scholarly journals First Report of Dieback and Leaf Lesions on Rhododendron sp. Caused by Phytophthora hedraiandra in the United States

Plant Disease ◽  
2006 ◽  
Vol 90 (1) ◽  
pp. 109-109 ◽  
Author(s):  
B. W. Schwingle ◽  
J. A. Smith ◽  
R. A. Blanchette ◽  
S. Gould ◽  
B. L. Blanchette ◽  
...  
Keyword(s):  
United States ◽  
Average Length ◽  
The United States ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Width Ratio ◽  
Its Sequence ◽  
Voucher Specimen ◽  
First Report ◽  
Quercus Species

Surveys for Phytophthora ramorum in Minnesota nurseries revealed the presence of P. hedraiandra de Cock & Man in't Veld and several other Phytophthora species but not P. ramorum. Symptomatic leaf and stem tissues from diseased Rhododendron and Quercus species were cultured on PARP, a selective growth medium for Phytophthora (3). The Phytophthora isolates obtained were later identified by sequencing the internal transcribed spacer (ITS) region of the rDNA and comparing the sequences with those in GenBank using BLAST searches (1). The ITS sequences of six cultures (GenBank Accession Nos. DQ139804-DQ139809), isolated during 2003 from various Rhododendron cultivars exhibiting leaf lesions and shoot dieback, showed 100% identity with the ITS sequence of P. hedraiandra (GenBank Accession No. AY707987) (2). This is a recently described pathogenic species from the Netherlands responsible for causing leaf spots on Viburnum spp. Since the ITS sequence of P. hedraiandra differs little from that of P. cactorum (2), we verified one isolate to be P. hedraiandra by sequencing the mitochondrial cytochrome c oxidase subunit I gene (cox1) (GenBank Accession No. DQ139810). Comparison of this sequence with the P. hedraiandra voucher specimen in GenBank (Accession No. AY769115) showed 99% identity, which was the closest match. Reproductive structures were measured on V8 juice agar. The average oogonium diameter for three isolates was 29 μm with a range of 26 to 32 μm, while the average antheridium length was 13 μm (11 to 15 μm). Sporangium length and width averages on crushed hemp seeds were 32 μm (28 to 36 μm) and 26 μm (21 to 30 μm), respectively, with the average length to width ratio of 1.25 (1.23 to 1.29). Pathogenicity tests on Rhododendron cv. Mikkeli were carried out using three of our P. hedraiandra isolates. Spore suspensions of 2 × 104 zoospores per ml were used to mist-spray shoots of five, 3-year-old plants for each isolate. Five controls were mist sprayed with water. After inoculation, plants were placed in plastic bags in a dark growth chamber (22°C) for 7 days and then moved to a greenhouse. Leaf blotches and shoot dieback were apparent 5 days after inoculation, and P. hedraiandra was reisolated from those symptomatic tissues and identified by an exact match of the ITS sequence. Necrotic areas lengthened from the shoot tips to the main stems of the plants while expanding into petioles and leaves. No symptoms were observed on control plants. To our knowledge, this is the first report of P. hedraiandra in the United States as well as the first report of Koch's postulates performed with P. hedraiandra on Rhododendron cv. Mikkeli. The significance of this disease to other woody plants in nurseries or the landscape is unknown, and further study is needed to determine the host range and extent of the disease that may occur from this introduction. References: (1) S. F. Altschul et al. J. Mol. Biol. 215:403, 1990. (2) A. W. A.M de Cock and C. A. Lévesque. Stud Mycol 50:481, 2004. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

scholarly journals First Report of Phytophthora hydropathica Causing Wilting and Shoot Dieback on Viburnum in Italy

Plant Disease ◽  
2014 ◽  
Vol 98 (11) ◽  
pp. 1582-1582 ◽  
Author(s):  
S. Vitale ◽  
L. Luongo ◽  
M. Galli ◽  
A. Belisario
Keyword(s):  
Natural Infection ◽  
Morphological Characteristics ◽  
Leaf Tissue ◽  
The United States ◽  
Selective Medium ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Width Ratio ◽  
Morphological Identification ◽  
First Report

