First report of the powdery mildew pathogen of hops, Podosphaeria macularis, naturally infecting cannabis (Cannabis sativa L., marijuana) plants under field conditions

Mungbean (Vigna radiata L.) is routinely grown in the experimental fields at the headquarters of the World Vegetable Center (23°6'30.88"N, 120°17'51.31"E) for breeding, research and germplasm multiplication. In a spring 2016 mungbean trial, about 50% of the plants were affected with powdery mildew. The white, powdery-like patches first appeared on the upper leaf surfaces, and soon developed to grey patches on both sides of the leaves. Purple to brown discoloration appeared on the underside of the infected leaf. Microscopy examination revealed that the causal organism was not Erysiphe polygoni, which had previously been documented as the powdery mildew pathogen on mungbean in Taiwan (Hartman et al. 1993). The fungus produced typical structures of the powdery mildew Euoidium, anamorph of the genus Podosphaera. The mycelium consisted of septate, flexuous hyphae with indistinct appressoria. The erect conidiophores arising from superficial hyphae varied from straight or slightly curved to curled. Three to ten conidia were borne in long chains with crenate edges. Foot-cells were straight, cylindrical and measured 30 to 52 µm long. Conidia were hyaline, ellipsoid-ovoid to barrel-shaped, with fibrosin bodies, and measured 27 to 33 (mean = 30.4) × 15 to 20 (mean = 16.6) µm. Germ tubes were clavate and occasionally forked, and were produced from the lateral sites of the conidia. No chasmothecia were found in the samples. The morphological characteristics were consistent with P. xanthii (Castagne) U. Braun & Shishkoff (Braun & Cook 2012). To confirm the identity, the internal transcribed spacer (ITS) region of rDNA and partialβ-tubulin gene (TUB2) for the isolate MG3 were amplified with the primers ITS4/ITS5 (White et al. 1990) and BtuF5/BtuR7a (Ellingham et al. 2019), respectively. BLASTn analysis revealed the ITS sequence (MN833717) was 100% identical to many records of P. xanthii whereas the TUB2 sequence (MW363957) was 100% identical to a record of P. fusca (syn. P. xanthii; KC333362) in NCBI GenBank. A pathogenicity test was conducted by dusting conidia from an infected leaf onto six healthy four-week-old mungbean plants (cv ‘Tainan No. 3’). Another three plants were not inoculated and were used as control. All the plants were maintained in a greenhouse at 25 to 28°C. All inoculated plants developed powdery mildew symptoms after 10 days, whereas the control plants remained symptomless. To our knowledge, this is the first report of P. xanthii causing disease on mungbean in Taiwan. P. xanthii also has been reported on mungbean in Thailand (Meeboon et al. 2016), while other records referring to E. polygoni infecting Vigna spp. are from Brazil and Fiji (Farr & Rossman 2020). Although both P. xanthii and E. polygoni have now been reported as causing powdery mildew on mungbean in Taiwan, which species predominates or is more important remains unclear. A comprehensive survey with accurate species identification is required to develop effective management of the disease, particularly for resistance breeding.

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First Report of Powdery Mildew Caused by Golovinomyces spadiceus on Industrial Hemp (Cannabis sativa) in Kentucky

Plant Disease ◽

10.1094/pdis-01-19-0049-pdn ◽

2019 ◽

Vol 103 (7) ◽

pp. 1773-1773 ◽

Cited By ~ 4

Author(s):

D. Szarka ◽

L. Tymon ◽

B. Amsden ◽

E. Dixon ◽

J. Judy ◽

...

Keyword(s):

Powdery Mildew ◽

Cannabis Sativa ◽

First Report ◽

Industrial Hemp

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First Report of Golovinomyces spadiceus Causing Powdery Mildew on Industrial Hemp (Cannabis sativa) in Ohio

Plant Disease ◽

10.1094/pdis-01-20-0198-pdn ◽

2020 ◽

Vol 104 (10) ◽

pp. 2727-2727

Author(s):

C. Farinas ◽

F. Peduto Hand

Keyword(s):

Powdery Mildew ◽

Cannabis Sativa ◽

First Report ◽

Industrial Hemp

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First Report of Powdery Mildew Caused by Podosphaera xanthii (syn. P. fusca) on Cocklebur in Korea

Plant Disease ◽

10.1094/pdis-10-12-0951-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 842-842 ◽

Cited By ~ 2

Author(s):

H. B. Lee

Keyword(s):

