First Report of Downy Mildew on Greenhouse and Landscape Coleus Caused by a Peronospora sp. in Louisiana and New York

In May 2005, two commercial greenhouse flower growers, one in Louisiana (LA) and one in New York (NY), submitted coleus, Solenostemon scutellarioides (L.) Codd, plants for diagnosis after observing stunted growth, inward curling and twisting of leaves, and leaf abscission on multiple cultivars. Downy mildew-like growth was observable with hand lens or a microscope on the abaxial leaf surfaces of affected plants. Irregular necrotic spotting was present on some, but not all, plants on which sporulation was evident. Microscopic examination of LA material led to tentative identification of the pathogen as Peronospora lamii A. Braun (2). The pale brown conidia ranged from 17 to 26 × 15 to 26 μm (average 23 × 19 μm). Conidiophores ranged from 345 to 561 × 9 to 15 μm. No oospores were found. Additional coleus plants with downy mildew were subsequently found in three retail nurseries in LA in early summer. In NY, infected coleus plants were observed in landscapes in Farmington, Rochester, Ithaca, and in two commercial greenhouses between August and October 2005. NY samples sent to the USDA/APHIS in Beltsville, MD were examined, and the fungus was found to have morphology consistent with P. lamii. Two pathogenicity trials were conducted in NY. Conidia were rubbed from an infected coleus leaf onto the leaves of six healthy potted coleus plants of five cultivars and two basil plants that were placed in a shaded plastic tent in the greenhouse where temperatures ranged from 17 to 22°C. A household humidifier was used to supply mist inside the tent for 5 h per day. Six noninoculated plants of each coleus cultivar and two basil plants, placed in the same environment, served as controls. Downy mildew sporulation and some curling and twisting of leaves were observed 14 days after inoculation on all inoculated plants for three of the five cultivars (Florida Rustic Orange, Aurora Peach, and Aurora Mocha). Cvs. Florida Sun Rose and Lava showed no symptoms or signs of downy mildew. An irregularly shaped brown lesion developed on one inoculated basil leaf, and downy mildew sporulation was evident on the abaxial surface 35 days after inoculation. All noninoculated control plants remained disease free. In a second trial, conidia were rinsed from infected coleus leaves and sprayed onto the abaxial leaf surfaces of three coleus cv. Aurora Mocha plants. Three noninoculated plants served as controls and all were placed in a humidity tent. Leaf twisting and downy mildew sporulation were observed 13 days later on all inoculated plants, and control plants showed no sporulation or symptoms. A downy mildew causing disease of greenhouse-grown basil in Europe, originally identified as P. lamii on the basis of morphology, has recently been reported to be taxonomically distinguishable from P. lamii when tested by molecular methods (1). ITS sequences of coleus downy mildew from NY and LA were nearly identical (99% homology) to those of basil downy mildew from Switzerland and Italy (1). To our knowledge, this is the first report of downy mildew occurrence on coleus. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) S. M. Francis. Peronospora lamii. Descriptions of Pathogenic Fungi and Bacteria. No. 688. CMI, Kew, England, 1981.

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First Report of Downy Mildew Caused by Peronospora lamii on Salvia splendens and Salvia coccinea

Plant Disease ◽

10.1094/pdis.2000.84.10.1154b ◽

2000 ◽

Vol 84 (10) ◽

pp. 1154-1154 ◽

Cited By ~ 5

Author(s):

G. E. Holcomb

Keyword(s):

