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

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.

Download Full-text

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.

Download Full-text

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

Plant Disease ◽

10.1094/pdis.2004.88.12.1382a ◽

2004 ◽

Vol 88 (12) ◽

pp. 1382-1382 ◽

Cited By ~ 1

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

First Report of Gray Leaf Spot on Perennial Ryegrass Turf in California

Plant Disease ◽

10.1094/pdis.2002.86.1.75c ◽

2002 ◽

Vol 86 (1) ◽

pp. 75-75 ◽

Cited By ~ 19

Author(s):

W. Uddin ◽

G. Viji ◽

L. Stowell

Keyword(s):

United States ◽

Perennial Ryegrass ◽

Leaf Spot ◽

Disease Incidence ◽

The United States ◽

Gray Leaf Spot ◽

Water Soluble ◽

Distilled Water ◽

First Report ◽

Polyethylene Bags

Gray leaf spot of perennial ryegrass (Lolium perenne L.) turf was first reported in the United States in 1991. The disease epidemic was primarily confined to golf course fairways in southeastern Pennsylvania (1). Subsequently, moderate to severe outbreaks of gray leaf spot occurred in perennial ryegrass fairways and roughs in numerous locations throughout the eastern and midwestern United States. In August 2001, a serious decline of perennial ryegrass turf was observed in a bermudagrass (Cynodon dactylon (L.) Pers) baseball field in Dodger Stadium in Los Angeles, CA, that had been overseeded with perennial ryegrass. The bermudagrass turf was not affected. The perennial ryegrass turf developed necrotic lesions that resulted in blighting of leaf blades. In laboratory assays, Pyricularia grisea (Cooke) Sacc., was consistently isolated from symptomatic ryegrass blades from turf samples collected from the site. Of the 12 P. grisea isolates collected from the assayed leaf blades, five isolates were selected for a pathogenicity assay. Twenty-five ‘Legacy II’ perennial ryegrass plants were grown from seeds in 4 × 4 in.-plastic pots, (10 × 10 cm) which were filled to 1 cm below the rim with granular calcine clay medium (Turface MVP, Allied Industrial Material Corp., Buffalo Grove, IL). Three weeks after seeding, plants were fertilized with a water-soluble 20-20-20 N-P-K fertilizer (1.3 g/liter of water) once per week. Treatments (isolates of P. grisea and a control) were arranged as a randomized complete block design with five replications. Five-week-old plants were sprayed with an aqueous suspension of P. grisea conidia (≈5 × 104 conidia per ml of sterilized distilled water with 0.1% Tween 20) using an atomizer until the leaves were completely wet. Plants sprayed with sterilized distilled water served as the control. After inoculation, individual pots were covered with clear polyethylene bags and placed in a controlled environment chamber maintained at 28°C and continuous fluorescent light (88 μE m-2 s-1). Four days after inoculation, necrotic lesions (<2 mm diameter) developed on ryegrass blades inoculated with each isolate of P. grisea. Lesions did not develop on leaves of control plants. Seven days after inoculation, the polyethylene bags were removed, and 50 symptomatic blades from each pot were collected, and disease incidence (percent infected leaves) and severity (index 0 to 10; 0 = none, 10 = >90% of the leaf blade necrotic ) were assessed. P. grisea was isolated from symptomatic leaves of plants inoculated with the fungus. Disease incidence and severity on inoculated plants were 92 to 96% and 8.8 to 10, respectively. There were no significant differences in disease incidence and severity (P = 0.05) among the isolates of P. grisea included in the test. To our knowledge, this is the first report of gray leaf spot of perennial ryegrass turf in California. Reference: (1) P. J. Landschoot and B. F. Hoyland. Plant Dis. 76:1280, 1992.

Download Full-text

First Report of Leaf Spot of Milky Bellflower (Campanula lactiflora) Caused by a Phoma sp. in Italy

Plant Disease ◽

10.1094/pdis-94-5-0638a ◽

2010 ◽

Vol 94 (5) ◽

pp. 638-638

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

C. Pellegrino ◽

M. L. Gullino

Keyword(s):

