First Report of Aerial Blight of Ruth's Golden Aster (Pityopsis ruthii) Caused by Rhizoctonia solani in the United States

Ruth's golden aster (Pityopsis ruthii (Small) Small: Asteraceae) is an endangered, herbaceous perennial that occurs only at a few sites along the Hiwassee and Ocoee rivers in Polk County, Tennessee. This species is drought, heat, and submergence tolerant and has ornamental potential as a fall flowering landscape plant. In 2012, we vegetatively propagated various genotypes and established plantings in a landscape at Poplarville, Mississippi. In June and July of 2013, during periods of hot and humid weather, several well-established plants exhibited black or brown necrotic aerial blight symptoms including desiccation of stems and leaves. Blighted leaf samples were surface sterilized (10% commercial bleach, active ingredient 8.25% sodium hypochlorite, 1 min), rinsed in sterile water, air-dried, and plated on 2% water agar amended with 3.45 mg fenpropathrin/liter (Danitol 2.4 EC, Valent Chemical, Walnut Creek, CA) and 10 mg/liter rifampicin (Sigma-Aldrich, St. Louis, MO). Rhizoctonia sp. was identified based on hyphal morphology and cultures were maintained on potato dextrose agar. Colonies were fast growing, consisting of light tan to brown mycelia and tufts of crystalline aerial hyphae. Within 10 days, brown exudates were present in cultures and there was no pigmented reverse to the agar. Hyphae were a mean of 5.2 μm wide (4.6 to 6.1 μm; n = 10) and each compartment contained three or more nuclei. Hyphae were constricted at septa with right angle branching and no clamp connections, which is typical for Rhizoctonia solani (1). Light- to medium-brown, oblong to irregularly shaped sclerotia measuring 1.2 mm long (0.7 to 2.1 mm) × 0.9 mm wide (0.5 to 1.2 mm; n = 20) were formed in cultures after 3 weeks of growth. Total genomic DNA was extracted from two different colonies grown in potato dextrose broth for 7 days, amplified with PCR using ITS1 and ITS4 primers for amplification of the 18S rDNA subunit (2), the products purified, and sequenced. A consensus sequence of 657 bp was deposited in GenBank (Accession Nos. KF843729 and KF843730) and was 96% identical to two R. solani Kühn ITS sequences in GenBank (HF678125 and HF678122). R. solani was grown on twice autoclaved oats for 2 weeks at 21°C and incorporated into Pro-Mix BX, low fertility soilless medium (Premier Horticulture, Rivière-du-Loup, Quebec, Canada) at 4% (w/w) to inoculate seven P. ruthii plants grown in 10 cm-diameter pots; seven additional plants were grown in the same medium amended with 4% (w/w) sterile oats. Plants were grown in a greenhouse and covered with a plastic dome to maintain high humidity. After 2 weeks, six of the seven inoculated plants exhibited the same aerial blight symptoms as did the original infected plants from the field; none of the control plants developed disease symptoms. Colony morphology and hyphal characteristics as well as the sequence for the ITS region of rDNA from the re-isolated fungus were identical to the original isolate. To our knowledge, this is the first report of R. solani infecting Ruth's golden aster. We are not aware of the disease occurring in wild populations of the plant, but may impact plants grown in the landscape or greenhouse. References: (1) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St Paul, MN, 1991. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, CA, 1990.

Download Full-text

First Report of Anthracnose of Onion Caused by Colletotrichum coccodes in Ohio

Plant Disease ◽

10.1094/pdis-01-14-0032-pdn ◽

2014 ◽

Vol 98 (9) ◽

pp. 1271-1271 ◽

Cited By ~ 2

Author(s):

F. Baysal-Gurel ◽

N. Subedi ◽

D. P. Mamiro ◽

S. A. Miller

Keyword(s):