United States ◽

Downy Mildew ◽

Pathogenic Fungi ◽

The United States ◽

Commonwealth Mycological Institute ◽

First Report ◽

Leaf Spots ◽

Salvia Splendens ◽

Leaf Surfaces ◽

Pathogenicity Tests

Angular chlorotic spots were observed on adaxial leaf surfaces of Salvia splendens (scarlet sage cvs. Empire Purple, Empire White, Red Pillar, and Red Hot Sally) and S. coccinea (scarlet or Texas sage cv. Lady in Red) in early May in Baton Rouge area nurseries. Leaf spots sometimes became necrotic and resulted in leaf drop. Abaxial leaf surfaces contained scattered patches of white mycelia with brown spores. Microscopic examination of mycelia revealed irregular dichotomously branched conidiophores with pointed tips and brown oval conidia. Conidiophores averaged 485 × 9 µm and conidia averaged 21 × 18 µm (16 to 26 × 15 to 23 µm) in dimensions. The fungus was identified as Peronospora lamii A. Braun (= P. swinglei Ellis & Everh.) based on these characters and its known occurrence on Salvia spp. and five other genera in the family Lamiaceae (2). Pathogenicity tests were performed by washing conidia from infected leaves into distilled water and mistinoculating S. coccinea cv. Lady in Red and S. splendens cv. Empire Purple with 50,000 spores/ml. Plants were held in a dew chamber at 20°C for 3 days, then moved to a greenhouse where temperatures ranged from 18 to 32°C. Typical angular chlorotic leaf spots developed on inoculated plants within 6 to 8 days and noninoculated plants remained healthy. The fungus did not sporulate under these greenhouse temperatures, but infected leaves that were removed and placed in a moist chamber at 25°C produced conidiophores and brown conidia typical of P. lamii within 2 to 3 days. P. lamii has been reported previously on S. officinalis (3) and S. reflexa (1) in the United States. This is the first report of downy mildew on S. coccinea and S. splendens. Appearance of the disease in retail nurseries that obtained plants from out of state (Arkansas) suggests a widespread occurrence of the disease on these host plants. References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (2) S. M. Francis. 1981. Peronospora lamii. Descriptions of Pathogenic Fungi and Bacteria No. 688. Commonwealth Mycological Institute, Kew, England. (3) R. T. McMillan and W. R. Graves. Plant Dis. 78:317, 1994.

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First Report of Impatiens Downy Mildew Outbreaks Caused by Plasmopara obducens Throughout the Hawai'ian Islands

Plant Disease ◽

10.1094/pdis-10-13-1017-pdn ◽

2014 ◽

Vol 98 (5) ◽

pp. 696-696 ◽

Cited By ~ 7

Author(s):

J. A. Crouch ◽

M. P. Ko ◽

J. M. McKemy

Keyword(s):

