First Report of Potato Stem Canker Caused by Rhizoctonia solani AG-5 in China

Potato (Solanum tuberosum L.) is grown worldwide as a major food crop. Potato stem canker is an important disease mainly caused by Rhizoctonia solani AG-3 (4). In 2011, samples of potato stem canker were collected from 26 sites in Heilongjiang Province, northeast China. Stem fragments taken from the margins of the healthy and diseased tissues were surface disinfected with 0.5% NaOCl for 2 min, rinsed with sterile water, then placed on potato dextrose agar (PDA) at 25°C in the dark. Twenty-two fungal isolates taken from single hyphal tips were identified as R. solani based on morphological traits. Colonies were light brown with abundant growth of mycelia and produced brown, irregular sclerotia after 20 days on PDA. Mycelium was 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 (five to 13 nuclei per 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) (1), and six out of 22 isolates anastomosed with R. solani AG-5. The internal transcribed spacer (ITS) region of rDNA was amplified from genomic DNA of the AG-5 isolates with primers ITS1 and ITS4. The ITS sequences (GenBank Accession Nos. JQ946291 to JQ946296) were 99% identical to R. solani isolate AG-5 ND1 (GenBank Accession No. HQ629863). Therefore, based on molecular characteristics and the anastomosis assay, these six isolates were confirmed to be R. solani AG-5. To determine the pathogenicity of R. solani AG-5 isolates, potato seed tubers (cv. Favorita) with 3- to 5-mm sprouts were inoculated with wheat seeds (sterilized by autoclaving twice at 121°C for 1 h with a 24-h interval) colonized with each isolate (2). Wheat seeds were placed 10 mm above the uppermost sprout tip (one seed per sprout). Plants were incubated in glasshouse conditions maintained at 25 to 27°C. After 3 weeks, all inoculated plants showed symptoms of potato stem canker disease, whereas control plants inoculated with sterilized wheat seeds remained healthy. R. solani AG-5 was consistently reisolated from symptomatic stems, and the identity was confirmed by morphological and molecular characteristics as previously described, fulfilling Koch's postulates. Potato stem canker caused by R. solani AG-5 was previously detected in Australia, South Africa, Finland, and Japan (3). However, to our knowledge, this is the first report of R. solani AG-5 on potato in China. Besides previously reported AGs 1, 3, and 4 implicated in Rhizoctonia disease in China, AG 5 should also be taken into account when designing programs for disease management in potato. References: (1) W. C. Kronland and M. E. Stanghellini. Phytopathology 78:820, 1988. (2) M. J. Lehtonen et al. Plant Pathol. 57:141, 2008. (3) M. J. Lehtonen et al. J. Agric. Food Sci. 18:223, 2009. (4) L. Tsror. J. Phytopathol. 158:649, 2010.

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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.

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First Report of Potato Stem Canker Caused by Binucleate Rhizoctonia AG-A in Jilin Province, China

Plant Disease ◽

10.1094/pdis-10-12-0912-pdn ◽

2013 ◽

Vol 97 (9) ◽

pp. 1246-1246 ◽

Cited By ~ 6

Author(s):

Y. G. Yang ◽

X. H. Wu

Keyword(s):

