First Report of Powdery Mildew of Tomato Caused by an Erysiphe sp. in Connecticut

In 1995 and 1996, powdery mildew was observed on several samples of field-grown tomato foliage (Lycopersicon esculentum Mill.; various cultivars) submitted to the CAES Plant Disease and Information Office. Symptoms included gray superficial mycelium with abundant sporulation on adaxial and abaxial leaf surfaces, followed in the field by dessication of the foliage and rapid defoliation. No cleistothecia were observed, and single-celled, hyaline, ellipsoidal conidia occurred, usually singly, on unbranched conidiophores. Pyriform conidia occurred at a frequency of less than 1%. Conidia ranged in length from 25.6 to 43.2 μm (mean = 33.6, SE = 0.4) and in width from 13.1 to 23.1 μm (mean = 18.2, SE = 0.2; n = 500). Fibrosin bodies were not observed, and vacuoles were present. Based on conidial characteristics, the fungus was identified as an unknown Erysiphe sp. To confirm pathogenicity, 2-week-old tomato seedlings (cv. Rutgers) were inoculated by shaking dry conidia onto the leaves and placed within plastic tents on a greenhouse bench. Control plants were treated identically but not inoculated. The inoculated plants developed foliar powdery mildew symptoms, and sporulation was observed. Susceptible cultivars that were naturally infected included Better Boy, Better Beef, Celebrity, Rutgers, Ultra Magnum, Ultra Sweet, Whopper, Yellow Brandywine; cherry type tomatoes Matts Wild Cherry and Sweet Chelsea; and plum type tomatoes Roma and Super San Marzano. Eastern black nightshade (Solanum ptycanthum Dunal), eggplant (S. melongena L. ‘Black Pride’), and tobacco (Nicotiana tabacum L. ‘C9’) were also naturally infected under greenhouse conditions. However, conidia size and number of conidia per conidiophore differed between hosts. Conidia from tobacco, eggplant, and nightshade averaged 37.8 × 19.1 μm (SE = 0.5 and 0.2, respectively) with a 95% CI of 35.5 to 40.0 × 18.1 to 20.3 μm (n = 300). Conidia from tomato were smaller, averaging 33.6 × 18.2 μm (SE = 0.3 and 0.2, respectively) with a 95% CI of 32.7 to 34.4 × 17.5 to 18.9 μm (n = 300). Factorial inoculation experiments between tomato and other hosts demonstrated cross-infectivity, but isolates originally from tobacco had significantly larger conidia when infecting tomato than isolates originally from tomato infecting tobacco. Powdery mildew isolates on tomato had fewer (P = 0.001) conidia per conidiophore (mean = 1.39, range = 1 to 4) than isolates infecting tobacco inoculated at the same time and held under the same conditions (mean = 2.54, range = 1 to 6). These results demonstrate considerable morphological variation in the powdery mildew fungus, perhaps associated with hosts such as tomato or other solanaceous plants. This is the first report of powdery mildew of tomato and tobacco in Connecticut. Powdery mildew of tomato has been reported to occur in the field in California, and in greenhouse tomatoes in New York (2). Powdery mildew of tobacco has only been reported on artificially inoculated plants in California (1). References: (1) C. R. Arredondo et al. Plant Dis. 80:1303, 1996. (2) D. M. Karasevicz and T. A. Zitter. Plant Dis. 80:709, 1996.

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First Report of Powdery Mildew on Pyrus calleryana Caused by Podosphaera leucotricha

Plant Disease ◽

10.1094/pdis-92-1-0176b ◽

2008 ◽

Vol 92 (1) ◽

pp. 176-176 ◽

Cited By ~ 1

Author(s):

L. Vajna ◽

L. Kiss

Keyword(s):

