First Report of Southern Blight of Mexican Petunia (Ruellia brittoniana) Caused by Sclerotium rolfsii in Taiwan

Mexican petunia (Ruellia brittoniana) is an herbaceous flowering perennial with strikingly colored flowers, widely cultivated commercially as a potted plant and a popular garden plant. In July of 2010, root and stem rot that caused death was observed on Mexican petunia at the flower nursery of the Council of Agriculture & Chiayi County in Taiwan. Plants had rotted and girdled stem bases. Necrotic areas were covered with fans of white mycelium as well as abundant spherical sclerotia. A fungus was isolated from infected tissue and sclerotia, and maintained on potato dextrose agar (PDA) plates incubated at 25°C without light. Colonies were white, cottony, often forming fans; pure cultures were prepared by transferring hyphal tips to PDA. Sclerotia formed after 10 days, initially white becoming dark brown with age, and 0.5 to 0.6 mm in diameter. To confirm identity of the causal fungus, the complete internal transcribed spacer (ITS) rDNA region of the causal fungus was amplified using the primers ITS4 and ITS5 (2) and sequenced. The resulting sequence of 687 bp was uploaded in NCBI. The sequence was 98% similar to sequences of Athelia rolfsii (Sclerotium rolfsii) in NCBI (Accession No. JN543691.1). Koch's postulates were performed using two inoculation techniques. The soil near the base of healthy Mexican petunia plants (four plants per pot) were exposed to recently matured sclerotia (10 sclerotia per plant) developed from pure fungal cultures or 10-mm-diameter agar plugs of mycelium (one plug per plant). Noninoculated plants, in a separate pot, were used as a control. All plants were incubated in a growth chamber at 28 to 33°C. Disease symptoms occurred on all inoculated plants by 5 to 7 days and included yellowing of leaves, basal stem rot, and wilt. Ten days after inoculation, inoculated plants were dead whereas control plants remained healthy. The pathogenicity test was repeated twice with similar results and S. rolfsii was reisolated from infected plants in each test. The pathogen has been reported to cause substantial loss of Mexican petunia in Louisiana (1). The disease is becoming more common in Taiwan and could cause losses in Mexican petunia production. To our knowledge, this is the first report of disease on Mexican petunia caused by S. rolfsii in Taiwan. References: (1) G. E. Holcomb. Plant Dis. 88:770, 2004. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, 1990.

Download Full-text

First Report of Southern Blight of Iresine herbstii Caused by Sclerotium rolfsii in Taiwan

Plant Disease ◽

10.1094/pdis-04-12-0372-pdn ◽

2012 ◽

Vol 96 (11) ◽

pp. 1692-1692

Author(s):

C. H. Fu ◽

Y. P. Huang ◽

F. Y. Lin

Keyword(s):