United States ◽

Leaf Spot ◽

Morphological Characteristics ◽

Its Region ◽

The United States ◽

Fluorescent Light ◽

Herbaceous Plant ◽

Pathogenicity Test ◽

First Report ◽

Perennial Herbaceous Plant

Campanula lactiflora (milky bellflower), a perennial herbaceous plant in the Campanulaceae, is used in park and gardens and sometimes cultivated for cut flower production. In June 2008, a previously unknown leaf spot was observed on C. lactiflora ‘New Hybrids’ plants from an experimental nursery located near Carmagnola (Torino, northern Italy). Leaves of infected plants showed extensive and irregular, dark brown, necrotic lesions that were slightly sunken with well-defined borders. Lesions initially ranged from 0.5 to 3 mm, eventually coalesced, and covered the entire leaf. Black pycnidia (107 to 116 μm in diameter) containing hyaline, ellipsoid, nonseptate conidia measuring 3.7 to 4.7 × 1.2 to 2.0 (average 4.3 × 1.6) μm were observed. On the basis of these morphological characteristics, the fungal causal agent of the disease could be related to the genus Phoma. In some cases, the basal leaves turned completely necrotic and the plant died. The disease affected 50% of plants. Diseased tissue was excised, immersed in a solution containing 1% sodium hypochlorite for 2 to 3 s, rinsed in water, and then cultured on potato dextrose agar (PDA) medium. A fungus developed that produced a greenish gray mycelium with a white border when incubated under 12 h/day of fluorescent light at 22 to 25°C. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 459-bp segment showed a 100% similarity with the sequence of a Didymella sp. (synonym Mycosphaerella), anamorphic stage of Phoma spp. The nucleotide sequence has been assigned GenBank Accession No. GU128503. Pathogenicity tests were performed by placing 8-mm-diameter mycelial disks removed from PDA cultures of the fungus isolated from infected plants on leaves of healthy potted 4-month-old C. lactiflora ‘New Hybrids’ plants. Eight disks were placed on each plant. Plants inoculated with PDA alone served as controls. Six plants per treatment were used. Plants were covered with plastic bags for 4 days after inoculation and maintained in a growth chamber with daily average temperatures ranging between 23 and 24°C. The first foliar lesions developed on leaves 5 days after inoculation, and after 8 days, 80% of leaves were severely infected. Control plants remained healthy. A Didymella sp. was consistently reisolated from leaf lesions. The pathogenicity test was completed twice. To our knowledge, this is the first report of the presence of a Didymella sp. on C. lactiflora in Italy. Mycosphaerella campanulae and M. minor were reported on C. americana and C. lasiocarpa in the United States (2). The economic importance of the disease currently is limited, but could become a more significant problem in the future if the cultivation of this species becomes more widespread. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.

Download Full-text

First Report of Alternaria Leaf Spot of Spathiphyllum sp. in Argentina

Plant Disease ◽

10.1094/pdis.2000.84.3.370a ◽

2000 ◽

Vol 84 (3) ◽

pp. 370-370 ◽

Cited By ~ 1

Author(s):

A. L. Cheheid ◽

E. R. Wright ◽

S. E. Lopez ◽

A. M. Rodríguez Codazzi

Keyword(s):

United States ◽

Leaf Spot ◽

The United States ◽

Fluorescent Light ◽

First Report ◽

Potted Plants ◽

Alternaria Leaf Spot ◽

Alternaria Sp ◽

Necrotic Spots

Brown necrotic spots surrounded by chlorotic areas have been observed on the leaf margins of Spathiphyllum sp. in many nurseries in and near Buenos Aires, Argentina, since 1997. Spots reached 0.7 × 2 cm and appeared mainly on older leaves of stressed plants. To determine the causal agent of the leaf spot, small pieces of diseased tissue were surface-sterilized for 2 min in 2% sodium hypochlorite and plated on potato dextrose agar. Gray olivaceous to almost black colonies developed in 3 to 4 days. Dark conidiophores, which formed singly or in small groups, were short, less than 100 μm, sometimes flexuous, and occasionally geniculate. The brown to black, obclavate, pyriform, or rostrate conidia were 20 to 25 μm long × 10 to 15 μm wide, with three to four transverse septa and one to three longitudinal or oblique septa. Chains of conidia 5 to 10 spores long were sometimes branched, appearing bushy. The foliage of 15 healthy potted plants previously injured with sterile needles and 15 healthy potted plants without injuries was inoculated with a suspension of 2.8 × 104 conidia per ml. Plants were maintained at 23°C and 100% relative humidity under fluorescent light (12 h light/12 h darkness) for 3 days. Chlorotic and necrotic spots began to develop on the apex and margins of injured and inoculated leaves after 10 days. Lesions tended to coalesce, finally measuring 2.2 × 0.7 cm after 26 days. Control plants, with and without injuries, sprayed with distilled water remained symptomless. Koch's postulates were satisfied after reisolating the fungus. Cultures in potato carrot agar and V8 agar after 7 days exhibited typical characteristics of Alternaria alternata (2–4). An Alternaria sp. has been found previously in the United States on Spathiphyllum sp. (1). This is the first report of Alternaria leaf spot of Spathiphyllum in Argentina. References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. (2) E. G. Simmons. Alternaria themes and variations (226–235): Classification of Citrus pathogens. Mycotaxon 70:263, 1999. (3) E. G. Simmons. Alternaria themes and variations (236–243): Host specific toxin producers. Mycotaxon 70:325, 1999. (4) E. G. Simmons and R. G. Roberts. Alternaria themes and variations (73). Mycotaxon 48:109, 1993.