Powdery Mildew ◽

Urban Areas ◽

Its Sequence ◽

Podosphaera Leucotricha ◽

Powdery Mildew Fungus ◽

First Report ◽

Host Genus ◽

Pyrus Calleryana ◽

Single Leaf ◽

Leaf Surfaces

Callery pear (Pyrus calleryana Decne.) is native to Asia and its varieties are planted as ornamentals in urban areas worldwide. It is also used as a source of resistance to fireblight in some breeding programs. In April 2007, symptoms of powdery mildew infection were observed on the foliage of almost every P. calleryana cv. Chanticleer tree planted along a 1.5-km road in Budapest, Hungary. These trees were planted 5 to 6 years ago and were the first callery pears used as ornamentals in Hungary. Powdery mildew infections were also detected on P. calleryana trees planted in other parts of the city. White powdery mildew mycelium appeared on the lower and sometimes upper leaf surfaces, especially on young shoots, and caused chlorotic spots on the upper leaf surfaces and severe distortions of leaves. The spread of the infection was monitored between April and August of 2007 in several sample sites. More than 100 trees that were examined became heavily infected by May 2007. Powdery mildew conidiophores were typical of the genus Oidium subgen. Fibroidium, the anamorph of the teleomorph genus Podosphaera (2). Conidia developed in chains, contained fibrosin bodies, germinated at one of their ends with germ tubes terminating in unlobed appressoria, and measured 16 to 27 × 10 to 15 μm. Hyphal appressoria were nipple shaped or inconspicuous. The teleomorph was not found. To precisely identify the pathogen, DNA was extracted from conidia collected with a sterile brush from a single leaf using a Qiagen DNeasy Plant Kit (Hilden, Germany), and the internal transcribed spacer (ITS) sequence of the ribosomal DNA was amplified and determined as described by Szentiványi et al. (3). The ITS sequence, deposited in GenBank under Accession No. EU148597, was identical to those determined in Podosphaera leucotricha (Ell. & Ev.) Salmon collected from apple in Australia (GenBank Accession No. AF073353) and Canada (GenBank Accession No. AY157844) and also from pear in Canada (GenBank Accession No. AY157845). Thus, the pathogen was identified as Podosphaera leucotricha on the basis of the host genus, morphology of the anamorph, and ITS sequence. Specimens were deposited under Accession No. BPI878262 at the U.S. National Fungus Collection. To our knowledge, Podosphaera leucotricha has not been reported on P. calleryana in any parts of the world so far. An Oidium sp. infecting this plant in Australia was listed by Amano (1), but the exact identity of that fungus is not known. Thus, this is the first report of an identified powdery mildew fungus on P. calleryana. References: (1) K. Amano. Host Range and Geographical Distribution of the Powdery Mildew Fungi. Japan Scientific Societies Press, Tokyo, 1986. (2) U. Braun et al. Pages 13-55 in: The Powdery Mildews: A Comprehensive Treatise. R. R Bélanger et al., eds. American Phytopathological Society, St Paul, MN, 2002. (3) O. Szentiványi et al. Mycol. Res. 109:429, 2005.

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First Report of Powdery Mildew Caused by Podosphaera fusca on Herba eupatorii in China

Plant Disease ◽

10.1094/pdis-11-12-1090-pdn ◽

2013 ◽

Vol 97 (7) ◽

pp. 995-995 ◽

Cited By ~ 2

Author(s):

J. P. Ding ◽

D. L. Pei ◽

Q. C. Zhang ◽

Q. C. Hong ◽

Y. Z. Ren ◽

...

Keyword(s):

