First Report of Damping-Off on Basella rubra Caused by Rhizoctonia solani Anastomosis Group 4 in Florida

Indian spinach (Basella rubra L.) is a red stem species of Basella that is cultivated worldwide as an ornamental and the aerial parts are also consumed as a vegetable. In May of 2011, symptoms of damping-off were observed on approximately 10% of the plants at the stem base around the soil line of seedlings in a greenhouse in Homestead, FL. Lesions were initially water soaked, grayish to dark brown, irregular in shape, and sunken in appearance on large plants, causing the infected seedlings to collapse and eventually die. Symptomatic stem tissue was surface sterilized with 0.6% sodium hypochlorite, rinsed in sterile distilled water, air dried, and plated on potato dextrose agar (PDA). Plates were incubated at 25°C in darkness for 3 to 5 days. A fungus was isolated in all six isolations from symptomatic tissues on PDA. Fungal colonies on PDA were light gray to brown with abundant growth of mycelia, and the hyphae tended to branch at right angles when examined under a microscope. A septum was always present in the branch of hyphae near the originating point and a slight constriction at the branch was observed. Neither conidia nor conidiophores were found from the cultures on PDA. The characteristics of hyphae, especially the right angle branching of mycelia, indicate close similarity to those of Rhizoctonia solani (2,3). The internal transcribed spacer (ITS) region of rDNA was amplified with the primers ITS1/ITS4 and sequenced (GenBank Accession No. JN545836). Subsequent database searches by the BLASTN program indicated that the resulting sequence had a 100% identity over 472 bp with the corresponding gene sequence of R. solani anastomosis group (AG) 4 (GenBank Accession No. JF701752.1), a fungal pathogen reported to cause damping-off on many crops. Pathogenicity was confirmed through inoculation of healthy India spinach plants with the hyphae of isolates. Four 4-week-old plants were inoculated with the isolates by placing a 5-mm PDA plug of mycelia at the stem base and covering with a thin layer of the soil. Another four plants treated with sterile PDA served as a control. After inoculation, the plants were covered with plastic bags for 24 h and maintained in a greenhouse with ambient conditions. Four days after inoculation, water-soaked, brown lesions, identical to the symptoms described above, were observed on the stem base of all inoculated plants, whereas no symptoms developed on the control plants. The fungus was isolated from affected stem samples, and the identity was confirmed by microscopic appearance of the hyphae and sequencing the ITS1/ITS4 intergenic spacer region, fulfilling Koch's postulates. This pathogenicity test was conducted twice. R. solani has been reported to cause damping-off of B. rubra in Ghana (1) and Malaysia (4). To our knowledge, this is the first report of damping-off caused by R. solani AG-4 on Indian spinach in Florida and the United States. With the increased interest in producing Asian vegetables for food and ornamental purposes, the occurrence of damping-off on Indian spinach needs to be taken into account when designing programs for disease management in Florida. References: (1) H. A. Dade. XXIX. Bull. Misc. Inform. 6:205, 1940. (2) J. R. Parmeter et al. Phytopathology 57:218, 1967. (3) B. Sneh et al. Identification of Rhizoctonia species. The American Phytopathological Society, St Paul, MN, 1991. (4) T. H. Williams and P. S. W. Liu. Phytopathol. Pap. 19:1, 1976.

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First Report of Leaf Blight on Fan Columbine (Aquilegia flabellata) Caused by Rhizoctonia solani AG 4 in Italy

Plant Disease ◽

10.1094/pdis-93-4-0433a ◽

2009 ◽

Vol 93 (4) ◽

pp. 433-433 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Rhizoctonia Solani ◽