United States ◽

Downy Mildew ◽

The United States ◽

Molecular Data ◽

Economic Losses ◽

Voucher Specimen ◽

First Report ◽

Plastic Bags ◽

Leaf Surfaces ◽

Impatiens Walleriana

Downy mildew of impatiens (Impatiens walleriana Hook.f.) was first reported from the continental United States in 2004. In 2011 to 2012, severe and widespread outbreaks were documented across the United States mainland, resulting in considerable economic losses. On May 5, 2013, downy mildew disease symptoms were observed from I. walleriana ‘Super Elfin’ at a retail nursery in Mililani, on the Hawai'ian island of Oahu. Throughout May and June 2013, additional sightings of the disease were documented from the islands of Oahu, Kauai, Maui, and Hawai'i from nurseries, home gardens, and botanical park and landscape plantings. Symptoms of infected plants initially showed downward leaf curl, followed by a stippled chlorotic appearance on the adaxial leaf surfaces. Abaxial leaf surfaces were covered with a layer of white mycelia. Affected plants exhibited defoliation, flower drop, and stem rot as the disease progressed. Based on morphological and molecular data, the organism was identified as Plasmopara obducens (J. Schröt.) J. Schröt. Microscopic observation disclosed coenocytic mycelium and hyaline, thin-walled, tree-like (monopodial branches), straight, 94.0 to 300.0 × 3.2 to 10.8 μm sporangiophores. Ovoid, hyaline sporangia measuring 11.0 to 14.6 × 12.2 to 16.2 (average 13.2 × 14.7) μm were borne on sterigma tips of rigid branchlets (8.0 to 15.0 μm) at right angle to the main axis of the sporangiophores (1,3). Molecular identification of the pathogen was conducted by removing hyphae from the surface of three heavily infected leaves using sterile tweezers, then extracting DNA using the QIAGEN Plant DNA kit (QIAGEN, Gaithersburg, MD). The nuclear rDNA internal transcribed spacer was sequenced from each of the three samples bidirectionally from Illustra EXOStar (GE Healthcare, Piscataway, NJ) purified amplicon generated from primers ITS1-O and LR-0R (4). Resultant sequences (GenBank KF366378 to 80) shared 99 to 100% nucleotide identity with P. obducens accession DQ665666 (4). A voucher specimen (BPI892676) was deposited in the U.S. National Fungus Collections, Beltsville, MD. Pathogenicity tests were performed by spraying 6-week-old impatiens plants (I. walleriana var. Super Elfin) grown singly in 4-inch pots with a suspension of 1 × 104 P. obducens sporangia/ml until runoff using a handheld atomizer. Control plants were sprayed with distilled water. The plants were kept in high humidity by covering with black plastic bags for 48 h at 20°C, and then maintained in the greenhouse (night/day temperature of 20/24°C). The first symptoms (downward curling and chlorotic stippling of leaves) and sporulation of the pathogen on under-leaf surfaces of the inoculated plants appeared at 10 days and 21 days after inoculation, respectively. Control plants remained healthy. Morphological features and measurements matched those of the original inoculum, thus fulfilling Koch's postulates. To our knowledge, this is the first report of downy mildew on I. walleriana in Hawai'i (2). The disease appears to be widespread throughout the islands and is likely to cause considerable losses in Hawai'ian landscapes and production settings. References: (1) O. Constantinescu. Mycologia 83:473, 1991. (2) D. F. Farr and A. Y. Rossman. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ July 16, 2013. (3) P. A. Saccardo. Syllogue Fungorum 7:242, 1888. (4) M. Thines. Fungal Genet Biol 44:199, 2007.

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First Report of Fulvia fulva, Causal Agent of Tomato Leaf Mold, in Greenhouses in Southeastern Spain

Plant Disease ◽

10.1094/pdis-92-9-1371b ◽

2008 ◽

Vol 92 (9) ◽

pp. 1371-1371 ◽

Cited By ~ 1

Author(s):

M. de Cara ◽

F. Heras ◽

M. Santos ◽

J. C. Tello Marquina

Keyword(s):

Pathogenic Fungi ◽

Malt Extract ◽

Conidial Suspension ◽

First Report ◽

Leaf Mold ◽

Southeastern Spain ◽

Solanum Lycopersicum L ◽

Plastic Bags ◽

Leaf Surfaces ◽

Fulvia Fulva

Tomato (Solanum lycopersicum L.) is produced in more than 9,000 ha of greenhouses in Almería (southeastern Spain). During 2006 and 2007, a new disease was observed on almost all plants in 37 greenhouses. Yellow spots on upper and lower leaf surfaces were accompanied by gray-to-dark brown mycelia, conidiophores, and conidia on lower leaf surfaces. Affected leaves became necrotic and withered. Six isolates grown on malt extract agar (MEA) were identified as Fulvia fulva (1). The one- to three-celled conidia ranged from 21.8 × 7.8 μm to 21.5 × 6.5 μm. On MEA, potato dextrose agar, and V8 juice agar, the pathogen grew slowly; colonies were only 1 cm in diameter after 30 days. Colony color was initially intense yellow but became dark brown with age. In a growth chamber (12,000 lux for 16 h per day, 23 to 28°C, and 60 to 95% relative humidity), six pots containing five tomato plants (cv. SanPedro) at the four-true-leaf stage were inoculated with a conidial suspension (103 CFU/ml) of F. fulva. Control plants were sprayed with water. The trial was repeated once. Immediately after inoculation, plants were sealed in plastic bags for 8 days. Symptoms of the disease and signs of the pathogen were observed on all inoculated plants 18 days after inoculation. To our knowledge, this is the first report of leaf mold of tomato in Almería and it is becoming common in the greenhouse industry in this region. Reference: (1) P. Holliday and J. L. Mulder. No. 487 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1976.

