First Report of Erysiphe sedi on Sedum spectabile in North America

Since 1997, powdery mildew infections have been repeatedly observed on Sedum spectabile plants, cv. Autumn Joy, grown as ornamentals in commercial greenhouses in New York. Circular patches of gray mycelia appeared and spread on upper and occasionally on lower leaf surfaces followed by necrosis of the leaf tissues and defoliation. The new disease reduced the market value of the infected ornamentals and required chemical control. The pathogen produced conidia singly on 2- to 3-celled conidiophores occurring on the ectophytic hyphae. Conidia were subcylindrical, measured 27 to 36 μm × 13 to 17 μm, and contained no fibrosin bodies. Germinating conidia produced a short germ tube, 5 to 30 μm, terminating in a lobed appressorium. Hyphal appressoria were lobed to multi-lobed, opposite or spread along the hyphae. Cleistothecia were not found. Based on conidial characteristics, the pathogen was identified as Erysiphe sedi Braun. To confirm pathogenicity, potted healthy S. spectabile plants were placed near infected plants in the greenhouse. In addition, detached S. spectabile leaves were inoculated with the pathogen by touching them to powdery mildew colonies and then placed in plates filled with one layer of polystyrene balls floated in water. Plates were covered and kept in the laboratory. Uninfected potted plants kept in another greenhouse and noninoculated detached leaves served as controls. After 1 week, powdery mildew appeared on all infected plants and leaves exposed to or inoculated with the pathogen. The pathogen was morphologically identical to the original fungus. No symptoms were observed on the controls. E. sedi is a common Asiatic powdery mildew species infecting many crassulaceous plants (1,2) and was introduced to Eastern Europe from Asia (2). To our knowledge, this is the first report of E. sedi in North America. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fisher Verlag, Jena, 1995.

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First Report of Powdery Mildew (Microsphaera palczewskii) on Siberian Pea Tree (Caragana arborescens) in North America

Plant Disease ◽

10.1094/pdis.2003.87.4.451b ◽

2003 ◽

Vol 87 (4) ◽

pp. 451-451 ◽

Cited By ~ 1

Author(s):

C. Nischwitz ◽

G. Newcombe

Keyword(s):

North America ◽

Powdery Mildew ◽

First Report ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Mean Diameter ◽

Caragana Arborescens ◽

The Mean ◽

Northern United States ◽

The U.S

Caragana arborescens Lam. is an exotic ornamental that can also be somewhat invasive. In July 2002, powdery mildew was observed on C. arborescens along the Idaho-Washington border in Moscow and Pullman, respectively. Leaves were colonized as soon as they emerged, and entire plants were affected. The fungus covered both leaf surfaces, but cleistothecia were more abundant on abaxial surfaces. The mean diameter of the cleistothecia was 91 (± 9.8) μm. Short-stalked asci averaged 67 (± 7.1) μm × 37 (± 5.2) μm, and the ascospores were 21 (± 2.0) μm × 13 (± 0.8) μm. There are records of four species of Microsphaera on C. arborescens in Europe and Asia. The measurements fit the description of Microsphaera palczewskii Jacz. (1), and the identification was confirmed by comparison with specimens of this fungus on C. arborescens from Sweden (U.S. National Fungus Collections: BPI 749057 and 749058). Specimens of M. grossulariae (Wallr. ex Fr.) Lev. on Ribes divaricatum Dougl. from California (BPI 558266) were also examined, but the cleistothecial appendages were distinctly different from those of the Idaho specimens. To our knowledge, this is the first reported occurrence in North America of powdery mildew on C. arborescens and the first report of M. palczewskii. The latter may have been introduced recently into North America because there are areas in southern Canada and the northern United States in which C. arborescens is unaffected by powdery mildew. Interestingly, it is only in recent decades that M. palczewskii has spread from Asia into Europe (2). Now, host and parasite have been reunited in North America as well. Specimens have been deposited in the U.S. National Fungus Collections (BPI). References: (1) U. Braun. A monograph of the Erysiphales (powdery mildews) J. Cramer, Berlin-Stuttgarg, 1987. (2) S. Huhtinen et al. Karstenia 41:31, 2001.

