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

Plant Disease ◽  
2014 ◽  
Vol 98 (3) ◽  
pp. 419-419 ◽  
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.

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

Plant Disease ◽  
2012 ◽  
Vol 96 (11) ◽  
pp. 1696-1696 ◽  
Author(s):  
P. P. Wang ◽  
X. H. Wu
Keyword(s):  
Sugar Beet ◽  
Disease Incidence ◽  
Soil Surface ◽  
Its Region ◽  
Molecular Characteristics ◽  
Damping Off ◽  
First Report ◽  
Binucleate Rhizoctonia ◽  
Hyphal Diameter ◽  
Wheat Seeds

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

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

Plant Disease ◽  
2013 ◽  
Vol 97 (6) ◽  
pp. 840-840
Author(s):  
Y. G. Yang ◽  
X. H. Wu
Keyword(s):  
Rhizoctonia Solani ◽  
Solanum Tuberosum L ◽  
Its Region ◽  
Stem Canker ◽  
The United States ◽  
Gansu Province ◽  
Molecular Characteristics ◽  
Potato Seed ◽  
First Report ◽  
Wheat Seeds

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

scholarly journals Identification of Rhizoctonia solani isolates from sugar beet roots by analyzing the ITS region of ribosomal DNA

2007 ◽  
pp. 161-171 ◽  
Author(s):  
Vera Stojsin ◽  
Dragana Budakov ◽  
Barry Jacobsen ◽  
Eva Grimme ◽  
Ferenc Bagi ◽  
...  
Keyword(s):  
Sugar Beet ◽  
Rhizoctonia Solani ◽  
Ribosomal Dna ◽  
Root Rot ◽  
Its Region ◽  
Anastomosis Group ◽  
Crown Rot ◽  
Internal Transcribed Spacer Region ◽  
The Usa ◽  
Crown And Root Rot

Rhizoctonia solani (K?hn) is one of the most important sugar beet pathogens Rhizoctonia solani anastomosis groups (AGs) 2-2 and 4 are proven to be the most common pathogenic strains on sugar beet. AG 2-2 (intraspecific groups IIIB and IV) can cause root and crown rot while damping-off of seedlings is most frequently attributed to AG 4. Four isolates of R. solani from sugar beet roots showing characteristic crown and root rot symptoms, collected from different localities in Vojvodina Province, were chosen and compared to the well-characterized R. solani isolate R9, AG 2-2 IV, from the USA. All Vojvodinian isolates showed medium level of pathogenicity and were able to cause crown and root rot symptoms on inoculated sugar beet roots. Based on anastomosis reaction, isolates from Vojvodina did not belong to the AG 2-2 group. Sequencing of the ITS (internal transcribed spacer) region of ribosomal DNA was performed on the Vojvodinian isolates from R9 in order to determine their relatedness. Sequence analysis showed that these isolates were different than R9 and were closely related (99-100% sequence homology) to anastomosis group 4, subgroup HG II.

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

Plant Disease ◽  
2012 ◽  
Vol 96 (10) ◽  
pp. 1579-1579 ◽  
Author(s):  
Y. Yang ◽  
X. Wu
Keyword(s):  
Rhizoctonia Solani ◽  
Solanum Tuberosum L ◽  
Its Region ◽  
Stem Canker ◽  
Molecular Characteristics ◽  
Potato Seed ◽  
Canker Disease ◽  
First Report ◽  
Agric Food ◽  
Wheat Seeds

Potato (Solanum tuberosum L.) is grown worldwide as a major food crop. Potato stem canker is an important disease mainly caused by Rhizoctonia solani AG-3 (4). In 2011, samples of potato stem canker were collected from 26 sites in Heilongjiang Province, northeast China. Stem fragments taken from the margins of the healthy and diseased tissues were surface disinfected with 0.5% NaOCl for 2 min, rinsed with sterile water, then placed on potato dextrose agar (PDA) at 25°C in the dark. Twenty-two fungal isolates taken from single hyphal tips were identified as R. solani based on morphological traits. Colonies were light brown with abundant growth of mycelia and produced brown, irregular sclerotia after 20 days on PDA. Mycelium was branched at right angles with a septum near the branch and a slight constriction at the branch base. Hyphal cells were determined to be multinucleate (five to 13 nuclei per cell) when stained with 4′-6-diamidino-2-phenylindole (DAPI). Anastomosis groups were determined by pairing with reference strains (kindly provided by N. Kondo, Hokkaido University, Japan) (1), and six out of 22 isolates anastomosed with R. solani AG-5. The internal transcribed spacer (ITS) region of rDNA was amplified from genomic DNA of the AG-5 isolates with primers ITS1 and ITS4. The ITS sequences (GenBank Accession Nos. JQ946291 to JQ946296) were 99% identical to R. solani isolate AG-5 ND1 (GenBank Accession No. HQ629863). Therefore, based on molecular characteristics and the anastomosis assay, these six isolates were confirmed to be R. solani AG-5. To determine the pathogenicity of R. solani AG-5 isolates, potato seed tubers (cv. Favorita) with 3- to 5-mm sprouts were inoculated with wheat seeds (sterilized by autoclaving twice at 121°C for 1 h with a 24-h interval) colonized with each isolate (2). Wheat seeds were placed 10 mm above the uppermost sprout tip (one seed per sprout). Plants were incubated in glasshouse conditions maintained at 25 to 27°C. After 3 weeks, all inoculated plants showed symptoms of potato stem canker disease, whereas control plants inoculated with sterilized wheat seeds remained healthy. R. solani AG-5 was consistently reisolated from symptomatic stems, and the identity was confirmed by morphological and molecular characteristics as previously described, fulfilling Koch's postulates. Potato stem canker caused by R. solani AG-5 was previously detected in Australia, South Africa, Finland, and Japan (3). However, to our knowledge, this is the first report of R. solani AG-5 on potato in China. Besides previously reported AGs 1, 3, and 4 implicated in Rhizoctonia disease in China, AG 5 should also be taken into account when designing programs for disease management in potato. References: (1) W. C. Kronland and M. E. Stanghellini. Phytopathology 78:820, 1988. (2) M. J. Lehtonen et al. Plant Pathol. 57:141, 2008. (3) M. J. Lehtonen et al. J. Agric. Food Sci. 18:223, 2009. (4) L. Tsror. J. Phytopathol. 158:649, 2010.