Powdery Mildew ◽

Its Sequence ◽

Distilled Water ◽

Conidial Suspension ◽

Powdery Mildew Fungus ◽

First Report ◽

Its Sequence Analysis ◽

Leaf Surfaces ◽

Asteraceae Family ◽

Podosphaera Fusca

Herba eupatorii, one of the most important Chinese medicinal herbs, belongs to the Asteraceae family. In June 2012, a previously unknown disease, tentatively identified as powdery mildew, was observed on H. eupatorii growing in Shangqiu, in eastern Henan Province, China. Symptoms began as white mycelium partially covering upper leaf surfaces; as the disease progressed, it spread to cover entire leaf surfaces. The infected leaves became yellow and necrotic at advanced stages of infection. Specimens consisting of infected leaves were maintained at the Plant-Microbe Interaction Laboratory at Shangqiu Normal University. Microscopic observations of the morphology of the fungus revealed oval primary conidia measuring 18 to 27 × 15 to 22 μm. A long unbranched germ tube that germinated laterally from the ends of conidia was observed in some samples. Conidiophores were cylindrical, simple unbranched, and composed of a basal cell with a swollen base and three to six barrel-shaped conidia formed in chains, measuring 112 to 180 × 9 to 12 μm. Mycelial appressoria were nipple-shaped. Chasmothecia were not observed in the collected samples. To verify the identity of the fungus, the internal transcribed spacer (ITS) rDNA was amplified with ITS1 and ITS4 primers (3) and sequenced. The sequences were deposited as GenBank Accession No. JX546297. Comparison with sequences in the GenBank database revealed that the ITS sequence was 100% homologous with the sequence of Podosphaera fusca on Calendula officinalis (AB525914) (2) and Syneilesis palmata (AB040349) (1). The ITS sequence analysis verified that the causal agent was P. fusca, which is reported to be a cosmopolitan powdery mildew fungus, parasitic on numerous plant species in the Asteraceae family. Koch's postulates were completed by inoculating healthy H. eupatorii plants with a conidial suspension (prepared in distilled water) of 105 conidia/ml collected from infected plants. Five plants were sprayed until the suspension ran off the leaves, while five additional plants were sprayed with distilled water as a control. Plants were maintained in a climate cell under the following conditions: day, 24°C, 16 h; night, 20°C, 8 h; 85% humidity. After 10 days, inoculated plants developed symptoms similar to those observed in the field, whereas control plants remained healthy. Further examination showed that the inoculated plants were infected by P. fusca. To our knowledge, this is the first report of P. fusca affecting H. eupatorii in China. Because there are no fungicides labeled for use on this plant, the appearance of powdery mildew caused by P. fusca could result in substantial production loss of H. eupatorii. References: (1) T. Hirata et al. Can. J. Bot. 78:1521, 2000. (2) S. Takamatsu et al. Persoonia 24:38, 2010. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

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First Report of Powdery Mildew on Greenhouse Tomatoes Caused by Oidium neolycopersici in Florida

Plant Disease ◽

10.1094/pdis.2001.85.12.1292b ◽

2001 ◽

Vol 85 (12) ◽

pp. 1292-1292 ◽

Cited By ~ 3

Author(s):

J. J. Marois ◽

M. T. Momol ◽

J. W. Kimbrough ◽

R. C. Hochmuth ◽

W. Dankers

Keyword(s):

New York ◽

Powdery Mildew ◽

Disease Incidence ◽

Control Measures ◽

Oidium Neolycopersici ◽

Razor Blade ◽

First Report ◽

White Mycelium ◽

Repeated Applications ◽

Greenhouse Tomatoes

In December 1999, typical signs of powdery mildew-dense white mycelium in irregular patterns often covering almost the entire upper surface of leaves-were observed in production greenhouses on tomato cv. Tradiro. Microscopic observations revealed mycelium with lobed appressoria and large, approximately cylindrical conidia that measured 38 to 45 × 16 to18 μm. Short germ tubes were at one end of the conidium and ended in a lobed appressorium. Conidiophores were straight with cylindrical foot-cells (≈40 to 42 μm), followed by two short cells (14 to18 μm). Based on these characteristics the fungus was identified as 0idium neolycopersici Kiss et al. (2) (formerly O. lycopersicum Braun [1]). Disease-free tomato cv. FL47 plants were inoculated at the fourth true-leaf stage with conidia by transferring fungal colonies collected from plants in production greenhouses with a single-edged razor blade to the adaxial surface of the test plants (six plants and three leaves per plant). Plants were grown in the greenhouse at 20 to 25°C. Powdery mildew, exhibiting the same morphological features, was observed 12 days later on inoculated tomato leaves. Powdery mildew on tomatoes in Suwannee Valley area greenhouses in Florida was quite common and severe in 1999 to 2000. Secondary cycles of the disease were observed, resulting in disease incidence up to 50 to 60% in some greenhouses, requiring repeated applications of sulfur for its management. This disease is expected to become a significant problem in greenhouse tomatoes, requiring regular disease control measures. This powdery mildew has not yet been observed in field-grown tomatoes in Florida. The pathogen has been reported in Connecticut on tomatoes grown under greenhouse and field conditions (3). To our knowledge, this is the first report of O. neolycopersici on greenhouse-grown tomatoes in Florida. References: (1) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fisher Verlag, New York, 1995. (2) L. Kiss et al. Mycol. Res. 105:684, 2001. (3) J. A. LaMondia et al. Plant Dis. 83:341, 1999.