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First Report of Downy Mildew Caused by Pseudoperonospora cubensis on Chayote (Sechium edule) in Taiwan

Plant Disease ◽

10.1094/pdis-92-12-1706c ◽

2008 ◽

Vol 92 (12) ◽

pp. 1706-1706 ◽

Cited By ~ 11

Author(s):

Y. Ko ◽

C. Y. Chen ◽

C. W. Liu ◽

S. S. Chen ◽

S. Maruthasalam ◽

...

Keyword(s):

Downy Mildew ◽

Plant Diseases ◽

Pseudoperonospora Cubensis ◽

First Report ◽

Agricultural Improvement ◽

Republic Of China ◽

Sechium Edule ◽

Leaf Surfaces ◽

Leaf Tissues ◽

The Republic

Chayote (Sechium edule) is cultivated on more than 500 ha in Taiwan for its edible shoots and fruit. In August 2005 and later, 40 to 75% of the chayote plants cultivated in the Taichung District Agricultural Improvement Station in Puli developed pale yellow, irregular spots on the upper leaf surfaces with corresponding sporulation on the lower leaf surfaces. The lesions eventually became necrotic and spread over the entire leaf surface, leading to defoliation. Pseudoperonospora cubensis, which was previously reported as the cause of downy mildew on squash (Cucurbita moschata), muskmelon (Cucumis melo), cucumber (Cucumis sativus), and sponge gourd (Luffa cylindrica) in Taiwan, was identified (1). Sporangiophores were 182 to 410 μm long, 4.8 to 7.2 μm wide, and dichotomously branched. Sporangia were grayish, ovoid to ellipsoidal, 18.2 to 38.6 μm long, and 13.5 to 25.2 μm wide. Biflagellate zoospores were 9.5 to 12.6 μm in diameter. Pathogenicity tests were conducted four times with six 2-week-old plants in each trial. A sporangial suspension (1 × 105 spores per ml) prepared from infected leaves (5 to 6 weeks after infection) was sprayed on all leaves until runoff. The plants were then covered with polythene bags and incubated for 48 h at 18 ± 1°C in a growth chamber. Control plants were sprayed with sterile water. Characteristic symptoms developed on all inoculated plants after 20 days, while control plants remained symptomless. Microscopic observation of leaf tissues of symptomatic plants confirmed the presence of P. cubensis. To our knowledge, this is the first report of P. cubensis causing downy mildew on chayote in Taiwan. References: (1) S. T. Hsu et al. List of Plant Diseases in Taiwan. The Phytopathological Society of the Republic of China, 2002.

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First Report of the Occurrence and Resistance to Mefenoxam of Peronospora belbahrii, Causal Agent of Downy Mildew of Basil (Ocimum basilicum) in Israel

Plant Disease ◽

10.1094/pdis-12-12-1126-pdn ◽

2013 ◽

Vol 97 (5) ◽

pp. 692-692 ◽

Cited By ~ 27

Author(s):

Y. Cohen ◽

M. Vaknin ◽

Y. Ben-Naim ◽

A. E. Rubin ◽

M. Galperin ◽

...

