First Report of Powdery Mildew Caused by Erysiphe platani on Sycamore (Platanus occidentalis) in South Korea

Platanus occidentalis L. (sycamore) is an important shade tree distributed throughout the Northern Hemisphere and in South Korea. It has been widely used as an ornamental tree, especially in urban regions and by roadsides. The average rate of roadside planting throughout South Korea covers about 5.7% (up to 38% in Seoul), equivalent to 0.36 million trees. In early July 2012, after a rainy spell in summer, an outbreak of powdery mildew on sycamore was first observed on roadside trees in Gwangju, a southern province of South Korea. A more extensive nationwide survey revealed no powdery mildew in northern or central regions of South Korea. The disease has spread rapidly within Gwangju, even though fungicide applications were carried out after the rainy spell. Major symptoms included white, superficial mycelia, grey to brown lesions on the surface of the leaves due to the presence of a hyperparasite (tentatively identified as Ampelomyces sp.), a slight chlorosis, and severe leaf distortion followed by defoliation. Conidiophores were produced singly, straight, and unbranched, with lengths of 35.2 to 315.2 μm (average 170.4 μm). Conidia were ellipsoid or doliiform, ranging in size from 34.9 to 47.4 μm (average 38.2 μm) long × 16.5 to 26.8 μm (average 23.9 μm) wide. Primary conidia had a truncate base and rounded apex; secondary conidia had both a truncate base and apex. The conidial outer surface had a reticulated wrinkling. Cleistothecia (i.e., sexual spore structures) were not found during the survey, which extended from July to October. These characteristics and the host species match those of Microsphaera platani (syn. Erysiphe platani), which was described on P. occidentalis in Washington State (2). Fungal rDNA was amplified using primers ITS1 and LR5F (4) for one sample (EML-PLA1, GenBank JX485651). BLASTn searches of GenBank revealed high sequence identity to E. platani (99.5% to JQ365943 and 99.3% to JQ365940). Recently, Liang et al. (3) reported the first occurrence of powdery mildew by E. platani on P. orientalis in China based only on its morphology. Thus, in this study, author could only use ITS sequence data from the United States and Europe to characterize the isolate. To date, nine records of powdery mildews of Platanus spp. have been reported worldwide: on P. hispanica from Brazil, Japan, Hungary, and Slovakia; P. orientalis from Israel; P. racemosa from the United States; P. × acerifolia from the United Kingdom and Germany; and Platanus sp. from Argentina and Australia (1). Interestingly, the hyperparasite, Ampelomyces sp., was found with E. platani, suggesting that there may be some level of biocontrol in nature. Pathogenicity was confirmed by gently pressing diseased leaves onto six leaves of healthy sycamore plants in the field in September. The treated leaves were sealed in sterilized vinyl pack to maintain humid condition for 2 days. Similar symptoms were observed on the inoculated leaves 10 days after inoculation. Koch's postulates were fulfilled by re-observing the fungal pathogen. To our knowledge, this is the first report of powdery mildew caused by E. platani on sycamore in South Korea. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. http://nt.ars-grin.gov/fungaldatabases/ , 2012. (2) D. A. Glawe. Plant Health Progress, doi:10.1094/PHP-2003-0818-01-HN, 2003. (3) C. Liang et al. Plant Pathol. 57:375, 2008. (4) T. J White et al., pp. 315-322 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., ed. Academic Press, New York, 1990.

Download Full-text

First Report of Powdery Mildew Caused by Erysiphe aquilegiae var. aquilegiae on Aquilegia flabellata in Italy