Leaf Tissue ◽

Its Region ◽

The United States ◽

Tween 20 ◽

Colletotrichum Coccodes ◽

Academic Press ◽

Conidial Suspension ◽

First Report ◽

Allium Cepa L ◽

Total Dna

Dry bulb onion (Allium cepa L. cvs. Pulsar, Bradley, and Livingston) plants with symptoms of anthracnose were observed in three commercial fields totaling 76.5 ha in Huron Co., Ohio, in July 2013. Symptoms were oval leaf lesions and yellowing, curling, twisting, chlorosis, and death of leaves. Nearly half of the plants in a 32.8-ha field of the cv. Pulsar were symptomatic. Concentric rings of acervuli with salmon-colored conidial masses were observed in the lesions. Conidia were straight with tapered ends and 16 to 23 × 3 to 6 μm (2). Colletotrichum coccodes (Wallr.) S. Hughes was regularly isolated from infected plants (2). Culturing diseased leaf tissue on potato dextrose agar (PDA) amended with 30 ppm rifampicin and 100 ppm ampicillin at room temperature yielded white aerial mycelia and salmon-colored conidial masses in acervuli. Numerous spherical, black microsclerotia were produced on the surface of colonies after 10 to 14 days. To confirm pathogen identity, total DNA was extracted directly from a 7-day-old culture of isolate SAM30-13 grown on PDA, using the Wizard SV Genomic DNA Purification System (Promega, Madison, WI) following the manufacturer's instructions. The ribosomal DNA internal transcribed spacer (ITS) region was amplified by PCR using the primer pair ITS1 and ITS4 (2), and sequenced. The sequence, deposited in GenBank (KF894404), was 99% identical to that of a C. coccodes isolate from Michigan (JQ682644) (1). Ten onion seedlings cv. Ebenezer White at the two- to three-leaf stage of growth were spray-inoculated with a conidial suspension (1 × 105 conidia/ml containing 0.01% Tween 20, with 10 ml applied/plant). Plants were maintained in a greenhouse (21 to 23°C) until symptoms appeared. Control plants were sprayed with sterilized water containing 0.01% Tween 20, and maintained in the same environment. After 30 days, sunken, oval lesions each with a salmon-colored center developed on the inoculated plants, and microscopic examination revealed the same pathogen morphology as the original isolates. C. coccodes was re-isolated consistently from leaf lesions. All non-inoculated control plants remained disease-free, and C. coccodes was not re-isolated from leaves of control plants. C. coccodes was reported infecting onions in the United States for the first time in Michigan in 2012 (1). This is the first report of anthracnose of onion caused by C. coccodes in Ohio. Unusually wet, warm conditions in Ohio in 2013 likely contributed to the outbreak of this disease. Timely fungicide applications will be necessary to manage this disease in affected areas. References: (1) A. K. Lees and A. J. Hilton. Plant Pathol. 52:3. 2003. (2) L. M. Rodriguez-Salamanca et al. Plant Dis. 96:769. 2012. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

Download Full-text

First Report of Potato Stem Canker Caused by Rhizoctonia solani AG4 HGII in Gansu Province, China

Plant Disease ◽

10.1094/pdis-09-12-0896-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 840-840

Author(s):

Y. G. Yang ◽

X. H. Wu

Keyword(s):