Sclerotium Rolfsii ◽

Soil Surface ◽

Herbaceous Plant ◽

First Report ◽

Southern Blight ◽

Potted Plants ◽

Agar Plug ◽

Initial Symptoms ◽

Pure Cultures ◽

Causal Fungus

Widely cultivated commercially, Iresine herbstii Hook is a potted herbaceous plant popular for its foliage, which varies from a dark red to brownish maroon. In the summer of 2010, a sudden wilt of I. herbstii plants was observed at a recreational farm in Taipei City in northern Taiwan. The initial symptoms were water-soaked lesions that became soft and then rotted. Necrotic areas on the stems were covered with fans of white mycelium as well as abundant spherical, brown sclerotia. A fungus was isolated from both infected tissue and sclerotia and maintained on potato dextrose agar (PDA) plates incubated at 25°C without light. Colonies were white and cottony, often forming mycelial fans. Pure cultures were prepared by transferring single hyphal tips to PDA. Sclerotia formed after 7 days. Sclerotia were initially white becoming dark brown with age and were 0.8 to 1 mm in diameter at maturity. These are typical features of Sclerotium rolfsii. Koch's postulates were performed by inoculating five healthy, potted I. herbstii plants with 10 fresh sclerotia placed on the soil surface around the base of each plant. In a second test, five healthy potted plants were inoculated with a single 10-mm-diameter mycelial agar plug placed at the stem base of each plant. Five noninoculated plants served as controls. All plants were incubated in a growth chamber at 25 to 35°C. Basal stem rot and wilt developed within 4 days on plants inoculated with sclerotia or mycelial plugs. All plants were dead by 7 days after inoculation whereas the controls remained healthy. The fungus was reisolated from the symptomatic tissue and produced sclerotia and mycelium consistent with S. rolfsii. To confirm identity of the causal fungus, the complete internal transcribed spacer (ITS) rDNA region of the causal fungus was amplified using the primers ITS4 and ITS5 (3) and sequenced. The resulting sequence of 687 bp was uploaded in NCBI (Accession No. JN543691.1). The sequence was 98% similar to sequences of Athelia rolfsii (anamoprh S. rolfsii). This disease has been observed on many species of plants (1, 2). To our knowledge, this is the first report of I. herbstii caused by S. rolfsii in Taiwan or any other part of the world. References: (1) T. T. Chang. Bull. Taiwan For. Res. Inst. 9:191, 1994. (2) Y. N. Wang et al. J. Exp. For. Nat. Taiwan Univ. 20:45, 2006. (3) T. J. White et al. PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990.

Download Full-text

First Report of Root Rot Caused by Sclerotium rolfsii on Daucus carota var. sativa in Southern Korea

Plant Disease ◽

10.1094/pdis-03-11-0233 ◽

2011 ◽

Vol 95 (12) ◽

pp. 1585-1585

Author(s):

J.-H. Kwon ◽

Y. H. Lee ◽

H.-S. Shim ◽

J. Kim

Keyword(s):

Daucus Carota ◽

Root Rot ◽

Pathogenic Fungus ◽

Sclerotium Rolfsii ◽

Agricultural Science ◽

Control Treatment ◽

Pathogenicity Test ◽

Optimum Temperature ◽

First Report ◽

Causal Fungus

Carrot (Daucus carota var. sativa DC.), an important root vegetable, is cultivated widely because of its dietary fiber and beta carotene. In June 2009 and June 2010, a disease suspected as root rot of carrot caused by Sclerotium rolfsii occurred in a 5-ha field in Jinju, Korea. Early symptoms consisted of water-soaked lesions on root and lower stem tissue near the soil line. Infected plants gradually withered and white mycelial mats appeared on the surface of roots. Numerous sclerotia were often produced on stem and root surfaces in contact with the soil. The heavily infected carrots became rotted and blighted and the whole plant eventually died. The freshly isolated pathogenic fungus was grown on potato dextrose agar (PDA) and examined microscopically. Optimum temperature for mycelia growth or sclerotia formation was 25 to 30°C. Numerous globoid sclerotia formed on the PDA after 18 days of mycelial growth. The sclerotia (1 to 3 mm in diameter) were white at first and then gradually turned dark brown. Aerial mycelia usually formed, consisting of many narrow hyphal strands 3 to 9 μm wide. The white mycelium formed a typical clamp connection after 5 days of growth at optimum temperature. To fulfill Koch's postulates, 10 carrot seedlings were inoculated with colonized agar discs (6 mm in diameter) of the causal fungus directly on the root and incubated in a humid chamber at 25°C for 24 h. Ten carrot seedlings were inoculated similarly with agar discs as the control treatment. After this period, the inoculated and noninoculated plants were maintained in a greenhouse. Eight days after inoculation, the disease symptoms seen in the field were reproduced and the fungus was reisolated from the artificially inoculated plants. To confirm identity of the causal fungus, the complete internal transcribed spacer (ITS) rDNA region of the causal fungus was amplified using the primers ITS1 and ITS4 (2) and sequenced. The resulting sequence of 684 bp was deposited in GenBank (Accession No. JF342557). The sequence was 99% similar to sequences of Athelia rolfsii (Sclerotium rolfsii) in GenBank. Cultures of S. rolfsii have been deposited with the Korean Agricultural Culture Collection (KACC 45154), National Academy of Agricultural Science, Korea. On the basis of symptoms, fungal colonies, the ITS sequence, and the pathogenicity test on the host plant, this fungus was identified as S. rolfsii Saccardo (1). To our knowledge, this is the first report of root rot of carrot caused by S. rolfsii in Korea. This disease is highly dependent upon environmental conditions, including warm weather and high humidity. Recent occurrence of the disease suggests that S. rolfsii could spread widely. References: (1) J. E. M. Mordue. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 410, 1974. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, Inc., New York, 1990.

