First Report of Pythium Root and Stalk Rot of Forage Corn Caused by Pythium arrhenomanes in Japan

Corn (Zea mays L.) is the most important forage crop in Japan. It was cultivated on 92,000 ha in 2011 and was mainly used as whole crop silage for cattle feed. In September 2009, a root and stalk rot disease was detected on corn plants cultivated in Tochigi, located in the central region of Japan. The symptoms of the disease included wilting of whole plants after the R5 (dent) stage (2) with drooping ears. Roots turned black and their number decreased. Further, the stalks became hollow and soft and harbored white hyphae. This tissue deterioration made machine harvest difficult. We obtained seven isolates of a Pythium-like organism by single hypha isolation from surface-sterilized pieces of diseased roots and stems on water agar and deposited one of the isolates at the NIAS genebank, Japan, under the accession no. MAFF511547. The isolate was grown in the dark on V8 juice agar medium for 10 days to produce oogonia. The oogonia were globose, light brown to yellow, smooth, 23.9 to 30.5 μm in size, and had 1 to 8 antheridia. Oospores were mostly plerotic, and oogonia walls were 1.3 to 2.7 μm thick. The morphology of the isolates was similar to that of Pythium arrhenomanes Drechsler and consistent with the species description (3). We analyzed the rDNA-ITS region sequences of the isolate as described by Kageyama et al. (1). The sequence (GenBank Accession No. AB903904) showed 99.1% (783/790 bp) similarity with that of P. arrhenomanes (AY598628). On the basis of morphological and rDNA sequence similarities, we identified the isolates obtained from corn as P. arrhenomanes. The pathogenicity of the isolate was confirmed by planting corn seedlings of the commercial Pioneer Brand hybrid 36B08 immediately after germination in five replicate pots containing soil mixed with 5% boiled barley grain by weight, incubated with or without the isolate for 7 days. After 10 days of incubation in a greenhouse at 20 to 25°C, only the inoculated plants exhibited symptoms of root and stalk rot. Since the inoculated organism was readily re-isolated from the diseased stems and roots, the pathogenicity of the isolate was confirmed. For field observation, the same hybrid of forage corn was sown in the fields in Nasushiobara, Tochigi, on 16 May 2011. The hybrid was sown in a row of 2 m, with 20 seeds planted at a distance of 10 cm with two replicates. For inoculum, the isolate was cultured on 5-cm-long wooden toothpicks, previously soaked in potato dextrose broth and placed on a V8 agar plate for 7 days at 25°C in the dark until covered by hyphae. The toothpicks were pierced into wounds made on the stems of corn plants, approximately 10 cm above the ground, using a thin iron needle. The wounds were about 2 mm in diameter and 2 cm deep. Field inoculation was conducted in late July at the R1 (silking) growth stage. Disease symptoms were observed in mid-September at R5, and only those plants that were inoculated with the toothpicks harboring the hyphae exhibited the typical stem rot symptoms. To our knowledge, this is the first report of root and stalk rot caused by P. arrhenomanes in forage corn in Japan. References: (1) K. Kageyama et al. J. Phytopathol. 151:485, 2003. (2) S. W. Ritchie et al. Spec. Rep. 48. Iowa State Univ. Coop Ext. Serv., Ames, 1993. (3) A. J. Van der Plaats-Niterink. Stud. Mycol. 21:1, 1981.

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First Report of Sheath Blight Caused by Waitea circinata Affecting Foxtail Millet (Setaria italica) in China

Plant Disease ◽

10.1094/pdis-06-14-0603-pdn ◽

2014 ◽

Vol 98 (10) ◽

pp. 1442-1442

Author(s):

Z. Y. Li ◽

N. Wang ◽

Z. P. Dong ◽

L. Dong ◽

H. Bai ◽

...

