First Report of Multinucleate Rhizoctonia solani AG4 HG-I Causing Crown and Root Rot on Strawberry in Italy

Murraya paniculata (L.) Jack, commonly called orange jessamine or orange jasmine (Rutaceae), is a small tropical tree that is native to Asia. This species, closely related to Citrus, is grown as an ornamental tree or hedge. During October of 2007, crown and root rot was observed on approximately 12,000 pot-grown, 4-month-old plants in a nursery in eastern Sicily, Italy. Basal leaves turned yellow and gradually became necrotic, and infected plants often died. Disease symptoms were observed on 1,800 (15%) plants. Isolations from affected tissues on potato dextrose agar (PDA) amended with streptomycin sulfate at 100 mg/liter recovered a fungus with mycelial and morphological characteristics consistent with Rhizoctonia solani Kühn. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Microscopic examination revealed that hyphae had a right-angle branching pattern, were constricted at the base of the branch near the union with main hyphae, and were septate near the constriction. The nuclear condition of hyphal cells was determined on cultures grown at 25°C on 2% water agar (WA) when stained with 3% safranin O solution and examined at ×400. Anastomosis groups were determined by pairing isolates on 2% WA in petri plates (4). Pairings were made with tester strains AG-1 IA, AG-2-2-1, AG-2-2IIIB, AG-2-2IV, AG-3, AG-4, AG-5, AG-6, and AG-11. Anastomosis was observed only with tester isolates of AG-4 producing both C2 and C3 reactions. 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 were consistent with other reports on anastomosis reactions (1). The identification of group AG-4 within R. solani has been confirmed by electrophoretic patterns of pectic enzymes (polygalacturonases) in vertical pectin-acrylamide gel stained with ruthenium red (2). Pathogenicity tests were conducted on potted, healthy, 6-month-old seedlings of orange jessamine. Twenty-five plants were inoculated by placing 1-cm2 PDA plugs from 5-day-old mycelial cultures near the base of the stem. The same number of plants inoculated with PDA plugs served as controls. Plants were maintained at 25°C and 95% relative humidity on a 12-h fluorescent light/dark regimen. Wilt symptoms, identical to ones observed in the nursery, developed 3 months after inoculation because of crown and root rot. Control plants remained disease free. The pathogen was reisolated from symptomatic tissues, completing Koch's postulates. Collar rot due to R. solani was previously detected on M. koenigii (3). To our knowledge, this is the first report of R. solani causing disease on M. paniculata. References: (1) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (2) R. H. Cruickshank and G. C. Wade. Anal. Biochem. 107:177, 1980. (3) A. C. Jain and K. A. Mahmud. Rev. Appl. Mycol. 32:460, 1953. (4) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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First Report of Crown and Root Rot Caused by Rhizoctonia solani AG-4 on Banana Passionflower (Passiflora mollissima) in Italy

Plant Disease ◽

10.1094/pdis-05-11-0411 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1194-1194 ◽

Cited By ~ 2

Author(s):