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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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First Report of Powdery Mildew on Greenhouse Tomatoes Caused by Oidium neolycopersici in Michoacan, Mexico

Plant Disease ◽

10.1094/pdis-91-12-1684c ◽

2007 ◽

Vol 91 (12) ◽

pp. 1684-1684

Author(s):

G. Rodríguez-Alvarado ◽

J. García-López ◽

R. Rodríguez-Fernández ◽

S. P. Fernández-Pavía ◽

E. Garay-Serrano

Keyword(s):

Powdery Mildew ◽

Disease Incidence ◽

Morphological Characteristics ◽

Severe Infection ◽

The United States ◽

Oidium Neolycopersici ◽

Razor Blade ◽

First Report ◽

Tomato Seedlings ◽

Greenhouse Tomatoes

During June and July of 2007, powdery mildew-infected tomato (Lycopersicum esculentum Mill. cv. Reserve) plants were observed in a commercial greenhouse with an open hydroponic system in Morelia County. Disease incidence increased from 0.5% to more than 90% in 1 month. Infected plants showed leaves with irregular areas of dense, white mycelium covering most of the upper surface. Microscopic analysis showed hyaline, septate hyphae with lobed appressoria. Conidia were ellipsoid to ovoid and 30 to 45 (38) μm × 15 to 20 (16) μm. Conidiophores were erect, 80 to 120 (103) μm, consisted of a foot cell 42 to 67 (56) μm, and two to three short cells. Conidia were produced singly. On the basis of the observed morphological characteristics, the fungus was identified as Oidium neolycopersici L. Kiss (1). Pathogenicity tests were conducted on fourth true-leaf tomato seedlings cv. Reserve under greenhouse conditions (22 ± 5°C). Inoculation was performed by transferring conidia from infected leaves to the leaves of uninfected tomato seedlings with a single-edged razor blade. Powdery mildew symptoms began to develop 7 days after inoculation. Symptoms and morphological characteristics were similar to those observed in the commercial greenhouse. Noninoculated plants remained healthy throughout the experiments. To our knowledge, this is the first report of O. neolycopersici causing powdery mildew on tomato in Michoacan, Mexico. This disease has been reported from Canada, Europe, Japan, the United States (2), and Venezuela (3) on greenhouse and field tomato crops. The observed high incidence and severe infection indicates that this disease may become an important problem in greenhouse tomatoes in Mexico. References: (1) L. Kiss et al. Mycol. Res. 105:684, 2001. (2) L. Kiss et al. Plant Dis. 89:491, 2005. (3) J. O. Montilla et al. Plant Dis. 91:910, 2007.