Keyword(s):

Foxtail Millet ◽

Agar Plate ◽

Negative Control ◽

Sheath Blight ◽

Setaria Italica ◽

Post Inoculation ◽

Potato Dextrose Broth ◽

First Report ◽

Rdna Its ◽

Waitea Circinata

Foxtail millet (Setaria italica) is planted widely in northern China, especially in Hebei, Shanxi, Shandong, and Henan provinces. Although several diseases reduce production of this important crop species, sheath blight is considered one of the important diseases of foxtail millet in China. Sheath blight is caused by a soil-borne pathogen and is difficult to control. Epidemics are most common at the late growth stage of foxtail millet. In August 2013, an outbreak was recorded in Shijiazhuang city, Hebei, with an incidence of about 60%. Typical disease symptoms consisted of large, irregular lesions with reddish-brown margin and as the disease progressed, the plants lodge. Three representative sheath fragments (each 1 cm long) were collected from diseased plants during that outbreak. The samples were disinfected with 0.5% (v/v) sodium hypochlorite, rinsed with sterile water, placed on a water agar plate, and then incubated at 26°C in the dark for two days. After the hyphae appeared, ~3-mm-long hyphal tips from typical colonies were excised and transferred to potato dextrose agar (PDA) plates. Three isolates were obtained and all showed typical features of Rhizoctonia-like fungus. Each isolate occupied its whole plate within 5 days of incubation at 26°C in the dark, and abundant aerial mycelia were produced. The color of all colonies was first orange, turning a salmon color when the mycelia matured. Orange sclerotia appeared after 2 weeks of incubation. The nuclei were stained with DAPI (2-(4-amidinophenyl)-1H-indole-6-carboxamidine) and observed under a fluorescent microscope. The hyphal cells were multinucleate and the mycelia branched at a right angle. For molecular identification of the pathogen, mycelia of each isolate were cultured in potato dextrose broth at 26°C for a week, and genomic DNA was extracted from mycelia and used as a template for PCR amplification. The primers set of ITS1 and ITS4 was used for amplification of rDNA-ITS from these isolates and the amplified rDNA-ITS regions of all isolates (GenBank Accession Nos. KJ765700, KJ765701, and KJ765702, respectively) were 99% identical to other Waitea circinata deposited in GenBank (1,2). To further confirm the pathogenicity of the isolates, freshly collected PDA plugs were inoculated on the lower leaf blades of 8-week-old seedlings of the foxtail millet variety Yugu 1. PDA plugs without the isolate were used as a negative control. Five plants were used for each isolate and negative control. After inoculation, pots were placed together in a moist chamber at 26°C. No symptoms developed on the control plants, while obvious lesions appeared on the sheaths of tested plants at 5 days post inoculation and later the plants were lodging. The fungus was re-isolated from diseased plants and confirmed to be W. circinata based on morphological characteristics and sequence analysis as previously described, completing Koch's postulates. Further, on the basis of morphological tests, pathogenicity assays, and molecular analyses, the pathogen of foxtail millet sheath blight was identified as W. circinata (4). Although Rhizoctonia solani AG-1, AG-4 has been reported in earlier studies as the pathogen causing foxtail millet sheath blight, there has been no previous report of the disease caused by W. circinata (3). To our knowledge, this is the first report of foxtail millet sheath blight caused by W. circinata in China. With the spread of high millet plant density and fertilizer application, this disease may become a major threat to foxtail millet; therefore, W. circinata should be taken into account when designing measures for disease control in foxtail millet. References: (2) K. A. de la Cerda et al. Plant Dis. 91:791, 2007. (1) M. Fiers et al. Eur. J. Plant. Pathol. 128:353, 2010. (4) W. D. Gao. Acta Phytopathol. Sinica 17:247, 1987. (3) T. Toda et al. Plant Dis. 89:536, 2005.