Rhizoctonia Solani ◽

Solanum Tuberosum L ◽

Its Region ◽

Stem Canker ◽

The United States ◽

Gansu Province ◽

Molecular Characteristics ◽

Potato Seed ◽

First Report ◽

Wheat Seeds

Black scurf and stem canker on potato (Solanum tuberosum L.), caused by Rhizoctonia solani, is an important disease throughout the world. Isolates of R. solani AG3 are the principal cause of these diseases on potato (2). In August 2011, at the tuber bulking growth stage, symptoms typically associated stem canker, including dark brown stem lesions, were observed on 20% of potato plants collected from 23 locations (about 2,000 ha) in Gansu Province, northwest China. Stem pieces (each 5 mm long) taken from the margins of the healthy and diseased tissues were surface-disinfected with 0.5% NaOCl for 2 min, rinsed with sterilized water, dried, then placed on potato dextrose agar (PDA) at 25°C in the dark. Twenty-nine fungal isolates taken from single hyphal tips were identified as R. solani based on morphological traits, including mycelium branched at right angles with a septum near the branch and a slight constriction at the branch base. Hyphal cells were determined to be multinucleate (4 to 10 nuclei/cell) when stained with 4′-6-diamidino-2-phenylindole (DAPI). Anastomosis groups were determined by pairing with reference strains (kindly provided by N. Kondo, Hokkaido University, Japan), and three isolates (designed GS-15, GS-24, and GS-25) anastomosed with isolates of R. solani AG4. The internal transcribed spacer (ITS) region of rDNA was amplified from genomic DNA of each of the three isolates with primers ITS1 and ITS4. The resulting sequences (GenBank Accession Nos. JX843818, JX843819, and JX843820) were 100% identical to those of >10 R. solani AG4 HGII isolates (e.g., HQ629873.1; isolate ND13). Therefore, based on the anastomosis assay and molecular characteristics, the three isolates were identified as R. solani AG4 HGII. To determine pathogenicity of the AG4 HGII isolates, potato seed tubers (cv. Favorita) with 3 to 5 mm long sprouts were inoculated with wheat seeds (sterilized by autoclaving twice at 121°C for 1 h with a 24 h interval between autoclavings) colonized with each isolate (1). One sprouted tuber was planted in a sterilized plastic pot (1 liter) with a single colonized wheat seed placed 10 mm above the uppermost sprout tip in a sand/sawdust mixture (1:2 v/v, with dry heat sterilization at 161°C for 4 h before use). Plants were incubated in a glasshouse maintained at 25 to 27°C. The test was performed on 20 plants for each isolate, and the experiment was repeated. After 3 weeks, control plants inoculated with sterilized wheat seeds remained asymptomatic, and no Rhizoctonia spp. were isolated from these plants, whereas all inoculated plants showed symptoms of stem canker. R. solani AG4 HGII was reisolated consistently from symptomatic stems, and the identity of the reisolates confirmed by the morphological and molecular characteristics mentioned above, fulfilling Koch's postulates. Potato stem canker caused by R. solani AG4 HGII was reported previously in the United States (3). To our knowledge, this is the first report of R. solani AG4 HGII causing stem canker on potato in Gansu Province, the main potato-producing area of China. R. solani AG4 HGII can cause sheath blight on corn in China (4), which is commonly grown in rotation with potato. This rotation could increase the risk of soilborne infection to either crop by R. solani AG4 HGII. References: (1) M. J. Lehtonen et al. Plant Pathol. 57:141, 2008. (2) L. Tsror. J. Phytopathol. 158:649, 2010. (3) J. W. Woodhall et al. Plant Dis. 96:1701, 2012. (4) X. Zhou et al. J. Shenyang Agric. Univ. 43:33, 2012.

Download Full-text

First Report of Rhizoctonia solani AG2-2IIIB Infecting Potato Stems and Stolons in the United States

Plant Disease ◽

10.1094/pdis-10-11-0899 ◽

2012 ◽

Vol 96 (3) ◽

pp. 460-460 ◽

Cited By ~ 3

Author(s):

J. W. Woodhall ◽

A. R. Belcher ◽

J. C. Peters ◽

W. W. Kirk ◽

P. S. Wharton

Keyword(s):

United States ◽

New York ◽

Sugar Beet ◽

Rhizoctonia Solani ◽

Its Region ◽

Stem Canker ◽

The United States ◽

Potato Disease ◽

First Report ◽

Plant Pathol

Rhizoctonia solani is an important pathogen of potato (Solanum tuberosum) causing qualitative and quantitative losses. It has been associated with black scurf and stem canker. Isolates of the fungus are assigned to one of 13 known anastomosis groups (AGs), of which AG3 is most commonly associated with potato disease (2,4). In August 2011, diseased potato plants originating from Rupert, ID (cv. Western Russet) and Three Rivers, MI (cv. Russet Norkotah) were received for diagnosis. Both samples displayed stem and stolon lesions typically associated with Rhizoctonia stem canker. The presence of R. solani was confirmed through isolation as previously described (4) and the Idaho and Michigan isolates were designated J11 and J8, respectively. AG was determined by sequencing the rDNA internal transcribed spacer (ITS) region using primers ITS5 and ITS4 (3). The resulting sequences of the rDNA ITS region of isolates J8 and J11 (GenBank Accession Nos. HE608839 and HE608840, respectively) were between 97 and 100% identical to that of other AG2-2IIIB isolates present in sequence databases (GenBank Accession Nos. FJ492075 and FJ492170, respectively). Koch's postulates were confirmed for each isolate by carrying out the following protocol. Each isolate was cultured on potato dextrose agar for 14 days. Five 10-mm agar plugs were then placed on top of seed tubers (cv. Maris Piper) in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were held in a controlled environment room at 18°C with 50% relative humidity and watered as required. After 21 days, plants were removed and assessed for disease. Typical Rhizoctonia stem lesions were observed and R. solani was successfully reisolated from symptomatic material. To our knowledge, this is the first report of AG2-2IIIB causing disease on potatoes in the United States. In the United States, AGs 2-1, 3, 4, 5, and 9 have all been previously implicated in Rhizoctonia potato disease (2). AG2-2IIIB should now also be considered a potato pathogen in the United States. Knowledge of which AG is present is invaluable when considering a disease management strategy. AG2-2IIIB is a causal agent of sugar beet (Beta vulgaris) root rot in Idaho (1). Sugar beet is commonly grown in crop rotation with potato and such a rotation could increase the risk of soilborne infection to either crop by AG2-2IIIB. References: (1) C. A. Strausbaugh et al. Can. J. Plant Pathol. 33:210, 2011. (2) L. Tsror. J. Phytopatol. 158:649, 2010. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, Inc., New York, 1990. (4) J. W.Woodhall et al. Plant Pathol. 56:286, 2007.

