First Report of Phytophthora capsici Causing Wilt on Hydropronically Grown Cucumber in Mexico

During August 2005, wilted cucumber (Cucumis sativus cv. Tasty Green) plants were observed in a commercial greenhouse with a closed hydroponic system in the state of Mexico. Disease incidence was 50%. Diseased plants were detected 15 days after transplanting, when plants were overwatered. Yield was severely reduced when disease affected mature plants. Wilted plants showed basal stem lesions and root rot. Phytophthora capsici was consistently isolated from diseased tissue on corn meal agar (CMA) with tartaric acid. Oomycete identification was based on sporangial and gametangial characteristics (2). Sporangia produced on blocks of CMA at 25°C were spherical, broadly ellipsoid or obovoid with one papillae, and deciduous with a long pedicel (1). The isolates were heterothallic, and oogonia with amphigynous antheridia were observed in pairings with an A1 isolate of P. capsici, therefore, the isolates were determined to be an A2. Pathogenicity tests were conducted on 2-month-old cucumber seedlings under controlled conditions (25°C). Inoculation was performed by placing small pieces of agar with mycelium of 5- to 7-day-old cultures on the stem base and wrapping with Parafilm. Control plants were inoculated with CMA agar. No symptoms were observed on the control. Plants inoculated with the P. capsici isolated from the diseased cucumbers showed a basal stem lesion, followed by wilting and death 7 to 14 days after inoculation. The isolate was also pathogenic on tomato and eggplant that were grown at the same time in the commercial greenhouse sharing the nutrient solution. P. capsici sporangia were observed on the roots of both hosts. To our knowledge, this is the first report of P. capsici affecting cucumber in a hydroponics system in Mexico. References: (1) M. Aragaki and J. Y. Uchida. Mycologia 93:137, 2001. (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society. St. Paul MN, 1996.

Download Full-text

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

Plant Disease ◽

10.1094/pdis-05-11-0411 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1194-1194 ◽

Cited By ~ 2

Author(s):

G. Polizzi ◽

D. Aiello ◽

V. Guarnaccia ◽

A. Panebianco ◽

P. T. Formica

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Fluorescent Light ◽

Disease Symptoms ◽

First Report ◽

Pathogenicity Tests ◽

Crown And Root Rot ◽

Safranin O

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

Download Full-text

First Report of Pythium polymastum on Broccoli and Cauliflower in California

Plant Disease ◽

10.1094/pdis.1998.82.11.1282a ◽

1998 ◽

Vol 82 (11) ◽

pp. 1282-1282 ◽

Cited By ~ 1

Author(s):

B. J. Aegerter ◽

R. M. Davis

Keyword(s):

Brassica Oleracea ◽

Root Rot ◽

Stem Rot ◽

Corn Meal ◽

Corn Meal Agar ◽

Damping Off ◽

First Report ◽

Potting Medium

Damping-off of broccoli (Brassica oleracea var. italica) and cauliflower (B. oleracea var. botrytis) seedlings occurred in several greenhouses in Fresno, CA, in 1997. Symptoms included wilting and root and stem rot. Pythium polymastum was consistently isolated from symptomatic tissues placed on corn meal agar amended with 10 ppm pimaricin, 250 ppm ampicillin, 10 ppm rifampicin, and 25 ppm pentachloronitro-benzene. On grass leaves in water, the fungus produced numerous aplerotic oospores in oogonia 43 to 50 μm in diameter (average 46 μm) with spines about 7 μm long. Spherical sporangia were only rarely observed. In the greenhouse, 4-week-old broccoli and cauliflower seedlings were transplanted into potting mix amended with a colonized vermiculite/rye/V8 juice medium to produce approximately 2,500 CFUs per gram of potting medium. Control plants were transplanted into noninfested potting mix. There were six replicate pots per treatment and three plants per pot. After 12 days, the potting mix was gently washed from the roots and the seedlings were dried and weighed. Symptoms on inoculated plants included wilting, severe root rot, black streaks on the lower stems, and death. The fungus was recovered from symptomatic tissues. There were no symptoms on the control plants. Infection by P. polymastum reduced dry weights of surviving broccoli and cauliflower seedlings by 82 and 58%, respectively. Similar results were obtained in a second experiment. This fungus was previously characterized as a pathogen of both cultivated and wild crucifers in Canada (1). This is the first report of P. polymastum in California. Reference: (1) T. C. Vanterpool. Can. J. Bot. 52:1205, 1974.