The genus Viburnum comprises over 150 species of shrubs and small trees such as Laurustinus (Viburnum tinus L.), which is one of the most widely used ornamental plants in private and public gardens. Furthermore, it commonly forms stands of natural woodland in the Mediterranean area. In autumn 2012, a survey was conducted to determine the presence of Phytophthora ramorum on Viburnum in commercial nurseries in the Latium region where wilting, dieback, and death of twigs were observed on 30% of the Laurustinus plants. A Phytophthora species was consistently recovered from soil rich in feeder roots from potted Laurustinus plants showing symptoms. Soil samples were baited with rhododendron leaves. Small pieces of leaf tissue cut from the margin of lesions were plated on P5ARPH selective medium (4). Pure cultures, obtained by single-hypha transfers on potato dextrose agar (PDA), were petaloid. Sporangia formation was induced on pepper seeds (3). Sporangia were almost spherical, ovoid or obpyriform, non-papillate and non-caducous, measuring 36.6 to 71.4 × 33.4 to 48.3 μm (average 53.3 × 37.4 μm) with a length/width ratio of 1.4. Chlamydospores were terminal and 25.2 to 37.9 μm in diameter. Isolates were considered heterothallic because they did not produce gametangia in culture or on the host. All isolates examined had 30 to 35°C as optimum temperatures. Based on these morphological characteristics, the isolates were identified as Phytophthora hydropathica (2). Morphological identification was confirmed by internal transcribed spacer (ITS), and mitochondrial partial cytochrome oxidase subunit 2 (CoxII) with BLAST analysis in the NCBI database revealing 99% identity with ITS and 100% identity with CoxII. The sequences of the three isolates AB234, AB235, and AB236 were deposited in European Nucleotide Archive (ENA) with the accession nos. HG934148, HG934149, and HG934150 for ITS and HG934151, HG934152, and HG934153 for CoxII, respectively. Pathogenicity tests were conducted in the greenhouse on a total of six 1-year-old shoots cut from V. tinus plants with two inoculation points each. Mycelial plugs cut from the margins of actively growing 8-day-old cultures on PDA were inserted through the epidermis into the phloem. Controls were treated as described above except that sterile PDA plugs replaced the inoculum. Shoots were incubated in test tubes with sterile water in the dark at 24 ± 2°C. After 2 weeks, lesions were evident at the inoculation points and symptoms were similar to those caused by natural infection. P. hydropathica was consistently re-isolated from the margin of lesions, while controls remained symptomless. In the United States in 2008, P. hydropathica was described as spreading from irrigation water to Rhododendron catawbiense and Kalmia latifolia (2). This pathogen can also attack several other horticultural crops (1), but to our knowledge, this is the first report of P. hydropathica causing wilting and shoot dieback on V. tinus. References: (1) C. X. Hong et al. Plant Dis. 92:1201, 2008. (2) C. X. Hong et al. Plant Pathol. 59:913, 2010. (3) E. Ilieva et al. Eur. J. Plant Path. 101:623, 1995. (4) S. N. Jeffers and S. B. Martin. Plant Dis. 70:1038, 1986.

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

Plant Disease ◽  
2014 ◽  
Vol 98 (5) ◽  
pp. 696-696 ◽  
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.

scholarly journals First Report of Stem Canker of Salsola tragus Caused by Diaporthe eres in Russia

Plant Disease ◽  
2009 ◽  
Vol 93 (1) ◽  
pp. 110-110 ◽  
Author(s):  
T. Kolomiets ◽  
Z. Mukhina ◽  
T. Matveeva ◽  
D. Bogomaz ◽  
D. K. Berner ◽  
...  
Keyword(s):  
United States ◽  
Biological Control ◽  
Biological Control Agent ◽  
Aqueous Suspension ◽  
Stem Canker ◽  
The United States ◽  
Invasive Weed ◽  
Voucher Specimen ◽  
First Report ◽  
Stem Lesions

