First Report of Powdery Mildew Caused by Leveillula taurica on Tomato and Pepper in Bolivia

Chlorotic and necrotic lesions typical of powdery mildew caused by L. taurica were observed in several tomato (Lycopersicon esculentum) and pepper (Capsicum annuum) fields in Santa Cruz State, Bolivia near the town of Mairana during September 2004. The tomato cultivars affected were Santa Clara, Superman, and Cool 45. Symptoms included bright yellow chlorotic lesions or brown necrotic lesions on different age leaves. Examination of samples collected from several fields revealed sporulation of L. taurica on abaxial leaf surfaces. The fungus had branched conidiophores, a tapered or pyriform apical conidium, with other conidia being more cylindrical (1,2). Conidial size was approximately 60 × 18 μm. Only the Oidiopsis stage was observed. Disease severity was high and caused a significant amount of leaf necrosis and partial defoliation on tomato. Only sporadic lesions were observed on pepper cv. YoloWonder and no significant foliar damage was observed. The growing region receives approximately 75 mm of rainfall annually with most of the rainfall occurring between October and April. Thus, powdery mildew was observed near the end of the normal 5-month dry season. It is likely that the disease has been in the region for some time based on observations from field personnel. Although reported from several other South American countries, to our knowledge, this is the first report of this disease in Bolivia. 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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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 (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 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 Oidium sp. Powdery Mildew and Tomato spotted wilt virus on Melampodium divaricatum

Plant Disease ◽

10.1094/pdis.2000.84.10.1152b ◽

2000 ◽

Vol 84 (10) ◽

pp. 1152-1152 ◽

Cited By ~ 2

Author(s):

G. E. Holcomb ◽

R. A. Valverde

Keyword(s):

Powdery Mildew ◽

Tomato Spotted Wilt Virus ◽

Virus Disease ◽

Impatiens Necrotic Spot Virus ◽

Enzyme Linked Immunosorbent Assay ◽

First Report ◽

Tomato Spotted Wilt ◽

Leaf Surfaces ◽

The Family ◽

Wilt Virus

Melampodium divaricatum (Rich. ex Pers.) DC. (=M. paludosum H.B.K.), a member of the family Asteraceae and native to South America, is a recent introduction for use as a summer bedding ornamental. In September 1999, melampodium plants in multiple Baton Rouge landscapes were observed with signs of powdery mildew and symptoms of a virus-like disease. Powdery mildew spread throughout one of the plantings by late November and infected flowers and leaves. An Oidium species sporulated on both leaf surfaces but was more common on the adaxial surface. Ellipsoid conidia were produced in chains, lacked fibrosin bodies, and averaged 31 × 19 µm. No sexual stage was observed. Eight of 63 plants (cv. Derby) in one of the plantings showed virus disease symptoms that included severe leaf mosaic, leaf malformation, and stunting. Leaves from infected plants were used to sap inoculate seedling plants of melampodium and Nicotiana benthamiana. Melampodium seedlings developed typical mosaic symptoms after 48 to 56 days. N. benthamiana developed severe chlorosis and mosaic, then wilted and died after 14 days. Noninoculated plants of both species remained healthy. The virus in both plant species was identified as Tomato spotted wilt virus (TSWV) by enzyme-linked immunosorbent assay (ELISA) (Agdia, Elkhart, IN). ELISA tests for presence of Impatiens necrotic spot virus were negative. This is the first report of powdery mildew and TSWV on M. divaricatum.

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First Report of Horse Chestnut Powdery Mildew Caused by Erysiphe flexuosa in Castilla y León, Spain

Plant Disease ◽

10.1094/pdis-91-11-1513a ◽

2007 ◽

Vol 91 (11) ◽

pp. 1513-1513 ◽

Cited By ~ 2

Author(s):

M. P. Campelo ◽

A. Lorenzana ◽

M. F. Marcos

Keyword(s):

Powdery Mildew ◽

Fungal Growth ◽

Botanical Garden ◽

Horse Chestnut ◽

Lower Leaf Surface ◽

Northern Spain ◽

First Report ◽

Castilla Y Leon ◽

Ornamental Tree ◽

Leaf Surfaces

Horse chestnut (Aesculus hippocastanum L.) is an important ornamental tree in many gardens in Castilla y León (northern Spain). During the summer and autumn of 2005 and 2006, disease signs resembling powdery mildew were observed in Condesa de Sagasta Boulevard and Quevedo Botanical Garden in León. Whitish fungal growth was visible macroscopically on the upper and lower leaf surfaces of both young and old leaves and petioles. The disease reduced tree attractiveness and could cause important aesthetic damage in the parks. Five symptomatic trees older than 30 years were observed in each park, and 10 leaves per tree were collected. Microscopic examinations of the leaf surfaces revealed ectophytic, hyaline hyphae with lobed appresoria, solitary or in pairs. Conidia were barrel to broadly subglobose and ranged from 23 to 37 μm long and 8 to 16 μm wide. They were produced singly on two- or three-celled conidiophores. Chasmothecia were produced in abundance, mostly on the lower leaf surface. They were globose, 120 to 160 μm in diameter, dark brown, and bore two types of appendages; long and flexuous with simple hook-like apices or short, simple, tapered, and rough walled. The long appendages measured 87 to 182 μm and the shorter ones measured 12 to 32 μm. Chasmothecia contained three to five asci, each developing six to eight hyaline, round, and single-celled ascospores when matured. Pathogenicity was confirmed on Aesculus sp. branches by healthy leaves being inoculated by touching them with powdery mildew-infected leaves. Noninoculated leaves served as controls. The appearance of colonies in the infected leaves was observed 15 days after the inoculation, but not in the controls. The pathogen was identified as Erysiphe flexuosa (Peck) U. Braun & S. Takamatsu, a North American powdery mildew. It has been recently introduced in Europe (1) and is now present in a number of countries (2). To our knowledge, this is the first report of E. flexuosa in this region of Spain. References: (1) N. Ale-Agha et al. Cryptogam. Mycol. 21:89, 2000. (2) K. Zimmermannová-Pastirčáková et al. Schlechtendalia 8:39, 2002.