Download Full-text

First Report of Passalora Leaf Spot of Quinoa Caused by Passalora dubia in the United States

Plant Disease ◽

10.1094/pdis-05-12-0472-pdn ◽

2013 ◽

Vol 97 (1) ◽

pp. 139-139 ◽

Cited By ~ 3

Author(s):

A. L. Testen ◽

J. M. McKemy ◽

P. A. Backman

Keyword(s):

United States ◽

Leaf Spot ◽

Biological Control Agent ◽

Chenopodium Quinoa ◽

Its Region ◽

The United States ◽

Tween 20 ◽

Potato Dextrose Broth ◽

First Report ◽

Rainy Period

The Andean seed crop quinoa, Chenopodium quinoa Willd., is an important export of Bolivia, Ecuador, and Peru. Key foliar diseases of quinoa include quinoa downy mildew (caused by Peronospora variabilis Gäum) (1), Ascochyta leaf spot (caused by Ascochyta sp.) (1), and a Cercospora-like leaf spot, the latter of which has been observed on cultivated quinoa (Jose B. Ochoa, unpublished) and native Chenopodium species. Passalora dubia (Riess) U. Braun (syn. Cercospora dubia) was tested in Europe as a biological control agent for Chenopodium album (3) and has been reported on C. album in the United States (U.S. National Fungus Collections). Quinoa field plots were established in Pennsylvania during summer 2011 and Cercospora-like leaf spot symptoms were first observed on quinoa in Centre Co. and Lancaster Co. in August 2011, after an extended rainy period. Foliar symptoms were round to oval, brown to grey-black lesions, less than 1 cm in diameter, with darker brown, reddish margins. Similar symptoms were observed on C. album weeds within both fields. Using a hand lens, conidia were observed within sporulating lesions. Conidia were hyaline and septate, 25 to 98 μm × 5 to 10 μm, and had an average of six cells per conidium. The fungus was isolated by picking single conidia from sporulating lesions (under a dissecting scope) and incubated on V8 agar in the dark at 20°C to induce sporulation. For DNA extraction, cultures were grown in potato dextrose broth amended with yeast extract. The internal transcribed spacer (ITS) region was amplified using primers ITS4 and ITS5 (2), and the resulting sequence shared 99% maximum identity with a vouchered isolate of P. dubia (GenBank EF535655). To test the pathogenicity of our P. dubia isolate, 5.9 × 103 conidia/ml (suspended in sterile water with 0.1% Tween 20) or the control solution with no conidia were sprayed, using an atomizer, onto 2-month-old quinoa plants, with 18 replications per treatment. Plants were covered with a humidity dome and maintained at >99% RH for 48 h. Plants were grown in the greenhouse at approximately 65% RH. After 1 month, circular to oval light brown lesions (<1 cm diameter) with darker margins were observed on approximately 10% of the leaves of inoculated plants, whereas no symptoms were observed on the control plants. Infected leaves were collected, incubated in a humidity chamber, and conidia were picked from sporulating lesions and inoculated onto V8 agar amended with 3% (w/v) fresh, ground quinoa plant tissue (4). Cultures were maintained at 20°C with 16-h photoperiod to induce sporulation. The identity of the reisolated fungus was confirmed morphologically and by DNA sequencing to be identical to the isolate used to test Koch's postulates. P. dubia was also isolated from C. album lesions and infected C. album may have served as a source of inoculum for quinoa. To our knowledge, this is the first report of Passalora leaf spot of quinoa in the United States. References: (1) S. Danielsen. Food Rev. Int. 19:43, 2003. (2) S. Goodwin et al. Phytopathology 91:648, 2001. (3) P. Scheepens et al. Integ. Pest. Man. Rev. 2:71, 1997. (4) M. Vathakos. Phytopathology 69:832, 1979.