Salsola tragus L. (Russian thistle) is a problematic invasive weed in the western United States and a target of biological control efforts. In September of 2007, dying S. tragus plants were found along the Azov Sea at Chushka, Russia. Dying plants had irregular, necrotic, canker-like lesions near the base of the stems and most stems showed girdling and cracking. Stem lesions were dark brown and contained brown pycnidia within and extending along lesion-free sections of the stems and basal portions of leaves. Diseased stems were cut into 3- to 5-mm pieces and disinfested in 70% ethyl alcohol. After drying, stem pieces were placed into petri dishes on the surface of potato glucose agar. Numerous, dark, immersed erumpent pycnidia with a single ostiole were observed in all lesions after 2 to 3 days. Axenic cultures were sent to the Foreign Disease-Weed Science Research Unit, USDA, ARS, Ft. Detrick, MD for testing in quarantine. Conidiophores were simple, cylindrical, and 5 to 25 × 2 μm (mean 12 × 2 μm). Alpha conidia were biguttulate, one-celled, hyaline, nonseptate, ovoid, and 6.3 to 11.5 × 1.3 to 2.9 μm (mean 8.8 × 2.0 μm). Beta conidia were one-celled, filiform, hamate, hyaline, and 11.1 to 24.9 × 0.3 to 2.5 μm (mean 17.7 × 1.2 μm). The isolate was morphologically identified as a species of Phomopsis, the conidial state of Diaporthe (1). The teleomorph was not observed. A comparison with available sequences in GenBank using BLAST found 528 of 529 identities with the internal transcribed spacer (ITS) sequence of an authentic and vouchered Diaporthe eres Nitschke (GenBank DQ491514; BPI 748435; CBS 109767). Morphology is consistent with that of Phomopsis oblonga (Desm.) Traverso, the anamorph of D. eres (2). Healthy stems and leaves of 10 30-day-old plants of S. tragus were spray inoculated with an aqueous suspension of conidia (1.0 × 106 alpha conidia/ml plus 0.1% v/v polysorbate 20) harvested from 14-day-old cultures grown on 20% V8 juice agar. Another 10 control plants were sprayed with water and surfactant without conidia. Plants were placed in an environmental chamber at 100% humidity (rh) for 16 h with no lighting at 25°C. After approximately 24 h, plants were transferred to a greenhouse at 20 to 25°C, 30 to 50% rh, and natural light. Stem lesions developed on three inoculated plants after 14 days and another three plants after 21 days. After 70 days, all inoculated plants were diseased, four were dead, and three had more than 75% diseased tissue. No symptoms occurred on control plants. The Phomopsis state was recovered from all diseased plants. This isolate of D. eres is a potential biological control agent of S. tragus in the United States. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878717). Nucleotide sequences for the ribosomal ITS regions (ITS 1 and 2) were deposited in GenBank (Accession No. EU805539). To our knowledge, this is the first report of stem canker on S. tragus caused by D. eres. References: (1) B. C. Sutton. Page 569 in: The Coelomycetes. CMI, Kew, Surrey, UK, 1980. (2) L. E. Wehmeyer. The Genus Diaporthe Nitschke and its Segregates. University of Michigan Press, Ann Arbor, 1933.

scholarly journals First Report of Leaf Spot Caused by a Cercosporella sp. on Centaurea solstitialis in Greece

Plant Disease ◽  
2004 ◽  
Vol 88 (12) ◽  
pp. 1382-1382 ◽  
Author(s):  
F. M. Eskandari ◽  
D. K. Berner ◽  
J. Kashefi ◽  
L. Strieth
Keyword(s):  
United States ◽  
Biological Control ◽  
Biological Control Agent ◽  
Aqueous Suspension ◽  
The United States ◽  
Centaurea Solstitialis ◽  
Voucher Specimen ◽  
Disease Symptoms ◽  
First Report ◽  
Leaf Spots