Plant Disease ◽

10.1094/pdis.2004.88.6.681a ◽

2004 ◽

Vol 88 (6) ◽

pp. 681-681

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

Northern Italy ◽

American Phytopathological Society ◽

First Report ◽

Powdery Mildews ◽

The Family ◽

White Mycelium ◽

The University

Aquilegia flabellata Sieb. and Zucc. (columbine) is a perennial garden species belonging to the family Ranunculaceae. During the summer of 2003, a severe outbreak of a previously unknown powdery mildew was observed in several gardens near Biella (northern Italy). Upper surfaces of leaves were covered with a white mycelium and conidia, and as the disease progressed infected leaves turned yellow and died. Foot cell was cylindric and appressorium lobed. Conidia were hyaline, ellipsoid, and measured 31.2 to 47.5 × 14.4 to 33 μm (average 38.6 × 21.6 μm). Fibrosin bodies were not present. Cleistothecia were globose, brown, had simple appendages, ranged from 82 to 127 (average 105) μm in diameter, and contained one to two asci. Ascocarp appendages measured five to eight times the ascocarp diameter. Asci were cylindrical (ovoidal) and measured 45.3 to 58.2 × 30.4 to 40.2 μm. Ascospores (three to four per ascus) were ellipsoid or cylindrical and measured 28.3 to 31.0 × 14.0 to 15.0 μ;m. On the basis of its morphology, the pathogen was identified as Erysiphe aquilegiae var. aquilegiae (1). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of five, healthy A. flabellata plants. Five noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a garden where temperatures ranged between 20 and 30°C. After 10 days, typical powdery mildew symptoms developed on inoculated plants. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of the presence of powdery mildew on Aquilegia flabellata in Italy. E. communis (Wallr.) Link and E. polygoni DC. were reported on several species of Aquilegia in the United States (2), while E. aquilegiae var. aquilegiae was previously observed on A. flabellata in Japan and the former Union of Soviet Socialist Republics (3). Specimens of this disease are available at the DIVAPRA Collection at the University of Torino. References: (1) U. Braun. Nova Hedwigia, 89:700, 1987. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) K. Hirata. Host Range and Geographical Distribution of the Powdery Mildews. Faculty of Agriculture, Niigata University, 1966.

Download Full-text

First Report of Powdery Mildew Caused by Golovinomyces spadiceus on Okra in the United States

Plant Disease ◽

10.1094/pdis-01-18-0179-pdn ◽

2018 ◽

Vol 102 (8) ◽

pp. 1664-1664 ◽

Cited By ~ 5

Author(s):

S. Moparthi ◽

M. Bradshaw ◽

K. Frost ◽

P. B. Hamm ◽

J. W. Buck

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

First Report

Download Full-text

First Report of Powdery Mildew Caused by Blumeria graminis f. sp. bromi on Bromus catharticus in China

Plant Disease ◽

10.1094/pdis-09-20-1983-pdn ◽

2020 ◽

Author(s):

Mo Zhu ◽

Jie Ji ◽

Xiao Duan ◽

Wenqi Shi ◽

YongFang Li

Keyword(s):

Powdery Mildew ◽

Sequence Data ◽

Morphological Characteristics ◽

Signs And Symptoms ◽

The United States ◽

Blumeria Graminis ◽

Henan Province ◽

Width Ratio ◽

Causal Organism ◽

First Report

Bromus catharticus, rescuegrass, is a brome grass that has been cultivated for herbage production, and been widely naturalized in many provinces of China, including Henan province. During April and May 2020, powdery mildew was found on leaves of Br. catharticus on the campus of Henan Normal University, Xinxiang city (35.3°N; 113.9°E), Henan Province, China. Abundant white or grayish irregular or coalesced circular powdery colonies were scattered on the adaxial surface of leaves and 70% of the leaf areas were affected. Some of the infected leaves either were chlorotic or senescent. About 60% of the observed plants showed powdery mildew symptoms. Conidiophores (n = 25) were 32 to 45 μm × 7 to 15 μm and composed of foot cells and conidia (mostly 6 conidia) in chains. Conidia (n = 50) were 25 to 35 μm × 10 to 15 μm, on average 30 × 13 μm, with a length/width ratio of 2.3. Chasmothecia were not found. Based on these morphologic characteristics, the pathogen was initially identified as Blumeria graminis f. sp. bromi (Braun and Cook 2012; Troch et al. 2014). B. graminis mycelia and conidia were collected, and total genomic DNA was extracted (Zhu et al. 2019). The rDNA internal transcribed spacer (ITS) region was amplified with primer pairs ITS1/ITS4. The amplicon was cloned and sequenced. The sequence (574 bp) was deposited into GenBank under Accession No. MT892940. BLASTn analysis revealed that MT892940 was 100% identical to B. graminis f. sp. bromi on Br. catharticus (AB000935, 550 of 550 nucleotides) (Takamatsu et al. 1998). Phylogenetic analysis of MT892940 and ITS of other B. graminis ff. spp. clearly indicated least two phylogenetically distinct clades of B. graminis f. sp. bromi and that MT892940 clustered with the Takamatsu vouchers. Leaf surfaces of five healthy plants were fixed at the base of a settling tower and then inoculated by blowing conidia from diseased leaves using pressurized air. Five non-inoculated plants served as controls. The inoculated and non-inoculated plants were maintained separately in two growth chambers (humidity, 60%; light/dark, 16 h/8 h; temperature, 18℃). Thirteen- to fifteen-days after inoculation, B. graminis signs and symptoms were visible on inoculated leaves, whereas control plants remained asymptomatic. The pathogenicity assays were repeated twice with the same results. The observed signs and symptoms were morphologically identical to those of the originally infected leaves. Accordingly, the causal organism of the powdery mildew was confirmed as B. graminis f. sp. bromi by morphological characteristics and ITS sequence data. B. graminis has been reported on Br. catharticus in the United States (Klingeman et al. 2018), Japan (Inuma et al. 2007) and Argentina (Delhey et al. 2003). To our best knowledge, this is the first report of B. graminis on Br. catharticus in China. Since hybridization of B. graminis ff. spp. is a mechanism of adaptation to new hosts, Br. catharticus may serve as a primary inoculum reservoir of B. graminis to infect other species (Menardo et al. 2016). This report provides fundamental information for the powdery mildew that can be used to develop control management of the disease in Br. catharticus herbage production.