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

Plant Disease ◽  
2016 ◽  
Vol 100 (12) ◽  
pp. 2427-2433 ◽  
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.

scholarly journals First Report of Crown and Root Rot Caused by Rhizoctonia solani AG-4 on Orange Jessamine in Italy

Plant Disease ◽  
2009 ◽  
Vol 93 (2) ◽  
pp. 204-204 ◽  
Author(s):  
D. Aiello ◽  
A. Vitale ◽  
E. Lahoz ◽  
R. Nicoletti ◽  
G. Polizzi
Keyword(s):  
Rhizoctonia Solani ◽  
Root Rot ◽  
Morphological Characteristics ◽  
Ruthenium Red ◽  
Fluorescent Light ◽  
First Report ◽  
Pectic Enzymes ◽  
Electrophoretic Patterns ◽  
Crown And Root Rot ◽  
Hyphal Diameter

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.

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

Plant Disease ◽  
2011 ◽  
Vol 95 (9) ◽  
pp. 1194-1194 ◽  
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.

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

Plant Disease ◽  
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.

scholarly journals First report of Diaporthe eres causing root rot of Coptis chinensis Franchet

Plant Disease ◽  
2021 ◽  
Author(s):  
PengYing MEI ◽  
Xuhong Song ◽  
Zhiyu Zhu ◽  
Longyun Li
Keyword(s):  
Root Rot ◽  
Elongation Factor ◽  
Its Region ◽  
Small Samples ◽  
Molecular Characteristics ◽  
Conidial Suspension ◽  
Coptis Chinensis ◽  
Base Pairs ◽  
First Report ◽  
Surface Sterilization

Chongqing coptis (Coptis chinensis Franchet) industry produces more than 60% of the Chinese coptis crop, and has been exported to many countries and regions. Since 2008, root rot has become a serious and widespread disease on coptis plants in Shizhu county with an average incidence of 40%, and yield losses up to 67%. Symptomatic coptis plants showed stunted growth, with the fibrous roots and main roots having brown or black, rotten, necrotic lesions. To our knowledge, Fusarium solani, F. carminascens, F. oxysporum and F. tricinctum have been previously reported as pathogens of coptis root rot (Luo et al. 2014; Cheng et al. 2020; Wu et al. 2020), but non Fusarium pathogens has not been reported yet. In order to identify new pathogens, 33 diseased roots were collected from Shizhu (30°18'N, 108°30'E) in October 2019. Small samples (0.5 cm in length) were cut from the border between diseased and healthy tissue, and then put on PDA after surface sterilization. Cultures were incubated at 25°C in dark until fungal colonies were observed. After subculturing for 3 times, 3 out of 21 isolates yielded a similar type of fungal colony. White, aerial, fluffy mycelium were formed and reached 8.3 cm diameter within 7 days, and dark pigmentation developed in the centre. Colonies turned to gray with age, and abundant dark brown pycnidia and black stromata were formed at maturity. Alpha conidia were aseptate, hyaline, fusiform to ellipsoidal, often biguttulate, measuring (6.0-8.5)×(2.0-3.0) μm. Beta conidia were aseptate, hyaline, linear to hooked, measuring (18-30)×(1.0-1.5) μm (Figure S1). For further identification, a multigene phylogenetic analysis was carried out. The internal transcribed spacer (ITS), translation elongation factor 1ɑ (tef1-ɑ), histone H3 (his3), calmodulin (cal), and β-tubulin (tub2) gene regions were amplified with ITS1/ITS4, EF1-728F/EF1-986R, CYLH3F/H3-1b, CAL228F/CAL737R, T1/Bt2b (White et al. 1990; Glass and Donaldson 1995; Carbone and Kohn 1999; Crous et al. 2004). GenBank accession numbers of isolate H13 were MT463391 for the ITS region, MT975573 for tef1-ɑ, MT975574 for his3, MT975575 for cal, and MT975576 for tub2. BLAST results showed the ITS, tef1-ɑ, his3, cal and tub2 sequences revealed 99.82% (553/554 base pairs), 100% (347/347 base pairs), 100% (474/474 base pairs), 99.39% (486/489 base pairs), and 99.14% (803/810 base pairs) homology respectively with those of Diaporthe eres (MN816416.1, KU557616.1, KC343564.1, KU557595.1, and KY569366.1). Thus, H13 were identified as D. eres based on its morphological and molecular characteristics. Pathogenicity of D. eres in coptis was investigated using the H13 isolate (1 of the 3 isolates). The roots of 10 healthy 2-year-old coptis plants were individually inoculated with 5 ml of a 106 conidia/mL conidial suspension and sterilized water was used to mock inoculate. Thirty days after inoculation, most of the inoculated coptis roots showed dark brown and rotten root, similar to those observed in the field, whereas mock inoculated roots showed healthy. D. eres was recovered from symptomatic roots and identified based on morphology. To our knowledge, this is the first report of D. eres causing root rot of coptis not only in China but anywhere in the world.

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