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First Report of Powdery Mildew on Azalea Cv. Mollis (Rhododendron japonicum × R. molle) in Italy

Plant Disease ◽

10.1094/pdis.2002.86.3.329c ◽

2002 ◽

Vol 86 (3) ◽

pp. 329-329

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United Kingdom ◽

Powdery Mildew ◽

Northern Italy ◽

First Report ◽

The United Kingdom ◽

Powdery Mildews ◽

Initial Symptoms ◽

Leaf Surfaces ◽

Microscopy Examination ◽

Selection Of

Rhododendron cultivation has a long history in northern Italy, where a wide selection of varieties and hybrids are grown. In summer 2001, a previously unknown powdery mildew was observed on azalea cv. Mollis (Rhododendron japonicum × R. molle) grown in several gardens in the province of Biella. Initial symptoms included chlorotic spots, followed by white fungal mycelia on both leaf surfaces. Eventually, infected leaves turned reddish and dropped prematurely. Fruit were also infected. On infected tissues, dark brown-to-black spherical cleistothecia developed, alone or in groups. The teleomorph was identified by light microscopy examination of cleistothecia. Cleistothecia measured 110 to 140 µm and were dark brown. They contained four to eight stalked or sessile asci that measured 35 to 45 µm × 40 to 55 µm, each containing six to eight ascospores. Ascospores were ellipsoid to ovoid and measured 12 to 18 µm × 20 to 25 µm. Cleistothecial characteristics were consistent with those described for Microsphaera azaleae but were different from those of the recently described species M. digitata reported in Belgium (1). The presence of conidia was rare in the specimens, so the anamorph could not be identified. To our knowledge, this is the first report of M. azaleae in Italy, but three outbreaks of powdery mildew on rhododendron were first reported in the United Kingdom on plants grown in glasshouses in the mid-1950s, 1969 and 1973 (1). Outdoors, powdery mildew was first reported on rhododendron in Europe in 1981. M. azaleae has been identified as the causal agent of rhododendron powdery mildew in the United Kingdom, Germany, and Switzerland (1). In most cases the disease is readily controlled by regular application of fungicides commonly used against powdery mildews of other crops. Reference: (1) A. J. Inman et al. J. Phytopathol. 148:17, 2000.

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Sawadaea Powdery Mildew of Box Elder (Acer negundo) in Wisconsin

Plant Disease ◽

10.1094/pdis-91-5-0636b ◽

2007 ◽

Vol 91 (5) ◽

pp. 636-636 ◽

Cited By ~ 1

Author(s):

G. Stanosz ◽

D. Smith ◽

J. Stanosz

Keyword(s):

New York ◽

North America ◽

Powdery Mildew ◽

Lower Surface ◽

Rdna Its ◽

Powdery Mildews ◽

Box Elder ◽

Norway Maple ◽

White Mycelium ◽

Powdery Mildew Pathogen

Box elder leaves affected by powdery mildew were collected from a single tree in an urban yard in the fall of 2006 in Madison, WI. As much as half of the area of the leaf blades, when viewed from above or below, was pale green-to-tan and necrotic. Mycelium was not visible to the eye on either the upper or lower leaf surfaces, but very sparse white mycelium was observed on the lower surface of leaves with the aid of a dissecting microscope. Chasmothecia were present singly or in groups of a few on the lower surface of leaves. Morphology of the chasmothecia, including simple and bifid appendages with uncinate to circinate apices, was sufficient to identify the pathogen to the genus Sawadaea (1). Other characters were not sufficiently distinct to make an identification of the species. However, DNA was extracted from the chasmothecia, and analysis of a 542-bp sequence of nuclear rDNA ITS (GenBank Accession No. EF122238) revealed a 100% match with the respective sequence obtained from Genbank for S. bicornis (Accession No. AB193380). A specimen from which these chasmothecia were obtained has been deposited in the U.S. National Fungus Collections (BPI 877328). S. bicornis is a European pathogen of maples, including box elder when grown there (1). Knowledge of the geographic distribution and hosts of Sawadaea powdery mildews in North America is extremely limited. S. bicornis was first reported in North America only recently, occurring in the states of Idaho and Washington on Norway maple (Acer platanoides) (3). The morphologically very similar European powdery mildew pathogen of maples, S. tulasnei, is known only from New York, Ohio, and Montreal, Canada (4), and an unidentified Sawadaea species on box elder has been reported from California (2). References (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena-Stuttgart-New York, 1995. (2) S. Hirose et al. Mycol. Res. 109:912, 2005. (3) C. Nischwitz and G. Newcombe. Plant Dis. 87:451, 2003. (4) J. Weiland and G. Stanosz. Plant Dis. 90:830, 2006.