Download Full-text

First Report of Southern Blight on Canadian Goldenrod (Solidago canadensis) Caused by Sclerotium rolfsii in China

Plant Disease ◽

10.1094/pdis-94-9-1172b ◽

2010 ◽

Vol 94 (9) ◽

pp. 1172-1172 ◽

Cited By ~ 7

Author(s):

W. Tang ◽

Y. Z. Zhu ◽

H. Q. He ◽

S. Qiang

Keyword(s):

Eastern China ◽

Sclerotium Rolfsii ◽

Soil Surface ◽

Pathogenicity Test ◽

Solidago Canadensis ◽

Uniform Size ◽

First Report ◽

Southern Blight ◽

Perennial Plant ◽

Nanjing City

Canadian goldenrod (Solidago canadensis L., Asteraceae) is a rhizomatous perennial plant native to North America that has invaded eastern China and continues to spread northward and westward. It is quite common on field borders, roadsides, and in undeveloped areas, posing a serious threat to native ecosystems and their biodiversity. During the late summers of 2007 and 2008, wilted Canadian goldenrod plants were occasionally found in invasive populations in the suburb of Nanjing city. Wilted plants were transplanted and maintained in a greenhouse at Nanjing Agricultural University. A white mass of fungal hyphae, which grew on the soil surface around the stem of the symptomatic S. canadesis plants and eventually covered the stem, was observed. Initially, the base of the stem became yellow, turned brown, and the light brown discoloration extended up the stem to a height of 3 to 7 cm. The leaves then collapsed, starting from the top until the entire plant wilted. The fungus produced numerous, small, roundish sclerotia of uniform size (0.7 to 2.0 mm in diameter), which were white at first and then became brown to dark brown. The fungus grew into the stems and downward into the rhizome area, but no sclerotia were detected inside the stem or root. Diseased tissue with sclerotia was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar amended with 100 mg/liter of streptomycin sulfate. On the basis of sclerotia morphology and the presence of clamp connections at hyphal septa, the fungus was identified as Sclerotium rolfsii. Pathogenicity of the isolate was confirmed by inoculating 1-year-old S. canadensis plants (average 1.5 m high) grown in pots. The inoculum consisted of cottonseed hulls infested with mycelium and sclerotia of the pathogen and was placed on the soil surface around the base of each unwounded plant. Noninoculated plants served as controls. The pathogenicity test was conducted twice. After inoculation, the plants were maintained at high humidity and 30°C for 3 days and then transferred to a greenhouse. All inoculated plants developed symptoms of southern blight. Inoculated plants developed symptoms of wilting 5 to 7 days after inoculation and were completely wilted within 15 to 20 days. Symptoms of wilting were soon followed by the appearance of white-to-light brown sclerotia on the collar region. Control plants remained symptomless and Sclerotium rolfsii was reisolated from inoculated plants. To our knowledge, this is the first report of southern blight of Canadian goldenrod caused by Sclerotium rolfsii in China.

Download Full-text

First Report of Southern Blight of Manglietia decidua Caused by Sclerotium rolfsii in China

Plant Disease ◽

10.1094/pdis-10-20-2194-pdn ◽

2020 ◽

Author(s):

Run Hua Yi ◽

Gui Gen Long ◽

Ke Yang Li ◽

Xiao Yang Wang ◽

Yan Huang ◽

...

