested as irregular to nearly circular, small yellow spots, with distinct depressions as well as surfaces covered in white mycelium. Over time, these spots gradually expanded and merged patches. In the final stages, the entire leaves turned into yellow and withered. Microscopic observations showed that fungal hyphae were septate, branched, and flexuous to straight and 5 to 9 µm wide, and appressoria were indistinct to slightly nipple-shaped. Conidia were hyaline and ellipsoid to oval with fibrosin bodies and measured 31 to 43 × 18 to 24 μm (n = 50) with a length/width ratio of 1.3 to 2.3. Conidiophores were unbranched, straight, 120 to 268 × 14 to 22 µm (n = 30), producing two to five immature conidia in chains. Foot cells of conidiophores were cylindrical, 39 to 84 × 8 to 14 μm (n = 30), followed by one to three short cells. Short cells were cylindrical, 12 to 32 × 8 to 15 μm (n = 50). The morphological characteristics were identical with the previous description of Podosphaera xanthii (Braun and Cook, 2012). Total DNA was extracted from conidia and mycelia by the Chelex method (Walsh et al., 1991). The ribosomal DNA internal transcribed spacer (ITS) and nuclear ribosomal large subunit (LSU) were amplified by using the primers ITS1/ITS4 (White et al., 1990) and LSU1/LSU2 (Scholin et al., 1994), respectively. The ITS (OR825802, OR825803 and OR825804, respectively) and LSU (OR825805, OR825806 and OR825807, respectively) sequences of three isolates, were deposited in GenBank. The BLAST results revealed that both the ITS and LSU region sequence were 100% identical to those of P. xanthii (ITS: MF043939, MG754404 and KJ698669; LSU: OQ061319, AB936277and OP218411). Phylogenetic analyses of ITS and LSU sequences showed that our three isolates were clustered with P. xanthii (KX842351, LC270782 and LC270779) with high statistical support (ML/MP/BI: 100%/97%/1.00). Combined with their morphological characteristics, these three isolates were identified as P. xanthii. Pathogenicity tests were performed by gently brushing conidia onto the leaves of five healthy S. grosvenorii plants. Five non-inoculated plants were used as the control. All plants were maintained in a greenhouse at 25 ± 2°C. One week after inoculation, similar symptoms were observed in the inoculated plants, whereas no symptoms occurred on the control plants. By microscopic observation, the fungus on the inoculated plants was morphologically identical to those on originally diseased plants. Powdery mildew caused by P. xanthii has been reported on Vernonia cinerea (Wu et al., 2023), Vigna unguiculata (Zhang et al., 2023), Cucumis melo (Meesam et al., 2023). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on S. grosvenorii in Guizhou, China. The occurrence of powdery mildew on S. grosvenorii may pose a potential threat to its large-scale cultivation. The pathogen could become a threat to other Cucurbitaceae members in the future.

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

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

First Report of Powdery Mildew Caused by Podosphaera xanthii on Phasey Bean (Macroptilium lathyroides) in China.

The forage legume phasey bean Macroptilium lathyroides (L.) Urb. is an annual or short-lived perennial of the family Fabaceae. It is native to the tropical and subtropical areas from North to South America, and is naturalized throughout the tropics and subtropics of the world (Tobisa and Nakano 2019). It is mainly used for forage, green manure, and slope protection (Silva et al. 2018). In addition, the nitrogen fixation ability of this plant can also improve the soil. In February 2022 and January 2023, powdery mildew symptoms were observed on 70% of M. lathyroides plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 100 to 233 × 8 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 36 to 56 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 24 to 34 ×13 to 20 m (length/width ratio = 1.5 to 2.3), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMML-23. To confirm the identification, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 575-bp sequence was deposited in GenBank (accession no. OR240256). A BLASTn search in GenBank of this sequence showed 100% similarity with the ITS sequences of P. xanthii isolates from China (MT242593, MK439611 and MH143483), Korea (MG754404), Vietnam (KM260704), Japan (MZ604267), and Puerto Rico (OP882310). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OR240255). This region shared 100% similarity with P. xanthii isolates (MK357436, LC371333, OP765401, and MZ604267) as well. To confirm pathogenicity, five healthy potted plants of M. lathyroides were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. This fungus has been reported causing powdery mildew on M. atropurpureum in Thailand (Meeboon et al. 2016). In the United States phasey bean powdery mildew caused by Erysiphe fallax has been previously reported (Poudel and Zhang 2019). To our knowledge, this is the first record of P. xanthii infecting M. lathyroides in China. Over the past 50 years of introduction, phasey bean has become one of the main leguminous forages for establishing artificial mixed seeding grasslands in southern China. We are concerned that the pathogen could become a threat to the widespread planting of M. lathyroides in the future.

