First Report of Aerial Blight of Peanut Caused by Rhizoctonia solani AG1-IA in Arkansas

In early September 2012, symptoms similar to aerial blight were observed on runner peanut (cv. Georgia 09B) in a commercial field in Randolph County, Arkansas (3). Leaves within the canopy closest to the soil had water-soaked, gray to green lesions or tan to brown lesions. Localized areas of matted leaves with mycelium occurred on stems and hyphae extended along stems and newly affected leaves. Dark brown spherical sclerotia (1.5 to 4 mm diam.) were produced on the surface of symptomatic peanut tissue (3). Aerial blight symptoms were observed in two peanut fields (~4 to 6 ha) that were furrow irrigated. Symptomatic plants were localized in a single circular pattern (~20 × 25 m) near the lower end of each field with the final disease incidence of less than 5%. Isolations from surface-disinfected leaves on potato dextrose agar consistently yielded light brown to brown colonies with sclerotia typical of Rhizoctonia solani AG1-IA. The fungus was confirmed to be R. solani AG1 by anastomosis reaction (2) with known cultures of AG1-IA isolated from soybean and rice in Arkansas. Sequencing of the rDNA ITS region 5.8s with primers ITS1 and ITS4 (1) supported the identification of the R. solani isolates as AG1-IA. The BLAST search revealed that the sequence had a 96 to 97% maximum sequence identity to several R. solani AG1-IA isolates collected from rice sheaths in China and Arkansas. Eight-week-old peanut plants (cv. Georgia 09B) growing in pots were sprayed until runoff (2 ml/plant) with a solution containing approximately 1 × 105 hyphal fragments/ml. Five inoculated plants were placed in a humidity chamber within a greenhouse where temperatures ranged from 28 to 33°C. After 14 days, water soaked, gray to green or light brown lesions developed on all inoculated plants along with hyphal strands along inoculated sections of the peanut with dark brown sclerotia. None of the plants inoculated with sterile water expressed symptoms. Rhizoctonia solani was consistently reisolated from symptomatic tissue plated on PDA. Inoculations were repeated on peanut cv. Flavor Runner 458, Florida 07, FloRun 107, and Red River Runner with similar results. Although R. solani AG1-IA is a common pathogen on rice and soybean, causing sheath blight and aerial blight, respectively, to our knowledge this is the first report of aerial blight of peanut in the region. Currently, there is a renewed interest in peanut production in the state. Production practices include furrow irrigation, which can distribute floating sclerotia to peanut vines and the rotation practiced with soybean and, less frequently, rice, could potentially increase inoculum for the subsequent crop. Thus, this may be a significant disease problem in the region or Mid-South where peanut is planted after rice or soybean and furrow irrigated. References: (1) S. Kuninaga et al. Curr. Genet. 32:237, 1997. (2) G. C. MacNish et al. Phytopathology 83:922, 1993. (3) H. A. Melouk and P. A. Backman. Management of soilborne fungal pathogens. Pages 75-85 in: Peanut Health Management. H. A. Melouk and F. M. Stokes, eds. The American Phytopathological Society, St. Paul, MN, 1995.

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First Report of Rhizoctonia solani AG4 HG-II Infecting Potato Stems in Idaho

Plant Disease ◽

10.1094/pdis-06-12-0568-pdn ◽

2012 ◽

Vol 96 (11) ◽

pp. 1701-1701 ◽

Cited By ~ 5

Author(s):

J. W. Woodhall ◽

P. S. Wharton ◽

J. C. Peters

Keyword(s):