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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 Erysiphe viburni on Viburnum tinus in California

Plant Disease ◽

10.1094/pdis.2004.88.4.425c ◽

2004 ◽

Vol 88 (4) ◽

pp. 425-425

Author(s):

S. T. Koike ◽

N. Shishkoff

Keyword(s):

New York ◽

Powdery Mildew ◽

Leaf Tissue ◽

First Report ◽

Mature Leaves ◽

Powdery Mildews ◽

Brown Discoloration ◽

Uninoculated Control ◽

Monterey County

In June 2003, landscape and potted nursery plants of laurustinus (Viburnum tinus) in Monterey County, California, were found to be infected with a powdery mildew. White, ectophytic mycelial and conidial growth were present primarily on adaxial leaf sides with only sparse growth on abaxial surfaces. Severely infected leaves were buckled and slightly twisted. Affected leaf tissue exhibited slight purple-to-brown discoloration. Appressoria were opposite and lobed. Conidia were produced singly, cylindrical in shape, and measured 31 to 42 × 14 to 19 μm. No fibrosin bodies were observed in the conidia, and the conidia germinated at the ends. Ascomata were not observed. The fungus was identified as Erysiphe (section Microsphaera) viburni Duby (= Microsphaera sparsa Howe = Microsphaera penicillata [M. sparsa is not completely synonymous with M. penicillata because M. sparsa is defined as only those mildews that attack viburnum, whereas M. penicillata was defined as attacking dogwood, alder, etc.]) (1,2). Pathogenicity was demonstrated by gently pressing infected leaves with abundant sporulation onto recently expanded leaves of four, large, potted laurustinus in standard 5-gallon nursery containers (19 liters). Twelve leaves per plant were inoculated. The plants were incubated in a greenhouse (23 to 25°C). After 9 to 10 days, powdery mildew colonies developed on approximately 50% of the inoculated leaves. Such colonies were morphologically similar to the original fungus. Uninoculated control plants did not develop powdery mildew. Using the same technique, inoculating fully mature leaves of the same plants did not result in disease. To our knowledge, this is the first report of Erysiphe viburni infecting V. tinus in California. At some landscaped areas the powdery mildew was extremely severe, causing plants to take on a whitish appearance and resulting in all new foliage being misshapen. E. viburni has also been reported to infect V. japonicum in California. References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustave Fischer. New York, 1995. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000.

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First Report of Powdery Mildew on Cornus florida in Connecticut Caused by Microsphaera pulchra

Plant Disease ◽

10.1094/pdis.1999.83.8.782b ◽

1999 ◽

Vol 83 (8) ◽

pp. 782-782 ◽

Cited By ~ 3

Author(s):

V. L. Smith

Keyword(s):

New York ◽

Powdery Mildew ◽

Tree Mortality ◽

Early Summer ◽

Cornus Florida ◽

Leaf Emergence ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Fallen Leaves ◽

Landscape Trees

Powdery mildew of dogwood (Cornus florida L.) has been observed on landscape trees since 1992, and has been increasing in severity recently. In 1998, mildewed leaves (n = 100) were collected from each of four locations in Connecticut. White mildew colonies first appeared in the early summer, 4 to 6 weeks after leaf emergence, and the initial colonies rapidly coalesced to cover the entire adaxial leaf surface. Incidence on observed trees reached nearly 100%. Premature autumn coloration and defoliation occurred on those trees where incidence was highest; tree mortality due solely to powdery mildew was not observed. Cleistothecia were apparent on both adaxial and abaxial leaf surfaces within 4 to 6 weeks of initial infection. Mycelium was white in color, and conidiophores were three-celled with a slightly bent foot cell. Fibrosin bodies were not present in conidia (n = 400), which measured 14.1 m ± 0.80 × 28.1 m ± 1.60 (mean + standard error of the mean). Cleistothecia measured 114.7 m ± 1.77 in diameter, and had 4 to 10 dichotomously branched appendages, which measured 140.7 m ± 3.95 in length (1.23× cleistothecial diameter). The fungus was identified as Microsphaera pulchra based on mycelial, conidial, and cleistothecial characteristics (1). In addition, cleistothecia were found on twigs and on fallen leaves of dogwood; these overwintering cleistothecia contained mature asci and mature ascospores in March 1999. Microsphaera penicillata recently was redescribed to include only that species causing powdery mildew on Alnus spp., and having appendages 1.5× cleistothecial diameter (2). The fungus causing powdery mildew in Connecticut previously had been reported to be M. penicillata, which was not found in the present study. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer, New York, 1995.