Solanum Tuberosum L ◽

Its Region ◽

Stem Canker ◽

Jilin Province ◽

Molecular Characteristics ◽

Potato Seed ◽

First Report ◽

Binucleate Rhizoctonia ◽

Blastn Analysis ◽

Wheat Seeds

Potato (Solanum tuberosum L.) stem canker caused by Rhizoctonia solani occurs in potato-growing regions all over the world and can result in severe losses in crop yield and quality. In late July 2011, potato subterraneous stems with stem cankers composed of brownish, sunken lesions were observed at 15% incidence in seven sites in Jilin Province, northeast China. Samples were collected, and stem pieces (each 5 mm long) taken from the margins of the healthy and diseased tissues were surface-disinfested with 0.5% NaOCl for 2 min, rinsed with sterilized water, dried, then placed on potato dextrose agar at 25°C in the dark. Three (designated JL-3, JL-5-1, and JL-6) of seven Rhizoctonia isolates that developed from single hyphal tip transfers were identified preliminarily as binucleate Rhizoctonia (BNR) isolates (teleomorph Ceratobasidium Rogers). The colonies were white or light gray with fluffy aerial hyphae and no sclerotia after 14 days in culture. Hyphal cells were binucleate when stained with 4′-6-diamidino-2-phenylindole. Average hyphal diameters (mean ± standard deviation) of isolates JL-3, JL-5-1, and JL-6 were 4.8 ± 0.5 μm (range 4.1 to 5.6 μm), 4.4 ± 0.4 μm (range 3.9 to 5.2 μm), and 4.5 ± 0.3 μm (range 4.0 to 5.0 μm), respectively. The internal transcribed spacer (ITS) region of ribosomal DNA was amplified from genomic DNA with primers ITS1 and ITS4 and sequenced. BLASTn analysis indicated that the resulting sequences (GenBank Accession Nos. JX885459, JX885460, and JX885461 for JL-3, JL-5-1, and JL-6, respectively) were 100% identical to that of a Ceratobasidium sp. AG-A isolate CHR08-10 (HQ270171). So the three isolates were identified as BNR AG-A based on morphological and molecular characteristics. To determine pathogenicity of the BNR isolates, potato seed tubers (cv. Favorita), each 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 potato tuber was planted in a plastic pot with a single colonized wheat seed placed 10 mm above the uppermost sprout tip in a sand/sawdust mixture (1:2 v/v). Plants were incubated in a glasshouse at 25 to 27°C, and assessed after 21 days. The test was performed on 20 plants/isolate and the experiment was repeated. The incidence of plants inoculated with JL-3, JL-5-1, and JL-6 that developed stem canker symptoms averaged 11.1, 23.5, and 28.6%, respectively, whereas all control plants inoculated with sterilized wheat seeds remained asymptomatic. Rhizoctonia spp. were not reisolated from the control plants, whereas BNR isolates were reisolated consistently from symptomatic stems of the inoculated plants, and the identity confirmed by morphological and molecular characteristics as described above, fulfilling Koch's postulates. BNR AG-A has been reported to be pathogenic on soybean (Glycine max), pea (Pisum sativum), snap bean (Phaseolus vulgaris), and pak choi (Brassica chinensis) in China (4). Isolates of R. solani AG-3 are most often associated with potato stem canker (2), although unidentified BNR isolates were reported to cause mild symptoms on potato sprouts in Finland (1), and small lesions on potato roots and stems in the United Kingdom (3). To our knowledge, this is the first report of BNR AG-A causing potato stem canker in Jilin Province, one of the main potato-producing areas of China. References: (1) M. J. Lehtonen et al. Plant Pathol. 57:141, 2008. (2) L. Tsror. J. Phytopatology 158:649, 2010. (3) J. W. Woodhall et al. New Dis. Rep. 23:31, 2011. (4) G. H. Yang et al. J. Phytopathology 153:333, 2005.

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First Report of Sugar Beet Rhizoctonia Crown and Root Rot Caused by Rhizoctonia solani AG-2-2IIIB in Shanxi Province of China

Plant Disease ◽

10.1094/pdis-12-12-1202-pdn ◽

2014 ◽

Vol 98 (3) ◽

pp. 419-419 ◽

Cited By ~ 3

Author(s):

C. Zhao ◽

X. H. Wu

Keyword(s):