Keyword(s):

Sclerotium Rolfsii ◽

Its Region ◽

Ground Level ◽

Healthy Plant ◽

Molecular Characteristics ◽

Pathogenicity Test ◽

Endangered Tree ◽

First Report ◽

Endangered Tree Species ◽

Southern Blight

Manglietia decidua, named ‘Hua manglietia’, belonging to the Magnoliaceae family, is one of the most important ornamental plant in China. In 2019 and 2020, an unknown disease caused 3- to 12-month plants of M. decidua to wither and die in the field in Zhanjiang, Guangdong province（N21°9’3”;E110°17’47”）. Initially, the infected plants showed leaves dehydration, chlorosis and wilting with water-soaked lesions on stems at ground level. About 7 days later, the plants completely wilted, collapsed and died. Delayed and stunted growth with wilting of foliage continued through the whole year. Dense white mycelial mat and small white-to-brown spherical sclerotia were observed on the surface of the stalk lesion when weather conditions were warm and humid. Approximately 10% of plants were infected. Especially from July to October 2020, up to 30% of about 500 plants were infected and died. To identify the causal agents of the disease, infected tissue and sclerotia were collected, surface disinfected in 75% alcohol for 30s and 30% hydrogen peroxide solution for 5 min, and washed with sterile water for 1 min. The surface disinfected tissue and sclerotia were put on potato dextrose agar containing ampicillin (50mg/L) and kept in an incubator at 25°C in the dark. Fast growing fungus colonies with white mycelium and numerous sclerotia developed in the plates after 6 to 8 days of incubation. The hyphae were septate, hyaline and formed typically clamp connection after 10 days of growth. Sclerotia were initially white and became tan to dark brown over time and 1.0 to 3.0 mm (2.13 mm on average, n=124) in diameter at maturity. For molecular identification，the ITS region was amplified using primer pair ITS1/ITS4 (White et al. 1990). A 666 bp PCR product was sequenced (GenBank accession no. MW093622) and shared above 99% sequence identity with some Athelia rolfsii isolates (GenBank accession Nos. HQ895869, KX499470 and AB075290). Based on morphological and molecular characteristics, the fungus was identified as Sclerotium rolfsii (teleomorph A. rolfsii) （Paul et al. 2017，Xu et al. 2010. Pathogenicity tests were conducted by inoculating ten healthy 1-year-old M. decidua plants grown in pots. Five sclerotia and mycelial mat obtained from 15-day-old cultures were buried adjacent to the stem of each unwounded healthy plant. Non-inoculated plants served as controls. After inoculation, the plants were maintained in a 25-28 ℃ greenhouse and watered regularly to keep the soil moisture content at about 15%. Symptoms of southern blight were observed on all inoculated plants, which began to wilt 7 to 10 days after inoculation and died within 15 to 20 days. The control plants remained healthy. S. rolfsii was again isolated from the artificially inoculated plants, but not from non-inoculated plants. The pathogenicity test was repeated twice and the results were the same. S. rolfsii has an extensive host range worldwide and the common host ornamental plants are Iris, Chrysanthemum, CymbidiumTrifolium, Jasminum, Begonia, and Stevia etc. in China. To our knowledge, this is the first report of southern blight caused by S. rolfsiii on M. decidua in China. M. decidua is a horticultural plant which belongs to the protected and endangered tree species. This finding is important to alert growers to realize the proper management of this disease during species protection and cultivar extension.

Download Full-text

Asian Foxtail (Uraria crinita), a New Host for Sclerotium rolfsii from Taiwan

Plant Disease ◽

10.1094/pdis-05-14-0448-pdn ◽

2014 ◽

Vol 98 (10) ◽

pp. 1438-1438 ◽

Cited By ~ 2

Author(s):

Y. M. Shen ◽

C. H. Chao ◽

H. L. Liu

Keyword(s):