Download Full-text

First Report of Rhizoctonia solani AG-1-IB Causing Leaf Blight of Sorrel (Rumex acetosa) in Brazil

Plant Disease ◽

10.1094/pdis-04-13-0443-pdn ◽

2014 ◽

Vol 98 (2) ◽

pp. 278-278

Author(s):

B. E. C. Miranda ◽

A. M. S. Cardoso ◽

R. W. Barreto

Keyword(s):

New York ◽

Rhizoctonia Solani ◽

Its Region ◽

The United States ◽

Anastomosis Group ◽

Culture Collection ◽

Representative Specimen ◽

Broad Host Range ◽

Rumex Acetosa ◽

First Report

Rumex acetosa L., common name sorrel (in Brazil, azedinha), is an herb from Europe and Asia commonly used either as a vegetable or a medicinal plant (1). No pathogen has been recorded on this plant species in Brazil, where it has been promoted as an alternative vegetable crop. During a routine inspection of a vegetable garden in the campus of the Universidade Federal de Viçosa (Viçosa, state of Minas Gerais, Brazil) in July 2011, a group of sorrel plants were found bearing blight symptoms. Infected leaves had laminae with soaked irregular necrotic areas and infected petioles had reddish lesions. Healthy leaves touched by neighboring blighted leaves became diseased. A mycelial web was always associated with necrotic tissues. A representative specimen was collected, dried in a plant press, and deposited in the local herbarium (VIC 39063). Pure cultures were obtained through direct transfer of mycelium to PDA plates and deposited in the culture collection at the Universidade Federal de Viçosa – Coleção Oswaldo Almeida Drummond (COAD 1265). Slides containing fungal structures were mounted in lactophenol and observed under a microscope (Olympus BX 51). The fungus had the following morphology: mycelium superficial, either filiform or monilioid and constricted at septae, 6 to 10 μm diameter, often branching at right angles or nearly so, typically bearing a septum at branches near the branching point. Additionally, large, poorly differentiated, dirty white sclerotia were formed in older cultures. When mounted in DAPI, 7-day-old mycelium was seen to bear 5 to 13 nuclei per cell. These characteristics suggested that the fungus was Rhizoctonia solani Kuhn (RS). Anastomosis group (AG) was determined by sequencing the rDNA internal transcribed spacer (ITS) region using primers ITS5 and ITS4 (4). A BLAST search revealed that the sequence (GenBank Accession No. KC887353) had 96% sequence identity with RS AG-1-IB GenBank accessions JN426850.1, GU596491.1, JQ692292.1, and JQ692291.1. Pathogenicity of the isolate obtained from sorrel was tested by inoculating four healthy individuals with culture plugs taken from the margin of actively growing cultures on V8 juice agar. Inoculated plants were placed in a dew chamber for 48 h and later transferred to the bench of a greenhouse. Necrosis appeared on all inoculated plants 2 days after inoculation, developing into severe blight after 7 days. RS was isolated from infected tissues. RS AG-1-IB is known as a broad host-range plant pathogen (3). This is its first report as a pathogen of sorrel in Brazil. The sole other published record of this disease on sorrel is from the United States (2). References: (1) N. R. Madeira et al. Hortic. Brasil. 26:428, 2008. (2) G. L. Peltier. Parasitic rhizoctonias in America. University of Illinois Agricultural Experiment Station, 1915. (3) B. Sneh, L. Burpee, and A. Ogoshi. Identification of Rhizoctonia species. APS Press, St Paul, MN, 1991. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, Inc., New York, 1990.