Aqueous Suspension ◽

Morphological Characteristics ◽

The United States ◽

Leaf Blight ◽

Herbaceous Plant ◽

Pathogenicity Test ◽

First Report ◽

Leaf Petiole

Aquilegia flabellata (Ranunculaceae), fan columbine, is a perennial herbaceous plant with brilliant blue-purple flowers with white petal tips. It can also be grown for cut flower production. In April of 2008, in several nurseries located near Biella (northern Italy), a leaf blight was observed on 10 to 15% of potted 30-day-old plants grown on a sphagnum peat substrate at 15 to 20°C and relative humidity of 80 to 90%. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along the leaf margins. Lesions expanded over several days along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, and abscised. 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 characteristics of Rhizoctonia solani 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 obtained from affected plants 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 with no anastomoses observed between the recovered and tester isolates. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 648-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 534555. For pathogenicity tests, the inoculum of R. solani was prepared by growing the pathogen on PDA for 10 days. Five plants of 30-day-old A. flabellata were grown in 3-liter pots. Inoculum consisting of an aqueous suspension of PDA and mycelium disks (5 g of mycelium + agar per plant) was placed at the collar of plants. Five plants inoculated with water and PDA fragments alone served as control treatments. Plants were maintained in a greenhouse at temperatures between 20 and 24°C. The first symptoms, similar to those observed in the nursery, developed 7 days after the artificial 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. The presence of R. solani AG1-IB on A. flabellata has been reported in Japan (4), while in the United States, Rhizoctonia sp. is described on Aquilegia sp. (3). This is, to our knowledge, the first report of leaf blight of A. flabellata 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 Phytopathological Society, St Paul, MN, 1989. (4) E. Imaizumi et al. J. Gen. Plant Pathol. 66:210, 2000.

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First Report of Web Blight on Oregano (Origanum vulgare L.) Caused by Rhizoctonia solani AG-1-IB in Italy

Plant Disease ◽

10.1094/pdis-02-13-0138-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1119-1119 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

P. Pensa ◽

A. Poli ◽

M. L. Gullino

Keyword(s):

Rhizoctonia Solani ◽

Its Region ◽

Morphological Characters ◽

Anastomosis Group ◽

Morphological Identification ◽

Pathogenicity Test ◽

Origanum Vulgare ◽

First Report ◽

Plastic Bags ◽

Hyphal Diameter

Origanum vulgare L., common name oregano, family Labiatae, is grown for its aromatic and medicinal properties and as ornamental. In the fall of 2012, a blight was observed in a farm located near Albenga (northern Italy) on 6% of 30,000 50-day-old plants, grown in trays in a peat/perlite mix. Semicircular, water soaked lesions appeared on leaves and stems, starting from the basal ones. As the disease progressed, blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage. Eventually, infected plants died. Leaf and stem fragments taken from the margin of the diseased tissues belonging to 10 plants were disinfected for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA). A fungus with the morphological characters of Rhizoctonia solani was consistently recovered. Three isolates of R. solani obtained from affected plants were successfully anastomosed with R. solani isolate AG 1 (ATCC 58946). Three pairings were made for each tester strain. The hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and death of adjacent cells was observed. Results were consistent with other reports on anastomosis reactions (2). Isolates from oregano were paired with R. solani isolates AG 2, 3, 4, 6, 7, or 11 and examined microscopically. Anastomosis was not observed in any of the pairings. Tests were conducted twice. Mycelium of 10-day-old isolates from oregano appeared reddish brown, coarse, and radiate. Numerous dark brown sclerotia, 0.3 to 1.0 mm diameter (average 0.7) developed within 10 days after transfer of mycelia to PDA in 90 mm diameter petri dishes at 21 to 24°C. The descriptions of mycelium and sclerotia were typical for subgroup IB Type 1 (4). The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced. BLASTn analysis (1) of the 538 bp showed a 99% homology with the sequence of R. solani FJ746937, confirming the morphological identification of the species. The nucleotide sequence has been assigned the GenBank Accession KC493638. For pathogenicity tests, one of the isolates assigned to the anastomosis group AG-1-IB was tested by placing 9 mm diameter mycelial disks removed from PDA 10-day-old cultures of the fungus on leaves of 90-day-old oregano plants (n = 35). Thirty-five plants inoculated with non-inoculated PDA disks served as controls. Plants were covered with plastic bags and maintained in a growth chamber at 25 ± 1°C with 12 h light/dark. The first symptoms, similar to those observed in the farm, developed 3 days after inoculation. Nine days after the artificial inoculation, 50% of plants were dead. About 10 colonies of R. solani were reisolated from infected leaves of inoculated plants. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. Symptoms caused by R. solani have been recently observed on O. vulgare in Greece (3). This is, to our knowledge, the first report of blight of O. vulgare caused by R. solani in Italy. 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, pp. 37-47, 1996. (3) C. D. Holevas et al. Benaki Phytopathol. Inst., Kiphissia, Athens, 19:1-96, 2000. (4) R. T. Sherwood. Phytopathology 59:1924, 1969.