Keyword(s):

Downy Mildew ◽

Infected Plant ◽

Disease Outbreak ◽

Ocimum Basilicum ◽

Causal Agent ◽

Economic Damage ◽

Jordan Valley ◽

First Report ◽

Leaf Surfaces ◽

Saturated Atmosphere

Downy mildew in basil was first reported from Uganda in 1933 (4). In 2004, it was reported from Italy (3) and, thereafter, from other countries around the world. In Israel, the disease was first observed in November 2011 in two greenhouses located in the northern part of the Jordan Valley. Within a month, second and third outbreaks of the disease occurred simultaneously near the southwest and southeast borders of Israel, 250 km from the initial disease outbreak. By the summer of 2012, the disease had appeared throughout the country, causing major economic damage. The causal agent, identified as Peronospora belbahrii (see below), produced chlorotic lesions on leaf blades with sporangia developing on the lower leaf surfaces. Lesions gradually turn necrotic, and infected leaves abscised. Sporangia were dark purple, oval, 30.4 ± 2.9 μm long × 21.4 ± 1.7 μm wide. Sporangiophores emerged from stomatal openings in a saturated atmosphere, were hyaline, 400 to 600 μm long, dichotomously branched, with three to five branches per sporangiophore, and bore a single sporangium on each branchlet tip. Oospores, seldom seen, were brown, round, and 46.2 ± 2.8 μm in diameter. Sporangia germinated directly, each producing a single germ tube that penetrated the periclinal wall of epidermal cells. PCR assays using sporangia and infected leaves as the template, and specific BAZ primers (1), produced a 134-bp band typical of P. belbahrii (1,2). Twenty isolates, collected from 12 locations in Israel from December 2011 to September 2012, were all sensitive to mefenoxam as the isolates did not cause symptoms on 15-leaf, potted basil plants (cv. Peri, Volcani Center, Israel) that were sprayed with 10 μg mefenoxam/ml (Ridomil Gold 48%, Syngenta, Basel, Switzerland) prior to inoculation. However, one isolate collected in early October 2012 from a severely infected plant in a greenhouse at Rehov in Bet-Shaan Valley, in which the plants had been treated with mefenoxam, was resistant to mefenoxan, showing abundant sporulation on leaves of potted basil plants that had been sprayed with 1,000 μg of mefenoxam/ml prior to inoculation. To our knowledge, this is the first report of the occurrence of downy mildew in basil in Israel. This is also the first global report of resistance to mefenoxam in P. belbahrii. References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) R. Djalali et al. Mycol. Progress 11:961, 2012. (3) A. Garibaldi et al., Plant Dis. 89:683, 2004. (4) C. G. Hansford. Rev. Appl. Mycol. 12:421, 1933.

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First Report of Ascochyta Leaf Spot Caused by Phoma exigua var. exigua on Common Bean in Greece

Plant Disease ◽

10.1094/pdis-92-4-0653c ◽

2008 ◽

Vol 92 (4) ◽

pp. 653-653 ◽

Cited By ~ 3

Author(s):

G. A. Bardas ◽

G. T. Tziros ◽

K. Tzavella-Klonari

Keyword(s):

