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

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.

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

Plant Disease ◽

10.1094/pd-89-0206a ◽

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.

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

Plant Disease ◽

10.1094/pdis-93-1-0110b ◽

2009 ◽

Vol 93 (1) ◽

pp. 110-110 ◽

Cited By ~ 1

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.

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

Plant Disease ◽

10.1094/pdis-91-4-0463a ◽

2007 ◽

Vol 91 (4) ◽

pp. 463-463 ◽

Cited By ~ 4

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.

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First Report of an Ovary Smut of Italian Thistle Caused by a Microbotryum sp. in Greece

Plant Disease ◽

10.1094/pd-90-0681b ◽

2006 ◽

Vol 90 (5) ◽

pp. 681-681 ◽

Cited By ~ 2

Author(s):

D. K. Berner ◽

M. B. McMahon ◽

J. Kashefi ◽

E. Erbe

Keyword(s):

United States ◽

Biological Control ◽

Biological Control Agent ◽

Science Research ◽

The United States ◽

Internal Transcribed Spacers ◽

Smut Fungi ◽

Invasive Weed ◽

Voucher Specimen ◽

First Report

Italian thistle (Carduus pycnocephalus L.), family Asteraceae, is a common weed in Greece. It is also a problematic invasive weed in the western United States and a target of biological control efforts. In May 2005, smutted capitula of Italian thistle were found in an abandoned field in Halkiades, Greece. A total of 38 smutted plants, representing approximately 20% of those plants present, were found in a portion of the field that was lightly infested with Italian thistle. In most cases, capitula of all diseased flowers were smutted. In one or two cases, capitula on some branches of the plants were smutted, whereas capitula on other branches were healthy. Diseased capitula were noticeably more globose than healthy ovoid capitula, and diseased capitula did not open completely. When diseased capitula were split open, the ovaries in all florets within the capitula were filled with powdery masses of smut teliospores. Diseased capitula were collected, air dried, and sent to the quarantine facility of the Foreign Disease-Weed Science Research Unit (FDWSRU), USDA/ARS, Fort Detrick, MD. Teliospores within the capitula were extracted and observed microscopically. Teliospores of isolate DB05-014 were relatively uniform in shape and size, globose, 12.0 to 17.3 × 12.3 to 18.0 μm (mean 14.5 × 15.1 μm), violet tinted pale to medium yellowish-brown; wall reticulate appearing as coarse, radiate wings on the spore margin, 5 to 7 polyangular meshes per spore diameter, muri, 0.7 to 2.0 μm high in optical median view appearing as gradually narrowing blunt spines, 0.5 to 1 μm wide at their basis; in scanning electron microscopy (SEM), the meshes were subpolygonal, wall and interspaces were finely verruculose. Teliospores were more globose and slightly smaller than the description of Microbotryum cardui (A. A. Fischer Waldh.) Vánky (2), but the mean sizes were within the described range. When compared with teliospores of M. cardui on C. acanthoides, the numbers of polyangular meshes per spore diameter were within the range of the description using SEM, but the muri were about one-half of the height of those described. Nucleotide sequences for the internal transcribed spacers (ITS 1 and 2) and 5.8S ribosomal region (GenBank Accession No. AY280460) were aligned with sequences of other smut fungi using the BLAST algorithm of the National Center for Biotechnology Information. The closest alignment of DB05-014 was with M. scorzonerae (590 of 627 bp identities or 94% with 2% gaps). No sequences of M. cardui were available for comparison, but only M. cardui has been reported on Carduus spp. (1,2). Another smut reported on a Carduus sp. is Thecaphora trailii (1). DB05-014 is a likely variant of M. cardui from a previously unknown host. Italian thistle is an annual plant that reproduces solely by seeds (achenes). Because of the lack of seed production on smutted plants and the systemic nature of the disease, this fungus has great potential as a biological control agent for Italian thistle in the United States. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 871812). To our knowledge this is the first report of a Microbotryum sp. parasitizing C. pycnocephalus. References: (1) K. Vánky. European Smut Fungi. Gustav Fischer Verlag, Stuttgart, Germany, 1994. (2) K. Vánky and D. Berner. Mycotaxon 85:307, 2003.