Download Full-text

First Report of Branch Rot of Lonicera japonica Caused by Sclerotium delphinii in China

Plant Disease ◽

10.1094/pdis-01-14-0053-pdn ◽

2014 ◽

Vol 98 (8) ◽

pp. 1155-1155

Author(s):

M. Zhang ◽

X. J. Wang ◽

Y. Li ◽

Y. H. Geng ◽

H. Y. Wu

Keyword(s):

Disease Incidence ◽

Its Region ◽

Lonicera Japonica ◽

First Report ◽

Plastic Bags ◽

Mycelial Plug ◽

Pathogenicity Tests ◽

White Mycelium ◽

Sclerotium Delphinii ◽

Stem Lesions

Honeysuckle flower (Lonicera japonica Thunb.) is a perennial, traditional Chinese medicine plant, widely cultivated in China. In early June 2013, heavy branch rot infection was observed on L. japonica in an approximately 10,000-m2 field in Linyi, Shandong, China. The disease incidence was 30 to 40%. Early symptoms appeared as small, elliptoid, pale brown lesions on the branches. Lesions expanded into 50 to 100 mm long and 3 to 7 mm wide, brown, elongated spots. The upper branches wilted after the lesions expanded around the stems. A fungus was consistently isolated from stem lesions on potato dextrose agar (PDA) that was morphologically similar to S. delphinii, with white mycelium, round to irregularly shaped reddish-brown sclerotia that were 2 to 4 mm diameter (2). The identity of the fungus was confirmed by DNA sequencing of the internal transcribed spacer (ITS) region (GenBank Accession No. KJ145328), which was 99% homologous to those of other S. delphinii isolates (JN241578 and AB075314) (1). Pathogenicity tests were conducted with three 2-year-old seedlings grown in 20-cm-diameter pots at 25 to 30°C during experiments in greenhouse. Ten branches from the three plants pricked by needle were inoculated with a mycelial plug (0.4 cm diameter) harvested from the periphery of a 4-day-old colony. An equal number of branches pricked by needle serving as controls were mock-inoculated with plugs of PDA medium. Inoculated branches were covered with plastic bags for 24 h to maintain high relative humidity and incubated at about 25°C. Plugs were removed 48 h after inoculation. After 3 days, nine inoculated branches showed symptoms identical to those observed in the field under natural conditions, whereas controls remained symptom-free. Re-isolation of the fungus from lesions on inoculated branches confirmed that the causal agent was S. delphinii. Pathogenicity tests were repeated three times by the same methods with the same results. To our knowledge, this is the first report of S. delphinii infecting Lonicera japonica in China. References: (1) I. Okabe and N. Matsumoto. Mycol. Res. 107:164, 2003. (2) Z. K. Punja and A. Damiani. Mycologia. 88:694, 1996.

Download Full-text

First Report of Sclerotinia Stem Rot and Death of Osteospermum spp. Hybrid Cultivars Caused by Sclerotinia sclerotiorum in Louisiana

Plant Disease ◽

10.1094/pd-89-0911a ◽

2005 ◽

Vol 89 (8) ◽

pp. 911-911 ◽

Cited By ~ 1

Author(s):

G. E. Holcomb

Keyword(s):