Rhizoctonia Solani ◽

Seed Tuber ◽

Its Region ◽

Stem Canker ◽

Potato Production ◽

Koch’S Postulates ◽

First Report ◽

Rdna Its ◽

Plant Pathol ◽

Koch's Postulates

The fungus Rhizoctonia solani is the causal agent of stem canker and black scurf of potato (Solanum tuberosum). R. solani is a species complex consisting of 13 anastomosis groups (AGs) designated AG1 to 13 (2, 3). Stems of potato (cv. Russet Norkotah) with brown lesions were recovered from one field in Kimberley, Idaho, in August 2011. Using previously described methods (3), R. solani was recovered from the symptomatic stems and one representative isolate (J15) was selected for further characterization. Sequencing of the rDNA ITS region of isolate J15 was undertaken as previously described (3) and the resulting rDNA ITS sequence (HE667745) was 99% identical to sequences of other AG4 HG-II isolates in GenBank (AF354072 and AF354074). Pathogenicity of the isolate was determined by conducting the following experiment. Mini-tubers of cv. Santé were planted individually in 1-liter pots containing John Innes Number 3 compost (John Innes Manufacturers Association, Reading, UK). Pots were either inoculated with J15, an isolate of AG3-PT (Rs08), or were not inoculated. Each treatment was replicated four times. Inoculum consisted of five 10-mm-diameter potato dextrose agar plugs, fully colonized by the appropriate isolate, placed in the compost approximately 40 mm above each seed tuber. Pots were held in a controlled environment room at 21°C with 50% relative humidity and watered as required. After 21 days, plants were assessed for disease. No symptoms of the disease were present in non-inoculated plants. In the Rs08 (AG3-PT) inoculated plants, all stems displayed large brown lesions and 20% of the stems had been killed. No stem death was observed in J15 (AG4 HG-II) inoculated plants. However, brown lesions were observed in three of the four J15 (AG4 HG-II) inoculated plants. These lesions were less severe than in plants inoculated with the Rs08(AG3-PT) inoculated plants and were present in 40% of the main stems. In the J15 (AG4 HG-II) inoculated pots, R. solani AG4 HG-II was reisolated from the five symptomatic stems, thereby satisfying Koch's postulates. To our knowledge, this is the first report of AG4 HG-II causing disease on potatoes in Idaho. AG4 has been isolated from potato previously from North Dakota, although the subgroup was not identified (1). The only previous report where AG4 HG-II was specifically determined to cause disease on potato was in Finland, but the isolate could not be maintained and Koch's postulates were not completed (3). The present study shows that AG4 HG-II can cause stem disease in potatoes, although disease does not develop as severely or as consistently as for AG3-PT. However, as demonstrated with isolates of AG2-1 and AG5, even mild stem infection can reduce tuber yield by as much as 12% (4). AG4 HG-II is a pathogen of sugar beet in Idaho, which was grown previously in this field. This history may have contributed to high levels of soilborne inoculum required to produce disease on potato. References: (1) N. C. Gudmestad et al. Page 247 in: J. Vos et al. eds. Effects of Crop Rotation on Potato Production in the Temperate Zones. Kluwer, Dordrecht, Netherlands, 1989. (2) M. J. Lehtonen et al. Agric. Food Sci. 18:223, 2009. (3) J. W. Woodhall et al. Plant Pathol. 56:286, 2007. (4) J. W. Woodhall et al. Plant Pathol. 57:897, 2008.

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

Plant Disease ◽

10.1094/pdis-92-4-0648b ◽

2008 ◽

Vol 92 (4) ◽

pp. 648-648 ◽

Cited By ~ 1

Author(s):

T. T. M. Thuan ◽

N. Tho ◽

B. C. Tuyen

Keyword(s):

Rhizoctonia Solani ◽

Sequence Similarity ◽

Its Region ◽

The Philippines ◽

Leaf Blight ◽

First Report ◽

Rdna Its ◽

Durio Zibethinus ◽

Leaf Spots ◽

Irregular Border

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

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First Report of Sclerotinia Blight of Peanut Caused by Sclerotinia minor in Arkansas

Plant Disease ◽

10.1094/pdis-02-14-0169-pdn ◽

2014 ◽

Vol 98 (7) ◽

pp. 1013-1013 ◽

Cited By ~ 2

Author(s):

T. R. Faske ◽

M. Emerson ◽

K. Hurd

Keyword(s):