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First Report of Web Blight on Rosemary (Rosmarinus officinalis) Caused by Rhizoctonia solani AG-1-IA in Italy

Plant Disease ◽

10.1094/pdis-11-12-1012-pdn ◽

2013 ◽

Vol 97 (6) ◽

pp. 844-844 ◽

Cited By ~ 4

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

P. Pensa ◽

A. Poli ◽

M. L. Gullino

Keyword(s):

Rhizoctonia Solani ◽

Ground Cover ◽

Its Region ◽

Morphological Characters ◽

Anastomosis Group ◽

Rosmarinus Officinalis ◽

Economic Losses ◽

Pathogenicity Test ◽

First Report ◽

Wheat Kernels

Rosmarinus officinalis L., family Labiatae, is an evergreen shrub used in gardens as an aromatic or ground cover plant. In the summer of 2012, a blight was observed in a farm located near Albenga (northern Italy) on 20% of 150,000 70-day-old plants, grown in trays. Water soaked lesions appeared on leaves and stems. As the disease progressed, blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage. A light mycelium spread on the substrate. Disease progressed from infected plants to healthy ones and, eventually, infected plants died. Leaf and stem fragments taken from the margin of the diseased tissues belonging to 10 plants were disinfected for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA). A fungus with the morphological characters of Rhizoctonia solani was consistently and readily recovered. Three isolates of R. solani obtained from affected plants were successfully paired with R. solani tester strains AG 1, 2, 3, 4, 6, 7, or 11 and examined microscopically. Three pairings were made for each recovered isolate. The isolates of R. solani from rosemary anastomosed only with tester strain AG 1 (ATCC 58946). Results were consistent with other reports on anastomosis reactions (2). Tests were repeated once. Mycelium of 10-day-old isolates from rosemary appeared light brown, compact, and radiate. Numerous dark brown sclerotia, 0.7 to 2.0 mm diameter (average 1.3), developed within 10 days at 20 to 26°C. The descriptions of mycelium and sclerotia were typical for subgroup IA Type 2 (4). The internal transcribed spacer (ITS) region of rDNA was amplified using the primers ITS1/ITS4 and sequenced (GenBank Accession No. KC005724). BLASTn analysis (1) of the 657-bp showed a 99% similarity with the sequence of R. solani GU596491. For pathogenicity tests, inoculum of R. solani was prepared by growing the pathogen on wheat kernels autoclaved in 1-liter glass flasks for 8 days. One of the isolates assigned to the anastomosis group AG 1 IA was tested. Fifteen 90-day-old rosemary plants were grown in 15-liter pots in a steam disinfested peat:pomice:pine bark:clay mix (50:20:20:10) infested with 3 g/liter of infested wheat kernels, placed at the base of the stem. Fifteen plants inoculated with non-infested wheat kernels served as control treatments. Plants were covered with plastic bags and arranged in a growth chamber at 20 to 24°C with 12 h light/dark for 15 days. The first symptoms, similar to those observed in the farm, developed 10 days after inoculation. About 10 colonies of R. solani were reisolated from infected leaves and stems of each inoculated plant. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. Symptoms caused by R. solani have been recently observed on R. officinalis in United States (3), India, and Brazil. This is, to our knowledge, the first report of blight of R. officinalis caused by R. solani in Italy. This disease could cause serious economic losses, because rosemary is one of the most cultivated aromatic plants in the Mediterranean region. 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) G. E. Holcomb. Plant Dis. 76:859, 1992. (4) R. T. Sherwood. Phytopathology 59:1924, 1969.

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First Report of Leaf Blight of Dianthus chinensis Caused by Rhizoctonia solani

Plant Disease ◽

10.1094/pdis.2000.84.12.1344d ◽

2000 ◽

Vol 84 (12) ◽

pp. 1344-1344

Author(s):

G. E. Holcomb ◽

D. E. Carling

Keyword(s):