Sclerotinia Sclerotiorum ◽

Disease Incidence ◽

Stem Rot ◽

Sclerotinia Stem Rot ◽

Greenhouse Production ◽

First Report ◽

Similar Disease ◽

Plastic Bag ◽

Pathogenicity Tests ◽

Stem Lesions

Osteospermum spp. Hybrids, belong to Asteraceae, commonly called African daisy or cape daisy with over 214 named cultivars, are popular flowering plants grown as winter landscape plants in southern Louisiana. During January of 2005, plants growing in a wholesale nursery using polyethylene-film-covered greenhouses were observed with symptoms of wilt that began with tan stem lesions and progressed to stem rot, wilt, and plant death. Plants had been purchased out-of-state as rooted cuttings and transplanted to a commercial bark potting mix in 11.4-cm (4.5-in.) plastic pots. Signs of fungal infection included the presence of white cottony mycelium and black sclerotia. Disease incidence was 50% on cv. Soprano White but less than 1% among the four other cultivars being grown (Ostica Blue Eye, Ostica Pink, Lemon Symphony, and Soprano Purple). Differences in disease incidence among cultivars may have been due to differences in susceptibility since all were grown on the same greenhouse bench. Sclerotinia sclerotiorum was consistently isolated from sections of diseased stems that had been surfaced disinfested (30 to 60 s in 70% ethyl alcohol) and placed on acidified potato dextrose agar. Inoculum for pathogenicity tests consisted of mixed mycelia and sclerotia that had been grown on twice-sterilized wheat grain for 14 days. Ten flowering-age Osteospermum sp. plants of cv. Soprano White were inoculated with 1 g of inoculum placed at the base of each plant. One group of five plants was kept in a dew chamber at 22°C for 40 h after which they were removed to a greenhouse. The second group of five plants was placed in a single, plastic bag with the top left open and kept in the greenhouse. Ten noninoculated plants of the same cultivar served as controls with five kept in the dew chamber for 40 h and the other five held in a plastic bag in the greenhouse. Inoculated plants that had been held in the dew chamber developed stem lesions and rot after 2 days, wilted permanently after 5 days, and were desiccated and dead by day 7. Inoculated plants held in the bag in the greenhouse followed a similar disease development pattern but did not show wilt symptoms until 8 days after inoculation and were dead after 12 days. White cottony mycelium and black sclerotia developed on stems and at the base of all inoculated plants. S. sclerotiorum was reisolated from inoculated diseased plants. All noninoculated control plants remained disease free. An outbreak of this disease was previously reported on Osteospermum spp. planted along highways in southern California (1). To our knowledge, this is the first report of the disease in Louisiana and the first report of its occurrence in greenhouse production of Osteospermum spp. Reference: (1) H. S. Gill. Plant Dis. Rep. 59:82, 1975

Download Full-text

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

Plant Disease ◽

10.1094/pdis-93-9-0972b ◽

2009 ◽

Vol 93 (9) ◽

pp. 972-972 ◽

Cited By ~ 2

Author(s):

G. Polizzi ◽

D. Aiello ◽

I. Castello ◽

A. Vitale

Keyword(s):

Rhizoctonia Solani ◽

Root Rot ◽

Disease Incidence ◽

Morphological Characteristics ◽

Fluorescent Light ◽

Centraalbureau Voor ◽

First Report ◽

Crown And Root Rot ◽

Stem Lesions ◽

Safranin O

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

Download Full-text

First Report of Pythium Root Rot of Rau Ram (Polygonum odoratum)

Plant Disease ◽

10.1094/pd-89-0340a ◽

2005 ◽

Vol 89 (3) ◽

pp. 340-340

Author(s):

E. N. Rosskopf ◽

C. B. Yandoc ◽

B. Stange ◽

E. M. Lamb ◽

D. J. Mitchell

Keyword(s):