Download Full-text

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.

Download Full-text

First Report of Alternaria Leaf Spot of Banana Caused by Alternaria alternata in the United States

Plant Disease ◽

10.1094/pdis-01-13-0007-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1116-1116 ◽

Cited By ~ 3

Author(s):

V. Parkunan ◽

S. Li ◽

E. G. Fonsah ◽

P. Ji

Keyword(s):

United States ◽

Alternaria Alternata ◽

Leaf Spot ◽

Morphological Characteristics ◽

The United States ◽

Its Sequencing ◽

Single Spore ◽

First Report ◽

Alternaria Leaf Spot ◽

Leaf Spots

Research efforts were initiated in 2003 to identify and introduce banana (Musa spp.) cultivars suitable for production in Georgia (1). Selected cultivars have been evaluated since 2009 in Tifton Banana Garden, Tifton, GA, comprising of cold hardy, short cycle, and ornamental types. In spring and summer of 2012, 7 out of 13 cultivars (African Red, Blue Torres Island, Cacambou, Chinese Cavendish, Novaria, Raja Puri, and Veinte Cohol) showed tiny, oval (0.5 to 1.0 mm long and 0.3 to 0.9 mm wide), light to dark brown spots on the adaxial surface of the leaves. Spots were more concentrated along the midrib than the rest of the leaf and occurred on all except the newly emerged leaves. Leaf spots did not expand much in size, but the numbers approximately doubled during the season. Disease incidences on the seven cultivars ranged from 10 to 63% (10% on Blue Torres Island and 63% on Novaria), with an average of 35% when a total of 52 plants were evaluated. Six cultivars including Belle, Ice Cream, Dwarf Namwah, Kandarian, Praying Hands, and Saba did not show any spots. Tissue from infected leaves of the seven cultivars were surface sterilized with 0.5% NaOCl, plated onto potato dextrose agar (PDA) media and incubated at 25°C in the dark for 5 days. The plates were then incubated at room temperature (23 ± 2°C) under a 12-hour photoperiod for 3 days. Grayish black colonies developed from all the samples, which were further identified as Alternaria spp. based on the dark, brown, obclavate to obpyriform catenulate conidia with longitudinal and transverse septa tapering to a prominent beak attached in chains on a simple and short conidiophore (2). Conidia were 23 to 73 μm long and 15 to 35 μm wide, with a beak length of 5 to 10 μm, and had 3 to 6 transverse and 0 to 5 longitudinal septa. Single spore cultures of four isolates from four different cultivars were obtained and genomic DNA was extracted and the internal transcribed spacer (ITS1-5.8S-ITS2) regions of rDNA (562 bp) were amplified and sequenced with primers ITS1 and ITS4. MegaBLAST analysis of the four sequences showed that they were 100% identical to two Alternaria alternata isolates (GQ916545 and GQ169766). ITS sequence of a representative isolate VCT1FT1 from cv. Veinte Cohol was submitted to GenBank (JX985742). Pathogenicity assay was conducted using 1-month-old banana plants (cv. Veinte Cohol) grown in pots under greenhouse conditions (25 to 27°C). Three plants were spray inoculated with the isolate VCT1FT1 (100 ml suspension per plant containing 105 spores per ml) and incubated under 100% humidity for 2 days and then kept in the greenhouse. Three plants sprayed with water were used as a control. Leaf spots identical to those observed in the field were developed in a week on the inoculated plants but not on the non-inoculated control. The fungus was reisolated from the inoculated plants and the identity was confirmed by morphological characteristics and ITS sequencing. To our knowledge, this is the first report of Alternaria leaf spot caused by A. alternata on banana in the United States. Occurrence of the disease on some banana cultivars in Georgia provides useful information to potential producers, and the cultivars that were observed to be resistant to the disease may be more suitable for production. References: (1) E. G. Fonsah et al. J. Food Distrib. Res. 37:2, 2006. (2) E. G. Simmons. Alternaria: An identification manual. CBS Fungal Biodiversity Center, Utrecht, Netherlands, 2007.

Download Full-text