Centaurea solstitialis L. (yellow starthistle [YST]), family Asteraceae, an invasive weed in California and the western United States is targeted for biological control. During the spring of 2004, an epidemic of dying YST plants was found near Kozani, Greece (40°22′07″N, 21°52′35″E, 634 m elevation). Rosettes of YST had small, brown leaf spots on most of the lower leaves. In many cases, these spots coalesced and resulted in necrosis of many of the leaves and death of the rosette. Along the roadside where the disease was found, >100 of the YST plants showed disease symptoms. Diseased plants were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA, ARS, Fort Detrick, MD. Diseased leaves were surface disinfested and placed on moist filter paper in petri dishes. Conidiophores and conidia were observed after 48 h. The fungal isolate, DB04-011, was isolated from these diseased leaves. Pathogenicity tests were performed by spray inoculating the foliage of 20 4-week-old YST rosettes with an aqueous suspension of 1 × 106 conidia per ml. Conidia were harvested from 2-week-old cultures grown on modified potato carrot agar (MPCA). Inoculated plants were placed in an environmental chamber at 23°C with 8 h of daily light and continuous dew for 48 h. Inoculated and control plants were moved to a 20°C greenhouse bench and watered twice per day. After 7 days, leaf spots were observed first on lower leaves. After 10–12 days, all inoculated plants showed typical symptoms of the disease. No symptoms developed on control plants. The pathogen, DB04-011, was consistently isolated from symptomatic leaves of all inoculated plants. Disease symptoms were scattered, amphigenous leaf spots in circular to subcircular spots that were 0.2 to 7 mm in diameter and brownish with distinct dark green margins. Intraepidermal stromata, 14 to 77 μm in diameter and pale yellow to brown, were formed within the spots. Conidiophores that arose from the stromata were straight, subcylindrical, simple, 70 to 95 × 2.8 to 4 μm, hyaline, smooth, and continuous or septate with conidial scars that were somewhat thickened, colorless, and refractive. Primary conidia were subcylindrical, slightly obclavate or fusiform, ovoid, 21 to 49 × 5 to 7.5 μm, 0 to 5 septate, hyaline, smooth, had a relatively rounded apex, and the hilum was slightly thickened. Conidial dimensions on MPCA were 11.2 to 39.2 × 4.2 to 7 μm (average 25.5 × 5.5 μm). Koch's postulates were repeated two more times with 20 and 16 plants. On the basis of fungal morphology, the organism was identified as a Cercosporella sp., (1,2; U. Braun and N. Ale-Agha, personal communication). To our knowledge, this is the first report of this genus of fungus parasitizing YST. Results of host range tests will establish if this isolate of Cercosporella has potential as a biological control agent of YST in the United States. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 844247). Live cultures are being maintained at FDWSRU and European Biological Control Laboratoryt (EBCL), Greece. References: (1) U. Braun. A Monograph of Cercosporella, Ramularia and Allied Genera (Phytopathogenic Hyphomycetes) Vol. 1. IHW-Verlage, Eching-by-Munich, 1995. (2) U. Braun. A Monograph of Cercosporella, Ramularia and Allied Genera (Phytopathogenic Hyphomycetes) Vol. 2. IHW-Verlage, 1998.

scholarly journals First Report of Leaf Spot Caused by Cercospora bizzozeriana on Lepidium draba in the United States

Plant Disease ◽  
2009 ◽  
Vol 93 (1) ◽  
pp. 108-108 ◽  
Author(s):  
A. J. Caesar ◽  
R. T. Lartey ◽  
D. K. Berner ◽  
T. Souissi
Keyword(s):  
United States ◽  
North America ◽  
Sugar Beet ◽  
Leaf Spot ◽  
The United States ◽  
Initial Report ◽  
Voucher Specimen ◽  
First Report ◽  
Leaf Spots ◽  
Lepidium Draba