Sequence Similarity ◽

Infected Plant ◽

Sclerotium Rolfsii ◽

Pathogenicity Test ◽

Academic Press ◽

New Host ◽

First Report ◽

Sclerotium Rot ◽

Rice Water ◽

Negative Controls

Asian foxtail (Uraria crinita (L.) Desv. ex DC.) is an herb cultivated for the use of roots and stems in Taiwanese cuisine. In September 2013, symptoms of leaf blight and basal rot were observed on U. crinita in a commercial field in Longjing District, Taichung, Taiwan, at an incidence of approximately 20%. White mycelia and brown sclerotia formed on the surfaces of the basal stems. The infected plant gradually wilted and eventually died. Diseased lower stem tissues were surface sterilized in 0.6% NaOCl, rinsed with sterile distilled water, and transferred to potato dextrose agar plates. The cultures were incubated at 25°C in the dark. The radial mycelial growth was 9.0 mm/day during the first 4 days, and the diameter of mature sclerotia was 1.76 mm following 3 weeks of incubation. The internal transcribed spacer (ITS) sequence of the isolate was amplified by PCR using the primers ITS5 and ITS4 (2). The amplicon was cloned, sequenced, and deposited in GenBank (Accession No. KJ677121). The sequence similarity was 99% compared with that of Sclerotium rolfsii Sacc. from Spain (GU080230) (1). Based on the characteristics, the fungus was identified as S. rolfsii. The fungal isolate (BCRC FU30230) was deposited in the Bioresource Collection and Research Center, Hsinchu, Taiwan. Pathogenicity tests were conducted on six 2-month-old potted U. crinita plants in a greenhouse. Prior to infesting the plant, fungal inoculum of S. rolfsii BCRC FU30230 was prepared by inoculating the isolate on autoclaved rice (rice/water/dextrose = 50:50:1) in a flask. After 20 days incubation at room temperature, rice colonized by S. rolfsii was placed near the base of the plants (approximately 30 g/plant) in the greenhouse. Sterile rice applied to an equal number of plants served as negative controls. All inoculated plants developed blight symptoms with mycelia and sclerotia produced near the bases of each seedling 1 week after inoculation at an average temperature of 26°C. The control plants remained healthy. The pathogen re-isolated from the inoculated plants was morphologically identical to the original isolate. The pathogenicity test was repeated by inoculated healthy plants with reduced inoculum (five granules/plant). A delay of symptom development was observed and similar results were obtained. To our knowledge, this is the first report of Sclerotium rot on U. crinita in Taiwan, and the first report on U. crinita as a host for S. rolfsii. References: (1) E. Remesal et al. Plant Dis. 94:280, 2010. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

Download Full-text

First Report of Southern Blight of Ruellia brittoniana Caused by Sclerotium rolfsii in Louisiana

Plant Disease ◽

10.1094/pdis.2004.88.7.770a ◽

2004 ◽

Vol 88 (7) ◽

pp. 770-770

Author(s):

G. E. Holcomb

Keyword(s):