Sugar Beet ◽

Rhizoctonia Solani ◽

Root Rot ◽

Its Region ◽

Northern China ◽

Shanxi Province ◽

Molecular Characteristics ◽

First Report ◽

Crown And Root Rot ◽

Wheat Seeds

Sugar beet (Beta vulgaris L.) is grown worldwide as the second largest sugar crop. Sugar beet crown and root rot is an economically serious disease mainly caused by Rhizoctonia solani (teleomorph Thanatephorus cucumeris) AG 2-2 and AG 4 (1). In July 2010, at the 25- to 27-leaf stage, symptoms typically associated with crown and root rot, including dark brown to black lesions at the base of the petioles or circular to oval dark lesions (up to 10.0 mm in diameter) at the taproot, were observed on 15% of sugar beet plants collected from three sites in Shanxi Province, northern China. Pieces of internal root tissues cut from the margins between symptomatic and healthy-appearing tissue were disinfected with 0.5% NaOCl for 2 min, rinsed three times with sterile water, then placed on water ager (WA) for incubation at 25°C in the dark. After 2 days, single hyphal tips of three Rhizoctonia-like isolates (designated SX-RSD1, SX-RSD2, and SX-RSD3) were transferred to potato dextrose ager (PDA). Colonies of all isolates were brown and developed dark brown sclerotia (0.5 to 1.0 mm diameter) on the media surface after 4 and 7 days, respectively. Mycelia were branched at right angles with septa near the branches and slight constrictions at the bases of the branches were present. Average hyphal diameters of the three isolates were 8.1, 7.3, and 7.6 μm, respectively. Hyphal cells were determined to be multinucleate (4 to 9 nuclei per cell) by staining with 4′-6-diamidino-2-phenylindole (DAPI) (2). Anastomosis groups were determined by pairing with reference strains (kindly provided by N. Kondo, Hokkaido University, Japan) (2), and all three isolates anastomosed with R. solani AG-2-2IIIB. All three isolates grew well on PDA at 35°C, which separates AG-2-2IIIB from AG-2-2 IV. The internal transcribed spacer (ITS) region of rDNA was amplified from genomic DNA of these isolates with primers ITS1 (5′-TCCGATGGTGAACCTGCGG-3′)/ITS4 (5′-TCCTCCGCTTATTGATATGC-3′). Sequences (GenBank Accession Nos. KC413984, KC413985, and KC413986) were over 99% identical to those of 19 R. solani AG-2-2 IIIB isolates (e.g., FJ492146.3; strain F510). Therefore, based on the molecular characteristics and the anastomosis assay, these three isolates were identified as R. solani AG-2-2IIIB. To determine the pathogenicity of the isolates, wheat seeds were autoclaved twice for 60 min at 121°C on consecutive days and inoculated with each isolate (3). Subsequently, wheat seeds (three seeds per plant) were placed around 8-week-old sugar beet (cv. HI0305) plants at 2 cm intervals to each root and 10 mm deep in soil. Plants were grown at 25 to 27°C for 7 days in a glasshouse. All inoculated plants developed symptoms of root rot, whereas control plants inoculated with sterilized wheat seeds remained healthy. R. solani AG-2-2IIIB was consistently re-isolated from the symptomatic root tissue and was confirmed by both morphological and molecular characteristics described above, fulfilling Koch's postulates. To our knowledge, this is the first report of R. solani AG-2-2IIIB on sugar beet in Shanxi Province of China. R. solani AG2-2IIIB has been reported to be pathogenic on wheat in China (4), which is often grown in rotation with sugar beet. This rotation could increase the risk of soilborne infection to either crop by R. solani AG2-2IIIB. References: (1) R. M. Harveson et al. Compendium of Beet Diseases and Pests, American Phytopathological Society. St. Paul, MN. 2009. (2) W. C. Kronland and M. E. Stanghellini. Phytopathology. 78:820, 1988. (3) M. J. Lehtonen et al. Plant Pathol. 57:141, 2008. (4) D. Z. Yu et al., Hubei Agric. Sci. 3:39, 2000.

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First Report of Stem Canker Disease of Pitaya (Hylocereus undatus and H. polyrhizus) Caused by Neoscytalidium dimidiatum in Taiwan

Plant Disease ◽

10.1094/pdis-08-11-0689-pdn ◽

2012 ◽

Vol 96 (6) ◽

pp. 906-906 ◽

Cited By ~ 18

Author(s):

M. F. Chuang ◽

H. F. Ni ◽

H. R. Yang ◽

S. L. Shu ◽

S. Y. Lai ◽

...