First report of powdery mildew caused by Erysiphe quercicola on Murraya paniculata in India

First report of powdery mildew caused by Erysiphe quercicola on Murraya paniculata in India

First report of powdery mildew on Vigna unguiculata caused by Podosphaera xanthii in China.

Vigna unguiculata belongs to the Legume family, and is an annual twining, herbaceous vine plant, which is native to Africa. V. unguiculata is the most economically beneficial type of off-season vegetables in Hainan, China because of its rich in nutrients such as protein, minerals, dietary fiber, and vitamins (Jayathilake et al. 2018). In April 2022, typical powdery mildew infection was observed on V. unguiculata leaves in Haikou, Hainan Province, China (20°3'40.428"N, 110°19'45.217"E). More than 70% leaves of 13 V. unguiculata plants displayed severe powdery mildew disease. The diseased leaves at first exhibited white rounded irregular patches, which gradually enlarged, fused and covered all the leaf as well as stems. Edges of the infected leaves crinkled upwards, and the leaves often fell off the plants at the late infection stage. On the infected leaves, many conidiophores and dense mycelium were observed by microscopic analysis. Hyphae were septate, branched, epigenous, and flexuous to straight. Hyphal appressoria were indistinct or slightly nipple-shaped, and the haustoria developed were in the shape of oval-sphere and 9 to 11μm long. Foot cells of conidiophores were straight, cylindrical, and measured 43 to 70 × 10 to 12 μm. The conidiophores arising straightly from a hyphal cell, were measured 168 to 252 (mean = 204) μm in length and produced 6 to 9 immature conidia in each chain. Conidia were ovate, pyriform or barrel-shaped, with fibrosin bodies, and measured 26 to 32 (mean = 29.4) × 16 to 20 (mean = 18.6) μm. The chasmothecia was not found in all samples. These morphological characteristics were typical of the conidial stage of the powdery mildew Podosphaera xanthii of genus Podosphaera (Braun and Cook 2012). To further confirm the identity of this causal fungus, the internal transcribed spacer (ITS) region, and the partial sequence of large subunit ribosomal RNA gene (28S rRNA), were amplified with primer pairs ITS1/ ITS4 (White et al. 1990) and NL1/NLP2 (Mori et al. 2000) from extracted genomic DNA. The obtained 563-bp ITS region and 715-bp 28S rRNA gene sequences were deposited in GenBank (ITS, OQ415534; 28S rRNA, OQ415545.1), and were compared with BLAST analysis in the GenBank nr database. The results revealed that the ITS region sequence was 99.82% identity with P. xanthii isolate HUVU-08 (MH143485.1), and the 28S rRNA gene partial sequence was 100% identity with P. xanthii isolate XHL1 (MK357442.1). On the basis of the morphological characteristics and sequence analysis, this fungus was identified as P. xanthii. Pathogenicity tests were performed by gently brushing conidia onto the leaves of six healthy potted V. unguiculata plants. Six non-inoculated plants were used as control. All plants were maintained in a greenhouse at 26 ± 2°C. After 2 weeks inoculation, similar symptoms were observed in the inoculated plants, whereas no symptoms occurred on the control plants. By microscopic observation, the fungus present on the inoculated plants was morphologically identical to those on originally diseased plants. Furthermore, ITS and 28S rRNA sequences of the re-isolated fungus individually displayed 100% identity with OQ415534 and OQ415545.1. So far, although powdery mildew disease caused by P. xanthii on different plants including Sigesbeckia orientalis (Mukhtar et al. 2022), Vigna radiata (Sheu et al. 2021), Cosmos bipinnatus (Kong et al. 2023), Verbena brasiliensis (Luecke et al. 2020), Cucurbita ficifolia (Choi et al. 2022), Glandularia tenera (Pei et al. 2023) and Verbena bonariensis (Choi et al. 2023) have been reported, to our knowledge, this is the first report of powdery mildew caused by P. xanthii on V. unguiculata in Hainan, China, which seriously threatens the utilization of V. unguiculata on off-season vegetables industry.