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First Report of Erysiphe sedi on Sedum spectabile in North America

Plant Disease ◽

10.1094/pdis.2001.85.11.1207b ◽

2001 ◽

Vol 85 (11) ◽

pp. 1207-1207 ◽

Cited By ~ 3

Author(s):

L. Kiss ◽

Margery L. Daughtrey

Keyword(s):

New York ◽

North America ◽

Powdery Mildew ◽

Market Value ◽

First Report ◽

Potted Plants ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Detached Leaves ◽

Leaf Tissues

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 Erysiphe cichoracearum Infecting Hedera canariensis var. azorica in Italy

Plant Disease ◽

10.1094/pdis.1999.83.2.198d ◽

1999 ◽

Vol 83 (2) ◽

pp. 198-198

Author(s):

C. Nali

Keyword(s):

New York ◽

Powdery Mildew ◽

Citrullus Lanatus ◽

Ornamental Plants ◽

Morphological Characteristics ◽

Hedera Helix ◽

Cucumis Sativus L ◽

First Report ◽

Erysiphe Cichoracearum ◽

English Ivy

A powdery mildew disease of variegated ivy (Hedera canariensis L. var. azorica) was observed on the Tyrrhenian coast in Tuscany (Italy) in spring 1998. Symptoms began as small, nearly circular reddish spots that later enlarged and coalesced. The hyaline mycelium produced abundant, ellipsoid conidia in long chains that ranged from 20 to 40 μm in length and from 12 to 25 μm in width. Cleistothecia were globose (100 to 120 μm diameter), dark brown (when mature) with a basal ring of mycelioid appendages, and contained several (up to 20) ovate asci, each generally containing two ascospores. Ascospores were hyaline, one-celled, ellipsoid (20 to 35 μm in length and 10 to 20 μm in width). The morphological characteristics of this fungus were those given for Erysiphe cichoracearum DC. Infection also was found on English ivy (Hedera helix L.). It is reported that this species is, occasionally, subject to powdery mildew caused by E. cichoracearum (1). Conidia from infected leaves were shaken onto leaves of melon (Cucumis melo L.), cucumber (Cucumis sativus L.), watermelon (Citrullus lanatus [Thunb.] Matsum. & Nakai), lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), tobacco (Nicotiana tabacum L.) and variegated and English ivy. After 7 days, the disease was observed on cucumber, melon, watermelon, tobacco, and variegated ivy. Examination confirmed that test plants were infected with E. cichoracearum. This is the first report of E. cichoracearum on variegated ivy in Italy. Reference: (1) P. P. Pirone. 1970. Diseases and Pests of Ornamental Plants. The Ronald Press, New York.

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Ontogenic Resistance of Leaves and Fruit, and How Leaf Folding Influences the Distribution of Powdery Mildew on Strawberry Plants Colonized by Podosphaera aphanis

Phytopathology ◽

10.1094/phyto-12-13-0345-r ◽

2014 ◽

Vol 104 (9) ◽

pp. 954-963 ◽

Cited By ~ 25

Author(s):

Belachew Asalf ◽

David M. Gadoury ◽

Anne Marte Tronsmo ◽

Robert C. Seem ◽

Andrew Dobson ◽

...

Keyword(s):

New York ◽

Powdery Mildew ◽

Rapid Development ◽

Differential Susceptibility ◽

Rapid Acquisition ◽

Age Related ◽

Significant Difference ◽

Leaf Surfaces ◽

Ontogenic Resistance ◽

Strawberry Cultivars

Ontogenic or age-related resistance has been noted in many pathosystems but is less often quantified or expressed in a manner that allows the concept to be applied in disease management programs. Preliminary studies indicated that leaves and fruit of three strawberry cultivars rapidly acquired ontogenic resistance to the powdery mildew pathogen, Podosphaera aphanis. In the present study, we quantify the development of ontogenic resistance in controlled inoculations of 10 strawberry cultivars using diverse isolates of P. aphanis in New York and Florida, USA, and in Norway. We report the differential and organ-specific development of ontogenic resistance in the receptacle and externally borne strawberry achenes. We further report that rapid development of ontogenic resistance prior to unfolding of emergent leaves, rather than differential susceptibility of adaxial versus abaxial leaf surfaces, may explain the commonly observed predominance of powdery mildew on the lower leaf surfaces. Susceptibility of leaves and fruit declined exponentially with age. Receptacle tissue of berries inoculated at four phenological stages from bloom to ripe fruit became nearly immune to infection approximately 10 to 15 days after bloom, as fruit transitioned from the early green to the late green or early white stage of berry development, although the achenes remained susceptible for a longer period. Leaves also acquired ontogenic resistance early in their development, and they were highly resistant shortly after unfolding and before the upper surface was fully exposed. No significant difference was found in the susceptibility of the adaxial versus abaxial surfaces. The rapid acquisition of ontogenic resistance by leaves and fruit revealed a narrow window of susceptibility to which management programs might be advantageously adapted.