Download Full-text

First Report of Powdery Mildew Caused by Podosphaera aphanis var. aphanis on Potentilla fruticosa in Italy

Plant Disease ◽

10.1094/pd-89-1362c ◽

2005 ◽

Vol 89 (12) ◽

pp. 1362-1362

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

Pathogenicity Test ◽

First Report ◽

Potentilla Fruticosa ◽

Erysiphe Polygoni ◽

Voucher Specimens ◽

White Mycelium ◽

Sphaerotheca Macularis

Potentilla fruticosa L. (bush cinquefoil), belonging to the family Rosaceae, is an ornamental plant used in parks and gardens. During the spring and summer of 2005, severe outbreaks of a previously unknown powdery mildew were observed in several private gardens located near Biella (northern Italy). The adaxial and abaxial surfaces of leaves as well as the stems were covered with white mycelium. Buds and flowers also were affected. As disease progressed, infected leaves turned yellow and dehisced. Conidia formed in chains and were hyaline, ovoid, and measured 24.0 to 36.0 × 15.8 to 24.0 μm (average 30.1 × 20.0 μm). Fibrosin bodies were present. Chasmothecia were numerous, sphaerical, amber colored, and diameters ranged from 84.0 to 98.4 μm (average 90.4 μm). Each chasmothecium contained one ascus with eight ascospores. Ascospores measured 26.5 to 27.2 × 13.2 to 15.6 μm (average 26.8 × 14.0 μm). On the basis of its morphology, the causal agent was determined to be Podosphaera aphanis (Wallr.) U. Braun & S. Takamatsu var. aphanis U. Braun (1). Pathogenicity was confirmed through inoculations by gently pressing diseased leaves onto leaves of healthy P. fruticosa plants. Three plants were inoculated. Three noninoculated plants served as a control. Plants were maintained at temperatures ranging from 12 to 23°C. Ten days after inoculation, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. The pathogenicity test was carried out twice. To our knowledge, this is the first report of powdery mildew on P. fruticosa in Italy. Erysiphe polygoni D.C. and Sphaerotheca macularis (Wallr.:Fr.) Lind were observed in the United States on P. fruticosa (2), while in Japan, the presence of S. aphanis var aphanis was reported (3). Voucher specimens are available at the AGROINNOVA Collection, University of Torino. References: (1) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000 (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) S. Tanda et al. J. Agric. Sci. 39:258, 1995.

Download Full-text

First Report of Powdery Mildew, Caused by an Oidium sp., on Poinsettia in California

Plant Disease ◽

10.1094/pdis.1998.82.1.128a ◽

1998 ◽

Vol 82 (1) ◽

pp. 128-128 ◽

Cited By ~ 3

Author(s):

S. T. Koike ◽

G. S. Saenz

Keyword(s):