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

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

First report of powdery mildew on Euonymus japonicus caused by Erysiphe euonymicola in Taiwan.

The Japanese spindle (Euonymus japonicus Thunb.) is commonly used as an ornamental hedge plant in Taiwan. In March 2020, a severe powdery mildew disease was observed on E. japonicus surrounding a city park spanning six hectares in Taichung city, Taiwan. Around 90% of the plants showed symptoms on the leaves and pedicels of young shoots. Similar symptoms were observed in other districts of Taichung city and Taipei city between March to June in subsequent years. Initial signs of infection manifest as circular chlorotic spots on the leaves, which are subsequently covered by white mycelia on either the upper or lower surfaces of the spots. In severe cases, both sides of the leaves become entirely covered by dense mycelia. Hyphal appressoria were solitary or in opposite paired, lobed to multilobed. Conidiophores grow erectly from the hyphae, consist of 2-3 cylindrical cells, 38.9 to 78.6 × 6.31 to 8.28 µm (n = 30). Foot cells are usually straight or slightly flexuous, 23.6 to 43.2 µm (n = 30), followed by 1 to 2 shorter cells. Ellipsoidal conidia are produced singly on the conidiophores, 24.1 to 36.3 × 10.6 to 14.97 µm (n = 30), without fibrosin bodies. Germ tubes are mostly subterminal, sometimes terminal, occasionally exhibiting a longitudinal pattern. Chasmothecia were not observed. These morphological characteristics correspond to the description of Erysiphe euonymicola U. Braun (Braun and Cook 2012), one of the Erysiphe species reported on E. japonicus. Genomic DNA was extracted from seven isolates obtained from different plants in the affected regions. The internal transcribed spacer (ITS) and 28S large subunit (LSU) of rDNA sequences (ITS accession nos.: OR073423-OR073429; LSU accession nos.: OR073448-OR073454) were amplified and sequenced using primer sets PMITS-1 / PMITS-2 (Cunnington et al. 2003) and NLP2 / PRM2 (Bradshaw and Tobin 2020), respectively. The resulting sequences exhibited identities ranging from 99.1 to 100% in ITS and 100% in LSU when compared to the corresponding sequences of E. euonymicola MUMH 133 (ITS: AB250228; LSU: AB250230) (Limkaisang et al. 2006). Phylogenetic analysis based on the concatenated sequences of ITS and LSU clustered the seven isolates within the same clade as three E. euonymicola isolates (MUMH 133, MUMH 6999 and MUMH 7012). Pathogenicity assays were conducted on one-meter tall E. japonicus plants by gently smearing infected leaves on all leaves of four healthy plants. Four uninoculated plants were used as control. All eight assayed plants were enclosed in plastic bags to maintain high humidity at 28 ± 2°C for 3 days. Chlorotic spots began to appear on leaves younger than one month old at 7 days post inoculation (dpi). By 28 dpi, all inoculated plants showed symptoms. Spots expanded or merged and formed a dense mycelial layer on leaves younger than three months, while mature dark green leaves were asymptomatic. No symptoms were observed on any leaves of the control plants. The morphological characteristics and sequences of ITS and LSU of the pathogen from the inoculated plants matched the above information. Based on these findings, E. euonymicola was identified as the causal agent of powdery mildew on E. japonicus, representing the first documented report of this disease in Taiwan. A voucher specimen TNM F0037001 (isolate EPM-1) was deposited in the National Museum of Natural Science, Taiwan. The pathogen has been frequently reported in recent years and significantly impacts the ornamental value of Euonymus spp. (Abbasi and Braun 2020; Lee et al. 2015; Li et al. 2011; Pei et al. 2022). This report also provides an evidence of an ongoing outbreak of the pathogen.