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 Colletotrichum chlorophyti Infecting Soybean Seed in Arkansas, United States

Plant Disease ◽

10.1094/pdis-04-13-0441-pdn ◽

2013 ◽

Vol 97 (11) ◽

pp. 1510-1510 ◽

Cited By ~ 4

Author(s):

H.-C. Yang ◽

J. M. Stewart ◽

G. L. Hartman

Keyword(s):

United States ◽

Soybean Seed ◽

Its Region ◽

Petri Dish ◽

The United States ◽

Post Inoculation ◽

Distilled Water ◽

Potato Dextrose Broth ◽

First Report ◽

Colletotrichum Spp

Colletotrichum chlorophyti was first reported in the United States in 2009 on soybean petioles (Glycine max [L.] Merr.) collected from Alabama, Illinois, and Mississippi (4). This species has not been reported to infect seed, unlike other Colletotrichum spp. (2). From the 2012 growing season, soybean seeds obtained from the National Agricultural Statistics Service representing 151 seed lots from growers' fields in 11 states were assayed by plating them on acidified potato dextrose agar (APDA). Before plating, seeds were surface disinfected by sequential immersion in 50% ethanol for 30 s, 20% commercial bleach for 1 min, two 1 min rinses in sterile distilled water, and kept at 25°C in the dark for 1 week. Infected seeds from one seed lot from Arkansas produced colonies similar to Colletotrichum spp. This seed lot was visually examined and divided into asymptomatic or discolored symptomatic seeds. Because of the limited number of seeds in the seed lot, 20 seeds that asymptomatic and 40 seeds that appeared symptomatic were assayed on APDA as previously described. Asymptomatic seeds did not produce any dark fungal colonies. Among the symptomatic seeds, five appeared to have flecked light gray seed coats with some larger grayish to black and irregular spots where cracks were sometimes formed, and they developed small black fungal masses or became entirely dark on the surface. Five fungal isolates were obtained from these infected seeds. On APDA, the isolates initially produced white to pink smooth-margined colonies, turned black with age, produced no aerial growth, and filled a 9 cm diameter petri dish within 10 days. DNA of one isolate was extracted for PCR and sequencing of the ITS region with ITS1 and ITS4 primers (3). From the BLAST analysis, the sequence was 100% identical to C. chlorophyti isolates, IMI 103806, and CBS 142.79 (Accession Nos. GU227894 and GU227895, respectively). To test for pathogenicity, the fungus was sub-cultured on APDA and eight APDA discs (4 mm diameter) were set into 50 ml potato dextrose broth inside a 250-ml flask and shook at a speed of 100 rpm at room temperature (24 ± 1°C) for 10 days. The mycelium was then weighed, fragmented with a blender, and resuspended in sterile distilled water to a final concentration of ~40 mg/ml. The mycelial suspension was sprayed on soybean seedlings of cv. Williams 82 (two plants/pot) at growth stage V1 to V2 until runoff. The inoculated plants were kept in a moist chamber (>90% relative humidity) for 48 h at 24 ± 1°C in the dark, and then transferred to normal plant growing conditions. At 5 days post-inoculation (dpi), the leaves showed typical symptoms caused by C. chlorophyti, including necrosis on the edge of young leaves and petioles, formation of irregular dark brown lesions, and leaves became scrolled (4). Setose acervuli, curved conidia with tapered ends (21.4 ± 1.1 × 3.8 ± 0.3 μm), and chlamydospores were found on the detached symptomatic leaves after 12 dpi. No perithecia formed. The morphology matched the description of C. chlorophyti (1,4). To our knowledge, this is the first report of C. chlorophyti in Arkansas and the first time that this species has been reported infecting seed of any plant. References: (1) S. Chandra and R. N. Tandon. Curr. Sci. 34:565, 1965. (2) G. L. Hartman et al. Page 13 in: Compendium of Soybean Diseases, APS Press, St. Paul, MN, 1999. (3) T. J. White et al. Page 315 in: PCR Protocols. A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990. (4) H.-C. Yang et al. Plant Dis. 96:1699, 2012.