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First Report of Powdery Mildew on Spanish Needles (Bidens bipinnata) Caused by Podosphaera xanthii in Korea

Plant Disease ◽

10.1094/pdis-10-12-0966-pdn ◽

2013 ◽

Vol 97 (10) ◽

pp. 1385-1385

Author(s):

H. B. Lee ◽

C. J. Kim ◽

H. Y. Mun

Keyword(s):

Powdery Mildew ◽

Its Region ◽

Broad Host Range ◽

Pathogenicity Test ◽

Podosphaera Xanthii ◽

Tropical Regions ◽

First Report ◽

Rdna Its ◽

Humid Condition ◽

Primer Sets

Spanish needles (Bidens bipinnata L.) is an annual herb that belongs to a genus of flowering plants in family Asteraceae native to United States, and tropical regions around world. The plant produces important flavonoid compounds quercitin and hyperoside that function as anti-allergens, anti-inflammatories, anti-microbials, and anti-cancer agents. Between July and October 2011 and 2012, white superficial mycelia were observed initially on leaf and stem portions, but later progressed to the flower head. Surveys showed that the disease was widespread in Gwangju and most areas of South Korea. Abundant, necrotic, dark brown spots showing chasmothecia were frequently observed in October and were abundant on the adaxial surface of leaves. Chasmothecia were blackish brown to yellow without typical appendages. They ranged from 51.2 to 71.1 (mean 66.8) μm in diameter. Conidia were formed singly and the primary conidia were ellipsoid, rounded at the apex, truncated base, and ranged from 25.4 to 33.2 (mean 27.3) μm long × 10.2 to 12.2 (mean 11.3) μm wide. Conidiophores were erect, 60.1 to 101.3 (mean 98.3) μm long × 6.2 to 9.2 (mean 7.3) μm wide. From extracted genomic DNA, the internal transcribed spacer (ITS) region inclusive of 5.8S and 28S rDNA was amplified with ITS1F (5′-TCCGTAGGTGAACCTGCGG-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′), and LROR (5′-ACCCGCTGAACTTAAGC-3′) and LR5F primer sets, respectively. rDNA ITS (GenBank Accession No. JX512555) and 28S (JX512556) homologies of the fungus (EML-BBPW1) represented 99.6% (532/534) and 100% (661/661) identity values with Podosphaera xanthii (syn. P. fusca) AB040349 and P. xanthii (syn. P. fusca) AB462798, respectively. The rDNA sequence analysis revealed that the causal fungus matched P. xanthii (syn. P. fusca), forming a xanthii/fusca group (3,4). A pathogenicity test was performed on three plants in a greenhouse. The treated leaves were sealed in vinyl pack in humid condition for 2 days. Seven days after inoculation, similar symptoms were observed on the inoculated Spanish needles plant leaves. No symptoms were observed on control plants treated with distilled water. Koch's postulates were fulfilled by re-observing the fungal pathogen on the inoculated leaves. Podosphaera (syn. Sphaerotheca) xanthii (or fusca) has been known as an ubiquitous species with a broad host range. So far, five records regarding P. xanthii (=P. fusca) have been found in plants of genus Bidens. P. xanthii has been reported to occur on B. cernua in Belarus and Switzerland. In addition, the powdery mildew species was reported to occur on B. frondosa and B. tripartita in Korea, Russia, and Switzerland (2). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on Spanish needles (B. bipinnata) in Korea. References: (1) U. Braun et al. Schlechtendalia 10:91, 2003. (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/ , 2012. (3) H. B. Lee. J. Microbiol. 51:1075, 2012. (4) S. Takamatsu, et al. Persoonia 24:38, 2010.

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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 Phytophthora palmivora, Causal Agent of Black Pod, on Cacao in Puerto Rico

Plant Disease ◽

10.1094/pdis-91-8-1051b ◽

2007 ◽

Vol 91 (8) ◽

pp. 1051-1051 ◽

Cited By ~ 3

Author(s):

B. M. Irish ◽

R. Goenaga ◽

S. Park ◽

S. Kang

Keyword(s):