First report of powdery mildew caused by Erysiphe corylacearum on hazelnut in Bulgaria.

In June 2020, during an observation of fruit-bearing hazelnut trees (Corylus avelana L., cv. Tonda Gentile), grown in a small private home garden in the region of Kavarna (North-Eastern Black Sea coast of Bulgaria), symptoms of powdery mildew were observed on each of the 15 trees. Compared to the widely spread in Bulgaria powdery mildew caused by Phyllactinia guttata and known with its powdery patches and differing chasmothecia exclusively formed on the abaxial leaf surface, the newly observed disease was characterized by the presence of concomitant pathogen's structures on both the abaxial and adaxial surfaces of the leaves, varying from single pustules to 90% severity on certain leaves, as well as on the husks which were 100% affected. Among the white mycelium, cylindrical conidiophores and singly produced conidia (22-34 x 16-22 µm; n = 50) were found. Scattered or in groups, black spherical chasmothecia (diameter of 85-115 µm; n = 30), possessing 8 to 12 appendages with dichotomous branched apices, were also observed in the autumn. Chasmothecia contained 3 to 5 subglobose asci (45-60 x 34-62 µm; n = 30), each ascus containing 8 hyaline and ellipsoid ascospores (15-22 x 9-16 µm; n = 50). From one field powdery mildew sample DNA was extracted using the Nucleospin Plant II kit (Macherey-Nagel, Germany) and the rDNA ITS region was amplified using primers PMITS1 and PMITS2 (Cunnington, J.H. et al., 2003). The amplicon was sequenced (Macrogen Europe, The Netherlands) and used in a BLAST analysis. This resulted in 100% homology with the ITS sequence of Erysiphe corylacearum. The obtained sequence was different from the ones of Erysiphe pseudocorylacearum (99.20% homology) and Erysiphe coryli-americanae (96.52% homology). The targeted sequence was submitted to GenBank (accession number OQ860748). Based on the symptoms, morphological characteristics and molecular identification, the pathogen was identified as Erysiphe corylacearum. Pathogenicity of the fungus was confirmed under lab conditions (natural day/light regime, 23-25°C) by shaking down conidia from naturally infected leaves on both sides of healthy leaves (2-years plantlets, cv. Tonda Gentile, 3 replicates) and incubation in a moist chamber (plastic bags) for the first 24 hours. First small fluffy white pustules appeared 6-7 days after inoculation, subsequently, the disease was progressing and the pathogen's conidiophores and conidia were morphologically identical to that first observed under natural infections in the private garden. The non-inoculated control plantlets (grown under the same conditions in a separate room) remained symptomless during the entire three weeks testing period. To our knowledge, this is the first report of Erysiphe corylacearum on hazelnut in Bulgaria. In October 2021, the same disease was also found in a hazelnut orchard (1.2 ha) located in the region of Pazardzhik (Central Southern part of the country). Globally, this report indicates the disease's expansion in the Black Sea region since its first observation in Turkey in 2013 (Sezer, A., et al. 2017; Heluta, V.P., et al. 2019; Meparishvili, G., et al. 2019; Rosati, M., et al. 2021) and elsewhere in Europe as well (Beenken, L., et al. 2020; Mezzalama, M., et al. 2021; Voglmayr, H., et al. 2021).

First Report of Powdery Mildew Caused by Podosphaera xanthii on Vernonia cinerea in China.