Keyword(s):

New York ◽

Aerial Mycelium ◽

Its Region ◽

Stem Canker ◽

Canker Disease ◽

First Report ◽

Neoscytalidium Dimidiatum ◽

Succulent Plant ◽

Sterile Medium ◽

Hylocereus Undatus

Pitaya (Hylocereus undatus and H. polyrhizus Britt. & Rose), a perennial succulent plant grown in the tropics, is becoming an emerging and important fruit plant in Taiwan. In September of 2009 and 2010, a number of pitaya plants were found to have a distinctive canker on stems. The disease expanded quickly to most commercial planting areas in Taiwan (e.g., Pintung, Chiayi, and Chunghua). Symptoms on the stem were small, circular, sunken, orange spots that developed into cankers. Pycnidia were erumpent from the surface of the cankers and the stems subsequently rotted. After surface disinfestation with 0.1% sodium hypochloride, tissues adjacent to cankers were placed on acidified potato dextrose agar (PDA) and incubated at room temperature for 1 week, after which colonies with dark gray-to-black aerial mycelium grew. Hyphae were branched, septate, and brown and disarticulated into 0- to 1-septate arthrospores. Sporulation was induced by culturing on sterile horsetail tree (Casuarina equisetifolia) leaves. Conidia (12.79 ± 0.72 × 5.14 ± 0.30 μm) from pycnidia were one-celled, hyaline, and ovate. The internal transcribed spacer (ITS) region of ribosomal DNA was PCR amplified with primers ITS1 and ITS4 (2) and sequenced. The sequence (GenBank Accession No. HQ439174) showed 99% identity to Neoscytalidium dimidiatum (Penz.) Crous & Slippers (GenBank Accession No. GQ330903). On the basis of morphology and nucleotide-sequence identity, the isolates were identified as N. dimidiatum (1). Pathogenicity tests were conducted in two replicates by inoculating six surface-sterilized detached stems of pitaya with either mycelium or conidia. Mycelial plugs from 2-day-old cultures (incubated at 25°C under near UV) were inoculated to the detached stems after wounding with a sterile needle. Conidial suspensions (103 conidia/ml in 200 μl) were inoculated to nonwounded stems. Noninoculated controls were treated with sterile medium or water. Stems were then incubated in a plastic box at 100% relative humidity and darkness at 30°C for 2 days. The symptoms described above were observed on inoculated stems at 6 to 14 days postinoculation, whereas control stems did not develop any symptoms. N. dimidiatum was reisolated from symptomatic tissues. To our knowledge, this is the first report of N. dimidiatum causing stem canker of pitaya. References: (1) P. W. Crous et al. Stud. Mycol. 55:235, 2006. (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, New York, 1990.

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First Report of Rhizoctonia solani AG4 HG-II Infecting Potato Stems in Idaho

Plant Disease ◽

10.1094/pdis-06-12-0568-pdn ◽

2012 ◽

Vol 96 (11) ◽

pp. 1701-1701 ◽

Cited By ~ 5

Author(s):

J. W. Woodhall ◽

P. S. Wharton ◽

J. C. Peters

Keyword(s):