Puerto Rico ◽

Germplasm Collection ◽

Its Region ◽

Phytophthora Palmivora ◽

Research Station ◽

Pathogenicity Test ◽

Small Surface ◽

Potato Dextrose Broth ◽

First Report ◽

Black Pod

Black pod or Phytophthora pod rot is the most economically important and widespread disease of cacao, Theobroma cacao L. Total losses due to Phytophthora exceed $400 million worldwide (1), and several species are known to attack cacao with P. palmivora (E.J. Butler) E. J. Butler as the most common. All plant parts are infected, but pod infections are particularly damaging. Symptoms resembling those of black pod disease were observed at the National Plant Germplasm Collection System of cacao at the USDA-ARS Tropical Agriculture Research Station (TARS) in Mayaguez, Puerto Rico for a number of years. During May of 2005, to determine the etiology of the disease, small, surface disinfested sections of pod lesions were placed on water agar and incubated for 4 days. The formation of papillate, deciduous, ellipsoidal to ovoid sporangia produced on sympodial sporangiophores on fruits, fit the description of P. palmivora and the identification was confirmed on cultures on water agar (2). Chlamydospores were readily observed in diseased pods and observed in pure cultures on V8 agar (2). Eight, single hyphal tips were transferred to potato dextrose agar (PDA) (Sigma-Aldrich, St. Louis, MO) and maintained as stock cultures. For pathogenicity tests, healthy mature pods were surface disinfested and placed in a humidity chamber lined with moist paper towels. Eight isolates were tested on four fruits per isolate and the pathogenicity test was repeated once. Inoculum was prepared by growing each isolate on PDA for 5 days with irradiation at 24°C, adding approximately 3.0 ml of water to each plate, dislodging the sporangia with a glass rod, mixing the suspension, estimating spore numbers with a hemacytometer, and adjusting to 104 sporangia per ml. A small, sterile scalpel was used to make an approximately 20.0 mm cut on the fruit epidermis, and approximately 0.2 ml of inoculum was placed on the wound. Pods were evaluated daily for 2 weeks. For molecular analysis, each of the eight cultures were grown in 50% potato dextrose broth to produce mycelia for DNA extraction using the FastDNA kit (Q-Biogen1, Irvine, CA). The internal transcribed spacer (ITS) region of the ribosomal RNA gene cluster was amplified, purified, and sequenced for all eight isolates. The ITS sequences of GenBank Accession Nos. DQ987915 to DQ987922 were identical and exhibited strong similarity (>99% identity) to that of three previously described isolates of P. palmivora from cacao (GenBank Accession Nos. AF 228097, AF467093, and AF467089). P. palmivora has been reported on citrus, coconut, black pepper, and Arracacia xanthorrhiza in Puerto Rico (2,3) and inoculum may have originated from these host or imported on cacao planted into the cacao collection before 2000. USDA-ARS-TARS is the official site for the cacao germplasm collection, thus, a detailed integrated pest management plan that includes the evaluation for resistance, sanitation measures, and use of fungicides to reduce disease levels has been implemented. Decreasing incidence and severity of this disease is a top priority. To our knowledge, this is the first report of P. palmivora on cacao in Puerto Rico. References: (1) M. C. T. Braga et al. Agrotropica 1:108, 1989. (2) D. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul, MN, 1996. (3) E. Rosa-Marquez. J. Agric. Univ. P. R. 84:53, 2000.

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First Report of Powdery Mildew Caused by Podosphaera xanthii (syn. P. fusca) on Cocklebur in Korea

Plant Disease ◽

10.1094/pdis-10-12-0951-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 842-842 ◽

Cited By ~ 2

Author(s):

H. B. Lee

Keyword(s):