United States ◽

Rhizoctonia Solani ◽

Gulf Coast ◽

The United States ◽

Anastomosis Group ◽

Early Spring ◽

Leaf Blight ◽

Infected Leaf ◽

First Report ◽

Bedding Plant

Dianthus chinensis (rainbow pink) is a popular seasonal bedding plant for the Gulf Coast of the United States and is primarily grown during the fall, winter, and early spring months. In August 1999, diseased plants were observed in a Baton Rouge, LA, propagation nursery with irregularly oval, tan leaf spots 3 to 10 mm in diameter. Heavily infected leaves became blighted and were killed, but plants survived and roots, crowns, and flowers were not affected. Infected leaf samples were surface-disinfected for 1 to 3 min in 70% ethyl alcohol, blotted dry, and sections were placed on 2% acidified water agar. A fungus that was identified as Rhizoctonia solani, and belonging to anastomosis group (AG)-1 IB, was consistently isolated from infected leaves. Inoculum was prepared by blending one 7-day-old plate culture, grown on acidified potato-dextrose agar, in 100 ml distilled deionized water. Pathogenicity tests were performed by dripping inoculum from a 10-ml pipette on leaf surfaces of healthy rainbow pink plants. Inoculated and noninoculated plants were held in a dew chamber at 26°C for 2 to 3 days and then removed to a greenhouse where temperatures ranged from 25 to 32°C. Inoculated plants developed water-soaked spots after 2 to 3 days that turned tan and became necrotic 5 to 10 days later. These symptoms were like those observed on the original diseased plants. R. solani was reisolated from inoculated plants, and noninoculated plants remained healthy. Although R. solani has been reported previously as a root and stem pathogen of D. chinensis (1), this is the first report of leaf blight disease caused by this fungus. Reference: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

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First Report of Leaf Blight Caused by Rhizoctonia solani AG 1B on Madagascar Periwinkle (Catharanthus roseus) in Italy

Plant Disease ◽

10.1094/pd-90-1361c ◽

2006 ◽

Vol 90 (10) ◽

pp. 1361-1361 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

Rhizoctonia Solani ◽

Catharanthus Roseus ◽

The United States ◽

Morphological Characters ◽

Leaf Blight ◽

Pathogenicity Test ◽

Madagascar Periwinkle ◽

Public Park ◽

First Report ◽

Leaf Petiole

Madagascar periwinkle (Catharanthus roseus), a plant belonging to the Apocynaceae family, is used for parks and gardens and sometimes grown in pots. At the end of the summer of 2005, a leaf blight was observed on plants in a public park of Torino. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along the leaf margins. Lesions expanded for several days along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage. Although lesions were not seen on the stem, affected plants often died leaving wide empty areas. Mycelia of the pathogen were often seen on and suspended between the leaves. Blight progressed from the leaves to the shoot tip. The diseased tissue was disinfected for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 μg/l streptomycin sulphate. A fungus with the morphological characters of Rhizoctonia solani was consistently and readily isolated and maintained in pure culture after single-hyphal tipping (4). The isolates of R. solani obtained from affected plants were successfully anastomosed with tester isolate AG 1 (ATCC 58946). The hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and cell death of adjacent cells was observed. These results are consistent with other reports on anastomosis reactions (2). Pairing was also made with AG 2, 3, 4, 5, 7, and 11, with no anastomoses observed between the isolates and testers. Sclerotia were subspheroid in shape and had a size of 1 mm, which indicated that this pathogen was in subgroup 1B (4). For pathogenicity tests, the inoculum of R. solani was prepared by growing the pathogen on PDA for 7 days. Plants of C. roseus were grown in 3-liter containers (2 plants per pot) on a steam disinfested substrate (peat/ pomix/pine bark/clay). Artificial inoculation was carried out on 7-day-old plants by placing numerous fragments of PDA cultures on the leaves of the plants. Plants inoculated with PDA alone served as control treatments. Three replicates were used. Plants were maintained in a glasshouse at 20 to 25°C. The first symptoms, similar to those observed in the public park, developed 5 days after inoculation, and R. solani was consistently reisolated from infected plants. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. This is, to our knowledge, the first report of R. solani on periwinkle in Italy. The same disease was reported in India (1) and the United States (3). References: (1) R. Balasubramanian and K. S. Bhama. Indian Phytopathol. 30:556, 1977. (2) D. E. Carling. Grouping in Rhizoctonia solani by hyphal anastomosis reactions. Pages 37–47 in: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. B. Sneh et al., eds. Kluwer Academic Publishers, the Netherlands, 1996. (3) A. K. Hagan and J. M. Mullen Plant Dis. 77:1169, 1993. (4) B. Sneh et al. Identification of Rhizoctonia Species. The American Phytopathological Society, St Paul, MN, 1991.

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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.

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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.