The herbaceous perennial Lepidium draba L. is an invasive weed of rangelands and riparian areas in North America and Australia. As of 2002, it had infested 40,500 ha of rangeland in Oregon and large areas in Wyoming and Utah. Little is known of plant pathogens occurring on L. draba, especially in the United States, that could be useful for biological control of the weed. Leaf spots were first noted on a stand of L. draba near Shepherd, MT in 1997. The spots were mostly circular but sometimes irregularly shaped and whitish to pale yellow. The pathogen was erroneously assumed to be Cercospora beticola since its morphological traits closely resembled that species and the area had large fields of sugar beet with heavy Cercospora leaf spot incidence. Diseased leaves of L. draba were collected in 1997 and 2007. Conidia, borne singly on dark gray, unbranched conidiophores produced on dark stromata late in the season, were elongate, hyaline, multiseptate, 38 to 120 × 2 to 6 μm (mostly 38 to 50 × 2 to 5 μm) and had bluntly rounded tips and wider, truncate bases. These characteristics were consistent with the description of C. bizzozeriana Saccardo & Berlese (2). To isolate the fungus, spores were picked from fascicles of conidiophores with a fine-tipped glass rod, suspended in sterile water, and spread on plates of water agar. Germinated spores were transferred to potato dextrose agar (PDA). The ITS1, 5.8S, and ITS2 sequences of this fungus (GenBank Accession No. EU887131) were identical to sequences of an isolate of C. bizzozeriana from Tunisia (GenBank Accession No. DQ370428). However, these sequences were also identical to those of a number of Cercospora spp. in GenBank, including C. beticola. We also compared the actin gene sequences of the Montana isolate of C. bizzozeriana (GenBank Accession No. FJ205397) and an isolate of C. beticola from Montana (GenBank Accession No. AF443281); the sequences were 94.6% similar, an appreciable difference. For pathogenicity tests, cultures were grown on carrot leaf decoction agar. Aqueous suspensions of 104 spores per ml from cultures were sprayed on 6-week-old L. draba plants. Plants were covered with plastic bags and placed on the greenhouse bench at 20 to 25°C for 96 h. Koch's postulates were completed by reisolating the fungus from the circular leaf spots that appeared within 10 days, usually on lower leaves. Spores of C. bizzozeriana were also sprayed on seedlings of sugar beet, collard, mustard, radish, cabbage, and kale under conditions identical to those above. No symptoms occurred. After the discovery of the disease in 1997, plants of L. draba in eastern Montana, Wyoming, and Utah were surveyed from 1998 to 2003 for similar symptoms and signs, but none were found. This, to our knowledge, is the first report of C. bizzozeriana in the United States. The initial report of the fungus in North America was from Manitoba in 1938 (1). It has recently been reported as occurring on L. draba in Tunisia (4) and Russia (3) and is reported as common in Europe (2). A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI No. 878750A). References: (1) G. R. Bisby. The Fungi of Manitoba and Saskatchewan. Natl. Res. Council of Canada, Ottawa, 1938. (2) C. Chupp. A Monograph of the Fungus Genus Cercospora. C. Chupp, Ithaca, NY, 1953. (3) Z. Mukhina et al. Plant Dis. 92:316, 2008. (4) T. Souissi et al. Plant Dis. 89:206, 2005.

scholarly journals First Report of a Leaf Spot Caused by Cercospora bizzozeriana on Lepidium draba subsp. draba in Tunisia

Plant Disease ◽  
2005 ◽  
Vol 89 (2) ◽  
pp. 206-206
Author(s):  
T. Souissi ◽  
D. K. Berner ◽  
H. J. Dubin
Keyword(s):  
United States ◽  
Biological Control ◽  
Biological Control Agent ◽  
Aqueous Suspension ◽  
The United States ◽  
Voucher Specimen ◽  
First Report ◽  
Leaf Spots ◽  
White Leaf ◽  
Lepidium Draba