Powdery Mildew ◽

Natural Infection ◽

Morphological Characteristics ◽

Its Region ◽

Xanthium Strumarium ◽

Podosphaera Xanthii ◽

First Report ◽

Rdna Its ◽

Causal Fungus ◽

Powdery Mildew Pathogen

Cocklebur (Xanthium strumarium L., Asteraceae) is an annual broadleaf weed native to the Americas and eastern Asia. The plant is known as one of the worst competitive weeds in soybean fields and also is known to have some phytopharmacological or toxicological properties. In October 2011, a powdery mildew disease was observed on cocklebur growing in a natural landscape at Geomun Oreum located in Jeju Island, South Korea. Initial signs appeared as thin white colonies, which subsequently developed abundant growth on adaxial leaf surfaces. As the disease progressed, brown discoloration extended down infected leaves which withered. Conidia were formed singly and terminally on conidiophores. Primary conidia (20.3 to 28.6 [average 25.1] μm long × 11.1 to 15.2 [14.3] μm wide, n = 30) were ellipsoid with a round apex and truncate base. Conidiophores were straight or slightly curved and 60.1 to 101.7 (97.3) μm long × 8.2 to 13.2 (11.3) μm wide. Chasmothecia were not observed. No fibrosin bodies were observed in the conidia. Morphological characteristics were consistent with descriptions of Podosphaera xanthii (syn. P. fusca) (2,4). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS) region inclusive of 5.8S and 28S rDNA was amplified from white patches consisting of mycelia and conidia on one leaf using ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′), and LROR (5′-ACCCGCTGAACTTAAGC-3′) and LR5F primer sets, respectively. The resulting sequences were deposited in GenBank (Accession Nos. JX502022 and JX964999). A NCBI BLASTn search revealed that the rDNA ITS (JX502022) and 28S (JX964999) homologies of isolate EML-XSPW1 represented 99.6% (512/514) and 100% (803/803) identity values with those of P. xanthii (AB040330 and AB462792, respectively). The rDNA ITS and 28S sequence analysis revealed that the causal fungus clustered with P. xanthii (syn. P. fusca), falling into the Xanthii/Fusca phylogenetic group (2,4). Pathogenicity was confirmed through inoculations made by gently pressing infected leaves onto mature leaves of healthy cocklebur plants in the field in August. The six inoculated leaves were sealed in sterilized vinyl bags to maintain humid conditions for 2 days. Seven days after inoculation, symptoms similar to those observed under natural infection were observed on the inoculated plant leaves. No symptoms developed on the uninoculated control plants. A fungal pathogen that was morphologically identical to the fungus originally observed on diseased plants was also observed on inoculated plants. Erysiphe cichoracearum, E. communis, Oidium asteris-punicei, O. xanthimi, P. xanthii, and P. fuliginea have all been reported to cause powdery mildew on cocklebur (1). P. xanthii was first reported on X. strumarium in Russia (3). To our knowledge, this is the first report of powdery mildew on cocklebur caused by P. xanthii in Korea. The powdery mildew pathogen may represent an option for biocontrol of the noxious weed in the near future. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases , December 11, 2012. (2) H. B. Lee. J. Microbiol. 51:1075, 2012. (3) V. A. Rusanov and T. S. Bulgakov. Mikol. Fitopatol. 42:314, 2008. (4) S. Takamatsu et al. Persoonia 24:38, 2010.

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First Report of Powdery Mildew Caused by Podosphaera (Sphaerotheca) fusca on Euryops pectinatus in North America

Plant Disease ◽

10.1094/pdis.2000.84.9.1048a ◽

2000 ◽

Vol 84 (9) ◽

pp. 1048-1048 ◽

Cited By ~ 1

Author(s):

G. S. Saenz ◽

S. T. Koike ◽

N. Shishkoff

Keyword(s):