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First Report of Leaf Blight Caused by Phoma exigua on Acroptilon repens in Turkey

Plant Disease ◽

10.1094/pdis.2003.87.12.1540c ◽

2003 ◽

Vol 87 (12) ◽

pp. 1540-1540 ◽

Cited By ~ 5

Author(s):

B. Tunali ◽

F. M. Eskandari ◽

D. K. Berner ◽

D. F. Farr ◽

L. A. Castlebury

Keyword(s):

United States ◽

Biological Control ◽

Aqueous Suspension ◽

Severe Disease ◽

The United States ◽

Potential Candidate ◽

Voucher Specimen ◽

Phoma Exigua ◽

First Report ◽

Acroptilon Repens

Acroptilon repens (L.) DC. (Russian knapweed, synonym Centaurea repens L., family Asteraceae) is becoming a noxious weed in wheat fields in Turkey. Because it is also an invasive weed in the northwestern United States, A. repens is a target of biological control efforts. In the summer of 2002, approximately 20 dying A. repens plants were found on a roadside near Cankiri, Turkey (40°21′41″N, 33°31′8″E, elevation 699 m). No healthy plants were found in the immediate area. Dying plants had irregular, charcoal-colored, necrotic lesions at the leaf tips and margins, and frequently, whole leaves and plants were necrotic. Symptomatic leaves were air-dried and sent to the Foreign Disease-Weed Science Research Unit, USDA/ARS, Fort Detrick, MD. There, diseased leaves were surface-disinfested and placed on moist, filter paper in petri dishes. Pycnidia producing one-celled hyaline conidia were observed after 4 to 5 days. Internal transcribed spacer regions 1 and 2, including the 5.8S ribosomal DNA, were sequenced for isolate 02-059 (GenBank Accession No. AY367351). This sequence was identical to sequences in GenBank from six well-characterized strains of Phoma exigua Desmaz (1). Morphology was also consistent with P. exigua (2) with the exception that material grown on alfalfa twigs produced pycnidia with 1 to 4 ostioles with necks as much as 80 μm long. Typically, pycnidia of P. exigua produced on agar have 1 to 2 ostioles that lack necks. Conidial dimensions on alfalfa were 4.1 to 7.6 × 1.7 to 3.2 μm (average 5.5 × 2.4 μm). Images of the fungus are located at http://nt.ars-grin.gov under the section ‘Fungi Online’. Stems and leaves of 20 3-week-old plants were spray inoculated with an aqueous suspension (1 × 107 conidia per ml) of conidia harvested from 25-day-old cultures grown on acidified potato dextrose agar, and placed in an environmental chamber at 25°C with constant light and continuous dew for 3 days. Plants were then moved to a greenhouse bench and watered twice daily. After 6 days, symptoms were observed on all plants. Once symptoms had progressed to the midveins of the leaves, the disease progressed rapidly on the plants, indicating the possibility of systemic infection or systemic movement of toxins. Phoma exigua was reisolated from the stems, petioles, and leaves of all inoculated plants. In a separate test, 12 plants were inoculated as described above, and 8 additional plants were sprayed with water only. After inoculation, plants were handled as described above. The first lesions developed after 3 days on all except the youngest leaves of inoculated plants. After 10 days, three inoculated plants were dead, and all other inoculated plants had large necrotic lesions. No symptoms developed on control plants. This isolate of Phoma exigua is a destructive pathogen on A. repens, and severe disease can be produced by inoculation of foliage with an aqueous suspension of conidia. These characteristics make this isolate of P. exigua a potential candidate for biological control of this weed in Turkey and the United States. To our knowledge, this is the first report of P. exigua on A. repens in Turkey. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 843350). References: (1) E. C. A. Abeln et al. Mycol. Res. 106:419, 2002. (2) H. A. Van der Aa et al. Persoonia 17:435, 2000.