G. Polizzi ◽

D. Aiello ◽

V. Guarnaccia ◽

A. Panebianco ◽

P. T. Formica

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Fluorescent Light ◽

Disease Symptoms ◽

First Report ◽

Pathogenicity Tests ◽

Crown And Root Rot ◽

Safranin O

The genus Passiflora (Passifloraceae family) contains more than 500 species and several hybrids. In Italy, some of these species and hybrids are grown as ornamental evergreen vines or shrubs. During August and September 2010, a crown and root rot was observed in a stock of approximately 6,000 potted 2-year-old plants of Passiflora mollissima (Kunth) Bailey, commonly known as the banana passionflower, in a nursery located in eastern Sicily (southern Italy). Disease incidence was approximately 20%. Disease symptoms consisted of water-soaked lesions at the crown and a root rot. Successively, older crown lesions turned light brown to brown and expanded to girdle the stem. As crown and root rot progressed, basal leaves turned yellow and gradually became necrotic and infected plants wilted and died. A fungus with mycelial and morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from crown lesions and brown decaying roots when plated on potato dextrose agar (PDA) amended with streptomycin sulfate at 100 μg/ml. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Mycelium was branched at right angles with a septum near the branch with a slight constriction at the branch base. Hyphal cells removed from 10 representative cultures grown at 25°C on 2% water agar were determined to be multinucleate when stained with 1% safranin O and 3% KOH solution (1) and examined at ×400. Anastomosis groups were determined by pairing isolates on 2% water agar in petri plates (4). Pairings were made with tester strains of AG-1, AG-2, AG-3, AG-4, AG-5, AG-6, and AG-11. Anastomosis was observed only with tester isolates of AG-4 (3). Pathogenicity tests were performed on container-grown, healthy, 3-month-old cuttings. Twenty plants of P. mollissima were inoculated near the base of the stem with five 1-cm2 PDA plugs from 5-day-old mycelial plugs obtained from two representative cultures. The same number of plants served as uninoculated controls. Plants were maintained at 25°C and 95% relative humidity with a 12-h fluorescent light/dark regimen. Wilt symptoms due to crown and root rot, identical to ones observed in the nursery, appeared 7 to 8 days after inoculation with either of the two isolates and all plants died within 20 days. No disease was observed on control plants. R. solani AG-4 was reisolated from symptomatic tissues and identified as previously described, confirming its pathogenicity. Damping-off or crown and root rot due to R. solani were previously detected on P. edulis in Brazil, Africa, India, Oceania, and Australia (2). To our knowledge, this is the first report of R. solani causing crown and root rot on P. mollissima. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) J. L. Bezerra and M. L. Oliveira. Fitopathol. Brasil. 9:273, 1984. (3) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (4) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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First Report of Petunia Root Rot Caused by Rhizoctonia solani in Argentina

Plant Disease ◽

10.1094/pdis.2004.88.1.86b ◽

2004 ◽

Vol 88 (1) ◽

pp. 86-86

Author(s):

E. R. Wright ◽

M. C. Rivera ◽

K. Asciutto ◽

L. Gasoni ◽

V. Barrera ◽

...

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Common Garden ◽

Anastomosis Group ◽

Fluorescent Light ◽

First Report ◽

Blue Solution ◽

Crown And Root Rot ◽

Species Taxonomy

Common garden petunias (Petunia × hybrida Hort. Vilm.-Andr.) are herbaceous annual plants with brightly colored flowers up to 10 cm in diameter. During the winter of 2002, crown and root rot were observed on plants (cv. Ultra) growing in five greenhouses in Buenos Aires. Affected plants were randomly distributed in the greenhouses, and mean disease incidence in all the greenhouses was 26%. Basal leaves turned yellow and gradually became necrotic, and infected plants were often killed. Small pieces of affected tissues were disinfested in 2% sodium hypochlorite for 1 min and plated on 2% potato dextrose agar (PDA). Fifteen isolates identified to the genus Rhizoctonia were obtained. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Hyphal branched at right angles, were constricted at the base of the branch near the union with main hyphae, and septate near the constriction. Basidia were not observed in the greenhouses or on the plates. Isolates were cultivated on water agar and incubated at 25°C for 3 days. Hyphal cells were determined to be multinucleate when stained with 1% aniline blue solution (2) and examined at ×400. Anastomosis group of one isolate was determined by using AG-4 HG II, AG-1 IA, AG-1 IB, AG-1 IC, AG-2 2-1, and AG-2 2IIIB tester strains of Rhizoctonia solani that includes isolates reported to be pathogenic on ornamentals (1). Anastomosis was observed only with strains of AG-4 HG II. Pathogenicity on this isolate was conducted on potted, healthy, adult plants that were 10 to 22 cm high and flowering. Thirty-five plants were inoculated by placing 1 cm2 pieces of PDA from 7-day-old mycelial cultures near the base of the stem. Twelve control plants were treated with 1 cm2 PDA plugs. Plants were kept at 22 to 24°C, >95% relative humidity, and 12 h of fluorescent light. Wilt symptoms due to basal stem rot appeared 7 days after inoculation, and all the inoculated plants died within 27 days. Control plants remained disease free. The pathogen was reisolated from symptomatic tissues, completing Koch's postulates. To our knowledge, this is the first report of R. solani causing disease on petunia in Argentina. References: (1) D. M. Benson and D. K. Cartwright. Ornamental diseases incited by Rhizoctonia spp. Pages 303–314 in: Rhizoctonia species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. B. Sneh et al., eds. Kluwer Academic Publishers, London, England, 1996. (2) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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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 Crown and Root Rot Caused by Rhizoctonia solani AG-4 on Coprosma repens and C. lucida in Italy