Disease Incidence ◽

Weed Species ◽

Sclerotinia Minor ◽

First Report ◽

Jackson County ◽

Sclerotinia Blight ◽

Agar Plug ◽

Randolph County ◽

Humidity Chamber ◽

History Of

In September, 2013, symptoms similar to Sclerotinia blight caused by Sclerotinia minor were observed on Runner peanut (cv. FloRun 107) in a commercial field near Pocahontas, Arkansas, in Randolph County (2). Blighted plants with wilted leaves were observed in several small (30 × 30 cm) clustered foci located near the end of a 20-ha, furrow-irrigated field. Peanut stems within the lower canopy of symptomatic plants had straw-colored lesions, with white fluffy mycelium and small (<2.0 mm diam.), black, irregularly shaped sclerotia. Stems on plants with severe symptoms were shredded in appearance, with small black sclerotia inside the stem tissue (2). Final disease incidence near harvest in mid-October was less than 1% of the field. Sclerotinia blight symptoms were also observed in 2013 on Runner (cvs. FloRun 107, Georgia 09B, and Florida 07) and Spanish peanut (cvs. OLin and OL06) research plots near Newport, AR, in Jackson County. Disease incidence among cultivars in these research plots was <1% for all cultivars except FloRun 107, which had a disease incidence of 2.6% for a 849.8 m2 plot. Isolations from surface-disinfected leaves on potato dextrose agar (PDA) consistently yielded white, fluffy mycelia with small (0.5 to 2.0 mm diam.), black, irregularly shaped sclerotia typical of S. minor (2). Six-week-old peanut plants (cv. FloRun 107) growing in pots were used to test pathogenicity. Each plant was inoculated by placing an agar plug (5 mm diam.), collected from the edge of an actively growing S. minor culture, on the main peanut stem. Plants (n = 5) were incubated for 8 days in a humidity chamber where temperatures ranged from 24 to 30°C and relative humidity remained >95%. Characteristic symptoms of Sclerotia blight were observed on all inoculated peanut plants whereas none of the plants (n = 3) inoculated with sterile PDA agar plugs expressed symptoms. Pathogenicity tests were repeated on peanut cvs. Flavor Runner 458 and Georgia 09B with similar results. S. minor was consistently isolated from symptomatic tissue on PDA, fulfilling Koch's postulates. To our knowledge, this is the first report of S. minor on peanut or any host in Arkansas or the Mid-South region. The two peanut fields with Sclerotinia blight had a history of soybean production, and S. minor may have gone undetected on soybean or one of many host weed species (1). Since S. minor is a major economic pathogen of peanut, commonly causing yield losses of 10% (2), it will likely be a significant factor in Arkansas and Mid-South peanut production. References: (1) M. S. Melzer et al. Can. J. Plant Pathol. 19:272, 1997. (2) D. M. Porter and H. A. Melouk. Sclerotinia blight. Page 34 in: Compendium of Peanut Diseases, 2nd ed. N. Kokalis-Burelle et al., eds. The American Phytopathological Society, St. Paul, MN, 1997.

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First report of Rhizoctonia solani Kühn AG 2-2 LP in Zoyzia japonica Steud in Brazil

Summa Phytopathologica ◽

10.1590/0100-5405/221916 ◽

2020 ◽

Vol 46 (4) ◽

pp. 289-298

Author(s):

Maria Aurea Saboya Chiaradia Picarelli ◽

Flavia Rodrigues Alves Patricio ◽

Ricardo Harakava ◽

Eliana Borges Rivas ◽

Addolorata Colariccio

Keyword(s):

Rhizoctonia Solani ◽

Mycelial Growth ◽

Its Region ◽

Anastomosis Group ◽

Large Patch ◽

First Report ◽

Rdna Its ◽

Rdna Its Region ◽

Important Disease

ABSTRACT The use of cultivated grasses in Brazil has grown by 40% between 2010 and 2015, and the species Zoysia japonica Steud, especially the cultivar ‘Esmeralda’, corresponds to 81% of the grass market in the country. The most important disease affecting zoysia grass, known as large patch, is caused by Rhizoctonia solani and occurs in the Brazilian lawns particularly during winter months. The aim of this study was to contribute to the identification and characterization of the anastomosis group of R. solani isolates from lesions typical of large patch collected from ‘Esmeralda’ grass at gardens and golf courses in the states of São Paulo and Bahia, Brazil. All 12 obtained isolates presented dark-brown colonies with aerial mycelial growth, multinucleated hyphae and absence of concentric zonation or sclerotia, and showed their greatest mycelial growth rate at 25°C. In pathogenicity experiments, except three out of R. solani isolates, reduced the growth of zoysia grass. Based on the analysis of sequences of the rDNA-ITS region, the isolates clustered with reference isolates of the anastomosis group AG 2-2 LP. Phylogenetic inference showed that the Brazilian isolates are grouped into two clades that shared the same common ancestral with 96% bootstrap. One of the clades includes only Brazilian isolates while the other one also includes American and Japanese R. solani isolates AG 2-2 LP. This is the first report and characterization of R. solani AG 2-2 LP in zoysiagrass in Brazil.