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First Report of Leaf Spot on Horseweed (Conyza canadensis) Caused by Septoria erigerontis in Turkey

Plant Disease ◽

10.1094/pdis-94-7-0918c ◽

2010 ◽

Vol 94 (7) ◽

pp. 918-918

Author(s):

I. Erper ◽

B. Tunali ◽

D. K. Berner

Keyword(s):

United States ◽

Biological Control ◽

Leaf Spot ◽

Biological Control Agent ◽

Aqueous Suspension ◽

The United States ◽

Fluorescent Light ◽

Conyza Canadensis ◽

Distilled Water ◽

First Report

Horseweed (Conyza canadensis (L).Cronq., Asteraceae) is an invasive exotic weed in Turkey and a problematic native weed in the United States where glyphosate-resistant populations of the weed have developed (2). These characteristics make horseweed a target for biological control efforts. In September 2009, small, brown leaf spots were observed on leaves of C. canadensis in Taflan, Turkey (41°25.398′N, 36°08.352′E). Globose, dark-walled pycnidia were also observed in brown spots on leaves. Diseased tissue was surface disinfested and placed on moist filter paper in petri plates. A fungus designated 09-Y-TR1 was isolated from the diseased leaves. Single-spore isolations were grown on potato dextrose agar (PDA). Cultures on PDA formed dark green-to-black colonies. Pycnidia matured after 3 to 4 weeks when plates were incubated at 23°C with a 12-h photoperiod (black light and cool white fluorescent light). Pycnidia were separate, immersed, and dark brown with a single apical ostiole. Matured conidia were one to three septate, filiform, straight to slightly curved, rounded at the apex, smooth walled, hyaline, and 22 to 40 × 1.4 to 2.5 μm. Morphology was consistent with Septoria erigerontis Peck (3). Comparison of the internal transcribed spacer (ITS) 1 and 2 sequence with available sequences of vouchered S. erigerontis specimens (GenBank EF535638.1, AY489273.1; KACC 42355, CBS 109094) showed 447 of 450 and 446 of 450 identities, respectively. Nucleotide sequences for the ribosomal ITS regions (ITS 1 and 2, including 5.8S rDNA) were deposited in GenBank (GU952666). For pathogenicity tests conidia were harvested from 3-week-old cultures grown on PDA, by brushing the surface of the colonies with a small paint brush, suspended in sterile distilled water, and filtered through cheese cloth. Conidia were then diluted in sterile distilled water plus 0.1% polysorbate 20 to a concentration of 5 × 106 conidia/ml. Stems and leaves of seven 5-month-old seedlings were spray inoculated with 10 ml of this aqueous suspension per plant. Inoculated plants and three noninoculated plants were placed in a dew chamber at 23°C in darkness and continuous dew, and after 48 h, plants were moved to a greenhouse bench. Symptoms were observed 2 days after inoculation. Disease severity was evaluated 2 weeks after inoculation by a rating system with a scale of 0 to 6 based on percentage of plant tissue necrosis, in which 0 = no symptoms, 1 = 1 to 5%, 2 = 6 to 25%, 3 = 26 to 75%, 4 = 76 to 95%, 5 = >95%, and 6 = dead plant. The average disease rating on inoculated plants was 3.55. No disease was observed on noninoculated plants. S. erigerontis was reisolated from all inoculated plants. To our knowledge, this is the first report of leaf spot on horseweed caused by S. erigerontis in Turkey where the fungus may have potential as a classical biological control agent. S. erigerontis has also been reported on C. canadensis in Korea and Portugal (1). In the United States, S. erigerontis has been reported on horseweed in several states (1) and these isolates may have potential as biological control agents of horseweed, particularly glyphosate-resistant horseweed, in the United States. References: (1) D. F. Farr et al. Fungal Databases. Systematic Mycology and Microbiology Laboratory, Online publication. ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , March 2010. (2) I. Heap. www.weedscience.org , 2006. (3) M. J. Priest. Fungi of Australia: Septoria. ABRS/CSIRO Publishing. Melbourne, 2006.