United States ◽

Powdery Mildew ◽

Pacific Northwest ◽

The United States ◽

Euphorbia Pulcherrima ◽

American Phytopathological Society ◽

First Report ◽

The Pacific ◽

Uninoculated Control ◽

Alternative Identification

In December 1996 and January 1997, powdery mildew was observed on potted poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants in Monterey County, CA. Mycelia were observed on stems, petioles, mature and immature leaves, and bracts. Severely diseased leaves became twisted and bent and senesced prematurely. The white mycelia were conspicuous, epiphytic, and amphigenous; hyphae measured 4.6 to 6.9 μm in diameter. Growth initially was in patches but eventually became effused. Appressoria were slightly lobed to lobed and sometimes opposite. Conidiophore foot cells were cylindrical, sometimes bent at the base, and slightly flexuous to flexuous. Foot cells measured 30.0 to 46.2 μm × 5.8 to 6.9 μm and were followed by one to two shorter cells. Conidia were cylindrical to slightly doliform and measured 25.4 to 32.3 μm × 11.6 to 18.5 μm. The length-to-width ratios of conidia generally were greater than 2.0. Conidia were produced singly, placing the fungus in the Pseudoidium-type powdery mildew group. Conidia germinated at the ends, and no fibrosin bodies were observed. Cleistothecia were not found. The fungus was identified as an Oidium species. Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted poinsettia plants (cvs. Freedom Red, Peter Star Marble, and Nutcracker White), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, powdery mildew colonies developed on the inoculated plants, and the pathogen was morphologically identical to the original isolates. Uninoculated control plants did not develop powdery mildew. This is the first report of powdery mildew on poinsettia in California. This fungus appears similar to Microsphaera euphorbiae but has longer, slightly flexuous foot cells that do not match the description for M. euphorbiae (1,2). An alternative identification would be Erysiphe euphorbiae; however, there are no available mitosporic descriptions for morphological comparisons (1,2). In the United States, powdery mildew of poinsettia previously has been reported in various states in the Pacific Northwest, Midwest, and Northeast. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

Download Full-text

First Report of Powdery Mildew Caused by Golovinomyces cichoracearum on Crotalaria juncea (‘Tropic Sun’ Sunn hemp)

Plant Disease ◽

10.1094/pdis-93-4-0427a ◽

2009 ◽

Vol 93 (4) ◽

pp. 427-427 ◽

Cited By ~ 4

Author(s):

A. J. Gevens ◽

G. Maia ◽

S. A. Jordan

Keyword(s):

United States ◽

Powdery Mildew ◽

Cover Crop ◽

Morphological Characteristics ◽

The United States ◽

Universal Primers ◽

Crotalaria Juncea ◽

First Report ◽

Golovinomyces Cichoracearum ◽

Sunn Hemp

Crotalaria juncea L. (Fabaceae), commonly known as sunn hemp, is a subtropical annual legume grown in the United States as a cover crop that improves soil quality, provides nitrogen, suppresses weeds and nematodes, and adds organic matter to soils. In Florida, sunn hemp is a warm- and short-season cover crop that is typically planted in June and cut and incorporated into soil in September. In 2008, powdery mildew was observed on sunn hemp in a research field in Hastings, FL. This disease is important because it has the potential to impact the health and quality of sunn hemp, and this particular powdery mildew can infect cucurbits that are grown in north Florida from late summer to fall. Fungal growth appeared as typical white, powdery mildew colonies initially seen on upper leaf surfaces, especially along the midvein of infected leaves, but moving to undersides as disease progressed; petioles and floral parts were disease free. As disease progressed, colonies enlarged and coalesced to cover the entire leaf surface; heavily infected leaves senesced and abscised. Infection was primarily seen on the lower, more mature leaves of plants and not on the top 0.6 m (2 feet) of the plant. Mycelia produced white accumulations of conidiophores and conidia. Hyphae were superficial with papillate appressoria and produced conidiophores with cylindrical foot cells that measured 48.5 × 10.0 μm (mean of 100 foot cell measurements) and short chains of conidia. Conidia were hyaline, short-cylindrical to ovoid, lacked fibrosin bodies, borne in chains, had sinuate edge lines with other immature conidia, and measured 22.5 to 40.0 (mean = 29.85 μm) × 12.5 to 20.0 μm (mean = 15.55 μm). The teleomorph was not observed. The nuclear rDNA internal transcribed spacer (ITS) regions were amplified by PCR, using universal primers ITS1 and ITS4, and sequenced (GenBank Accession No. FJ479803). On the basis of morphological characteristics of the asexual, imperfect state that are consistent with published reports of Golovinomyces cichoracearum (2) and ITS sequence data that indicated 100% homology with G. cichoracearum from Helianthus annus (GenBank Accession No. AB077679), this powdery mildew was identified as caused by G. cichoracearum of the classification Golovinomyces Clade III (3). Pathogenicity was confirmed by gently pressing disease leaves onto leaves of healthy C. juncea plants. Inoculated plants were placed into plastic bags containing moist paper towels to maintain high humidity. The temperature was maintained at 24°C, and after 2 days, powdery mildew colonies developed in a manner consistent with symptoms observed under field conditions. A powdery mildew on Crotalaria was previously identified as caused by Microsphaera diffusa Cooke & Peck (1). To our knowledge, this is the first report of G. cichoracearum causing powdery mildew on C. juncea. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) D. A. Glawe et al. Online publication. doi: 10.1094/PHP-2006-0405-01-BR. Plant Health Progress, 2006. (3) S. Takamatsu et al. Mycol. Res. 110:1093, 2006.