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First Report of Seedling Blight Caused by Rhizoctonia solani on Dioscorea nipponica in China

Plant Disease ◽

10.1094/pdis-94-7-0915c ◽

2010 ◽

Vol 94 (7) ◽

pp. 915-915

Author(s):

Q. Bai ◽

N. Wang ◽

J. Gao

Keyword(s):

Rhizoctonia Solani ◽

Disease Incidence ◽

Northeast Asia ◽

Morphological Characteristics ◽

Seedling Blight ◽

First Report ◽

Rdna Its ◽

Its Gene ◽

Pathogenicity Tests ◽

Safranin O

Throughhill yam (Dioscorea nipponica Makino), a perennial winding herb and a member of the Discoreaceae, is distributed principally in northeast Asia. It is used to produce medicine for treating coronary heart disease, diabetes mellitus, and inflammation. In China, this species is cultivated in many provinces such as Liaoning, Jilin, Heilongjiang, Hebei, Inner Mongolia, and Shanxi. In July 2006, seedling blight was observed on D. nipponica with disease incidence ranging from 37 to 75% in commercial fields in Antu County, China. In the early stages of disease development, water-soaked lesions appeared at the stem base and on leaves near the ground. Lesions later turned dark brown and necrotic. Leaves eventually became chlorotic, stem and petioles collapsed gradually, and plants died. Mycelium was observed to be growing on the surface of infected tissues and adjacent plants, and brown, hard sclerotia were produced on stem or petiole surfaces. A fungus with morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from diseased tissues that were plated on potato dextrose agar (PDA). Mycelium was branched at right angles with a septum near the branch and a slight constriction at the branch base. Cells from hyphae grown on 2% water agar at 25°C 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 with 12 tester strains representing all subgroups of AG1 to AG5 on 2% water agar in petri plates (2). The anastomosis grouping of isolates Rs1, Rs2, and Rs5 was determined to be AG1-IB and that of isolates Rs3 and Rs6 was determined to be AG2-1. The rDNA internal transcribed spacer (ITS) gene sequence of isolates Rs1, Rs2, and Rs5 (GenBank Accession Nos. GU585667, GU596490, and GU594691) had 100, 99, and 100% nucleotide identity, respectively, with AG1-IB (GenBank Accession No. FG440191). The rDNA-ITS of isolates Rs3 and Rs6 (GenBank Accession Nos. GU596493 and GU594692) exhibited 99% homology with AG2-1 (GenBank Accession No. EU513135). Pathogenicity tests were performed on healthy, potted 2-year-old plants of D. nipponica. Twenty plants were wound inoculated by placing 0.6-cm mycelial plugs from 3-day-old PDA cultures on leaves and stems. Twenty plants were treated with PDA plugs as controls. Plants were maintained at 25°C and 95% relative humidity on a 12-h light/dark regimen. Typical symptoms of leaf and stem rotting identical to those observed in the commercial field appeared 4 days after inoculation and all inoculated plants died within 10 days. No disease symptoms were observed on control plants. Rhizoctonia solani was consistently reisolated from symptomatic tissues. To our knowledge, this is the first report of R. solani causing seedling blight on D. nipponica in the world. References: (1) R. J. Bandoni. Mycologia 71:873, 1979. (2) C. C. Tu and J. W. Kimbrough. Mycologia 65:941, 1973.

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First report of Colletotrichum siamense Causing Blossom Blight on Thai basil (Ocimum basilicum L.) in Malaysia

Plant Disease ◽

10.1094/pdis-06-20-1371-pdn ◽

2020 ◽

Author(s):

Siti Izera Ismail ◽

Nur Adlina Rahim ◽

Dzarifah Zulperi

Keyword(s):