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Leaf Anthracnose, a New Disease of Swallow-Worts Caused by Colletotrichum lineola from Russia

Plant Disease ◽

10.1094/pdis-04-11-0318 ◽

2011 ◽

Vol 95 (12) ◽

pp. 1586-1586 ◽

Cited By ~ 6

Author(s):

D. Berner ◽

C. Cavin ◽

Z. Mukhina ◽

D. Kassanelly

Keyword(s):

United States ◽

Biological Control ◽

Dna Sequences ◽

Aqueous Suspension ◽

Science Research ◽

The United States ◽

Research Unit ◽

Leaf Spots ◽

Pure Cultures ◽

Appressoria Formation

Black swallow-wort, Vincetoxicum nigrum (L.) Moench (= Cynanchum louiseae Kartesz & Gandhi), and pale swallow-wort, V. rossicum (Kleopow) Borhidi (= Cynanchum rossicum (Kleopow) Borhidi), are invasive plants belonging to the family Apocynaceae and are the targets of biological control efforts to control their spread in the United States. In 2010, a disease on a related species, V. scandens Sommier & Levier, was observed in the Krasnodar area of Russia. Disease symptoms were many small, dark red-to-purple leaf spots, approximately 2 to 5 mm in diameter, with white centers. Leaf spots were found on the upper leaf surface. Leaf tips and margins of leaves bearing many of these spots were necrotic. Symptomatic leaves were collected and sent to the BSL-3 containment facility at the Foreign Disease-Weed Science Research Unit (FDWSRU) of the USDA, ARS in Frederick MD. Surface-disinfested symptomatic leaves were incubated at 20 to 25°C in sterile moist chambers. After several days, acervuli and brown setae were observed inside the leaf spots. Pure cultures, designated FDWSRU 10-002, were obtained by transferring spore masses with sterile glass needles onto 20% V8 juice agar. Seeds of V. scandens, collected in Russia, were placed in a freezer at –20°C for 6 weeks and then germinated in sterile petri plates on moist filter paper. The seedlings were then transplanted and grown in a 20°C greenhouse under 12 h of light. Koch's postulates were fulfilled as follows: 2-month-old plants each of V. scandens, V. nigrum, and V. rossicum were inoculated with spores from 2-week-old cultures of isolate 10-002. Plants were inoculated by spraying an aqueous suspension of 106 spores per ml onto each plant until all leaves were wet. Plants were placed in 20 to 24°C dew chambers for 18 h and then placed in a 20°C greenhouse. Two weeks later, diseased leaves with the same symptoms observed in the field were harvested from each species, and the fungus was reisolated from seven of seven inoculated V. scandens plants, one of two V. nigrum plants, and four of four V. rossicum plants. Measurements of fungus fruiting structures were taken from cultures grown on synthetic nutrient-poor agar (SNA) (1). Conidiophores were brown, septate, and branched. Conidia were one-celled, hyaline, smooth walled, ovoid to oblong, falcate, and 20.1 to 26.2 × 1.7 to 3.6 μm (mean ± s.d. = 23.5 ± 1.3 × 2.6 ± 0.4 μm). Lengths of the conidia conformed to the description of Colletotrichum lineola Corda (1), but the conidia were slightly narrower than described. To induce appressoria formation, approximately 104 conidia were placed on sterile dialysis membranes on top of SNA in petri dishes that were wrapped in foil and incubated at 24°C for 24 h. After this time, appressoria were observed with a microscope at ×400 magnification. The appressoria were dark brown, smooth walled, ellipsoidal, and 5.5 to 25.5 × 3.6 to 12.1 μm (mean ± s.d. = 13.4 ± 4.0 × 7.3 ± 2.1 μm), which conformed to the description of appressoria of C. lineola Corda (1). DNA sequences of ITS1, 5.8S, and ITS2 were submitted to GenBank (No. HQ731491), and after BLAST analysis, aligned 100% to 15 previously identified isolates of C. lineola in GenBank. Voucher specimens of the fungus have been deposited in the U.S. National Fungus Collection and were designated as BPI 881105 and BPI 881106. Host range and efficacy tests are planned to determine the suitability of C. lineola for biological control of swallow-worts in the United States. Reference: (1) U. Damm et al. Fungal Divers. 39:45, 2009.