Lepidium draba (L.) subsp. draba (synonym = Cardaria draba (L.) Desv.), commonly known as white-top or hoary-cress (1), family Brassicaceae, is a common weed and emerging problem in wheat in Tunisia. It is also a problematic invasive weed in the northwestern United States and a target of biological control efforts. During the summer of 2002, dying L. draba plants were found around Tunis, Tunisia. Plants had grayish white leaf spots on most of the leaves. In some cases, the leaf spots dropped out of the leaves producing “shot-holes”. In most cases, the leaf spots coalesced, and the leaves wilted and died. Diseased leaves were collected, air-dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. The air-dried leaves were observed microscopically, and numerous conidiophores and conidia were observed on both sides of the leaves within and around the lesions. The fungus isolated (DB03-009) conformed to the description of Cercospora bizzozeriana Saccardo & Berlese (2). Conidiophores were unbranched, pale olive-brown, 1 to 5 geniculate, and uniform in color and width. Conidia were hyaline, straight to slightly curved, multiseptate, and 57 to 171 × 3.8 to 6.7 µm (average 103 to 4.6 µm). Stems and leaves of 12 rosettes (10 to 15 cm in diameter) of 6-week-old L. draba plants were spray inoculated with an aqueous suspension of conidia (1 × 105/ml) harvested from 6- to 8-day-old cultures grown on carrot leaf decoction agar. Six of the plants and two noninoculated plants were placed in a dew chamber at 22°C in darkness and continuous dew. The other half of the plants and two noninoculated plants were placed on a greenhouse bench at approximately 25°C and covered with clear polyethylene bags. After 72 h, plants from the dew chamber were moved to a greenhouse bench, and the bagged plants were uncovered. All plants were watered twice daily. After 9 days, symptoms were observed on the plants that had been bagged but not on the plants from the dew chamber. Symptoms were identical to those observed in the field in Tunisia and included “shot holes”. No symptoms were observed on noninoculated plants. C. bizzozeriana was reisolated from the leaves of all symptomatic plants. Completion of Koch's postulates was repeated with an additional five plants. This isolate of C. bizzozeriana is a destructive pathogen on L. draba subsp. draba, and severe disease can be produced by inoculation of foliage with an aqueous suspension of conidia. This isolate is a good candidate for mycoherbicide development in Tunisia where the weed and pathogen are indigenous. However, some commercially grown Brassica species were found susceptible to this isolate, which will preclude its use as a classical biological control agent in the United States. To our knowledge, this is the first report of C. bizzozeriana on L. draba subsp. draba in Tunisia. A voucher specimen has been deposited at the U.S. National Fungus Collections (BPI 843753). Live cultures are being maintained at FDWSRU and the Institut National Agronomique de Tunisie, Tunis, Tunisia. References: (1) I. A. Al-Shehbaz and K. Mummenhoff. Novon 12:5, 2002. (2) C. Chupp. A Monograph of the Fungus Genus Cercospora. C. Chupp, Ithaca, New York, 1953.

scholarly journals First Report of Erysiphe quercicola Causing Powdery Mildew on Ubame Oak in Korea

Plant Disease ◽  
2011 ◽  
Vol 95 (1) ◽  
pp. 77-77 ◽  
Author(s):  
H. B. Lee ◽  
C. J. Kim ◽  
H. Y. Mun ◽  
K. -H. Lee
Keyword(s):  
Powdery Mildew ◽  
Sequence Data ◽  
Width Ratio ◽  
Microbiology Laboratory ◽  
Voucher Specimen ◽  
First Report ◽  
Erysiphe Quercicola ◽  
Powdery Mildews ◽  
Quercus Species ◽  
National University