Common Bean ◽

Leaf Spot ◽

Morphological Characteristics ◽

Pathogenic Fungi ◽

Weather Conditions ◽

Conidial Suspension ◽

Phoma Exigua ◽

First Report ◽

Plastic Bags ◽

And Control

Common bean (Phaseolus vulgaris L.) is cultivated extensively in Greece for dry and fresh bean production. During 2005 and 2006, a disease with typical blight symptoms was observed occasionally on dark red kidney, brown kidney, and black bean plants in most bean-producing areas of Greece. It rarely was destructive unless the crop had been weakened by some unfavorable environmental conditions. Infected leaves had brown-to-black lesions that developed concentric zones 10 to 30 mm in diameter and also contained small, black pycnidia. Concentric dark gray-to-black lesions also appeared on branches, stems, nodes, and pods. Infected seeds turned brown to black. Plants sometimes showed defoliation and pod drop. The fungus was consistently isolated on potato dextrose agar from diseased leaves and pods and identified as Phoma exigua var. exigua Sutton and Waterstone on the basis of morphological characteristics of conidia and pycnidia (1,2). Spores were massed in pycnidia from which they were forced in long, pink tendrils under moist weather conditions. Conidia were cylindrical to oval, allantoid, hyaline, pale yellow to brown, usually one-celled, and 2 to 3 × 5 to 10 μm. To satisfy Koch's postulates, a conidial suspension (1 × 106 conidia per ml) of the fungus was sprayed onto leaves and stems of bean seedlings (first-leaf stage) (cv. Zargana Hrisoupolis). Both inoculated and control seedlings (inoculated with sterile water) were covered with plastic bags for 72 h in a greenhouse at 23°C. Inoculated plants showed characteristic symptoms of Ascochyta leaf spot 12 to 15 days after inoculation. The fungus was reisolated from lesions that developed on the leaves and stems of all inoculated plants. The pathogen is present worldwide on bean. To our knowledge, this is the first report of P. exigua var. exigua on common bean in Greece. References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. ARS, USDA, 2007. (2) B. C. Sutton and J. M. Waterstone. Ascochyta phaseolorum. No. 81 in: Descriptions of Pathogenic Fungi and Bacteria. CMI/AAB, Kew, Surrey, England, 1966.

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First Report of Diaporthe phaseolorum on Sunflower (Helianthus annuus) in Croatia

Plant Disease ◽

10.1094/pdis-93-10-1074c ◽

2009 ◽

Vol 93 (10) ◽

pp. 1074-1074 ◽

Cited By ~ 2

Author(s):

K. Vrandecic ◽

J. Cosic ◽

D. Jurkovic ◽

T. Duvnjak ◽

L. Riccioni

Keyword(s):

New York ◽

Helianthus Annuus ◽

Morphological Characteristics ◽

Aerial Mycelium ◽

Petri Dish ◽

Aluminum Foil ◽

Pathogenic Fungi ◽

Fungal Species ◽

Universal Primers ◽

First Report

Sunflower (Helianthus annuus L.) is a crop that is grown worldwide for the production of edible oil. In Croatia, it has considerable economic significance. From 2004 to 2007, sunflower stems showed light-to-dark brown lesions of different sizes and shapes. The lesions were observed for the presence of pycnidia in affected areas. Isolations from infected tissue on potato dextrose agar (PDA) yielded in two fungal species. One, which was isolated in most cases, was the well known sunflower pathogen Diaporthe helianthi Munt. Cvet. Morphological characteristics, stromata pattern, formation of alpha and beta conidia, and ascostromata characteristic of the other isolated fungus matched the description of D. phaseolorum (Cooke & Ellis) Sacc. (2). D. phaseolorum frequency was 5%. On PDA, the fungus formed white, floccose, aerial mycelium that filled a petri dish (9 cm) in 6 days. D. phaseolorum produces conidiomata in black stromatic structures, which consist of pycnidia with alpha and beta conidia. The alpha conidia were unicellular, hyaline, ellipsoidal to fusiform, and 5.6 to 10.0 × 1.9 to 4.8 μm. The beta conidia were hyaline, elongated, filiform, straight, curved at one or both ends, and 11.7 to 27.6 × 0.7 to 2.0 μm. After 50 days, perithecia were formed. Asci were clavate and 27.64 to 40.1 × 5.70 to 8.2 μm. Eight ascospores formed within asci. Ascospores were two-celled, elliptic, hyaline, and slightly constricted at the septa, and 8.93 to 13.5 × 2.1 to 4.0 μm. Amplification and sequencing of the internal transcribed spacer (ITS) rDNA region were performed with ITS4 and ITS5 universal primers (3) on two isolates (Su9 and Su10) and data were deposited in GenBank (Accession Nos. GQ149763 and GQ149764). Comparison of sequences available in GenBank revealed that the ITS sequence was identical to D. phaseolorum found on Stokesia laevis Hill (Greene) (U11323/U11373) and identical to the strain CBS 116020 isolated from Aster exilis Elliot. (AY745018). On the basis of the obtained results of morphological characteristics and molecular approaches, the pathogen was identified as D. phaseolorum. Pathogenicity evaluation consisted of artificial infections on field-grown sunflower plants at the full button stage as described by Bertrand and Tourvielle (1). A leaf test was done by placing a mycelial plug of 5 × 5 mm from a cork borer of two isolates (Su9 and Su10) on the tip of the main vein. The inoculation site was covered with moistened, cotton wool and wrapped in aluminum foil to prevent the inoculum from drying out. Ten plants of each of the four replications were inoculated. Control plants were inoculated with pure PDA plugs. Lesions of 12 to 40 mm long were observed on the sunflower leaf 10 days after inoculation. Control plants did not develop symptoms. The pathogen was reisolated from the infected plants. To our knowledge, this is the first report of the finding of D. phaseolorum on sunflower in Croatia and we have no literature data about the occurrence of this fungus on sunflower in the world. References: (1) F. Bertrand and D. Tourvielle. Inf. Tech. CETIOM 98:12,1972. (2) E. Punithalingma and P. Holliday. No. 336 in: Descriptions of Pathogenic Fungi and Bacteria. CMI/CAB, Kew, Surrey, England, 1972. (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, Inc., New York, 1990.