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First Report of Damping-Off of Swiss Chard Caused by Rhizoctonia solani AG-4 HG I and Binucleate Rhizoctonia AG-A in China

Plant Disease ◽

10.1094/pdis-91-11-1516a ◽

2007 ◽

Vol 91 (11) ◽

pp. 1516-1516 ◽

Cited By ~ 3

Author(s):

G. H. Yang ◽

R. L. Conner ◽

Y. Y. Chen

Keyword(s):

Rhizoctonia Solani ◽

Root Zone ◽

The United States ◽

Infested Soil ◽

Damping Off ◽

First Report ◽

Binucleate Rhizoctonia ◽

5.8S Rdna ◽

Stem Blight ◽

Swiss Chard

During July, 2003, damping-off of Swiss chard (Beta vulgaris subsp. cicla L.) was observed in a seedling (approximately 1 month after germination) field (approximately 2 ha) in Yuanmou County in the Cuxiong District of Yunnan, China. More than 80% of the seedlings showed symptoms of the disease. Symptoms on newly emerged plants consisted of wilting, a brown necrosis of the lower taproot, and eventual death of seedlings. Among the 15 isolates of Rhizoctonia spp. isolated from Swiss chard with damping-off symptoms, 12 isolates of Rhizoctonia solani with dark brown sclerotia on potato dextrose agar (PDA) anastomosed with tester isolates of each subgroup AG-4 HG I, AG-4 HG II, and AG-4 HG III, giving a C2 hyphal fusion (1) reaction at a high frequency. The other three binucleate Rhizoctonia spp. (BNR) isolates whose mycelia were white with floccose aerial hyphae on PDA anastomosed freely with two BNR AG-A tester isolates producing a C2 hyphal reaction. The 5.8S rDNA-ITS of a single isolate of R. solani and a single isolate of BNR was sequenced. The sequence of the AG-4 isolate (GenBank Accession No. EF679777) exhibited 99 to 100% homology with isolates of R. solani AG-4, subgroup 4HG I (GenBank Accession No. AY154307). The sequence from the AG-A isolate (GenBank Accession No. EF679778) exhibited 98% homology with BNR AG-A (GenBank Accession Nos. AB000040 and AF354092). Swiss chard (cv. Baijin) seedlings (approximately 5 cm high) were planted in potting soil at a density of one seedling per vinyl pot (8 cm diameter, 9 cm high). Two isolates each of R. solani and BNR were used in pathogenicity testing. Each seedling was inoculated in the root zone with approximately 7 g of artificially infested soil. Control plants were inoculated with autoclaved soil. The experiments were conducted three times, each time with three replicates, in a greenhouse with a photoperiod of 16 h of light and 8 of h dark at 30 and 16°C, respectively. After 7 days, disease severity was measured based on a scale in which 0 = no symptom; 1 = small lesions on seedlings, no blight; 2 = leaves blight, no stem blight; 3 = stem blight; and 4 = plant dead. The two AG-4 and two of AG-A isolates were pathogenic on the Swiss chard seedlings and caused damping-off symptoms with a disease index 1.7 to 4.0, and there were no significant differences (P = 0.05) among them. We reisolated and confirmed the presence of R. solani and BNR AG-A from diseased plants. AG-3 isolates were reported to cause the damping-off of Swiss chard in the United States (2). To our knowledge, this is the first report of damping-off of Swiss chard caused by Rhizoctonia solani AG-4 HG I and BNR AG-A. References: (1) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reaction. Kluwer Academic Publishers, Dordecht, the Netherlands, 1996. (2) S. T. Koike and K. V. Subbarao. Plant Dis. 83:695, 1999.

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First Report of Web Blight on Winter Savory (Satureja Montana “Repandens”) Caused by Rhizoctonia solani AG-1-IA in Italy

Plant Disease ◽

10.1094/pdis-12-11-1075-pdn ◽

2012 ◽

Vol 96 (4) ◽

pp. 585-585 ◽

Cited By ~ 1

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

P. Pensa ◽

M. T. Amatulli ◽

M. L. Gullino

Keyword(s):