Rhizoctonia Solani ◽

Seed Tuber ◽

Its Region ◽

Stem Canker ◽

Potato Production ◽

Koch’S Postulates ◽

First Report ◽

Rdna Its ◽

Plant Pathol ◽

Koch's Postulates

The fungus Rhizoctonia solani is the causal agent of stem canker and black scurf of potato (Solanum tuberosum). R. solani is a species complex consisting of 13 anastomosis groups (AGs) designated AG1 to 13 (2, 3). Stems of potato (cv. Russet Norkotah) with brown lesions were recovered from one field in Kimberley, Idaho, in August 2011. Using previously described methods (3), R. solani was recovered from the symptomatic stems and one representative isolate (J15) was selected for further characterization. Sequencing of the rDNA ITS region of isolate J15 was undertaken as previously described (3) and the resulting rDNA ITS sequence (HE667745) was 99% identical to sequences of other AG4 HG-II isolates in GenBank (AF354072 and AF354074). Pathogenicity of the isolate was determined by conducting the following experiment. Mini-tubers of cv. Santé were planted individually in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were either inoculated with J15, an isolate of AG3-PT (Rs08), or were not inoculated. Each treatment was replicated four times. Inoculum consisted of five 10-mm-diameter potato dextrose agar plugs, fully colonized by the appropriate isolate, placed in the compost approximately 40 mm above each seed tuber. Pots were held in a controlled environment room at 21°C with 50% relative humidity and watered as required. After 21 days, plants were assessed for disease. No symptoms of the disease were present in non-inoculated plants. In the Rs08 (AG3-PT) inoculated plants, all stems displayed large brown lesions and 20% of the stems had been killed. No stem death was observed in J15 (AG4 HG-II) inoculated plants. However, brown lesions were observed in three of the four J15 (AG4 HG-II) inoculated plants. These lesions were less severe than in plants inoculated with the Rs08(AG3-PT) inoculated plants and were present in 40% of the main stems. In the J15 (AG4 HG-II) inoculated pots, R. solani AG4 HG-II was reisolated from the five symptomatic stems, thereby satisfying Koch's postulates. To our knowledge, this is the first report of AG4 HG-II causing disease on potatoes in Idaho. AG4 has been isolated from potato previously from North Dakota, although the subgroup was not identified (1). The only previous report where AG4 HG-II was specifically determined to cause disease on potato was in Finland, but the isolate could not be maintained and Koch's postulates were not completed (3). The present study shows that AG4 HG-II can cause stem disease in potatoes, although disease does not develop as severely or as consistently as for AG3-PT. However, as demonstrated with isolates of AG2-1 and AG5, even mild stem infection can reduce tuber yield by as much as 12% (4). AG4 HG-II is a pathogen of sugar beet in Idaho, which was grown previously in this field. This history may have contributed to high levels of soilborne inoculum required to produce disease on potato. References: (1) N. C. Gudmestad et al. Page 247 in: J. Vos et al. eds. Effects of Crop Rotation on Potato Production in the Temperate Zones. Kluwer, Dordrecht, Netherlands, 1989. (2) M. J. Lehtonen et al. Agric. Food Sci. 18:223, 2009. (3) J. W. Woodhall et al. Plant Pathol. 56:286, 2007. (4) J. W. Woodhall et al. Plant Pathol. 57:897, 2008.

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First Report of Sugar Beet Seedling Damping-Off Caused by Binucleate Rhizoctonia AG-A in China

Plant Disease ◽

10.1094/pdis-05-12-0492-pdn ◽

2012 ◽

Vol 96 (11) ◽

pp. 1696-1696 ◽

Cited By ~ 6

Author(s):

P. P. Wang ◽

X. H. Wu

Keyword(s):

Sugar Beet ◽

Disease Incidence ◽

Soil Surface ◽

Its Region ◽

Molecular Characteristics ◽

Damping Off ◽

First Report ◽

Binucleate Rhizoctonia ◽

Hyphal Diameter ◽

Wheat Seeds

Sugar beet (Beta vulgaris L.) is grown worldwide and produces one-third of the world's sugar supply. Sugar beet seedling Rhizoctonia damping-off is an important disease mainly caused by Rhizoctonia solani AG-2, AG-4, and AG-5 (2). In 2010, diseased sugar beet seedlings with about 20% incidence affected by damping-off, which showed dark brown lesions on the stems just below the soil surface and portions of the roots, were collected from nurseries in three locations in Heilongjiang province, northeast China. Root fragments taken from the margins of healthy tissues and lesions on roots were surface disinfected with 0.5% sodium hypochlorite for 2 min, rinsed with sterile water, then placed on potato dextrose agar (PDA) and incubated at 25°C in the dark. Three (designed HLJ-RAA1, HLJ-RAB1, HLJ-RAB2) of nine Rhizoctonia isolates were obtained from diseased tissues and preliminarily identified as binucleate Rhizoctonia (BNR) anamorph (teleomorph Ceratobasidium Rogers) species-like. Fungal colonies were white with large amounts of floccose, aerial hyphae. Hyphal cells were determined to be binucleate when stained with 4′-6-diamidino-2-phenylindole (DAPI) (1). No sclerotia were produced after 14 days on PDA. Average hyphal diameter of the three isolates were 4.2, 4.3, and 4.8 μm, respectively. Further, the internal transcribed spacer (ITS) region of rDNA was amplified from the genomic DNA extracted from hyphae by bead beating in 2% CTAB solution using stainless steel beads with primers ITS1 and ITS4. The ITS sequences (GenBank Accession Nos. JX073668, JX073669, and JX073670) were over 99% identical to those of more than 50 Ceratobasidium sp. AG-A isolates (e.g., GenBank Accession No. JQ688054.1; strain HY-15). Therefore, based on morphological and molecular characteristics, these isolates were identified to be BNR AG-A. To determine the pathogenicity of the isolates, sugar beet (cv. HI0305) seedlings were inoculated with wheat seeds colonized with each of the isolated Rhizoctonia strains (one seed per seedling), and grew in pots under greenhouse conditions (3). After 3 weeks, some inoculated plants showed damping-off as observed in the nurseries, whereas noninoculated control plants (sterile wheat seeds only) remained healthy. Disease incidence from the trials averaged 53.3%, 70%, and 53.3% for the isolates HLJ-RAA1, HLJ-RAB1, and HLJ-RAB2, respectively. The three BNR cultures of the pathogens were consistently reisolated from symptomatic roots, and their identities confirmed by morphological and molecular characteristics as described above, fulfilling Koch's postulates. BNR AG-A was previously reported to be pathogenic to soybean, pea, snap bean, and pak choy in China (4). However, to our knowledge, this is the first report of BNR AG-A causing sugar beet seedling damping-off in China. Sugar beet is often grown in crop rotation with soya bean and such a rotation could increase the risk of soilborne infection to either crop by BNR AG-A. References: (1) W. C. Kronland and M. E. Stanghellini. Phytopathology 78:820, 1988. (2) E. O'Sullivan and J. A. Kavanagh. Plant Pathol. 40:128, 1991. (3) C. E. Windels and D. J. Nabben. Phytopathology 79:83, 1989. (4) G. H. Yang et al. J. Phytopathol. 153:333, 2005.