Vernonia cinerea (L.)Less. is an annual herbaceous plant of the Asteraceae family, which is widely distributed throughout Southeast Asia, India, and the tropical and subtropical regions of China. This herb is known to contain various bioactive compounds and is commonly used in traditional system of medicine in China and India (Singh et al. 2021). During the spring of 2022 and 2023, powdery mildew symptoms were observed on 70% of V. cinerea plants on the Hainan Medical University campus (19° 58' 53″ N; 110° 19' 47″ E) in Haikou, Hainan Province, China. Powdery mildew colonies covered the leaf surfaces and stems of affected plants, causing discoloration and defoliation. Mycelia were superficial and hyphal appressoria were nipple-shaped. Conidiophores (n =30) were unbranched, cylindrical, 104 to 188 × 11 to 15 µm, and produced three to five immature conidia in chains with a crenate outline. Foot cells (n =30) were cylindrical, straight or sometimes curved at the base, and 32 to 57 µm long. Conidia (n =100) were ellipsoid-ovoid to doliiform, 19 to 45 ×16 to 26 m (length/width ratio = 1.2 to 2.4), with well-developed fibrosin bodies, and produced germ tubes from the lateral position. Based on these morphological characteristics, the pathogen was provisionally identified as Podosphaera xanthii (Braun and Cook 2012). The teleomorph was not observed. A specimen was deposited in the Hainan Medical University Plant Pathology Herbarium as HMVC-22. To confirm the genus identification and ascertain a putative species, genomic DNA was extracted from mycelium, conidiophores, and conidia using a fungal DNA kit (Omega Bio-Tek, USA). The rDNA internal transcribed spacer (ITS) region was amplified with primers ITS1/ITS4 (White et al. 1990) and sequenced directly. The resulting 577-bp sequence was deposited in GenBank (accession no. OP765400). A BLASTn search in GenBank of this sequence showed 100% similarity with the ITS sequences of P. xanthii isolates from China (MT260063, MT739423 and MT131253), Thailand (LC270780), and Vietnam (KM260731). Additionally, the 28S rDNA region was amplified using the primer pairs NL1 and NL4 (O´Donnell 1993; accession no. OP765401). This region shared 100% similarity with P. xanthii isolates (LC371333, LC270780, and AB936277) as well. Powdery mildew from Hainan sample belonged to the P. xanthii group with strong bootstrap values support 99% in maximum likelihood phylogenetic tree based on ITS and 28S gene sequences. To confirm pathogenicity, five healthy potted plants of V. cinerea were inoculated by gently pressing a powdery mildew-infected leaf onto 15 young leaves. Five non-inoculated plants served as controls. All plants were maintained in a greenhouse at 24 to 30°C, 70% relative humidity, with a 16-h photoperiod. After 7 days, inoculated leaves showed powdery mildew symptoms whereas no symptoms were observed on control plants. The fungal colonies observed on inoculated plants were morphologically identical to those found on the originally infected leaves collected from Hainan Province. Based on the morphological characteristics and molecular identification, the fungus was identified as P. xanthii. In different countries and regions, Erysiphe cichoracearum has been previously reported on some Vernonia species, including V. Galamensis from southern parts of Ethiopia (Hundesa and Mekonnen 2017). To our knowledge, this is the first record of P. xanthii infecting V. cinerea in China. We are concerned that the pathogen could become a threat to the widespread planting of V. cinerea in the future.

First report of powdery mildew caused by Podosphaera xanthi ion Luffa cylindrica in Egypt and its control

First report of powdery mildew caused by Podosphaera xanthi ion Luffa cylindrica in Egypt and its control

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 Erysiphe cruciferarum on Centella asiatica in China.