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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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First Report of Powdery Mildew Caused by Oidium Subgenus Pseudoidium on Lonicera caprifolium in Italy

Plant Disease ◽

10.1094/pdis.2004.88.9.1045b ◽

2004 ◽

Vol 88 (9) ◽

pp. 1045-1045

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

Powdery Mildew ◽

Growing Season ◽

Northern Italy ◽

First Report ◽

Leaf Surfaces ◽

Voucher Specimens ◽

Inoculation Procedure ◽

White Mycelium ◽

The University

Honeysuckle (Lonicera caprifolium L., family Caprifoliaceae) is a climbing shrub used in gardens to cover walls and supports. During the summer of 2003, severe outbreaks of a previously unknown powdery mildew were observed on this species in some gardens near Biella (northern Italy). The first symptoms included extensive chlorosis on leaves, followed by the appearance of white mycelium on the adaxial and abaxial leaf surfaces. As the disease progressed, infected leaves turned yellow and died. Conidia were hyaline, ellipsoidal, and measured 27.6 to 43.2 × 12.2 to 21.6 μm (average 35.7 × 17.6 μm). Foot cells were cylindric and appressoria lobed. Fibrosin bodies were not present. Cleistothecia were not observed during the growing season. The pathogen was identified as Oidium subgenus Pseudoidium (2). The inoculation procedure involved gently pressing diseased leaves onto leaves of healthy L. caprifolium plants. Three plants of L. caprifolium were used as replicates. Noninoculated plants served as control. Inoculated and noninoculated plants were maintained in a garden at temperatures ranging from 15 to 25°C. After 10 days, typical symptoms of powdery mildew developed on inoculated plants. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of powdery mildew on L. caprifolium in Italy. The presence of powdery mildew on different species of Lonicera has been reported in several countries, particularly, Microsphaera miurae U. Braun on L. morowii A. Gray in Germany (1), M. lonicerae (DC.) Winter on L. peryclimenum L. in England (3), and M. lonicerae-ramosissimae on L. ramosissima Fr. & Sav. in Japan (4). The conidia of M. lonicerae are smaller than those of the Oidium sp. reported on L. caprifolium. Voucher specimens are available at DIVAPRA Collection at the University of Torino. References: (1) U. Braun. Mycotaxon 16:417, 1983. (2) U. Braun and S. Takamatsu. Schlechtendalia 4:1, 2000. (3) J. Robbins. Cecidology 15:15, 2000. (4) S. Tanda. Mycoscience 41:155, 2000.

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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 Caused by Golovinomyces orontii on Corn-Salad in the United States

Plant Disease ◽

10.1094/pd-89-0686c ◽

2005 ◽

Vol 89 (6) ◽

pp. 686-686 ◽

Cited By ~ 1

Author(s):

S. T. Koike ◽

G. S. Saenz

Keyword(s):

United States ◽

Powdery Mildew ◽

Mycelial Growth ◽

Leaf Growth ◽

The United States ◽

First Report ◽

Powdery Mildews ◽

Leaf Surfaces ◽

Germ Tubes ◽

Symptoms And Signs

Corn-salad or lamb's lettuce (Valerianella locusta) is a specialty leafy green, annual vegetable that is grown commercially in California for use in salads. During the summer (June through August) of 2004, field plantings in coastal California (Monterey County) showed symptoms and signs of a powdery mildew. White, ectophytic mycelia and conidia were present on leaves and petioles. Extensively colonized leaves were slightly twisted and later developed a tan necrosis. Mycelial growth was spread out, flat, sometimes dense, and colonized both sides of the leaf. Growth was more extensive on the upper leaf surfaces. Hyphae were 5 to 7.5 μm wide with nipple-shaped appressoria. Conidiophores were straight and had foot cells that were simple, mostly curved, measured 50 to 65 × 10 to 12.5 μm, and followed by two to three cells of equal size. Conidia developed in short chains. Conidia were cylindric to doliform, measured 27.5 to 32.5 × 15 to 17.5 μm, and lacked fibrosin bodies. Conidial length-to-width ratios were usually less than or equal to 2.0. Conidia germinated at the ends (cichoracearum-type) and had germ tube lengths that ranged from short to 1.0 to 1.5 times the length of the conidium; germ tubes had swollen tips. Cleistothecia were not observed. On the basis of these characteristics, the fungus is identified as Golovinomyces (Erysiphe) orontii(Cast.) Heluta (1). To demonstrate pathogenicity, heavily colonized corn-salad leaves from commercial plantings were collected and gently pressed onto leaves of potted corn-salad plants. Plants were then maintained in a greenhouse (22 to 24°C). After 8 to 10 days, symptoms and signs of powdery mildew developed on the foliage of inoculated plants, and the pathogen morphology matched that of the originally observed pathogen. Noninoculated control plants did not develop powdery mildew. To our knowledge, this is the first report of powdery mildew of corn-salad caused by G. orontii in the United States. This corn-salad disease has been reported from a number of countries in Europe (2). Because the presence of powdery mildew on the harvested foliage made the leaves unmarketable, part of the crop could not be sold. References: (1) U. Braun. Nova Hedwigia 89:1, 1987. (2) U. Braun. The Powdery Mildews (Erysiphales) of Europe. Gustav Fischer Verlag, Jena, Germany, 1995.

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