Download Full-text

First Report of Powdery Mildew of Platanus occidentalis Caused by Erysiphe platani in Korea

Plant Disease ◽

10.1094/pdis-10-12-0982-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 843-843 ◽

Cited By ~ 2

Author(s):

Y. J. La ◽

S. E. Cho ◽

H. D. Shin

Keyword(s):

North America ◽

Powdery Mildew ◽

Its Region ◽

The United States ◽

Control Measures ◽

Base Substitution ◽

Width Ratio ◽

First Report ◽

Platanus Occidentalis ◽

Young Leaves

Platanus occidentalis L., called American sycamore or American plane, is native to North America. The trees are commonly planted throughout the world on the sides of roads and in parks. In June 2012, diseased leaves exhibiting signs of powdery mildew from a park in Daegu City of Korea were sent to Plant Clinic of Seoul National University for diagnosis. Our observations in Daegu City during September and October 2012 showed that nearly 99% of the approximately 1,000 trees surveyed were infected with a powdery mildew. Voucher specimens (n = 6) were deposited at the Korea University Herbarium (KUS). Symptoms were characterized by chlorosis, distortion, or cupping of young leaves. White superficial colonies developed amphigenously on leaves. Hyphae were flexuous to straight, branched, septate, 4 to 7 μm wide, and had lobed appressoria. Conidiophores were 120 to 350 × 5 to 7.5 μm and produced conidia singly. Foot-cells of conidiophores were straight, cylindric, and 115 to 200 μm long. Conidia were hyaline, ellipsoid-ovoid, measured 33 to 47.5 × 17.5 to 29 μm with a length/width ratio of 1.5 to 2.0, lacked distinct fibrosin bodies, and showed reticulate wrinkling of the outer walls. Germ tubes were produced on the subterminal position of conidia. No chasmothecia were observed. The structures and measurements were compatible with those of the anamorphic state of Erysiphe platani (Howe) U. Braun & S. Takam. (1). To confirm the identification, the complete internal transcribed spacer (ITS) region of the rDNA from isolate KUS-F26959 was amplified with nested PCR and sequenced. The resulting sequence of 625 bp was deposited in GenBank (Accession No. JX997805). A GenBank BLAST search of this sequence showed only one base substitution with the four sequences (JQ365940 to JQ365943) of E. platani on Platanus spp. Pathogenicity was confirmed through inoculation tests by gently pressing diseased leaves onto young leaves of three 2-year-old disease-free seedlings. Three non-inoculated plants were used as control. Plants were maintained in a greenhouse at 24 to 30°C. Inoculated leaves developed symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was morphologically identical to that observed on the original diseased leaves, fulfilling Koch's postulates. Since E. platani first was recorded in the United States in 1874, it has been regarded as endemic in North America. From the second half of the 20th century, introduction and expansion of the range of this fungus to South America, South Africa, Australia and New Zealand, Europe, and Asia have been reported (1,2). To our knowledge, this is the first report of E. platani infections of P. occidentalis in Korea. This species was recorded on P.× hispanica from Japan in 1999 (4) and on P. orientalis from China in 2006 (3), suggesting invasive spread of the sycamore powdery mildew in East Asia. Since American sycamores are widely planted in Korea, control measures should be made to prevent further spread of the disease. References: (1) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No.11. CBS, Utrecht, 2012. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Syst. Mycol. Microbiol. Lab., Online publication, ARS, USDA, Retrieved October 22, 2012. (3) C. Liang et al. Plant Pathol. 57:375, 2008. (4) S, Tanda. J. Agric. Sci., Tokyo Univ. Agric. 43:253, 1999.