Download Full-text

First Report of Leaf Blight on Hosta fortunei Caused by Rhizoctonia solani AG 4 in Italy

Plant Disease ◽

10.1094/pdis-93-4-0432c ◽

2009 ◽

Vol 93 (4) ◽

pp. 432-432 ◽

Cited By ~ 3

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Rhizoctonia Solani ◽

Aqueous Suspension ◽

Its Region ◽

The United States ◽

Morphological Characters ◽

Leaf Blight ◽

Pathogenicity Test ◽

First Report ◽

Leaf Petiole

Hosta fortunei (Liliaceae) is used in semishaded areas of gardens for its lavender-colored flowers produced in midsummer. In April of 2008, in a greenhouse at the University of Torino, located in Grugliasco (northern Italy), a leaf blight was observed on 15% of potted 60-day-old plants growing at temperatures ranging between 20 and 25°C and relative humidity of 60 to 90%. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along leaf margins. Lesions expanded for several days along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, and clung to the shoots. Severely infected plants died. Diseased tissue was disinfested for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA) amended with 25 mg/liter streptomycin sulfate. A fungus with the morphological characters of Rhizoctonia solani (4) was consistently recovered, then transferred and maintained in pure culture. Ten-day-old mycelium grown on PDA at 22 ± 1°C appeared light brown, rather compact, and had radial growth. Sclerotia were not present. Isolates of R. solani obtained from affected plants were successfully anastomosed with tester isolate AG 4 (AG 4 RT 31 obtained from tobacco plants). Results were consistent with other reports on anastomosis reactions (2). Pairings were also made with tester isolates of AG 1, 2.1, 2.2, 3, 6, 7, 11, and BI, but no anastomosis was observed. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 646-bp fragment showed a 100% homology with the sequence of R. solani AG-4 AB000018. The nucleotide sequence has been assigned GenBank Accession No. FJ 534556. For pathogenicity tests, the inoculum of R. solani was prepared by growing the pathogen on PDA for 10 days. Six-month-old plants of H. fortunei were grown in 1-liter pots. Inoculum, which consisted of an aqueous suspension of PDA and mycelium disks (10 g of mycelium per pot), was placed at the collar of plants. Plants inoculated with water and PDA fragments alone served as control treatments. Five plants per treatment were used. Plants were maintained in a growth chamber at 20 ± 1°C. The first symptoms, similar to those observed in the nursery, developed 15 days after inoculation. R. solani was consistently reisolated from infected leaves and stems. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. R. solani was reported on plants belonging to the genus Hosta in the United States (3). This is, to our knowledge, the first report of leaf blight of H. fortunei caused by R. solani in Italy as well as in Europe. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. E. Carling. Grouping in Rhizoctonia solani by hyphal anastomosis reactions. In: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Kluwer Academic Publishers, The Netherlands, 1996. (3) D. F. Farr et al. Fungi on Plants and Products in the United States. The American Phytopathology Society, St Paul, MN, 1989. (4) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St Paul, MN, 1991.

Download Full-text

First Report of Ascochyta Blight of Field Pea Caused by Ascochyta pisi in South Dakota

Plant Disease ◽

10.1094/pdis-94-6-0789a ◽

2010 ◽

Vol 94 (6) ◽

pp. 789-789 ◽

Cited By ~ 1

Author(s):

F. M. Mathew ◽

R. S. Goswami ◽

S. G. Markell ◽

L. Osborne ◽

C. Tande ◽

...

Keyword(s):