Root Rot ◽

High Speed ◽

Sclerotium Rolfsii ◽

Stem Rot ◽

Basal Stem Rot ◽

First Report ◽

Southern Blight ◽

Agar Plug ◽

Leaf Yellowing ◽

Pathogenicity Tests

Ruellia brittoniana, Mexican petunia, is an herbaceous flowering perennial grown in hardiness zones 8 to 10 in the southern and western United States. Popular dwarf forms with flower colors of white, pink, and blue are used as ground covers and borders. In April of 2003, root and stem rot that caused plant death was observed on cv. Katie (dwarf form, pink flowers) at a wholesale nursery in southern Louisiana. Plants were growing in a vermiculite and sand mix. The grower had purchased the plants from an out-of-state source, and approximately one-half of 1,440 plants were dead or dying. Symptoms included wilt, basal stem rot, and root rot. Peripheral roots were covered with a white mycelial layer that contained white sclerotial initials and small, brown sclerotia. Fungal isolates from infected roots grown on potato dextrose agar (PDA) produced white mycelia and 1- to 2-mm-diameter dark brown sclerotia. Sclerotia were nearly round with smooth surfaces and distributed over the entire colony. Isolates were identified as Sclerotium rolfsii on the basis of mycelial characteristics and color, size, and distribution of sclerotia. Two-month-old seedlings (6 to 10 cm high) of R. brittoniana, from seed of cv. Katie, were used in pathogenicity tests. Inoculum was grown in 10-cm-diameter plastic, culture dishes on PDA medium. Blended inoculum was prepared from a single 1-week-old culture that was composed of mycelia and sclerotia and blended 4 to 6 s at high speed in 100 ml of distilled water. In test one, 5 ml of inoculum was placed at the base of each inoculated plant. In test two, a single 5-mm-diameter agar plug with mycelium plus four sclerotia was placed beside plant stems near soil line. In test three, 5 ml of blended inoculum was dripped on exposed roots after plants were removed from pots. In test four, exposed plant roots were dipped in the blended inoculum. Each test contained 10 inoculated plants, and 10 noninoculated plants served as controls. All plants were placed in a dew chamber maintained at 28°C for 2 days and then returned to a greenhouse to observe development of symptoms and signs of disease. In tests one and two, basal stem rot and wilt developed on inoculated plants after 2 days and after 5 to 8 days all were dead. Inoculated plants from tests three and four were alive 4 months after inoculation, but were showing symptoms including leaf yellowing and drop, moderate to severe root rot, and some plants had begun to show white mycelia and white sclerotial initials on peripheral roots by January 2004. All noninoculated plants remained healthy and S. rolfsii was reisolated from infected plants in each test. To my knowledge, this is the first report of S. rolfsii causing disease on R. brittoniana.

Download Full-text

First Report of Southern Blight Caused by Sclerotium rolfsii on St.-John's-Wort

Plant Disease ◽

10.1094/pdis.1999.83.7.696c ◽

1999 ◽

Vol 83 (7) ◽

pp. 696-696 ◽

Cited By ~ 2

Author(s):

A. P. Keinath ◽

J. W. Rushing ◽

R. J. Dufault

Keyword(s):

Sclerotium Rolfsii ◽

Soil Surface ◽

The United States ◽

Pathogenicity Test ◽

First Report ◽

Southern Blight ◽

St John’S Wort ◽

St John's Wort ◽

Pathogenicity Tests ◽

Hypericum Perforatum L

Interest in commercial production of common St.-John's-wort (Hypericum perforatum L.), an herb that is dried, processed, and used as an anti-depressant medication, is increasing. In August 1998, St.-John's-wort growing in the field at Charleston, SC, showed blight symptoms. Leaves on prostrate branches turned reddish-yellow, then brown, and then abscised. As the disease progressed, branches and approximately 10% of the plants were killed. Coarse, white mycelia were present on the bases of dead branches. Segments cut from symptomatic branches were disinfested in 0.5% sodium hypochlorite and placed on potato dextrose agar (PDA) at 25°C. Sclerotium rolfsii Sacc. was isolated from one of 12 branches with discolored leaves and six of six dead branches. For pathogenicity tests, sclerotia were harvested from 6-week-old cultures on PDA. Ten-week-old St.-John's-wort plants, growing in potting mix in 10-cm pots, were inoculated by placing four sclerotia on the soil surface 1 to 1.5 cm from the main stem of each plant. Plants were grown in a greenhouse at 90% relative humidity and 25 to 35°C. Single blighted branches were observed on three plants 12 days after inoculation and all plants were blighted 28 days after inoculation. S. rolfsii was recovered from 10 and 9 of 10 plants inoculated with isolates of S. rolfsii from St.-John's-wort and tomato, respectively. All 10 noninoculated plants remained symptomless. The pathogenicity test was repeated and the results were similar. This is the first report of S. rolfsii causing Southern blight on St.-John's-wort in the United States.