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First Report of Peronospora sp. Causing Downy Mildew Disease on Geum sp. in Maryland and New York

Plant Disease ◽

10.1094/pdis-09-17-1503-pdn ◽

2018 ◽

Vol 102 (7) ◽

pp. 1463 ◽

Cited By ~ 1

Author(s):

E. C. Wallace ◽

M. L. Daughtrey ◽

K. A. Rane ◽

C. Salgado-Salazar ◽

J. A. Crouch

Keyword(s):

New York ◽

Downy Mildew ◽

First Report ◽

Downy Mildew Disease

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First Report of Impatiens Downy Mildew Caused by Plasmopara obducens in Ohio

Plant Disease ◽

10.1094/pdis-06-12-0545-pdn ◽

2012 ◽

Vol 96 (11) ◽

pp. 1699-1699 ◽

Cited By ~ 5

Author(s):

F. Baysal-Gurel ◽

N. J. Taylor ◽

J. Chatfield ◽

S. A. Miller

Keyword(s):

Downy Mildew ◽

Ribosomal Subunit ◽

Lower Surface ◽

Economic Losses ◽

First Report ◽

Purification System ◽

Total Dna ◽

Impatiens Walleriana ◽

The Uk ◽

Disease Free

Single and double flowered impatiens (Impatiens walleriana Hook.f.) plants with symptoms of downy mildew were found in commercial greenhouses in Delaware, Wayne, and Holmes counties, Ohio, in April 2012. Plants were stunted and defoliated. Symptoms on remaining leaves included general chlorosis without discrete spots and downward curling of leaves. A downy white growth was observed on the lower surface of infected leaves. The disease was widespread in affected greenhouses and incidence in cvs. Shimmer Coral, Accent Mix, and Super Elfin was nearly 90%. The downy growth consisted of coenocytic mycelia, monopodial sporangiophores, and ovoid, hyaline sporangia typical of Plasmopara obducens (J. Schröt.) J. Schröt in Cohn (1,2,4). Sporangia were borne on branchlets measuring 5 to 15 μm long (average 10 μm) at right angles to the main axis of the sporangiophore. Sporangia were 9.4 to 17.5 × 12.8 to 16.3 μm. No oospores were observed. Total DNA was extracted directly from plant tissue with the Wizard SV Genomic DNA Purification System (Promega, Madison, WI) following the manufacturer's instructions. Large ribosomal subunit DNA was amplified by PCR using primers NL-1 and NL-4 (3). Amplicons of 690 bp and 834 bp were produced from each diseased sample, while only the 690-bp amplicon was produced from healthy tissue. DNA from each amplicon of sample IDM041712 was purified using the Wizard SV Gel and PCR Clean-Up System (Promega), sequenced, and the sequence of the diagnostic 834-bp amplicon was deposited in GenBank (JX142134). The sequence of the 834-bp amplicon was 99% similar to those of P. obducens isolates from Serbia (HQ246451) (1), the UK (AY587558), and Austria (EF196869). The sequence of the 690-bp amplicon (JX142135) was 99% similar to that of I. walleriana (HQ223336). Twelve young impatiens ‘Shimmer Coral’ plants were inoculated with sporangia washed from infected leaves (1 × 104 sporangia/ml). Plants were incubated at room temperature for 24 h in a moist chamber and then maintained in a greenhouse (21 to 23°C) until symptoms appeared. Control plants were sprayed with sterile water and maintained in the same environment. After 12 to 14 days, typical symptoms of downy mildew developed on the inoculated plants and microscopic examination revealed the same pathogen morphology as the original isolate. All non-inoculated control plants remained disease free. To our knowledge, this is the first report of downy mildew on impatiens in Ohio. This disease caused considerable economic losses in Ohio in 2012 and is likely to be a recurring problem requiring intensive preventative management. References: (1) A. Bulajic et al. Plant Dis. 95:491, 2011. (2) O. Constantinescu. Mycologia 83:473, 1991. (3) W. Maier et al. Can. J. Bot. 81:12, 2003. (4) S. N. Wegulo et al. Plant Dis. 88:909, 2004.