Plant Disease ◽

10.1094/pdis-93-9-0972b ◽

2009 ◽

Vol 93 (9) ◽

pp. 972-972 ◽

Cited By ~ 2

Author(s):

G. Polizzi ◽

D. Aiello ◽

I. Castello ◽

A. Vitale

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Fluorescent Light ◽

Centraalbureau Voor ◽

First Report ◽

Crown And Root Rot ◽

Stem Lesions ◽

Safranin O

Coprosma (J.R. Forster & G. Forster), a genus containing approximately 90 species, occurs principally in New Zealand, Hawaii, Australia, New Guinea, and islands of the Pacific. In Italy, some of these species, including many variegated varieties and hybrids, are grown as ornamental evergreen shrubs or small trees. In June 2008, a crown and root rot was observed in a stock of approximately 12,000 potted 3-year-old plants of Coprosma repens cv. Yvonne and C. lucida in a nursery in eastern Sicily. Disease incidence was approximately 30%. Disease symptoms consisted of water-soaked lesions at the crown of the trunk and a root rot. Successively, older stem lesions turned orange to brown. As a consequence, leaves initially became chlorotic, gradually became necrotic, and death of the plant followed. A fungus with mycelial and morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from crown and root lesions when plated on potato dextrose agar (PDA) amended with streptomycin sulfate at 100 μg/ml. Fungal colonies were initially white, turned brown with age, and produced irregularly shaped, brown sclerotia. Mycelium was branched at right angles with a septum near the branch and a slight constriction at the branch base. Hyphal cells removed from cultures grown at 25°C on 2% water agar were determined to be multinucleate when stained with 1% safranin O and 3% KOH solution (1) and examined at ×400. Anastomosis groups were determined by pairing isolates on 2% water agar in petri plates (3). Pairings were made with tester strains of AG-1 IA, AG-2-2-1, AG-2-2IIIB, AG-2-2IV, AG-3, AG-4, AG-5, AG-6, and AG-11. Anastomosis was observed only with tester isolates of AG-4, giving C2 and C3 reactions (2). Two representative isolates obtained from symptomatic tissues of C. lucida and C. repens cv. Yvonne were deposited at the Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (DISTEF CL1 = CBS-124593 and DISTEF CR1 = CBS-124594, respectively). Pathogenicity tests were performed on container-grown, healthy, 3-month-old cuttings. Ten plants of C. lucida and ten plants of C. repens cv. Yvonne were inoculated near the base of the stem with five 1-cm2 PDA plugs from 5-day-old mycelial cultures. The same number of plants served as uninoculated controls. Plants were maintained at 25°C and 95% relative humidity on a 12-h fluorescent light/dark regimen. Symptoms identical to ones observed in the nursery appeared 5 days after inoculation and all plants died within 15 days. No disease was observed on control plants. A fungus identical in culture morphology to R. solani AG-4 was consistently reisolated from symptomatic tissues, confirming its pathogenicity. To our knowledge, this is the first report of R. solani causing crown and root rot on the genus Coprosma. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) D. E. Carling. Page 37 in: Grouping in Rhizoctonia solani by Hyphal Anastomosis Reactions. Kluwer Academic Publishers, the Netherlands, 1996. (3) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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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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First Report of Pythium aphanidermatum Crown and Root Rot of Industrial Hemp in the United States

Plant Disease ◽

10.1094/pdis-09-16-1249-pdn ◽

2017 ◽

Vol 101 (6) ◽

pp. 1038 ◽

Cited By ~ 7

Author(s):

J. Beckerman ◽

H. Nisonson ◽

N. Albright ◽

T. Creswell

Keyword(s):

United States ◽

Root Rot ◽

The United States ◽

Pythium Aphanidermatum ◽

First Report ◽

Crown And Root Rot ◽

Industrial Hemp

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First Report of a Phytopythium litorale Species Causing Crown and Root Rot on Rhododendron pulchrum in China

Plant Disease ◽

10.1094/pdis-04-21-0830-pdn ◽

2021 ◽

Author(s):

Yaxing Li ◽

Yangfan Feng ◽

Cuiping Wu ◽

Junxin Xue ◽

Binbin Jiao ◽

...