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First Report of Leaf Spot Caused by Cercospora bizzozeriana on Hoary Cress in Russia

Plant Disease ◽

10.1094/pdis-92-2-0316c ◽

2008 ◽

Vol 92 (2) ◽

pp. 316-316

Author(s):

Z. M. Mukhina ◽

D. Kassanelly ◽

D. K. Berner ◽

H. J. Dubin

Keyword(s):

Biological Control Agent ◽

Aqueous Suspension ◽

Science Research ◽

Research Unit ◽

Invasive Weed ◽

Voucher Specimen ◽

First Report ◽

Leaf Spots ◽

White Leaf ◽

Hoary Cress

Hoary cress (Lepidium draba (L.) subsp. draba (synonym = Cardaria draba (L.) Desv.) (1), family Brassicaceae, is a common weed in Russia but it is an aggressive invasive weed in the northwestern United States. In the summer of 2006, dying hoary cress plants were found near Kugoyeyskoye in the Krylovskoy area of the Krasnodar Region of Russia. Plants had grayish white leaf spots on most of the leaves. In some cases, the diseased 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 leaves within and around the lesions. The fungus isolated (DB06-018) conformed to the description of Cercospora bizzozeriana Saccardo & Berlese (2). Conidiophores were 1 to 5 geniculate, unbranched, pale olive-brown, and uniform in color and width (4 μm). Conidia were multiseptate, hyaline, cylindric, straight to slightly curved, and measured 57 to 171 μm (average 103) long × 3.8 to 6.7 μm (average 4.6) wide. Leaves of rosettes (10 to 15 cm in diameter) of four hoary cress plants were spray inoculated with an aqueous suspension of conidia (1 × 105/ml) and mycelia harvested from 6- to 8-day-old cultures grown on V8 medium. Inoculated plants and two noninoculated plants were placed in a dew chamber at 20°C in darkness and continuous dew. After 96 h, plants were moved from the dew chamber to a greenhouse bench. All plants were watered twice daily. After 12 days, symptoms were observed on all inoculated plants. Symptoms were identical to those observed in the field in Russia. No symptoms were observed on noninoculated plants. C. bizzozeriana was reisolated from the leaves of all symptomatic plants. Nucleotide sequences were obtained for the internal transcribed spacer regions ITS1 and ITS2 and the 5.8S ribosomal RNA gene (GenBank Accession No. EU031780) and aligned with the same sequences obtained from another C. bizzozeriana isolate (GenBank Accession No. DQ370428) collected in Tunisia. There was 100% alignment of the two sequences with no gaps. Both isolates of C. bizzozeriana are destructive pathogens on hoary cress and locally severe epidemics have been observed in both Russia and Tunisia (4). This fungus has also been reported in North America (3) and has the potential as a biological control agent where the weed is a problem. To our knowledge, this is the first report of C. bizzozeriana on L. draba subsp. draba in Russia. A voucher specimen has been deposited with the U.S. National Fungus Collections (BPI 878175). Live cultures are being maintained at FDWSRU. 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. (3) I. L. Conners. Res. Bra. Can. Dep. Agric. 1251:1, 1967. (4) T. Souissi et al. Plant Dis. 89:206, 2005.