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First Report of Peronospora parasitica on Wild Rocket (Diplotaxis tenuifolia) in Italy

Plant Disease ◽

10.1094/pdis.2004.88.12.1381c ◽

2004 ◽

Vol 88 (12) ◽

pp. 1381-1381 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

New York ◽

Downy Mildew ◽

Causal Agent ◽

Pathogenicity Test ◽

Conidial Suspension ◽

Peronospora Parasitica ◽

First Report ◽

Downy Mildews ◽

Air Temperatures ◽

Wild Rocket

Several species of Diplotaxis (D. tenuifolia, D. erucoides, and D. muralis), known as wild rocket, are now widely cultivated in Italy. Wild rocket is used in Mediterranean cuisine as salad, a component of packaged salad products, and as a garnish for food. During the fall of 2002, a foliar disease of D. tenuifolia was observed in the field or greenhouse on several commercial farms in the Liguria Region of northern Italy. Symptoms appeared as small, irregular, dark brown-to-black speckling on the adaxial surfaces of leaves. The speckled areas sometimes expanded into larger spots. These symptoms were followed by leaf yellowing and the appearance of sporangiophores and sporangia on the lower and upper leaf surfaces. Sporangiophores were dichotomously branched with slender curved tips. Sporangia were ovoid, measuring 20 to 28 (average 22) μm long and 15 to 25 (average 19) μm wide. The causal agent of the disease was identified as Peronospora parasitica (3). Pathogenicity was established by inoculating 10 30-day-old plants of D. tenuifolia grown in pots in a peat/pumice/clay/composted bark mix (60:20:10:10), with a conidial suspension (102 conidia per ml). Ten noninoculated plants maintained under the same conditions served as the control. Plants were maintained in a glasshouse at air temperatures ranging between 10 and 26°C (average 16°C) and relative humidity at 85%. The pathogenicity test was done twice. Downy mildew symptoms developed within 12 days, and the same fungus was observed on inoculated plants. Noninoculated plants did not develop symptoms. To our knowledge, this is the first report of P. parasitica on D. tenuifolia in Italy. P. parasitca has been reported as the causal agent of downy mildew on D. muralis in England (1) and on cultivated rocket (Eruca sativa) in California (2). References: (1) J. Fraymouth. Trans. Br. Mycol. Soc. 39:79, 1956. (2) S. T. Koike. Plant Dis. 82:1063, 1998. (3) D. M. Spencer. The Downy Mildews. Academic Press. New York, 1981.

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