Disease Incidence ◽

Its Region ◽

Ocimum Basilicum ◽

Distilled Water ◽

Single Spore ◽

First Report ◽

Plastic Bags ◽

Colletotrichum Siamense ◽

Primer Sets ◽

Acca Sellowiana

Thai basil (Ocimum basilicum L.) is widely cultivated in Malaysia and commonly used for culinary purposes. In March 2019, necrotic lesions were observed on the inflorescences of Thai basil plants with a disease incidence of 60% in Organic Edible Garden Unit, Faculty of Agriculture in the Serdang district (2°59'05.5"N 101°43'59.5"E) of Selangor province, Malaysia. Symptoms appeared as sudden, extensive brown spotting on the inflorescences of Thai basil that coalesced and rapidly expanded to cover the entire inflorescences. Diseased tissues (4×4 mm) were cut from the infected lesions, surface disinfected with 0.5% NaOCl for 1 min, rinsed three times with sterile distilled water, placed onto potato dextrose agar (PDA) plates and incubated at 25°C under 12-h photoperiod for 5 days. A total of 8 single-spore isolates were obtained from all sampled inflorescence tissues. The fungal colonies appeared white, turned grayish black with age and pale yellow on the reverse side. Conidia were one-celled, hyaline, subcylindrical with rounded end and 3 to 4 μm (width) and 13 to 15 μm (length) in size. For fungal identification to species level, genomic DNA of representative isolate (isolate C) was extracted using DNeasy Plant Mini Kit (Qiagen, USA). Internal transcribed spacer (ITS) region, calmodulin (CAL), actin (ACT), and chitin synthase-1 (CHS-1) were amplified using ITS5/ITS4 (White et al. 1990), CL1C/CL2C (Weir et al. 2012), ACT-512F/783R, and CHS-79F/CHS-345R primer sets (Carbone and Kohn 1999), respectively. A BLAST nucleotide search of ITS, CHS-1, CAL and ACT sequences showed 100% similarity to Colletotrichum siamense ex-type cultures strain C1315.2 (GenBank accession nos. ITS: JX010171 and CHS-1: JX009865) and isolate BPDI2 (CAL: FJ917505, ACT: FJ907423). The ITS, CHS-1, CAL and ACT sequences were deposited in GenBank as accession numbers MT571330, MW192791, MW192792 and MW140016. Pathogenicity was confirmed by spraying a spore suspension (1×106 spores/ml) of 7-day-old culture of isolate C onto 10 healthy inflorescences on five healthy Thai basil plants. Ten infloresences from an additional five control plants were only sprayed with sterile distilled water and the inoculated plants were covered with plastic bags for 2 days and maintained in a greenhouse at 28 ± 1°C, 98% relative humidity with a photoperiod of 12-h. Blossom blight symptoms resembling those observed in the field developed after 7 days on all inoculated inflorescences, while inflorescences on control plants remained asymptomatic. The experiment was repeated twice. C. siamense was successfully re-isolated from the infected inflorescences fulfilling Koch’s postulates. C. siamense has been reported causing blossom blight of Uraria in India (Srivastava et al. 2017), anthracnose on dragon fruit in India and fruits of Acca sellowiana in Brazil (Abirami et al. 2019; Fantinel et al. 2017). This pathogen can cause a serious threat to cultivation of Thai basil and there is currently no effective disease management strategy to control this disease. To our knowledge, this is the first report of blossom blight caused by C. siamense on Thai basil in Malaysia.

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First Report of Damping-Off Caused by Rhizoctonia solani AG-4 on Mediterranean Fan Palm in Italy

Plant Disease ◽

10.1094/pdis-94-1-0125a ◽

2010 ◽

Vol 94 (1) ◽

pp. 125-125 ◽

Cited By ~ 3

Author(s):

G. Polizzi ◽

D. Aiello ◽

I. Castello ◽

V. Guarnaccia ◽

A. Vitale

Keyword(s):