Centella asiatica belongs to the Umbelliferae family of perennial herbaceous plants, which are grown worldwide for use as health supplements, edible vegetables and traditional herbs, and are of vital medicinal and edible value in China. (Biswas et al. 2021). In October 2022, the investigation in the 800 m2 garden of Lanzhou (36°06' N,103°43' E) found that more than 80% of C. asiatica plants were infected by powdery mildew, and the leaf infection rate was 90%. The disease severely affects the actual value of C. asiatica. At the beginning of the disease, thin, radial, irregular white colonies appear on the leaves and gradually spread to the stems. The white colony then expands and thickens, covering the upper surface of the whole leaf, and gradually spreading to the lower parts of the stem and leaf. In severe cases, the leaves wither and die. A small portion of fungal spores was glued from the leaf surface with adhesive tape and placed in sterile water for microscopic examination (Zhang et al. 2022). The conidiophore is upright, cylindrical, composed of 3-4 cells, and its size is 72 to 110 × 8 to 10 μm. Conidial pedicels have 16 to 26 μm long cylindrical podocytes. Monoconidia are cylindrical or oval in shape, 16 to 37 μm long, width 11 to 18 μm (n=80). Conidia lack an obvious cellulose body. The bud tube is formed from the end of conidia, and papillary appressorium develops on the epiphytic mycelia. Based on these morphological characteristics, the pathogen was initially identified as Erysiphe cruciferarum (Braun et al. 2012). To validate the identity, the internal transcribed spacer (ITS) of the pathogen (JXC) rDNA was amplified by PCR and sequenced with PM6/ITS5 and PM5/ITS4 primers (Takamatsu et al. 2001). The resulting sequences were registered to GenBank (GenBank Accession OP935627 and OQ253404). At the same time, the ITS sequence size was 535 bp and 521 bp respectively. The ITS sequence of the JXC was 99% (527/534) identical to E.cruciferarum (KT588635) on Eschscholzia californica in Slovakia and 99% (527/534) identical to E.cruciferarum (KC878683) on Chinese Cabbage in China. The ITS sequences from GenBank were subjected to conduct maximum likelihood phylogenetic analysis by MEGA 7.0. The data indicate that strain JXC and E. cruciferarum are clustered on the same branch. The pathogenicity test was performed according to Koch's postulate. By gently pressing the infected leaves on five healthy potted C. asiatica. Meanwhile, five uninoculated plants were used as controls (Zhang et al. 2022). The plants were put into a greenhouse culture (25℃, 14 h light, 10 h dark, humidity ≥ 70%). After 12 days, the inoculated plants showed symptoms of powdery mildew, while the control group had no symptoms. The fungus on the inoculated plant was re-isolated, and identified as E. cruciferarum based on morphological observations and molecular identification. The powdery mildew caused by E.cruciferarum has been reported on Indian mustard in Korea and Chinese cabbage in China, respectively (Kim et al. 2009; Zhao et al. 2014). To our knowledge, this is the first report of C. asiatica powdery mildew caused by E.cruciferarum in China. This finding poses a potential threat to the quality and yield of C. asiatica plants, while providing a preventive basis for the cultivation of C. asiatica.

First Report of Powdery Mildew Caused by Golovinomyces bolayi on Veronica persica in Central China.

Veronica persica, Persian speedwell, is a flowering plant belonging to the family Plantaginaceae. Due to its showy flowers, this plant is widely planted in many home gardens, city parks and universities in China. From April to June 2021, signs and symptoms of powdery mildew were found on leaves of V. persica growing on the campus of Henan Normal University, Henan Province, China. Signs initially appeared as thin white colonies and subsequently white powdery masses were abundant on the adaxial and abaxial surfaces of leaves and covered up to 99 % of the leaf area. The infected leaves showed chlorotic, deformed or senescence features. About 150 V. persica plants were monitored and more than 90 % of the plants showed these signs and symptoms. Conidiophores (n = 20) were 108 to 220 × 10 to 13 μm and composed of foot cells, followed by short cells and conidia. Conidia were hyaline, doliiform-subcylindrical shaped, 21 to 37 × 15 to 22 μm, and showed distinct fibrosin bodies. Conidial germ tubes were produced at the perihilar position. No chasmothecia were observed. The observed morphological characteristics were consistent with those of previously documented Golovinomyces bolayi (Braun and Cook 2012). To further confirm the powdery mildew fungus, structures of the pathogen were harvested and total genomic DNA was isolated using the method previously described by Zhu et al. (2019, 2021). Using the primers ITS1/ITS4, the internal transcribed spacer (ITS) region of rDNA was amplified (White et al. 1990) and the amplicon was sequenced. The resulting sequence was deposited into GenBank under Accession No. MZ343575 and was 100 % identical (592/592 bp) to G. bolayi on Kalanchoe blossfeldiana (LC417096) (Braun et al. 2019). The additional phylogenetic analysis clearly illustrated that the identified fungus and G. bolayi were clustered in the same branch (Zhu et al. 2022a; Zhu et al. 2022b). To test pathogenicity, healthy V. persica plants were collected from the campus of Henan Normal University and leaf surfaces of three plants were inoculated by dusting fungal conidia from mildew-infested leaves using pressurized air. Three plants without inoculation served as a control. The spore-treated and non-treated plants were separately placed in two growth chambers (temperature, 18℃; humidity, 60%; light/dark, 16h/8h). Seven- to eight-days post-inoculation, pathogen signs were noticeable on inoculated plants, whereas control plants remained healthy. Similar results were obtained by conducting the pathogenicity assays twice. Therefore, based on the analysis, G. bolayi was identified and confirmed as the causal agent of the powdery mildew. This pathogen has been reported on V. persica in Iran (Golmohammadi et al. 2019). However, to our best knowledge, there is no report concerning the powdery mildew caused by G. bolayi on V. persica in China. Recently, G. bolayi was segregated from species clades of G. orontii complex (Braun et al. 2019). Our record of the molecular characterization of G. bolayi will support the further phylogeny and taxonomy analysis of the G. orontii complex. The sudden outbreak of powdery mildew caused by G. bolayi on V. persica may detract from plant health and ornamental value. The identification and confirmation of this disease expands the understanding of this causal agent and will offer support for future powdery mildew control.