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

Plant Disease ◽

10.1094/pdis-93-1-0108b ◽

2009 ◽

Vol 93 (1) ◽

pp. 108-108 ◽

Cited By ~ 1

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.

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First Report of Rust Caused by Puccinia carduorum on Italian thistle in Tunisia

Plant Disease ◽

10.1094/pdis-92-1-0174a ◽

2008 ◽

Vol 92 (1) ◽

pp. 174-174 ◽

Cited By ~ 1

Author(s):

D. Mejri ◽

T. Souissi ◽

D. Berner

Keyword(s):

United States ◽

Aqueous Suspension ◽

The United States ◽

Northern Tunisia ◽

Disease Symptoms ◽

First Report ◽

Leaf Stage ◽

Plastic Bags ◽

Spraying Plants ◽

Geographical Locations

Italian thistle (Carduus pycnocephalus L.) is a common and increasingly important weed in Tunisia. It is also problematic in the western United States and a target of biological control. In surveys conducted in northern Tunisia from 2003 to 2005, Italian thistle plants in many locations were found diseased by rust. Eighty-five isolates of rust were collected from Italian thistle during these surveys. Each isolate was collected from a single plant and stored individually as mixtures of urediniospores and teliospores at 4°C or in liquid nitrogen. Urediniospores and teliospores of all isolates were similar in morphology and matched the description of Puccinia carduorum Jacky (3). Isolate B1003 (BPI No. 878207), collected from Béja, Tunisia, was arbitrarily selected for further study. Comparison of internal transcribed spacer (ITS) regions of B1003 (GenBank Accession No. EF050059) with other ITS sequences indicated a 97% similarity to P. carduorum (GenBank Accession No. PCU57351) from Carduus nutans subsp. leiophyllus. Eight Italian thistle plants, grown from seeds collected in Béja, were inoculated in the 3- to 5-leaf stage with urediniospores of B1003 by spraying plants with an aqueous suspension of urediniospores at 106 spores per ml with approximately 0.03 ml of surfactant until they were thoroughly wet. Four plants were sprayed with water plus surfactant only. All plants were covered with plastic bags and placed in a growth chamber at 18/20°C night/day temperatures. Bags were removed 24 h after inoculation and plants were monitored daily for symptoms. Plants sprayed with water plus surfactant only did not develop symptoms. Six inoculated plants developed disease symptoms similar to those observed on samples collected during the surveys. White flecks appeared within 7 days of inoculation and developed into brown pustules 10 days after inoculation. Pustules enlarged and produced urediniospores until they covered both sides of diseased leaves. One month after appearance of symptoms, diseased leaves turned yellow and died. Urediniospores from these plants were used to inoculate six plants each at the 2- to 5-, 6- to 8-, and >8-leaf stages. All plants became diseased and produced uredinia. Plants in the 2- to 5-leaf stage were more severely diseased than other plants. P. carduorum was introduced to the United States in a field test for control of C. nutans subsp. leiophyllus (musk thistle) and has become established in a number of states (1). An isolate of this fungus has also been found from C. tenuiflorus (slender-flower thistle) in California (4). However, neither isolate causes substantial disease on Italian thistle from California (2,4). Isolates of P. carduorum from C. pycnocephalus in Greece, Italy, and Turkey caused little disease on most Italian thistle collections from California (2), indicating variability in susceptibility among plants as well as in virulence among rust isolates from different geographical locations. To our knowledge, this is the first report of P. carduorum parasitizing Italian thistle in Tunisia. Tests will be conducted to determine the host range of this isolate among C. pycnocephalus collections and other species. References: (1) A. B. A. M. Baudoin and W. L. Bruckart. Plant Dis. 80:1193, 1996. (2) W. L. Bruckart and G. L. Peterson. Phytopathology 81:192, 1991. (3) D. B. O. Savile. Can. J. Bot. 48:1553, 1970. (4) A. K. Watson and K. Brunetti. Plant Dis. 68:1003, 1984.

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