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First Report of Powdery Mildew Caused by Erysiphe heraclei on Peucedanum japonicum in Korea

Plant Disease ◽

10.1094/pdis-09-14-0895-pdn ◽

2015 ◽

Vol 99 (1) ◽

pp. 161-161 ◽

Cited By ~ 1

Author(s):

I. Y. Choi ◽

S. H. Hong ◽

S. E. Cho ◽

J. H. Park ◽

H. D. Shin

Keyword(s):

Powdery Mildew ◽

Organic Farming ◽

Disease Incidence ◽

Morphological Characteristics ◽

Its Region ◽

Petroselinum Crispum ◽

Width Ratio ◽

First Report ◽

Potted Plants ◽

Powdery Mildews

Peucedanum japonicum Thunb., belonging to the family Apiaceae, is distributed in many Asian countries, including Korea. This plant was recently developed as an edible green and is cultivated under organic farming in Korea. In June 2013, plants showing typical symptoms of powdery mildew were found with approximately 50% disease incidence in polyethylene-film-covered greenhouses in Iksan City, Korea. Symptoms first appeared as circular white colonies, which subsequently showed abundant mycelial growth on the leaves, often covering the whole surface. Infected plants were unmarketable mainly due to signs of white fungal growths and reddish discoloration on the leaves. The same symptoms were found on P. japonicum in poly-tunnels in Iksan City and Jinan County of Korea in 2014. Voucher specimens (n = 3) were deposited in the Korea University Herbarium (KUS). Appressoria were lobed, and solitary or in opposite pairs. Conidiophores were cylindrical, 80 to 145 × 8 to 10 μm, and composed of three to four cells. Foot-cells of conidiophores were straight to substraight, cylindrical, and 25 to 63 μm long. Singly produced conidia were oblong-elliptical to oblong, occasionally ovate, 35 to 50 × 13 to 16 μm with a length/width ratio of 2.3:3.1, with angular/rectangular wrinkling of outer walls, and lacked distinct fibrosin bodies. Germ tubes were produced on the perihilar position of conidia. Primary conidia were apically conical, basally truncate, and generally smaller than the secondary conidia. No chasmothecia were found. These structures are typical of the powdery mildew Pseudoidium anamorph of the genus Erysiphe. The specific measurements and morphological characteristics were consistent with those of E. heraclei DC. (2). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA from KUS-F27872 was amplified with primers ITS1/ITS4 and sequenced. The resulting 560-bp sequence was deposited in GenBank (Accession No. KM491178). The obtained ITS sequence shared >99% similarity with those of E. heraclei from apiaceous hosts, e.g., Daucus carota (KC480605), Pimpinella affinis (AB104513), and Petroselinum crispum (KF931139). Pathogenicity was confirmed through inoculation by gently dusting conidia onto leaves of five healthy potted plants. Five non-inoculated plants served as controls. Inoculated plants developed symptoms after 6 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical in morphology to those observed in the field. Powdery mildew of P. japonicum caused by E. heraclei has been reported in Japan (4), and numerous reports of E. heraclei on various species of Peucedanum plants have been made in most part of Europe and East Asia (Japan and far eastern Russia) (1,3). However, this is the first report of powdery mildew caused by E. heraclei on P. japonicum in Korea. Occurrence of powdery mildews is a threat to the quality and marketability of this plant, especially in organic farming. References: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Societies Press, Tokyo, 1986. (2) U. Braun and R. T. A. Cook. Taxonomic Manual of the Erysiphales (Powdery Mildews), CBS Biodiversity Series No.11. CBS, Utrecht, 2012. (3) D. F. Farr and A. Y. Rossman. Fungal Databases, Syst. Mycol. Microbiol. Lab., online publication. ARS, USDA. Retrieved August 18, 2014. (4) S. Tanda and C. Nakashima. J. Agric. Sci., Tokyo Univ. Agric. 47:54, 2002.