Rhizoctonia Solani ◽

Late Summer ◽

Its Region ◽

Morphological Characters ◽

Anastomosis Group ◽

Pathogenicity Test ◽

First Report ◽

Hyphal Diameter ◽

Wheat Kernels ◽

Satureja Montana

Satureja montana L. (winter savory “Repandens”) is an evergreen shrub. In late summer 2010, blight was observed on a farm near Albenga (northern Italy) on 3% of 500 potted 2-month-old plants. Semicircular, water-soaked lesions appeared first on stems then on leaves. As the disease progressed, blighted leaves turned brown, withered, clung to the shoots, and matted on the surrounding foliage within 5 to 6 days. Stem fragments taken from the margin of the diseased tissues of 10 plants were disinfected for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA) amended with 100 μg/liter streptomycin sulfate. A fungus with morphological characters of Rhizoctonia solani was consistently isolated. Three isolates of R. solani obtained from affected plants were successfully anastomosed with R. solani isolate AG 1 (ATCC 58946). Three pairings were made for each tested strain. Hyphal diameter at the point of anastomosis was reduced, the anastomosis point was obvious, and death of adjacent cells was observed. Results were consistent with other reports on anastomosis reactions (2). Isolates from winter savory were paired with R. solani isolates AG 2, 3, 4, 6, 7, or 11 and examined microscopically. Anastomosis was not observed in any of the pairings. Tests were repeated once. Mycelium of 10-day-old isolates from winter savory appeared light brown, compact, and radiate. Numerous, dark brown sclerotia, 1 to 4 mm in diameter (average 1.7), developed within 20 days after transfer of mycelia to PDA in 90-mm-diameter petri dishes and incubated (11-h daylight, 13-h dark) at 21 to 24°C. Descriptions of mycelium and sclerotia were typical for subgroup IA Type 2 (3). The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and sequenced. BLASTn analysis (1) of the 696 bp showed a 99% homology with the sequence of R. solani. The nucleotide sequence has been assigned GenBank No. JQ313811. For pathogenicity tests, inoculum of R. solani was prepared by growing the pathogen on wheat kernels autoclaved in 1-liter glass flasks (30 min at 121°C and 1 atm) for 15 days. One of the isolates assigned to the anastomosis group AG 1 IA was tested. Five 90-day-old plants of S. montana were inoculated. Each plant grown in 2-liter pots in a steam disinfested peat/pumice/pine bark/clay mix (50:20:20:20:10) was inoculated with 10 g of infested wheat kernels placed at the base of the stem. Five plants inoculated with noninfested wheat kernels served as the control. Plants covered with plastic bags were arranged randomly in a growth chamber at 20 ± 1°C with 12-h light/dark for 5 days. Symptoms, similar to those observed in the farm, developed 4 days after inoculation. Ten colonies of R. solani were reisolated from infected leaves and stems of each inoculated plant. Control plants remained healthy. The pathogenicity test was carried out twice. Symptoms caused by R. solani have been recently observed on S. hortensis in Poland (4). This is, to our knowledge, the first report of blight of S. montana caused by R. solani in Italy. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. E. Carling. Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Kluwer Academic Publishers, The Netherlands, 1996. (3) R. T. Sherwood. Phytopathology 59:1924, 1969. (4) B. Zimowska. Herba Polonica 56:29, 2010.

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Sensitivity of Rhizoctonia solani AG-2-2 from Sugar Beet to Fungicides

Plant Disease ◽

10.1094/pdis-04-16-0525-re ◽

2016 ◽

Vol 100 (12) ◽

pp. 2427-2433 ◽

Cited By ~ 4

Author(s):

Sahar Arabiat ◽

Mohamed F. R. Khan

Keyword(s):

Sugar Beet ◽

Rhizoctonia Solani ◽

Root Rot ◽

The United States ◽

Damping Off ◽

Growth Assay ◽

The Mean ◽

Crown And Root Rot ◽

Mean Concentration

Rhizoctonia damping-off and crown and root rot caused by Rhizoctonia solani are major diseases of sugar beet (Beta vulgaris L.) worldwide, and growers in the United States rely on fungicides for disease management. Sensitivity of R. solani to fungicides was evaluated in vitro using a mycelial radial growth assay and by evaluating disease severity on R. solani AG 2-2 inoculated plants treated with fungicides in the greenhouse. The mean concentration that caused 50% mycelial growth inhibition (EC50) values for baseline isolates (collected before the fungicides were registered for sugar beet) were 49.7, 97.1, 0.3, 0.2, and 0.9 μg ml−1 and for nonbaseline isolates (collected after registration and use of fungicides) were 296.1, 341.7, 0.9, 0.2, and 0.6 μg ml−1 for azoxystrobin, trifloxystrobin, pyraclostrobin, penthiopyrad, and prothioconazole, respectively. The mean EC50 values of azoxystrobin, trifloxystrobin, and pyraclostrobin significantly increased in the nonbaseline isolates compared with baseline isolates, with a resistant factor of 6.0, 3.5, and 3.0, respectively. Frequency of isolates with EC50 values >10 μg ml−1 for azoxystrobin and trifloxystrobin increased from 25% in baseline isolates to 80% in nonbaseline isolates. Although sensitivity of nonbaseline isolates of R. solani to quinone outside inhibitors decreased, these fungicides at labeled rates were still effective at controlling the pathogen under greenhouse conditions.

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