Download Full-text

First Report of Southern Blight Caused by Sclerotium rolfsii on Common Bean (Phaseolus vulgaris) in Italy

Plant Disease ◽

10.1094/pdis-12-12-1165-pdn ◽

2013 ◽

Vol 97 (10) ◽

pp. 1386-1386 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

G. Ortu ◽

M. L. Gullino ◽

M. Testa

Keyword(s):

Phaseolus Vulgaris ◽

Common Bean ◽

Sclerotium Rolfsii ◽

Crown Rot ◽

Control Treatment ◽

Pathogenicity Test ◽

Green Beans ◽

First Report ◽

Southern Blight ◽

White Mycelium

Common bean (Phaseolus vulgaris L.) is grown worldwide for consumption of dry or green beans. During late spring of 2012, yellowing and wilting symptoms were observed in a commercial bean field cv. Lingua di fuoco in Cagliari Province (Sardinia, southern Italy) on 30% of plants 4 to 5 months after sowing. The first symptoms developed in May, when temperatures reached 18 to 30°C. Affected plants showed crown rot, necrosis of the cortex, and foliar chlorosis. As disease progressed, plants collapsed. In the presence of abundant moisture, white mycelium developed on the senescent tissue along with light to dark brown sclerotia (3.0 to 4.8 mm in diameter). Symptomatic tissue was disinfested for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 25 mg streptomycin sulfate/liter. The fungus that was isolated consistently from symptomatic plants onto PDA at 23°C grew rapidly in culture with silky-white, sterile mycelium, formed light to dark brown sclerotia (each 1.8 to 3.2 mm in diameter) after 7 days, and readily produced aerial hyphae. These morphological features are typical of Sclerotium rolfsii (2). The internal transcribed spacer (ITS) region of ribosomal DNA (rDNA) was amplified for one isolate using ITS1/ITS4 primers (4), and sequenced (GenBank Accession No. KF002510). BLASTn analysis (1) of the 656-bp segment showed 87% homology with the ITS sequence of an S. rolfsii isolate (JF819727). Pathogenicity of one isolate was confirmed by inoculating healthy P. vulgaris plants cv. Lingua di fuoco grown in 2-liter pots in a steamed potting mix containing 50% Tecno2 (70% white peat and 30% clay) and 50% Tiesse 3 (60% white peat, 20% clay, and 20% perlite) (Turco Silvestro terricci, Bastia d'Albenga, SV, Italy). Inoculum consisting of mycelium and sclerotia of the pathogen produced from 10-day-old cultures on PDA was mixed in the soil at 0.5 g/liter substrate. Four 7-day-old plants per pot, with three replicate pots, were used for inoculation. The same number of control plants grown in the same substrate were inoculated with non-colonized PDA as a negative control treatment. The pathogenicity test was repeated. Plants were kept in a growth chamber at 30°C and 85% RH. Inoculated plants developed symptoms of leaf yellowing within 10 days, followed by crown rot, appearance of white mycelium and sclerotia, and eventual wilting. Control plants remained asymptomatic. Isolations from inoculated plants demonstrated the absence of latent infections by the fungus S. rolfsii, but the fungus was not reisolated from non-inoculated control plants. To our knowledge, this is the first report of S. rolfsii infecting P. vulgaris in Italy. Southern blight has been reported on common bean in sub-tropical and tropical areas of the world (3), where it can cause severe crop losses. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) J. E. M. Mordue. CMI Descriptions of Pathogenic Fungi and Bacteria No. 410, 1974. (3) H. F. Schwartz et al. Page 20 in: Compendium of Bean Diseases. American Phytopathological Society Press, St. Paul, MN, 2005. (4) T. J. White et al. PCR Protocols. Page 315 in: A Guide to Methods and Applications. Academic Press, San Diego, CA, 1990.

Download Full-text

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

Plant Disease ◽

10.1094/pdis-94-9-1171c ◽

2010 ◽

Vol 94 (9) ◽

pp. 1171-1171 ◽

Cited By ~ 1

Author(s):

D. X. Zeng ◽

X. L. Wu ◽

Y. H. Li

Keyword(s):

Southern China ◽

Aerial Mycelium ◽

Its Region ◽

Soil Extract ◽

Phytophthora Nicotianae ◽

Stem Rot ◽

Molecular Characteristics ◽

Its Sequence ◽

First Report ◽

Pure Cultures

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

Download Full-text