Rhizoctonia Solani ◽

Disease Incidence ◽

Morphological Characteristics ◽

Mediterranean Area ◽

Western Mediterranean ◽

Fluorescent Light ◽

Damping Off ◽

Centraalbureau Voor ◽

First Report ◽

Stem Lesions

Mediterranean fan palm (Chamaerops humilis L.), one of just two autochthonous European palms, is native to the western Mediterranean Region in southwestern Europe and northwestern Africa. It can be found growing wild in the Mediterranean area. In Europe, this species is very popular as an ornamental plant. In March 2009, a widespread damping-off was observed in a stock of approximately 30,000 potted 1-month-old plants of C. humilis cv. Vulcano in a nursery in eastern Sicily. Disease incidence was approximately 20%. Disease symptoms consisted of lesions at the seedling shoot (plumule). Stem lesions were initially orange, turned brown, and followed by death of the entire plumule or eophyll. A fungus with mycelial and morphological characteristics of Rhizoctonia solani Kühn was consistently isolated from 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 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 on 2% water agar in petri plates (3). Anastomosis was observed only with tester isolates of AG-4, giving both C2 and C3 reactions (2). One representative isolate obtained from symptomatic tissues was deposited at the Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (CBS No. 125095). Pathogenicity tests were performed on container-grown, healthy, 1-month-old seedlings. Twenty plants of C. humilis cv. Vulcano were inoculated near the base of the stem with two 1-cm2 PDA plugs from 5-day-old mycelial cultures. The same number of plants served as uninoculated controls. Plants were incubated in a growth chamber and maintained at 25°C and 95% relative humidity on a 12-h fluorescent light/dark regimen. Symptoms identical to those observed in the nursery appeared 5 days after inoculation and all plants died within 20 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 in the world of R. solani causing damping-off on Mediterranean fan palm. 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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First Report of Leaf Spot Disease Caused by Colletotrichum gloeosporioides on Chinese Bean Tree in China

Plant Disease ◽

10.1094/pdis-03-12-0261-pdn ◽

2013 ◽

Vol 97 (1) ◽

pp. 138-138 ◽

Cited By ~ 1

Author(s):

B. Z. Fu ◽

M. Yang ◽

G. Y. Li ◽

J. R. Wu ◽

J. Z. Zhang ◽

...

Keyword(s):

Leaf Spot ◽

Colletotrichum Gloeosporioides ◽

Disease Incidence ◽

Phylogenetic Analyses ◽

Morphological Characteristics ◽

Leaf Spot Disease ◽

First Report ◽

Spot Disease ◽

Rdna Its ◽

Its Sequence Analysis

Chinese bean tree, Catalpa fargesii f. duciouxii (Dode) Gilmour, is an ornamental arbor plant. Its roots, leaves, and flowers have long been used for medicinal purposes in China. During July 2010, severe outbreaks of leaf spot disease on this plant occurred in Kunming, Yunnan Province. The disease incidence was greater than 90%. The symptoms on leaves began as dark brown lesions surrounded by chlorotic halos, and later became larger, round or irregular spots with gray to off-white centers surrounded by dark brown margins. Leaf tissues (3 × 3 mm), cut from the margins of lesions, were surface disinfected in 0.1% HgCl2 solution for 3 min, rinsed three times in sterile water, plated on potato dextrose agar (PDA), and incubated at 28°C. The same fungus was consistently isolated from the diseased leaves. Colonies of white-to-dark gray mycelia formed on PDA, and were slightly brown on the underside of the colony. The hyphae were achromatic, branching, septate, and 4.59 (±1.38) μm in diameter on average. Perithecia were brown to black, globose in shape, and 275.9 to 379.3 × 245.3 to 344.8 μm. Asci that formed after 3 to 4 weeks in culture were eight-spored, clavate to cylindrical. The ascospores were fusiform, slightly curved, unicellular and hyaline, and 13.05 to 24.03 × 10.68 to 16.02 μm. PCR amplification was carried out by utilizing universal rDNA-ITS primer pair ITS4/ITS5 (2). Sequencing of the PCR products of DQ1 (GenBank Accession No. JN165746) revealed 99% similarity (100% coverage) with Colletotrichum gloeosporioides isolates (GenBank Accession No. FJ456938.1, No. EU326190.1, No. DQ682572.1, and No. AY423474.1). Phylogenetic analyses (MEGA 4.1) using the neighbor-joining (NJ) algorithm placed the isolate in a well-supported cluster (>90% bootstrap value based on 1,000 replicates) with other C. gloeosporioides isolates. The pathogen was identified as C. gloeosporioides (Penz.) Penz. & Sacc. (teleomorph Glomerella cingulata (Stoneman) Spauld & H. Schrenk) based on the morphological characteristics and rDNA-ITS sequence analysis (1). To confirm pathogenicity, Koch's postulates were performed on detached leaves of C. fargesii f. duciouxii, inoculated with a solution of 1.0 × 106 conidia per ml. Symptoms similar to the original ones started to appear after 10 days, while untreated leaves remained healthy. The inoculation assay used three leaves for untreated and six leaves for treated. The experiments were repeated once. C. gloeosporioides was consistently reisolated from the diseased tissue. C. gloeosporioides is distributed worldwide causing anthracnose on a wide variety of plants (3). To the best of our knowledge, this is the first report of C. gloeosporioides causing leaf spots on C. fargesii f. duciouxii in China. References: (1) B. C. Sutton. Page 1 in: Colletotrichum: Biology, Pathology and Control. CAB International. Wallingford, UK, 1992. (2) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. Academic Press, San Diego, 1990. (3) J. Yan et al. Plant Dis. 95:880, 2011.