South Dakota ◽

Consensus Sequence ◽

Ascochyta Blight ◽

Its Region ◽

The United States ◽

Field Pea ◽

Conidial Suspension ◽

First Report ◽

Production Region ◽

Ascochyta Pisi

Tan lesions approximately 1.7 × 0.8 cm with distinct dark brown margins and small pycnidia were observed on leaves of field peas (Pisum sativum L. ‘Agassiz’) growing in Campbell County, South Dakota (45°45.62′N, 100°9.13′W) in July 2008. Small pieces of symptomatic leaves were surface sterilized (10% NaOCl for 1 min, 70% EtOH for 1 min, and sterile distilled H2O for 2 min) and placed on potato dextrose agar (PDA) for 7 days under fluorescent lights with a 12-h photoperiod to induce sporulation. A pure culture was established by streaking a conidial suspension on PDA and isolating a single germinated spore 3 days later. The culture was grown on clarified V8 media for 10 days. Conidia were 10 to 16 × 3 to 4.5 μm and uniseptate with a slightly constricted septum, similar to those of Ascochyta pisi Lib. The exuding spore mass from pycnidia growing on the medium was carrot red. No chlamydospores or pseudothecia were observed (1,2). To confirm the identity of A. pisi, DNA was extracted from the lyophilized mycelium of the 10-day-old culture with the DNeasy Plant Mini Kit (Qiagen, Valencia, CA). Internal transcribed spacer (ITS) regions I and II were amplified with PCR primers ITS 5 and ITS 4 (3). PCR amplicons were cleaned and directly sequenced in both directions using the primers. A BLASTN search against the NCBI nonredundant nucleotide database was performed using the consensus sequence generated by alignment of the forward and reverse sequences for this region. The consensus sequence (GenBank Accession No. GU722316) most closely matched A. pisi var. pisi strain (GenBank Accession No. EU167557). These observations confirm the identity of the fungus as A. pisi. A suspension of 1 × 106 conidia/ml of the isolate was spray inoculated to runoff on 10 replicate plants of 2-week-old, susceptible green field pea ‘Sterling’. Plants were incubated in a dew chamber for 48 h at 18°C and moved to the greenhouse bench where they were maintained at 20 to 25°C with a 12-h photoperiod for 1 week. Tan lesions with dark margins appeared 7 days after inoculation and disease was assessed after 10 days (4). No symptoms were observed on water-treated control plants. A. pisi was reisolated from lesions and confirmed by DNA sequencing of the ITS region, fulfilling Koch's postulates. Currently, states bordering South Dakota (North Dakota and Montana) lead the United States in field pea production. Although acreage is limited in South Dakota, the identification of A. pisi in this region is serious. The disease is yield limiting and foliar fungicides are used for disease management (1). To our knowledge, this is the first report of Ascochyta blight on P. sativum caused by A. pisi occurring in South Dakota and the MonDak production region (the Dakotas and Montana). References: (1) T. W. Bretag et al. Aust. J. Agric. Res. 57:88, 2006. (2) A. S. Lawyer. Page 11 in: The Compendium of Pea Diseases. D. J. Hagedorn, ed. The American Phytopathological Society, St Paul, MN, 1984. (3) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990. (4) J. M. Wroth. Can. J. Bot. 76:1955, 1998.

Download Full-text

First Report of Dollar Spot of Sandbur Caused by Sclerotinia homoeocarpa in Oklahoma

Plant Disease ◽

10.1094/pdis-03-14-0244-pdn ◽

2014 ◽

Vol 98 (8) ◽

pp. 1160-1160

Author(s):

F. Flores ◽

N. R. Walker

Keyword(s):

Warm Season ◽

Its Region ◽

Small Subunit ◽

Type I ◽

Academic Press ◽

Sclerotinia Homoeocarpa ◽

Dollar Spot ◽

First Report ◽

Small Subunit Rdna ◽

Disturbed Soils

Sandbur (Cenchrus incertus Curtis) is a warm-season, annual, noxious, grassy weed native to southern North America. It is common in sandy, disturbed soils and can also be found in home lawns and sport fields where low turf density facilitates its establishment. In July 2013, after a period of frequent rainfall and heavy dew, symptoms of dollar spot-like lesions (1) were observed on sandbur plants growing in a mixed stand of turf-type and native warm-season grasses in Logan County, Oklahoma. Lesions, frequently associated with leaf sheaths, were tan and surrounded by a dark margin. Symptomatic leaves were surface sterilized and plated on potato dextrose agar amended with 10 ppm rifampicin, 250 ppm ampicillin, and 5 ppm fenpropathrin. After incubation, a fungus morphologically identical to Sclerotinia homoeocarpa Bennett was consistently isolated. The nuclear ribosomal internal transcribed spacer (ITS) region of two different isolates, SCL2 and SCL3, were amplified using primers ITS4 and ITS5 (2). The DNA products were sequenced and BLAST analyses were used to compare sequences with those in GenBank. The sequence for isolate SLC2 was 869 bp, contained a type I intron in the 18S small subunit rDNA, and was identical to accession EU123803. The ITS sequence for isolate SLC3 was 535 bp and identical to accession EU123802. Twenty-five-day-old seedlings of C. incertus were inoculated by placing 5-mm-diameter agar plugs, colonized by mycelia of each S. homoeocarpa isolate, onto two of the plants' leaves. Plugs were held in place with Parafilm. Two plants were inoculated with each isolate and sterile agar plugs were placed on two leaves of another seedling as control. Plants were incubated in a dew chamber at 20°C and a 12-h photoperiod. After 3 days of incubation, water-soaked lesions surrounded by a dark margin appeared on inoculated plants only. Fungi that were later identified as S. homoeocarpa isolates SLC2 and SLC3 by sequencing of the ITS region were re-isolated from symptomatic leaves, fulfilling Koch's postulates. To our knowledge, this is the first report of dollar spot on sandbur. References: (1) R. W. Smiley et al. Page 22 in: Compendium of Turfgrass Diseases. 3rd ed. The American Phytopathological Society, St. Paul, MN, 2005. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