Keyword(s):

Root Rot ◽

Morphological Characters ◽

Morphological Features ◽

Crown Rot ◽

Sterile Water ◽

First Report ◽

Inoculation Method ◽

Platanus Orientalis ◽

Crown And Root Rot ◽

Root Tissues

During a survey of pathogenic oomycetes in Nanjing, China from June 2019 to October 2020, at least ten adjacent Rhododendron pulchrum plants at a Jiangjun Mountain scenic spot showed symptoms of blight, and crown and root discoloration . Symptomatic root tissues collected from three 6-year-old plants were rinsed with water, cut into 10-mm pieces, surface sterilized with 70% ethanol for 1 min, and plated onto 10% clarified V8 PARP agar (cV8A-PARP) containing pimaricin (20 mg/liter), ampicillin (125 mg/liter), rifampicin (10 mg/liter), and pentachloronitrobenzene (20 mg/liter). Four Pythium-like isolates were recovered after three days of incubation at 26°C, and purified using hyphal-tipping. Ten agar plugs (2×2 mm2) of each isolate were grown in 10 mL of 10% clarified V8 juice (cV8) in a 10 cm plate at 26°C for 3 days to produce mycelial mats, and then the cV8 was replaced with sterile water. To stimulate sporangial production, three to five drops of soil extract solution were added to each plate. Sporangia were terminal, ovoid to globose, and the size is 24 to 45.6 (mean 34.7) (n=10.8) in length x 23.6 to 36.0 (mean 29.8) (n=6.2) in width. Gametangia were not observed in cV8A or liquid media after 30 days. For colony morphology, the isolates were sub-cultured onto three solid microbial media (cV8A-PARP, potato dextrose agar, corn meal agar) . All isolates had identical morphological features in the three media. Complete ITS and partial LSU and cox2 gene regions were amplified using primer pairs ITS1/ITS4, NL1/NL4, and FM58/FM66 , respectively. The ITS, LSU, and cox2 sequences of isolate PC-dj1 (GenBank Acc. No. MW205746, MW208002, MW208003) were 100.00% (936/936 nt), 100.00% (772/772 nt), and 99.64% (554/556 nt) identical to those of JX985743, MT042003, and GU133521, respectively. We built a maximum-likelihood tree of Phytopythium species using the concatenated dataset (ITS, LSU, cox2) to observe interspecific differences. Based on the morphological characters and sequences, isolate PC-djl was identified as Phytopythium litorale . As the four isolates (PC-dj1, PC-dj2, PC-dj3 and PC-dj4) tested had identical morphological characters and molecular marker sequences, the pathogenicity of the representative isolate, PC-dj1, was tested using two inoculation methods on ten one-year-old R. pulchrum plants. For the first inoculation method, plants were removed from the pot, and their roots were rinsed with tap water to remove the soil. Each of these plants was placed in a glass flask containing 250 mL of sterile water and 10 blocks (10 x 10 mm2) of mycelial mats harvested from a three-day-old culture of P. litorale, while the other plant was placed in sterile water as a control, and incubated at 26°C. After three days, symptoms including crown rot, root rot and blight was observed on the inoculated plants whereas the control remained asymptomatic. For the second inoculation method, ten plants were dug up to expose the root ball. Ten three-day-old cV8A plugs (5×5 mm2) from a PC-dj1 culture or sterile cV8A plugs were evenly insert into the root ball of a plant before it was planted back into the original pots. Both plants were maintained in a growth chamber set at 26°C with a 12/12 h light/dark cycle and irrigated as needed. After 14 to 21 days, the inoculated plant had symptoms resembling those in the field , while the control plant remained asymptomatic. Each inoculation method was repeated at triplicate and the outcomes were identical. Phytopythium isolates with morphological features and sequences identical to those of PC-dj1 were recovered from rotted crown and root tissues of all inoculated plants. Previously, P. litorale was found causing diseases of apple and Platanus orientalis in Turkey, fruit rot and seedling damping-off of yellow squash in southern Georgia, USA. This is the first report of this species causing crown and root rot on R. pulchrum, an important ornamental plant species in China. Additional surveys are ongoing to determine the distribution of P. litorale in the city of Nanjing.

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