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First Report of Mucor spp. Causing Root Rot of Radix pseudstellariae in Guizhou Province of China

Plant Disease ◽

10.1094/pdis-07-20-1634-pdn ◽

2020 ◽

Author(s):

Hongmiao Wu ◽

Jiachun Wu ◽

Feng Li ◽

Ling Zheng ◽

Jingkai Fan ◽

...

Keyword(s):

Root Rot ◽

Disease Incidence ◽

Acid Soils ◽

Its Region ◽

Significant Loss ◽

Day Length ◽

Guizhou Province ◽

First Report ◽

Chinese Medicinal Plants ◽

Branched Chains

Radix pseudostellariae L. is one of the most common and highly-prized Chinese medicinal plants with various pharmacological effects, and mainly produced in acid soils in the Guizhou and Fujian provinces of southwestern and southeastern China, respectively (Wu et al. 2020). However, consecutive monoculture of R. pseudostellariae results in severe root rot and decline in biomass and quality of underground tubers. Root tubers of R. pseudostellariae are typically planted in December and harvested in next June. Root rot commonly starts developing in May. The disease incidence of root rot was ranging from 37 to 46% in root portions and basal stem of R. pseudostellariae under the consecutive monoculture fields in Shibing County, Guizhou Province, China (108°12ʹE, 27°03ʹN) (Li et al. 2017). Severe root rot was observed in Shibing County in May 2018. Infected plants displayed curly, withered, and yellow leaves, blight, retarded growth, root rot, and yield losses. Abundant whitish mycelia were observed on roots and surrounding soil. Two fungal isolates, designated GZ20190123 and GZ20190124, were obtained from symptomatic roots cultured on potato dextrose agar (PDA). The optimum temperature range for growth of the two isolates was 25 to 30°C. The optimum pH range for the growth of GZ20190123 was 5 to 5.5, whereas GZ20190124 grew better between pH 5 to 8.5. The mean mycelial growth rates of GZ20190123 and GZ20190124 at 30°C were 2.1 and 1.5 cm/day, respectively. Conidia of the two isolates were ovoid or obclavate and were produced in single or branched chains. The internal transcribed spacer (ITS) region was amplified with primers ITS1 and ITS4 (White et al. 1990). The sequences were deposited in GenBank as accession No. MN726736 for GZ20190123 and MN726738 for GZ20190124. Sequence comparison revealed 99% (GZ20190123) and 97% (GZ20190124) identity with previously reported isolate xsd08071 of Mucor racemosus Bull. (accession No. FJ582639.1) and isolate BM3 of Mucor fragilis Bainier (accession No. MK910058.1), respectively, which was confirmed by phylogenetic analysis. The two isolates were tested for pathogenicity on R. pseudostellariae. Six roots of R. pseudostellariae were surface-sterilized with 75% ethanol and stab inoculated with mycelia using a sterile toothpick for each isolate. Sterile distilled water was stab inoculated to twelve roots to serve as the control. Treated roots were incubated in a greenhouse with 16 h day length [light intensity 146.5 μmol/(m2·s)] and day/night temperature 26°C/18°C. The inoculated roots showed the expected symptoms on roots and sprouts 7 days after inoculation, whereas the control roots with sprouts did not show any symptom. The fungi were re-isolated from the diseased roots and confirmed as expected M. racemosus or M. fragilis based on the ITS sequences, which satisfied Koch’s postulates. Thus, isolate GZ20190123 was identified as M. racemosus and GZ20190124 as M. fragilis. Previously, M. racemosus and M. fragilis have been reported as a pathogen on tomato (Kwon and Hong 2005) and grape (Ghuffar et al. 2018), respectively. To our knowledge, this is the first report of M. racemosus and M. fragilis causing root rot of R. pseudostellariae in southwestern China, where the disease could cause a significant loss to production of this important medicinal plant.