United States ◽

New York ◽

North America ◽

Powdery Mildew ◽

Fungal Growth ◽

The United States ◽

Voucher Specimen ◽

First Report ◽

Humidity Chamber ◽

Powdery Mildew Pathogen

Gray-leaved Euryops (Euryops pectinatus Cass., Asteraceae) is an evergreen shrub that is widely planted in landscapes in the United States. In the fall of 1999, powdery mildew was observed on E. pectinatus planted in landscapes in Redlands (San Bernardino County), CA. Symptoms consisted only of slight cupping of leaves. Fungal growth was observed on stems, leaves, petioles, and pedicels and was ectophytic and amphigenous. The white mycelium was patchy to effuse. Hyphal appressoria were indistinct (1). Conidiophore foot cells were cylindric and sometimes were tapered toward or constricted at the base. Foot cells measured 30 to 50 by 10 to 12 μm and were followed by one to two shorter cells. Conidia were cylindric to slightly doliform, borne in chains of two to three, and measured 26 to 38 by 14 to 18 μm. Conidial length to width ratios ranged from 1.7 to 2.4. Catenate conidia had crenate edge lines (3). Conidia possessed conspicuous fibrosin bodies and from their sides produced short germ tubes without appressoria. Cleistothecia were not observed. Based on these characters, the fungus was identified as Podosphaera fusca (Fr.) U. Braun & N. Shishkoff (Podosphaera sect. Sphaerotheca) (1,2). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of healthy E. pectinatus plants. Plants were incubated in a humidity chamber at 22 to 24°C and after 12 to 14 days powdery mildew colonies developed. E. pectinatus cv. Viridis, a cultivar that lacks the extensive pubescence of E. pectinatus, also developed disease when inoculated. This appears to be the first report of powdery mildew on E. pectinatus in North America. A voucher specimen has been deposited into the University of California Herbarium (accession # UC1738635). P. fusca was also observed on cv. Viridis in a nursery in New York in 1999. It is unclear where this pathogen originated. P. fusca parasitizes a large number of asteraceous species including dandelion (Taraxacum officinalis) and sowthistle (Sonchus spp.) weeds, which occur in the area and sometimes are infected with powdery mildew. The Euryops powdery mildew pathogen may be a race that is different than those found on other composites in the United States. The fungus was observed on plants in shaded areas but not on plants in full sun. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (3) H. D. Shin and Y. J. La. Mycotaxon 46:445, 1993.

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First Report of Powdery Mildew Caused by Podosphaera macularis on Hemp in Oregon

Plant Health Progress ◽

10.1094/php-04-21-0071-br ◽

2021 ◽

Author(s):

Taylor Bates ◽

Mary Holzberger-Block ◽

Michele Wiseman ◽

Andrea Garfinkel ◽

David Gent ◽

...

Keyword(s):

Powdery Mildew ◽

Cannabis Sativa ◽

Natural Conditions ◽

Powdery Mildew Fungus ◽

Management Implications ◽

First Report ◽

Podosphaera Macularis

In Oregon, hemp (Cannabis sativa) production has increased substantially after cultivation was legalized in the 2014 and 2018 Farm Bills. Typically, hemp species are affected by powdery mildew caused by Golovinomyces species. This paper reports on hop powdery mildew caused by Podosphaeria macularis, found colonizing hemp in natural conditions. The occurrence of the hop powdery mildew fungus on hemp may have management implications for both the hemp and hop industry.

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First Report of Pepper Powdery Mildew Caused by Leveillula taurica in Oklahoma

Plant Disease ◽

10.1094/pdis.1999.83.11.1072b ◽

1999 ◽

Vol 83 (11) ◽

pp. 1072-1072 ◽

Cited By ~ 4

Author(s):

J. P. Damicone ◽

A. J. Sutherland

Keyword(s):

Powdery Mildew ◽

Capsicum Annuum ◽

First Report ◽

Leveillula Taurica ◽

Leaf Surfaces ◽

Leaf Drop ◽

Bell Peppers ◽

Potential Impact ◽

Powdery Mildew Pathogen ◽

Field Production

During April 1999, bell peppers (Capsicum annuum L.) from a commercial hydroponics greenhouse in Oklahoma County, OK, were severely affected by powdery mildew caused by Leveillula taurica (Lév.) Arnaud (anamorph Oidiopsis taurica (Lév.) Salmon). Defoliation levels (50 to 75%) were similar for cvs. Valencia, Lavender Islander, Sweet Chocolate, Aladdin, Purple Beauty, Golden Summer, Chocolate Beauty, Early Sunsation, Fat N'Sassy, Lilac, Sweet Rainbow Mix, and Ivory. Fruit from infected plants were small and unmarketable. Newly infected leaves exhibited light powdery colonies that were visible on abaxial leaf surfaces. On older leaves, abaxial leaf surfaces were completely covered by powdery mildew. Severely infected leaves developed chlorotic and necrotic patches on adaxial leaf surfaces prior to leaf drop. L. taurica was identified by the presence of endophytic mycelia, often-branched conidiophores, and dimorphic conidia borne singly or in short chains (1). In 50 measurements of each type, pyriform conidia averaged 67.8 ± 5.3 × 17.9 ± 2.2 μm and cylindrical conidia averaged 62.7 ± 6.2 × 15.7 ± 2.0 μm. Although conidia were slightly longer and narrower than those reported for isolates of L. taurica from pepper in California (2), dimensions were within the range reported for the species (1). The teleomorph of this powdery mildew pathogen was not observed. Peppers were grown from seed on the site. The source of L. taurica for the outbreak and the potential impact of powdery mildew on field production of peppers are unknown. Tomatoes in another hydroponics greenhouse within 100 m were not affected. This is the first report of L. taurica in Oklahoma. References: (1) H. J. Boesewinkel. Bot. Rev. 46:167, 1980. (2) J. C. Correll et al. Plant Dis. 71:248, 1987.