Download Full-text

First Report of Powdery Mildew on Spiraea japonica Caused by Podosphaera spiraeae in the United States

Plant Disease ◽

10.1094/pdis-09-17-1419-pdn ◽

2018 ◽

Vol 102 (3) ◽

pp. 682

Author(s):

S. Moparthi ◽

G. G. Grove ◽

M. Bradshaw

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

First Report

Download Full-text

First Report of QOI-insensitive Powdery Mildew (Erysiphe polygoni) on Sugar Beet in the United States

Plant Disease ◽

10.1094/pdis-12-13-1217-pdn ◽

2014 ◽

Vol 98 (7) ◽

pp. 1004-1004 ◽

Cited By ~ 2

Author(s):

M. D. Bolton ◽

O. T. Neher

Keyword(s):

United States ◽

Disease Management ◽

Powdery Mildew ◽

Sugar Beet ◽

Untreated Control ◽

The United States ◽

Nucleotide Position ◽

Cytb Gene ◽

First Report ◽

Erysiphe Polygoni

The $2.1 billion United States sugar beet (Beta vulgaris L.) industry is the primary provider of domestic sucrose. Sugar beet powdery mildew is caused by Erysiphe polygoni DC and occurs principally in sugar beet growing regions in the western United States. In these regions, the quinone outside inhibitor (QOI) fungicides pyraclostrobin (Headline, BASF, NC) and trifloxystrobin (Gem, Bayer Crop Science, NC) have been important tools to manage powdery mildew since registration in 2002 and 2005, respectively. However, researchers in Idaho reported poor disease management despite QOI application starting in 2011. In 2013, a research plot near Parma, ID, containing natural powdery mildew infection received treatments of pyraclostrobin, trifloxystrobin, or was untreated (control). Since there was no significant reduction in disease levels between QOI-treated blocks and untreated control blocks, experiments were conducted to clone a partial fragment of the E. polygoni cytochrome b (cytb) gene to gain insight into the molecular basis of QOI resistance in this pathosystem. The primers MDB-920 (5′-CACATCGGAAGAGGTTTATA-3′) and MDB-922 (5′-GGTATAGATCTTAATATAGCATAG-3′) were designed based on consensus sequences of several fungal cytb genes obtained from GenBank (data not presented) and used to amplify a 575-bp fragment of the E. polygoni cytb gene using DNA isolated from 12 infected leaf samples collected in September 2013 from the Parma research plot. Each sample consisted of three leaves harvested from three plants (one leaf per plant) in an experimental block. All DNA extraction, PCR, and sequencing procedures were as described previously (1). PCR products derived from six QOI-treated samples and six untreated samples were sequenced directly. Without exception, all QOI-treated samples harbored a point mutation at nucleotide position 143 that encoded a G143A mutation compared with cytb sequence from untreated samples. The two identified cytb haplotypes have been deposited in GenBank under accession numbers KF925325 and KF925326. This is the first report of QOI resistance and the associated cytb G143A mutation in E. polygoni. The G143A mutation has been reported in most QOI-resistant pathogens to date (2). When the G143A mutation dominates in a pathogen population, there is a consistent association with a loss of disease management despite QOI application (3). Careful monitoring and judicious use of QOI fungicides will be necessary to ensure QOI fungicides remain efficacious for sugar beet powdery mildew management in the United States. References: (1) M. D. Bolton et al. Pest Manag. Sci. 69:35, 2013. (2) N. Fisher and B. Meunier. FEMS Yeast Res. 8:183, 2008. (3) U. Gisi et al. Pest Manag. Sci. 58:859, 2002.

Download Full-text

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

Plant Disease ◽

10.1094/pdis-10-21-2362-pdn ◽

2021 ◽

Author(s):

Benzhong Fu ◽

Qing Yan

Keyword(s):

United States ◽

Powdery Mildew ◽

The United States ◽

Camelina Sativa ◽

Its Sequences ◽

Flowering Plant ◽

Biofuel Crop ◽

First Report ◽

Erysiphe Cruciferarum ◽

Query Cover

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.

Download Full-text