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First Report of Web Blight on Rebutia perplexa Caused by Rhizoctonia solani AG 2-2-IIIB in Italy

Plant Disease ◽

10.1094/pdis-10-13-1063-pdn ◽

2014 ◽

Vol 98 (5) ◽

pp. 697-697 ◽

Cited By ~ 1

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

P. Pensa ◽

G. Ortu ◽

M. L. Gullino

Keyword(s):

Rhizoctonia Solani ◽

Aerial Mycelium ◽

Its Region ◽

Molecular Characteristics ◽

Fluorescent Light ◽

Pathogenicity Test ◽

Mycelium Growth ◽

Daily Growth ◽

First Report ◽

Wheat Kernels

Rebutia perplexa, Cactaceae family, is a clumping fine thorny cactus, producing several flushes of pink flowers. In the spring of 2013, a blight was observed in a farm located near Imperia (northern Italy) on 2% of 2,000 3-year-old plants, grown in plastic pots. Affected plants showed pale brown discoloration of stems, starting from the base, and eventually collapsed. Flowers also rotted and wilted. In the presence of high relative humidity, a rare, whitish mycelium developed on the surface of the substrate. Eventually, infected plants died. Symptomatic tissues of the stem were taken from 10 plants and plated on potato dextrose agar (PDA). A fungus with the morphological characters of Rhizoctonia solani (3) was consistently recovered. Three representative isolates obtained from affected plants were successfully paired with tester strains of R. solani (AG 1, AG 2-2-IIIB, AG 2-2-IV, AG 4, AG 7, AG 11) (2) and examined microscopically. Three replicated pairings were made for each tester strain. The Rebutia isolates anastomosed only with AG 2-2-IIIB tester strain with high hyphal fusion frequency. The hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and death of adjacent cells was observed, indicating anastomosis reactions (1). Tests were performed twice. Mycelium of 15-day-old isolates maintained at 27 to 30°C, appeared whitish or pale buff in color, coarse, with a concentric zonation, scarce aerial mycelium, and without sclerotia. The optimum temperature for mycelium growth was 30°C (daily growth rate: 24.6 mm) and isolates grew also at 35°C. The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced. BLASTn analysis of the 523-bp amplicon (GenBank Accession No. KF719318) showed a 99% homology with the sequence of the R. solani AG 2-2-IIIB isolate GU811672. The nucleotide sequence has been assigned the GenBank Accession No. KF719318. Therefore, on the basis of molecular characteristics, anastomosis tests, temperature growth, and cultural characteristics, the isolates from R. perplexa were identified as R. solani AG 2-2-IIIB. For pathogenicity tests, 3 g of colonized wheat kernel from 10-day-old cultures of a representative isolate of the fungus was added per 1 l of substrate in 12 potted healthy plants of R. perplexa. The inoculum was prepared by inoculating wheat kernels with the mycelium of 10-day-old cultures of the fungus and incubating at 25 ± 1°C (12 h fluorescent light, 12 h dark). Twelve plants inoculated with non-infested wheat kernels served as controls. Plants were covered with plastic bags and maintained in a growth chamber at 25 ± 1°C. The first symptoms, similar to those observed in the farm, developed 5 days after inoculation. Fifteen days after the artificial inoculation, all inoculated plants were dead. R. solani was re-isolated only from the stems of symptomatic plants. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. This is, to our knowledge, the first report of blight of R. perplexa caused by R. solani in Italy as well as worldwide. References: (1) 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, pp. 37-47, 1996. (2) A. Ogoshi. Ann. Rev. Phytopathol. 25:125, 1987. (3) B. Sneh et al. Identification of Rhizoctonia species. APS Press, St Paul, MN, 1991.