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First Report of Fruit Rot of Melon Caused by Fusarium asiaticum in China

Plant Disease ◽

10.1094/pdis-08-20-1857-pdn ◽

2020 ◽

Author(s):

Fangmin Hao ◽

Quanyu Zang ◽

Weihong Ding ◽

Erlei Ma ◽

Yunping Huang ◽

...

Keyword(s):

Disease Incidence ◽

Elongation Factor ◽

Morphological Characteristics ◽

Its Region ◽

Fruit Rot ◽

Post Inoculation ◽

Basal Cells ◽

First Report ◽

Fusarium Asiaticum ◽

Sterile Needle

Melon (Cucumis melo L.) is a member of the Cucurbitaceae family, an important economical and horticultural crop, which is widely grown in China. In May 2020, fruit rot disease with water-soaked lesions and pink molds on cantaloupe melons was observed in several greenhouses with 50% disease incidence in Ningbo, Zhejiang Province in China. In order to know the causal agent, diseased fruits were cut into pieces, surface sterilized for 1 min with 1% sodium hypochlorite (NaClO), 2 min with 75% ethyl alcohol, rinsed in sterile distilled water three times (Zhou et al. 2018), and then placed on potato dextrose agar (PDA) medium amended with streptomycin sulfate (100 μg/ml) plates at 25°C for 4 days. The growing hyphae were transferred to new PDA plates using the hyphal tip method, putative Fusarium colonies were purified by single-sporing. Twenty-five fungal isolates were obtained and formed red colonies with white aerial mycelia at 25°C for 7 days, which were identified as Fusarium isolates based on the morphological characteristics and microscopic examination. The average radial mycelial growth rate of Fusarium isolate Fa-25 was 11.44 mm/day at 25°C in the dark on PDA. Macroconidia were stout with curved apical and basal cells, usually with 4 to 6 septa, and 29.5 to 44.2 × 3.7 to 5.2 μm on Spezieller Nährstoffarmer agar (SNA) medium at 25°C for 10 days (Leslie and Summerell 2006). To identify the species, the internal transcribed spacer (ITS) region and translational elongation factor 1-alpha (TEF1-α) gene of the isolates were amplified and cloned. ITS and TEF1-α was amplified using primers ITS1/ITS4 and EF1/EF2 (O’Donnell et al. 1998), respectively. Sequences of ITS (545 bp, GenBank Accession No. MT811812) and TEF1-α (707 bp, GenBank Acc. No. MT856659) for isolate Fa-25 were 100% and 99.72% identical to those of F. asiaticum strains MSBL-4 (ITS, GenBank Acc. MT322117.1) and Daya350-3 (TEF1-α, GenBank Acc. KT380124.1) in GenBank, respectively. A phylogenetic tree was established based on the TEF1-α sequences of Fa-25 and other Fusarium spp., and Fa-25 was clustered with F. asiaticum. Thus, both morphological and molecular characterizations supported the isolate as F. asiaticum. To confirm the pathogenicity, mycelium agar plugs (6 mm in diameter) removed from the colony margin of a 2-day-old culture of strain Fa-25 were used to inoculate melon fruits. Before inoculation, healthy melon fruits were selected, soaked in 2% NaClO solution for 2 min, and washed in sterile water. After wounding the melon fruits with a sterile needle, the fruits were inoculated by placing mycelium agar plugs on the wounds, and mock inoculation with mycelium-free PDA plugs was used as control. Five fruits were used in each treatment. The inoculated and mock-inoculated fruits were incubated at 25°C with high relative humidity. Symptoms were observed on all inoculated melon fruits 10 days post inoculation, which were similar to those naturally infected fruits, whereas the mock-inoculated fruits remained symptomless. The fungus re-isolated from the diseased fruits resembled colony morphology of the original isolate. The experiment was conducted three times and produced the same results. To our knowledge, this is the first report of fruit rot of melon caused by F. asiaticum in China.

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