Occurrence of Powdery Mildew Caused by Erysiphe astragali on Astragalus scaberrimus in Inner Mongolia, China.

Astragalus scaberrimus Bunge, a perennial herb, is widely distributed in North and central China, Russia, and Mongolia (POWO, 2023). Due to its tolerance to drought, cold, high salt, low nutrients and alkaline soil, this plant is widely cultivated in China as a forage crop, for water and soil conservation, and for its medicinal properties (Meng, 2015). In 2022, powdery mildew-like signs and symptoms were seen on leaves of A. scaberrimuns cultivated on the campus of Inner Mongolia Agricultural University, Hohhot, Inner Mongolia China. White powder-like masses covered up to 99% of the leaf area with infected plants showing weak growth and senescence. More than 70% of plants (n = 180) exhibited these powdery mildew-infected symptoms. Conidiophores were 70-120 μm long (n = 20) and composed of a basal foot cell, followed by two cells and a conidium. Cylindrical- or ovoid-shaped conidia were 30-45µm long by 9-15 µm wide (n = 20). Brown or light-brown chasmothecia were 100-140 μm in diameter, with flexuous appendages. Based on these morphological characteristics, the fungus was tentatively identified as an Erysiphe sp. (Braun and Cook, 2012; Schmidt and Braun, 2020). Fungal structures were isolated from diseased leaves and genomic DNA of the pathogen was extracted utilizing the method described by Zhu et al. (2022). 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 (GenBank accession no.: MW142495) showed 100% identity (645/645 bp) with Erysiphe astragali, which was reported on A. glycyphyllos in Golestan province, Iran (accession no. OP806834). Pathogenicity tests were conducted by brushing the conidia from infected A. scaberrimus leaves onto leaves of four healthy plants, while, the four control plants were brushed in the same manner. All the treated plants were placed in separate growth chambers maintained at 19℃, 65% humidity, with 16 h light/8 h dark photoperiod. 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 reisolated and identified as E. astragali based on morphological and molecular analysis, thereby fulfilling Koch's postulates. E. astragali causing powdery mildew on A. glycyphyllus were previously reported in Germany with Genbank accesion number of MZ265150 and MZ265151 (Bradshaw et al., 2022). This, to our knowledge, is the first report of powdery mildew caused by E. astragali on A. scaberrimus. The severe occurrence of this destructive powdery mildew disease on A. scaberrimus may adversely affect the utility of the plant for soil conservation or cultivation for medicinal purposes. Identifying the causal agent of powdery mildew will support efforts for the future control and management of diseases on A. scaberrimus.