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First Report of Sawadaea tulasnei Powdery Mildew of Norway Maple (Acer platanoides) in Wisconsin

Plant Disease ◽

10.1094/pdis-92-3-0485a ◽

2008 ◽

Vol 92 (3) ◽

pp. 485-485

Author(s):

B. Hudelson ◽

D. Smith ◽

G. Stanosz ◽

M. Hanson

Keyword(s):

New York ◽

Powdery Mildew ◽

Acer Platanoides ◽

Rdna Its ◽

Powdery Mildews ◽

Beaver Dam ◽

Norway Maple ◽

Leaf Surfaces ◽

White Mycelium ◽

Powdery Mildew Pathogen

Leaves affected by powdery mildew were collected from a Norway maple tree in early October 2007 in Beaver Dam, WI (Dodge County). Diseased leaves were present throughout the crown of this tree, with white mycelium in irregular and often vein-associated spots and often covering as much as 50% of the upper surfaces of leaves. Examination of the lower surfaces revealed necrosis of the areas underlying mycelium. Blades of samaras also bore white mycelium. Chasmothecia were present singly or in groups on the mycelium. Morphology of chasmothecia, including simple and bifid appendages with uncinate to circinate apices, was sufficient to identify the pathogen to the genus Sawadaea (1). Data for nuclear rDNA ITS sequence (546 bp) obtained for a specimen (GenBank Accession No. EU247884) exactly matched sequences for Sawadea tulasnei (GenBank Accession Nos. AB 193363, 478 bp; AB193385, 490 bp; AB193390 and AB193391, 546 bp). This data was 96% similar (528 of 552 nucleotides) to that of another European powdery mildew pathogen, S. bicornis (GenBank Accession No. AB193380), which is also reported to occur on maples in Idaho, Washington, and Wisconsin (2,3). A further survey revealed the same fungus on several additional nearby Norway maples along streets and in yards (including varieties with both darkly colored and variegated leaves), but on these trees very few leaves were affected and usually less than 5% of the upper leaf surfaces bore mycelium. This pathogen was not observed on leaves of either red (A. rubrum) or silver maples (A. saccharinum) examined in the same area. S. tulasnei was previously known in North America only by collections in New York, Ohio, and Montreal, Canada (4), but our observation indicates that the geographic distribution of this pathogen is probably much broader and overlaps with that of S. bicornis. Specimens from Beaver Dam, WI have been deposited in the U.S. National Fungus Collections (BPI 878273). References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena-Stuttgart, New York, 1995. (2) C. Nischwitz and G. Newcombe. Plant Dis. 87:451, 2003. (3) G. Stanosz et al. Plant Dis. 91:636, 2007. (4) J. Weiland and G. Stanosz. Plant Dis. 90:830, 2006.

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First Report of Powdery Mildew Caused by Golovinomyces asterum var. solidaginis on Invasive Weed Solidago gigantea in Korea

Plant Disease ◽

10.1094/pdis-02-13-0154-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1120-1120 ◽

Cited By ~ 1

Author(s):

S. E. Cho ◽

J. H. Park ◽

S. H. Hong ◽

H. D. Shin

Keyword(s):