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Discovery and Genetic Mapping of PM1, a Powdery Mildew Resistance Gene in Cannabis sativa L.

Frontiers in Agronomy ◽

10.3389/fagro.2021.720215 ◽

2021 ◽

Vol 3 ◽

Author(s):

Paul D. Mihalyov ◽

Andrea R. Garfinkel

Keyword(s):

Powdery Mildew ◽

Pacific Northwest ◽

Cannabis Sativa ◽

Genetic Resistance ◽

The United States ◽

Snp Markers ◽

The Pacific ◽

Powdery Mildew Pathogen ◽

Lrr Protein

Powdery mildew is among the most common diseases of both hemp- and marijuana-type cultivated Cannabis sativa. Despite its prevalence, no documented studies have characterized sources of natural genetic resistance in this pathosystem. Here we provide evidence for the first resistance (R) gene in C. sativa, represented by a single dominant locus that confers complete resistance to an isolate of the powdery mildew pathogen Golovinomyces ambrosiae, found in the Pacific Northwest of the United States. Linkage mapping with nearly 10,000 single nucleotide polymorphism (SNP) markers revealed that this R gene (designated PM1) is located on the distal end of the long arm of one of the largest chromosomes in the C. sativa genome. According to reference whole genome sequences and Sanger sequencing, the marker was tentatively placed in a cluster of R genes of the nucleotide-binding site (NBS) and leucine-rich repeat (LRR) protein type. PM1's dominant behavior, qualitative penetrance, and a co-segregating qPCR marker to track its inheritance were confirmed in two separate genetic backgrounds totaling 185 recombinant F1 plants. The goal of this study is to provide a foundation for the discovery and characterization of additional sources of genetic resistance to pathogens that infect C. sativa.

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First Report of Powdery Mildew on Nandina domestica (Berberidaceae) in North America

Plant Disease ◽

10.1094/pdis.2000.84.6.705c ◽

2000 ◽

Vol 84 (6) ◽

pp. 705-705 ◽

Cited By ~ 1

Author(s):

G. S. Saenz ◽

S. T. Koike ◽

H. J. Scheck

Keyword(s):

North America ◽

Powdery Mildew ◽

Santa Barbara ◽

Voucher Specimen ◽

First Report ◽

The United Kingdom ◽

Humidity Chamber ◽

Powdery Mildew Pathogen ◽

The University ◽

Germ Tubes

Nandina domestica Thunb. (heavenly bamboo) is an ornamental plant that is widely planted in landscapes in California and other states. Since 1996, powdery mildew disease has been seen on outdoor landscape N. domestica in various regions of California (Alameda, Monterey, Riverside, and Santa Barbara counties). Symptoms consist of reddening of leaf and stem tissues colonized by the fungus and curling and twisting of infected leaves. The following observations were the same for all collected isolates. White ectophytic mycelium was observed on leaves and petioles. Mycelium on leaves was amphigenous, mostly epiphyllous, and effused or in patches. Hyphal appressoria were nipple-shaped to lobed and sometimes opposite in orientation. Conidiophores were cylindrical, straight, sometimes slightly flexuous, 22 to 32 × 6 to 8 μm in dimension, and followed by one to two shorter cells. Conidia were cylindrical, produced singly, and 27 to 42 × 11.5 to 14 μm in dimension. Fibrosin bodies were not observed. Conidial germ tubes were approximately twice the length of the spore, originated from the ends of the spore, and terminated in simple appressoria. Cleistothecia were not present. Based on these characteristics, the fungus was identified as Microsphaera berberidis (DC) Lév. (1). Pathogenicity was confirmed by gently pressing diseased leaves on leaves of healthy N. domestica plants. Plants were incubated in a humidity chamber at 22 to 24°C, and after 10 to 14 days, powdery mildew colonies developed. A voucher specimen was deposited in the University of California Herbarium (UC 1738622). Additional inoculation experiments showed that four other N. domestica cultivars were susceptible (Compacta Nana, Gulf Stream, Harbour Dwarf, and Royal Princess). Helfer (2) noted several possible candidates for the Nandina powdery mildew pathogen in the United Kingdom. However, due to the conidial characteristics of that fungus and the paucity of character descriptions for the several species mentioned, no species name was given to the Edinburgh isolate. In contrast, the mitosporic characteristics of our isolates fit the description for M. berberidis. This is the first report of powdery mildew on N. domestica in North America. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) S. Helfer. Plant Dis. 79:424, 1995.

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