Ubame oak (Quercus phillyraeoides A. Gray) is native to eastern Asia, including China, Korea, and Japan. In 2009 and 2010, a powdery mildew on Q. phillyraeoides growing in clusters and singly was observed in three locations on the campus of Chonnam National University, Gwangju, Korea. White superficial conidia of the powdery mildew fungus occurred on adaxial and abaxial surfaces. However, the white powdery growth was more abundant on the adaxial surface. Leaf symptoms commonly appeared white from May to October. Along with the typical white powdery mildew, spot and/or necrotic symptoms with irregular violet-to-wine red surfaces were also frequently observed on overwintered leaves. A voucher specimen has been deposited in EML (Environmental Microbiology Laboratory) herbarium collection, Chonnam National University (EML-QUP1). Conidia were commonly formed singly but also occurred in chains. Primary conidia were obovoid to ellipsoid, with a rounded apex and subtruncate base. Secondary conidia were generally obovoid to ellipsoid or sometimes cylindrical but dolioform when mature. The size was 30.1 to 43.2 (average 37.7) × 14.1 to 21.1 (average 18.1) μm with length/width ratio of 1.8 to 2.4 (average 2.1). Conidiophores were erect and up to 102.2 μm long. No chasmothecia were found. From extracted genomic DNA, the internal transcribed spacer (ITS) region inclusive of 5.8S rDNA was amplified with ITS1F (5′-CTTGGT CATTTAGAGGAAGT-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′) primers (4). Sequence analysis by BLASTN search indicated that EML-QUP1 (GenBank Accession No. HQ328834) was closest to E. quercicola (GenBank Accession No. AB292691) with >99% identity (478 of 480), forming a monophyletic quercicola clade in the resulting phylogenetic analysis. The causal fungus was determined to be Erysiphe quercicola on the basis of morphology and sequence data analysis. Major genera including Cystotheca, Erysiphe, Microsphaera, and Phyllactinia have been reported to cause powdery mildews on Quercus plants. Until now, 22 Erysiphe species including E. abbreviata, E. alphitoides, E. calocladophora, E. gracilis, E. polygoni, and E. quercicola have been reported to cause powdery mildews on Quercus spp. (1). Of these, four Erysiphe species including E. alphitoides, E. gracilis, E. quercicola, and an unidentified Erysiphe sp. have been found on Q. phillyraeoides from Japan (1–3). E. quercicola was reported to occur on five Quercus species: Q. crispula, Q. phillyraeoides, and Q. serrata in Japan, Q. robur in Australia, and Quercus sp. in Australia, Iran, and Thailand (1). To our knowledge, this is the first report of leaf powdery mildew caused by E. quercicola on Q. phillyraeoides in Korea. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved October 7, 2010, from http://nt.ars-grin.gov/fungaldatabases/ , 2010. (2) S. Limkaisang et al. Mycoscience 47:327, 2006. (3) S. Takamatsu et al. Mycol. Res. 111:809, 2007. (4) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

scholarly journals First Report of Powdery Mildew Caused by Podosphaera (Sphaerotheca) fusca on Euryops pectinatus in North America

Plant Disease ◽  
2000 ◽  
Vol 84 (9) ◽  
pp. 1048-1048 ◽  
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.

scholarly journals First Report of Leaf Spot Caused by Cladosporium herbarum on Centaurea solstitialis in Greece

Plant Disease ◽  
2007 ◽  
Vol 91 (4) ◽  
pp. 463-463 ◽  
Author(s):  
D. K. Berner ◽  
E. L. Smallwood ◽  
M. B. McMahon ◽  
D. G. Luster ◽  
J. Kashefi
Keyword(s):  
United States ◽  
Biological Control ◽  
The United States ◽  
Centaurea Solstitialis ◽  
Unknown Etiology ◽  
Malt Extract ◽  
Causal Organism ◽  
Voucher Specimen ◽  
First Report ◽  
Cladosporium Herbarum

Centaurea solstitialis L. (yellow starthistle), family Asteraceae, an invasive weed in California and the western United States, is targeted for biological control. In the summer of 2003, an epidemic of unknown etiology on dying C. solstitialis plants was observed near Kozani, Greece (40°22′07″N, 21°52′35″E, elevation, 634 m). Plants had necrotic light brown leaf spots on the lower leaves and the decurrent leaf bases along the stems. Often, necrotic lesions extended along the stems to the capitula. Virtually all plants in a solid stand of C. solstitialis (approximately 0.5 ha) showed disease symptoms. Diseased plants were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. On the basis of culture growth (45-cm diameter after 2 weeks at 25°C on malt extract agar), fungal morphology (1), and comparison with 21 internal transcribed spacer sequences in GenBank, the putative causal organism was identified as Cladosporium herbarum (Pers.:Fr.) Link. (teleomorph = Davidiella tassiana (De Not.) Crous & U. Braun). Sixteen C. solstitialis plants in the rosette stage and 16 plants in the bolted stage were inoculated with an aqueous suspension of spores (106 conidia ml-1) and placed in an environmentally controlled chamber at 25°C with 8 h of dew and 12 h of light daily. Plants in the rosette stage were resistant, but the fungus was very aggressive on bolted plants. Within 4 to 6 days of inoculation, necrosis developed on leaves and stems and then spread up the stems to the capitula, often resulting in plant death. The fungus also infected developing flowers. Cladosporium herbarum was reisolated from each of the 16 bolted C. solstitialis plants in two separate tests at the FDWSRU and from all bolted inoculated plants at the European Biological Control Laboratory (EBCL) in Greece. In the greenhouse at the EBCL, the pathogen readily spread to (and was isolated from) another 10 noninoculated C. solstitialis plants in close vicinity to the inoculated C. solstitialis plants. Results of host range tests will establish if this isolate of Cladosporium herbarum has the potential as a biological control agent of C. solstitialis in the United States and does not pose a threat to other Centaurea spp. used in horticulture. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 863446). Live cultures are being maintained at the FDWSRU and EBCL, Greece. To our knowledge, this is the first report of a disease caused by Cladosporium herbarum on C. solstitialis. Reference: (1) M. H. M. Ho et al. Mycotaxon 72:115, 1999.