Powdery Mildew ◽

Natural Infection ◽

Morphological Characteristics ◽

Its Region ◽

Xanthium Strumarium ◽

Podosphaera Xanthii ◽

First Report ◽

Rdna Its ◽

Causal Fungus ◽

Powdery Mildew Pathogen

Cocklebur (Xanthium strumarium L., Asteraceae) is an annual broadleaf weed native to the Americas and eastern Asia. The plant is known as one of the worst competitive weeds in soybean fields and also is known to have some phytopharmacological or toxicological properties. In October 2011, a powdery mildew disease was observed on cocklebur growing in a natural landscape at Geomun Oreum located in Jeju Island, South Korea. Initial signs appeared as thin white colonies, which subsequently developed abundant growth on adaxial leaf surfaces. As the disease progressed, brown discoloration extended down infected leaves which withered. Conidia were formed singly and terminally on conidiophores. Primary conidia (20.3 to 28.6 [average 25.1] μm long × 11.1 to 15.2 [14.3] μm wide, n = 30) were ellipsoid with a round apex and truncate base. Conidiophores were straight or slightly curved and 60.1 to 101.7 (97.3) μm long × 8.2 to 13.2 (11.3) μm wide. Chasmothecia were not observed. No fibrosin bodies were observed in the conidia. Morphological characteristics were consistent with descriptions of Podosphaera xanthii (syn. P. fusca) (2,4). To confirm the identity of the causal fungus, the internal transcribed spacer (ITS) region inclusive of 5.8S and 28S rDNA was amplified from white patches consisting of mycelia and conidia on one leaf using ITS1 (5′-TCCGTAGGTGAACCTGCGG-3′) and LR5F (5′-GCTATCCTGAGGGAAAC-3′), and LROR (5′-ACCCGCTGAACTTAAGC-3′) and LR5F primer sets, respectively. The resulting sequences were deposited in GenBank (Accession Nos. JX502022 and JX964999). A NCBI BLASTn search revealed that the rDNA ITS (JX502022) and 28S (JX964999) homologies of isolate EML-XSPW1 represented 99.6% (512/514) and 100% (803/803) identity values with those of P. xanthii (AB040330 and AB462792, respectively). The rDNA ITS and 28S sequence analysis revealed that the causal fungus clustered with P. xanthii (syn. P. fusca), falling into the Xanthii/Fusca phylogenetic group (2,4). Pathogenicity was confirmed through inoculations made by gently pressing infected leaves onto mature leaves of healthy cocklebur plants in the field in August. The six inoculated leaves were sealed in sterilized vinyl bags to maintain humid conditions for 2 days. Seven days after inoculation, symptoms similar to those observed under natural infection were observed on the inoculated plant leaves. No symptoms developed on the uninoculated control plants. A fungal pathogen that was morphologically identical to the fungus originally observed on diseased plants was also observed on inoculated plants. Erysiphe cichoracearum, E. communis, Oidium asteris-punicei, O. xanthimi, P. xanthii, and P. fuliginea have all been reported to cause powdery mildew on cocklebur (1). P. xanthii was first reported on X. strumarium in Russia (3). To our knowledge, this is the first report of powdery mildew on cocklebur caused by P. xanthii in Korea. The powdery mildew pathogen may represent an option for biocontrol of the noxious weed in the near future. References: (1) D. F. Farr and A. Y. Rossman. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases , December 11, 2012. (2) H. B. Lee. J. Microbiol. 51:1075, 2012. (3) V. A. Rusanov and T. S. Bulgakov. Mikol. Fitopatol. 42:314, 2008. (4) S. Takamatsu et al. Persoonia 24:38, 2010.

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First Report of Phytopythium helicoides Causing Stalk Rot on Corn in China

Plant Disease ◽

10.1094/pdis-02-21-0429-pdn ◽

2021 ◽

Author(s):

Xueying Xie ◽

Hongzi Zhou ◽

Susu Fan ◽

Xinjian Zhang

Keyword(s):