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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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First Report of Powdery Mildew (Oidium sp.) on Pincushion Flower (Scabiosa columbaria) in New York

Plant Disease ◽

10.1094/pdis-93-3-0316b ◽

2009 ◽

Vol 93 (3) ◽

pp. 316-316 ◽

Cited By ~ 1

Author(s):

T. Jankovics ◽

L. Kiss ◽

R. E. Niks ◽

M. L. Daughtrey

Keyword(s):

New York ◽

Powdery Mildew ◽

The Netherlands ◽

Morphological Characteristics ◽

The United States ◽

Its Sequences ◽

Herbarium Specimens ◽

Chelidonium Majus ◽

Oidium Neolycopersici ◽

First Report

Scabiosa columbaria (Dipsacaceae) is a popular perennial ornamental in the United States. It is native to Europe and was introduced to North America by nursery trade only recently. In the spring of 2006, symptoms of powdery mildew infection were observed on overwintered plants of S. columbaria cv. Butterfly Blue in a nursery in Cutchogue, NY. White powdery mildew mycelia with abundant sporulation were observed on upper and lower leaf surfaces. The portions of leaves with powdery mildew colonies often showed purplish discoloration. Conidia were cylindric to doliiform, measured 20 to 33 × 10 to 15 μm, and were produced singly on 60 to 130 μm long conidiophores consisting of a foot-cell measuring 20 to 50 × 6 to 10 μm, followed by one to three, 12 to 40 μm long cells. Hyphal appressoria were lobed or multilobed. The teleomorph stage was not found. On the basis of these characteristics, the pathogen was identified as an Oidium sp. belonging to the subgenus Pseudoidium. Recently, an anamorphic powdery mildew fungus with similar morphological characteristics, identified as Erysiphe knautiae, was reported on S. columbaria cv. Butterfly Blue in Washington (2). E. knautiae is a common powdery mildew species of dipsacaceous plants such as Scabiosa spp. and Knautia spp. in Europe and Asia (1). To determine whether the fungus reported here was E. knautiae, DNA was extracted from its mycelium, and the internal transcribed spacer (ITS) region of the ribosomal DNA was amplified and sequenced as described earlier (4). No ITS sequences are available in public DNA databases for E. knautiae, thus, we determined this sequence in a specimen of E. knautiae collected from Knautia arvensis in The Netherlands. Herbarium specimens of the Oidium sp. infecting S. columbaria in New York and E. knautiae from the Netherlands were deposited at the U.S. National Fungus Collections under accession numbers BPI 878259 and BPI 878258, respectively. The ITS sequence from Oidium sp. infecting S. columbaria in New York (GenBank Accession No. EU377474) differed in two nucleotides from that of E. knautiae infecting K. arvensis in the Netherlands (GenBank Accession No. EU377475). These two ITS sequences were also more than 99% similar to those of some newly emerged anamorphic powdery mildew fungi: Oidium neolycopersici and other Oidium spp. infecting Chelidonium majus, Passiflora caerulea, and some crassulaceous plants (3,4). Thus, it is unclear whether the fungus reported here was E. knautiae known from Eurasia or an Oidium sp. that has acquired pathogenicity to S. columbaria. To our knowledge, this is the first report of powdery mildew on S. columbaria in New York. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. A. Glawe and G. G. Grove. Online publication. doi:10.1094/PHP-2005-1024-01-BR. Plant Health Progress, 2005. (3) B. Henricot. Plant Pathol. 57:779, 2008. (4) T. Jankovics et al. Phytopathology 98:529, 2008.

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