scholarly journals First Record of Phytophthora nicotianae Causing Leaf Blight on Rhododendron in Greece

Plant Disease ◽  
2011 ◽  
Vol 95 (6) ◽  
pp. 777-777
Author(s):  
P. Tsopelas ◽  
E. J. Paplomatas ◽  
S. E. Tjamos ◽  
K. Elena
Keyword(s):  
United States ◽  
Its Region ◽  
Maximum Growth ◽  
First Record ◽  
The United States ◽  
Culture Collection ◽  
Phytophthora Species ◽  
Phytophthora Ramorum ◽  
Phytophthora Nicotianae ◽  
Potted Plants

Species of Rhododendron and resulting hybrids are very important hosts of the quarantine pathogen Phytophthora ramorum, since they play a major role in the spread of the pathogen in Europe. However, many other Phytophthora species infect these hosts, causing similar symptoms. Widmer (4) listed 17 Phytophthora species as foliar pathogens of rhododendron in the United States. A survey was conducted in Greece in October 2009, in which potted plants of Rhododendron spp. were inspected for symptoms of necrotic lesions on leaves and buds caused by P. ramorum. Symptomatic plants were observed in one of the nurseries inspected in the Triphylia Region in southwestern Peloponnese. Isolations from symptomatic leaves on PARBhy-V8 selective agar medium (1) yielded Phytophthora isolates. Colonies on V8 juice agar appeared white and cottony, with a radial growth of 4.2 to 4.6 mm per day at 28°C with a maximum growth temperature of 36°C. Sporangia were produced abundantly on the medium surface and in water; the sporangia were broadly ovoid and papillate and 35 to 50 × 25 to 35 μm. Chlamydospores, 25 to 40 μm in diameter, were observed in 2-week-old cultures, while no sexual structures were observed. Three of the isolates examined were identified as P. nicotianae B. de Haan on the basis of morphological and physiological features (3,4). Genomic DNA was extracted from pure cultures of an isolate and the internal transcribed spacer (ITS) region was amplified using the ITS4/5 primer pair. Sequence analyses by BLAST indicated that the isolates were most similar to P. nicotianae (GenBank Accession No. AJ 854295.1) with sequence identity values of 99%. One of the isolates was deposited in the culture collection of the University of Athens (ATHUM 6519). Detached wounded leaves of Rhododendron hybrid cv. Red Jack were inoculated with agar plugs. Necrotic lesions, similar to those observed in the nursery, appeared on the inoculated leaves after 7 days of incubation at 26°C, while no symptoms developed on control leaves inoculated with sterile agar plugs. The pathogen was consistently reisolated from infected leaves, but not from the controls. P. nicotianae, being a thermophilic species, is the most common Phytophthora species in Greece, reported on more than 30 plant species (2). This pathogen has been reported on Rhododendron spp. in the United States (3,4), but to our knowledge, there was no record of this pathogen on these hosts as yet in Europe and this is the first published report of the pathogen on Rhododendron in Greece. References: (1) A. Belisario et al. Plant Dis. 87:101, 2003. (2) K. Elena. Technical Bulletin No 13. Benaki Phytopathological Institute. Athens, Greece (in Greek), 1999. (3) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (4) T. L. Widmer. Online publication. doi: 10.1094/PHP-2010-0317-01-RS, Plant Health Progress, 2010.

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