Relative Humidity ◽

Cytochrome C ◽

Cytochrome C Oxidase ◽

Negative Control ◽

Corn Stalk ◽

Fusarium Spp ◽

First Report ◽

Stalk Rot ◽

Leaf Stage ◽

Corn Plants

Corn (Zea mays L.) is one of the most important grain crops in the world, especially in China. Besides, corn stalks are often used in production of bio-fuels (Xue et al., 2017). Recently, the production and quality of corn have been severely influenced by corn stalk rot in China caused by Fusarium spp. (Yu et al., 2017). At the end of June of 2019, a field survey of corn was carried out in Tai’an City, western Shandong Province, China. During the survey, the average day time temperature ranged between 22-28°C with intermittent rainfall, the relative humidity was 50-70%. In this survey, the symptomatic corn plants showed signs of necrosis and rotting on stalks and root collars. Five fields were surveyed and symptomatic corn plants were observed in three fields. The incidence rate of disease was about 5%, and the disease was more of a problem in low-lying areas. A total of twenty-eight symptomatic corn plants (7-12 per field), hybrid Denghai-618, at the 3-4 leaf stage were collected and tested for the presence of pathogens. The diseased tissues were excised, surface-sterilized with 75% ethanol for 30 seconds, rinsed for 3 to 5 times with sterile distilled water, and plated on potato dextrose agar (PDA). All plates were incubated at 28°C for 48 hours, emerging colonies were sub-cultured onto PDA plates. Forty-two isolates were obtained, and twenty-seven isolates were identified as Fusarium spp. The remaining fifteen isolates had similar morphology, with colonies that were white and cottony in texture after incubation at 28°C for three days on PDA. The suitable temperature range for growth of hyphae was between 15°C to 40°C, and sporangia were ellipsoidal, papillate, and 23 - 34×21 - 31 µm in diameter. Oogonia (smooth, 22 - 30 μm in diameter) were present in the cultures after 28 days at 28°C. The isolates were identified using both morphological characteristics and DNA sequencing. Identity of the oomycete was confirmed using the BLAST algorithm available through the GenBank with the DNA sequences of rDNA internal transcribed spacer region (ITS), cytochrome c oxidase Ⅰ (coxⅠ) gene and cytochrome c oxidase Ⅱ (coxⅡ) gene, which were amplified using the primers ITS1/ITS4 (White et al. 1990), FM35/FM59 and FM66/FM58 (Martin 2000), respectively. The fifteen isolates selected for sequence analysis had identical gene sequences, and hence, only sequences for isolate RMSD1 were submitted to GenBank (ITS - MW440691, coxI - MW450815 and cox II - MW450816). The ITS, coxI and coxII sequences of the isolate RMSD1 showed 97% identity (751/774 bp), 99% identity (1087/1098 bp) and 99% identity (548/554 bp) with Phytopythium helicoides Accession nos: HQ643382, FR774199, and AB108014, respectively. The pathogenicity of RMSD1 was tested on the corn hybrid Denghai-618. Three-leaf-stage corn plants (N = 15) were inoculated with mycelial agar disks (3 to 4 mm in diameter) colonized with RMSD1 placed on their root-collars. Sterile PDA disks (3 to 4 mm in diameter) served as the negative control (N = 9). Inoculated plants were placed in the growth chamber at 28°C, 60% relative humidity, 16 h / 8 h light regime cycle. Ten days post-inoculation, the inoculated plants showed necrosis, with symptoms of stem rot similar to those observed in the field. The inoculation experiments were repeated twice with the same results, fulfilling Koch’s postulates. The root-collars and stems of negative control remained asymptomatic, and P. helicoides was not isolated. Previously, P. helicoides has been reported as a pathogen of strawberry (Zhan et al. 2020) and kiwi fruits (Wang et al. 2015) from China, but not from corn. To our knowledge, it is the first report of P. helicoides causing corn stalk rot in China. In the future, P. helicoides can be considered as a potential candidate causing stem and collar-rot of corn in China, but not the only one. There are other microbes that can produce similar symptoms on corn, and control methods for pathogenic oomycetes differ from those for fungi.

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First Report of Rhexocercosporidium panacis Causing Rusty Root of Panax ginseng in Northeastern China

Plant Disease ◽

10.1094/pdis-01-14-0082-pdn ◽

2014 ◽

Vol 98 (11) ◽

pp. 1580-1580 ◽

Cited By ~ 4

Author(s):

X. H. Lu ◽

A. J. Chen ◽

X. S. Zhang ◽

X. L. Jiao ◽

W. W. Gao

Keyword(s):