North America ◽

Powdery Mildew ◽

Morphological Characteristics ◽

Width Ratio ◽

Limiting Factor ◽

Indigenous Plants ◽

Invasive Weed ◽

First Report ◽

Solidago Gigantea ◽

Powdery Mildews

Solidago gigantea Aiton (syn. S. serotina Aiton), known as giant goldenrod, is native to North America and has been invasive in Europe and Asia. In Korea, this plant was accidentally introduced around the 1960s and has become widely naturalized by replacing indigenous plants and disrupting the native ecosystem (3). In October 2012, hundreds of giant goldenrod plants growing wild in riverine areas and roadsides were found affected by a powdery mildew in Busan, Korea. Voucher specimens were deposited in the Korea University Herbarium (KUS). Symptoms first appeared as circular to irregular white patches, which subsequently showed abundant hyphal growth on both sides of the leaves. Appressoria on the mycelium were nipple-shaped to moderately lobed. Conidiophores measured 120 to 240 × 10 to 12.5 μm, were arising laterally from hyphal mother cells, and produced 2 to 6 immature conidia in chains with a sinuate outline, followed by 2 to 3 cells. Foot-cells in conidiophores were 42 to 70 μm long and characterized by a distinctly curved base. Conidia were hyaline, ellipsoid to ovate, measured 28 to 42 × 17 to 24 μm (length/width ratio = 1.4 to 2.1), contained small oil drops, lacked distinct fibrosin bodies, and produced germ tubes on the subterminal position. No chasmothecia were observed. The morphological characteristics described above were typical of the Euoidium type anamorph of the genus Golovinomyces, and the fungus measurements and structures were consistent with those of G. asterum var. solidaginis U. Braun (1). To confirm the identity of the causal fungus, the complete ITS region of rDNA from isolate KUS-F27219 was amplified with primers ITS5 and P3 (4) and sequenced. The resulting 508-bp sequence was deposited in GenBank (Accession No. KC513763). A GenBank BLAST search of this sequence revealed >99% similarity with the ITS sequences of G. cichoracearum from Australia (GQ183940 ex Solidago sp.) and Japan (AB077625 ex S. altissima L. and AB077627 ex S. virgaurea subsp. asiatica Kitam. ex Hara). The G. cichoracearum isolates on Solidago spp. listed above are now placed in G. asterum var. solidaginis (1). Pathogenicity was confirmed through inoculation by gently pressing diseased leaves onto leaves of five healthy potted giant goldenrods. Five non-inoculated plants served as controls. Plants were maintained in a greenhouse at 24 to 30°C. Inoculated plants developed signs and symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on inoculated plants was morphologically identical to that originally observed, fulfilling Koch's postulates. Association of S. gigantea with Golovinomyces powdery mildews has been known in North America, South America, Europe, New Zealand, Central Asia (Iran, Kazakhstan, and Kyrgyzstan), and Japan (2). To our knowledge, this is the first report of powdery mildew caused by G. asterum var. solidaginis on S. gigantea in Korea. Our field observations suggest that the powdery mildew could be a limiting factor to suppress the expansion of this invasive weed in Korea. 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 January 22, 2013. (3) S. M. Oh et al. Kor. J. Weed Sci. 22:280, 2002. (4) S. Takamatsu et al. Mycol. Res. 113:117, 2009.

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First Report of Powdery Mildew on Dollar-plant (Crassula ovata) Caused by an Oidium sp.

Plant Disease ◽

10.1094/pdis.1999.83.2.199c ◽

1999 ◽

Vol 83 (2) ◽

pp. 199-199 ◽

Cited By ~ 2

Author(s):

L. Kiss

Keyword(s):

Powdery Mildew ◽

The United States ◽

Diseased Plant ◽

Powdery Mildew Fungus ◽

History Museum ◽

First Report ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Hungarian Natural History Museum ◽

Germ Tubes

Dollar-plant (Crassula ovata) is a perennial, succulent ornamental grown worldwide. In 1998, powdery mildew colonies were observed on the adaxial leaf surfaces of a 4-year-old specimen maintained outdoors. Symptoms included necrosis of the infected tissues and defoliation 2 months after the appearance of the first colonies. Conidia were produced in chains on unbranched conidiophores. Hyphal appressoria were lobed to multi-lobed, mostly opposite or spread. Conidia were ellipsoid to cylindrical, measured 34 to 48 μm × 17 to 26 μm, and contained no fibrosin bodies. On water agar, conidia produced a single germ tube from the end of the conidium. Germ tubes were either very short with lobed appressoria, or were two to three times longer than conidia, and terminated in lobed or unlobed appressoria. Cleistothecia were not produced. The pathogen was identified as an Oidium sp. belonging to the genus Erysiphe sect. Galeopsidis (1). To confirm pathogenicity, small, potted C. ovata plants were placed near the diseased plant in the laboratory. After 2 weeks, powdery mildew appeared on the small plants, and the pathogen was morphologically identical to the original fungus. This is the first report of a powdery mildew fungus on C. ovata, and it is different from both species of the Erysiphaceae identified on other Crassula spp. (1,2). Infected C. ovata leaves were deposited at the Department of Botany of the Hungarian Natural History Museum in Budapest under the accession number BP 91732. References: (1) U. Braun. 1995. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

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