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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.

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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.

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First Report of Root and Stem Rot Caused by Phytophthora nicotianae on Peperomia tetraphylla in China

Plant Disease ◽

10.1094/pdis-94-9-1171c ◽

2010 ◽

Vol 94 (9) ◽

pp. 1171-1171 ◽

Cited By ~ 1

Author(s):

D. X. Zeng ◽

X. L. Wu ◽

Y. H. Li

Keyword(s):

Southern China ◽

Aerial Mycelium ◽

Its Region ◽

Soil Extract ◽

Phytophthora Nicotianae ◽

Stem Rot ◽

Molecular Characteristics ◽

Its Sequence ◽

First Report ◽

Pure Cultures

Peperomia tetraphylla, an evergreen herb, is becoming increasingly popular as a potted ornamental plant in southern China. In the summer of 2008, in some commercial flower nurseries in Shenzhen, Guangdong Province, P. tetraphylla showed extensive black stem and root rot, with leaves dropping from the rotten stem. Small pieces (approximately 3 mm2) of stems and leaves were excised from the margins of the black lesions, surface disinfected for 30 s to 1 min in 0.1% HgCl2, plated onto potato dextrose agar (PDA), and incubated at 25°C in the dark. All the plated samples yielded Phytophthora, and microscopic examination of pure cultures grown on PDA plates showed arachnoid colonies with abundant aerial mycelium, chlamydospores, and a few sporangia. Numerous sporangia were formed in sterile soil extract. Sporangia were ovoid or obpyriform, noncaducous, with prominent solitary papillae, and measured 31 to 52 μm (average 38 μm) × 21 to 34 μm (average 27 μm). Chlamydospores were spherical and 21 to 34 μm in diameter (average 28 μm). The internal transcribed spacer (ITS) region of rDNA of a single isolate was amplified using primers ITS4/ITS5 and sequenced (2). The ITS sequence, when submitted for a BLAST search in the NCBI database, showed 100% homology with the sequences of two reference isolates of Phytophthora nicotianae (Accession Nos. AY833526 and EU433396) and the consensus ITS sequence was deposited in the NCBI as Accession No. GQ499373. The isolate was identified as Phytophthora nicotianae on the basis of morphological and molecular characteristics (1). Pathogenicity of the isolate was confirmed by inoculating 1-year-old plants of P. tetraphylla growing in pots. The isolate was grown for 7 days on PDA plates and mycelial plugs, 5 mm in diameter and taken from the advancing margins of the colonies, were buried approximately 1 cm deep near the base of the stem in such a way that the mycelium on the plugs was in contact with the surface of the stem, which had been wiped earlier with 70% ethanol and gently wounded with a needle. Plants treated the same way but inoculated with sterile PDA plugs served as control plants. Three plants in each pot were inoculated and there were five replications each for the treatment and the control. All plants were kept in a greenhouse at 22 to 32°C. After 6 to 7 days, the inoculated plants showed black lesions around the mycelial plugs; symptoms of root and stem rot developed rapidly thereafter and the plants collapsed within 2 weeks. All symptoms on the inoculated plants were identical to those observed in naturally diseased plants, whereas the control plants remained healthy. The same fungus was consistently reisolated from the inoculated plants. To our knowledge, this is the first report of Phytophthora nicotianae on P. tetraphylla in China. References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996. (2) J. B. Ristaino et al. Appl. Environ. Microbiol. 64:948, 1998.

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