Panax Ginseng ◽

Agar Plate ◽

Its Region ◽

Culture Collection ◽

Northeastern China ◽

Post Inoculation ◽

Academic Press ◽

First Report ◽

Irregular Shapes ◽

Its Sequence Analysis

In northeastern China, Asian ginseng (Panax ginseng) roots exhibited reddish brown lesions of various sizes, irregular shapes, and diffuse margins, typical of rusty root disease. The lesions remain superficial, smooth, and limited to the epidermal and peridermal tissues. In September 2013, 10 symptomatic roots were collected from each of three fields in Jilin and Heilongjiang provinces. One piece of symptomatic skin tissue from each root was excised, surface-disinfested in 1% NaClO for 3 min, rinsed three times with sterile water, and then placed on tetracycline-amended (50 μg/ml) potato dextrose agar. After incubation at 22 ± 1°C in the dark for a week, small olivaceous black colonies developed from the symptomatic tissue from five of the 30 samples. No spores were observed. A single hyphal tip of each colony was transferred to a fresh V8 agar plate to purify the culture. Two-week-old colonies on V8 agar were olivaceous gray, and 42 to 46 mm in diameter with an outer white margin (3 to 5 mm wide). Conidia produced in V8 broth after 3 weeks with a 12-h photoperiod were straight and hyaline, cylindrical or subcylindrical with no or one septum. Mature conidia were 12.8 to 21.8 × 2.2 to 4.5 μm (mean 18.2 × 3.0 μm, n = 100 conidia for each of three isolates). Three isolates selected randomly were further identified by analyzing the partial sequences of the ITS region of rDNA with primers ITS4 and ITS5 (5), and partial sequences of β-tubulin with the primers tub2F and tub2R (1). Sequences of the three isolates (GenBank Accession Nos. KJ149287, KJ149288, and KJ149290 to 93) showed 99% to 100% homology with previously identified and deposited Rhexocercosporidium panacis isolates (DQ2499992 and DQ457119) for both loci (3). Therefore, the three isolates were identified as R. panacis and deposited in China General Microbiological Culture Collection Center (CGMCC3.17259 to 61). Pathogenicity of R. panacis in Asian ginseng was investigated using these three isolates as described previously with slight modifications (4). Bare roots of 3-year-old Asian ginseng were surface-disinfested as described above, and inoculated with mycelial plugs (4 mm diameter) cut from the margin of actively growing colonies of the isolates on V8 agar. Three mycelial plugs were placed on each root at 3-cm intervals and four roots (replicates) were inoculated for each isolate. Four additional roots were inoculated with non-colonized agar plugs as control. The treated roots were placed on moist filter paper in an enamel tray. The plates were sealed with plastic wrap to prevent desiccation and incubated in the dark at 18 ± 1°C. Four weeks post inoculation, all the inoculated ginseng roots showed red-brown lesions, which turned to dark red or black over time. R. panacis was recovered from symptomatic roots for all isolates and confirmed by ITS sequence analysis. The mock-inoculated control roots remained symptomless and no R. panacis was isolated. The inoculation experiment was repeated and showed the same results. R. panacis was reported in 2006 to infect roots of Panax quinquefolius (2,3,4). To our knowledge, this is the first report of R. panacis causing rusty root of P. ginseng. References: (1) P. R. Hirsch et al. Mycol. Res. 104:435, 2000. (2) Z. K. Punja et al. Can. J. Plant Pathol. 35:503, 2013. (3) R. D. Reeleder. Mycologia. 99:91, 2007. (4) R. D. Reeleder et al. Phytopathology 96:1243, 2006. (5) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

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

Plant Disease ◽

10.1094/pdis-11-13-1181-pdn ◽

2014 ◽

Vol 98 (6) ◽

pp. 855-855

Author(s):

R. N. Trigiano ◽

T. A. Rinehart ◽

M. M. Dee ◽

P. A. Wadl ◽

L. Poplawski ◽

...

Keyword(s):

Rhizoctonia Solani ◽

Consensus Sequence ◽

Its Region ◽

The United States ◽

Low Fertility ◽

Academic Press ◽

Potato Dextrose Broth ◽

First Report ◽

Landscape Plant ◽

Hyphal Morphology

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.