Download Full-text

First Report of Leaf Blight and Stem Canker of Pachysandra terminalis Caused by Pseudonectria pachysandricola in Korea

Plant Disease ◽

10.1094/pdis-09-11-0813 ◽

2012 ◽

Vol 96 (2) ◽

pp. 287-287

Author(s):

K. S. Han ◽

J. H. Park ◽

S. E. Cho ◽

H. D. Shin

Keyword(s):

United States ◽

Its Region ◽

Stem Canker ◽

The United States ◽

Culture Collection ◽

Leaf Blight ◽

First Report ◽

Cornell University ◽

Plastic Bags ◽

Young Leaves

Pachysandra terminalis Siebold & Zucc., known as Japanese pachysandra, is a creeping evergreen perennial belonging to the family Buxaceae. In April 2011, hundreds of plants showing symptoms of leaf blight and stem canker with nearly 100% incidence were found in a private garden in Suwon, Korea. Plants with the same symptoms were found in Seoul in May and Hongcheon in August. Affected leaves contained tan-to-yellow brown blotches. Stem and stolon cankers first appeared as water soaked and developed into necrotic lesions. Sporodochia were solitary, erumpent, circular, 50 to 150 μm in diameter, salmon-colored, pink-orange when wet, and with or without setae. Setae were hyaline, acicular, 60 to 100 μm long, and had a base that was 4 to 6 μm wide. Conidiophores were in a dense fascicle, not branched, hyaline, aseptate or uniseptate, and 8 to 20 × 2 to 3.5 μm. Conidia were long, ellipsoid to cylindric, fusiform, rounded at the apex, subtruncate at the base, straight to slightly bent, guttulate, hyaline, aseptate, 11 to 26 × 2.5 to 4.0 μm. A single-conidial isolate formed cream-colored colonies that turned into salmon-colored colonies on potato dextrose agar (PDA). Morphological and cultural characteristics of the fungus were consistent with previous reports of Pseudonectria pachysandricola B.O. Dodge (1,3,4). Voucher specimens were housed at Korea University (KUS). Two isolates, KACC46110 (ex KUS-F25663) and KACC46111 (ex KUS-F25683), were accessioned in the Korean Agricultural Culture Collection. Fungal DNA was extracted with DNeasy Plant Mini DNA Extraction Kits (Qiagen Inc., Valencia, CA). The complete internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced using ABI Prism 337 automatic DNA sequencer (Applied Biosystems, Foster, CA). The resulting sequence of 487 bp was deposited in GenBank (Accession No. JN797821). This showed 100% similarity with a sequence of P. pachysandricola from the United States (HQ897807). Isolate KACC46110 was used in pathogenicity tests. Inoculum was prepared by harvesting conidia from 2-week-old cultures on PDA. Ten young leaves wounded with needles were sprayed with conidial suspensions (~1 × 106 conidia/ml). Ten young leaves that served as the control were treated with sterile distilled water. Plants were covered with plastic bags to maintain a relative humidity of 100% at 25 ± 2°C for 24 h. Typical symptoms of brown spots appeared on the inoculated leaves 4 days after inoculation and were identical to the ones observed in the field. P. pachysandricola was reisolated from 10 symptomatic leaf tissues, confirming Koch's postulates. No symptoms were observed on control plants. Previously, the disease was reported in the United States, Britain, Japan, and the Czech Republic (2,3), but not in Korea. To our knowledge, this is the first report of P. pachysandricola on Pachysandra terminalis in Korea. Since this plant is popular and widely planted in Korea, this disease could cause significant damage to nurseries and the landscape. References: (1) B. O. Dodge. Mycologia 36:532, 1944. (2) D. F. Farr and A. Y. Rossman. Fungal Databases. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ , September 24, 2011. (3) I. Safrankova. Plant Prot. Sci. 43:10, 2007. (4) W. A. Sinclair and H. H. Lyon. Disease of Trees and Shrubs. 2nd ed. Cornell University Press, Ithaca, NY, 2005.

Download Full-text