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Identification and Isolation Pattern of Globisporangium spp. from a Sanionia Moss Colony in Ny-Ålesund, Spitsbergen Is., Norway from 2006 to 2018

Microorganisms ◽

10.3390/microorganisms9091912 ◽

2021 ◽

Vol 9 (9) ◽

pp. 1912

Author(s):

Motoaki Tojo ◽

Natsumi Fujii ◽

Hironori Yagi ◽

Yuki Yamashita ◽

Katsuyuki Tokura ◽

...

Keyword(s):

Plant Pathogens ◽

Agar Plate ◽

Its Region ◽

Recent Decade ◽

Polar Regions ◽

Survey Period ◽

Isolation Frequency ◽

Rdna Its ◽

In Vitro Inoculation

Globisporangium spp. are soil-inhabiting oomycetes distributed worldwide, including in polar regions. Some species of the genus are known as important plant pathogens. This study aimed to clarify the species construction of Globisporangium spp. and their long-term isolation pattern in Sanionia moss in Ny-Ålesund, Spitsbergen Is., Norway. Globisporangium spp. were isolated at two-year intervals between 2006 and 2018 at a Sanionia moss colony, Ny-Ålesund, Spitsbergen Is., Norway. The isolates were obtained by using three agar media and were identified based on sequences of the rDNA-ITS region and cultural characteristics. Most of the Globisporangium isolates obtained during the survey were identified into six species. All six species were grown at 0 °C on an agar plate and used to infect Sanionia moss at 4 and/or 10 °C under an in vitro inoculation test. The total isolation frequency of Globisporangium gradually decreased throughout the survey period. The isolation frequency varied among the six species, and four of the species that showed a high frequency in 2006 were rarely isolated after 2016. The results suggested that Globisporangium inhabiting Sanionia moss in Ny-Ålesund has a unique composition of species and that most of the species reduced their population over the recent decade.

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First Report of Rhizoctonia solani Subgroup AG 1-ID Causing Leaf Blight on Durian in Vietnam

Plant Disease ◽

10.1094/pdis-92-4-0648b ◽

2008 ◽

Vol 92 (4) ◽

pp. 648-648 ◽

Cited By ~ 1

Author(s):

T. T. M. Thuan ◽

N. Tho ◽

B. C. Tuyen

Keyword(s):

Rhizoctonia Solani ◽

Sequence Similarity ◽

Its Region ◽

The Philippines ◽

Leaf Blight ◽

First Report ◽

Rdna Its ◽

Durio Zibethinus ◽

Leaf Spots ◽

Irregular Border

During the rainy season in Vietnam, leaf blight disease caused by Rhizoctonia solani often occurs on 3- to 5-year-old durian (Durio zibethinus). Symptoms appear as large, pale brown, blighted lesions with an irregular border. In excessive moisture conditions, yellowish white hyphae appear on the lesions, and the affected leaves turn dark brown and wilt. There are no reports describing the anastomosis groups (AG) and subgroups of Rhizoctonia solani occurring in durian. In June of 2004, two isolates of R. solani were obtained from leaf blight lesions on durian growing in Binh Duong and Dong Nai provinces. The durian isolates were identified as AG 1 based on hyphal anastomosis. In pathogenicity tests, the durian isolates infected cucumber, mung bean, and leaf mustard seedlings grown on water agar in petri dishes. The rDNA-ITS sequence of the durian isolates was determined (GenBank Accession Nos. EF197797 and EF197798) and aligned with those of AG 1-IA, AG 1-IB, AG 1-IC, and AG 1-ID available in the GenBank database. The sequence similarity of the total rDNA-ITS region (including 5.8S) within the durian isolates was 99.9%. The sequence similarity of the durian isolates and AG 1-ID isolates was 99.1 to 100%, but similarity with other AG 1 subgroups was 89.1 to 94.0%. The results suggest that the two Vietnam durian isolates of R. solani are members of AG 1-ID. AG 1-ID has only been reported causing necrotic leaf spots on coffees in the Philippines (1). To our knowledge, this is the first report of R. solani AG 1-ID on durian and the first report of the presence of R. solani AG 1-ID in Vietnam. Reference: (1) A. Priyatmojo et al. Phytopathology 91:1054, 2001.

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