Root Rot ◽

Vascular System ◽

Pond Water ◽

Centraalbureau Voor ◽

First Report ◽

Pathogenicity Tests ◽

Symptomatic Tissue ◽

Pythium Helicoides ◽

Production House ◽

Test Plants

Polygonum odoratum (= Persicaria odorata), known as rau ram or sang hum, is native to southeastern Asia and is a common herb in Vietnamese cuisine (1). It has been studied most extensively for its aromatic compound content (2). In Florida, rau ram commonly is grown hydroponically in greenhouses using large, cement beds with recirculated water. The plants form dense mats from which new growth is trimmed for market. During January of 2002, a severe dieback was observed in one production house in Saint Lucie County, FL. Plants with less severe symptoms were yellowed and stunted. Roots of symptomatic plants were largely decayed with root symptoms beginning as a tip necrosis. The cortex of severely affected roots slipped off easily, leaving a stringy vascular system. Plating of symptomatic tissue from 20 randomly selected plant samples was performed with multiple general and selective media including potato dextrose agar, corn meal agar with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (3). All colonies produced were identified as Pythium helicoides Drechsler on the basis of sporangial, oogonial, and antheridial characteristics (4). Isolates had proliferous, obovoid, papillate sporangia, and were homothallic with smooth-walled oogonia and thick-walled, aplerotic oospores. Multiple antheridial attachments per oogonium were common with the antheridium attached along its entire length. Pathogenicity tests were conducted using P. odoratum plants grown from commercial transplants. Two tests were performed. Each test was conducted using eight inoculated and eight control plants. In the first test, plants were maintained in 10-cm pots immersed in sterilized pond water for the duration of the test. Plants were inoculated with five 7- × 70-mm sections of freshly growing mycelial culture per plant using 10-day-old cultures of Pythium helicoides grown on water agar. Chlorosis was observed at approximately 2 months after inoculation. Root necrosis was observed in inoculated plants approximately 5 months after inoculation. This test was performed in the greenhouse with temperatures ranging from 20 to 30°C. The second test was performed in growth chambers at 35 to 40°C. Plants were maintained in 10-cm pots immersed in Hoagland's solution and were inoculated with four 6-mm plugs per plant. Symptoms were observed on inoculated plants at this temperature within 1 week of inoculation. No chlorosis or root decay was observed in noninoculated, immersed plants. The pathogen was reisolated from inoculated, symptomatic tissue. To our knowledge, this is the first report of root rot of P. odoratum caused by Pythium helicoides. References: (1) R. E. Bond. Herbarist 55:34, 1989. (2) N. X. Dung et al. J. Essent. Oil Res. 7:339, 1995. (3) M. E. Kannwischer and D. J. Mitchell. Phytopathology 68:1760, 1978. (4) A. J. van der Plaats-Niterink. Monograph of the Genus Pythium. Vol. 21, Studies in Mycology. Centraalbureau voor Schimmelcutltures, Baarn, The Netherlands, 1981.

Download Full-text

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.

Download Full-text

First Report of Anthracnose of Papaya (Carica papaya L.) Caused by Colletotrichum siamense in China

Plant Disease ◽

10.1094/pdis-10-20-2154-pdn ◽

2021 ◽

Author(s):

Yujie Zhang ◽

Wenxiu Sun ◽

Ping Ning ◽

Tangxun Guo ◽

SuiPing Huang ◽

...

Keyword(s):

Carica Papaya ◽

Disease Incidence ◽

Aerial Mycelium ◽

Postharvest Disease ◽

Distilled Water ◽

First Report ◽

Surface Samples ◽

Initial Symptoms ◽

Colletotrichum Siamense ◽

Pathogenicity Tests

Papaya (Carica papaya L.) is a rosaceous plant widely grown in China, which is economically important. Anthracnose caused by Colletotrichum sp. is an important postharvest disease, which severely affects the quality of papaya fruits (Liu et al., 2019). During April 2020, some mature papaya fruits with typical anthracnose symptoms were observed in Fusui, Nanning, Guangxi, China with an average of 30% disease incidence (DI) and over 60% DI in some orchards. Initial symptoms of these papayas appeared as watery lesions, which turned dark brown, sunken, with a conidial mass appearing on the lesions under humid and warm conditions. The disease severity varied among fruits, with some showing tiny light brown spots, and some ripe fruits presenting brownish, rounded, necrotic and depressed lesions over part of their surface. Samples from two papaya plantations (107.54°E, 22.38°N) were collected, and brought to the laboratory. Symptomatic diseased tissues were cut into 5 × 5 mm pieces, surface sterilized with 2% (v/v) sodium hypochlorite for 1 minute, and rinsed three times with sterilized water. The pieces were then placed on potato dextrose agar (PDA). After incubation at 25°C in the dark for one week, colonies with uniform morphology were obtained. The aerial mycelium on PDA was white on top side, and concentric rings of salmon acervuli on the underside. A gelatinous layer of spores was observed on part of PDA plates after 7 days at 28°C. The conidia were elliptical, aseptate and hyaline (Zhang et al., 2020). The length and width of 60 conidia were measured for each of the two representative isolates, MG2-1 and MG3-1, and these averaged 13.10 × 5.11 μm and 14.45 × 5.95 μm. DNA was extracted from mycelia of these two isolates with the DNA secure Plant Kit (TIANGEN, Biotech, China). The internal transcribed spacer (ITS), partial actin (ACT), calmodulin (CAL), chitin synthase (CHS), β-tubulin 2 (TUB2) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) regions were amplified by PCR and sequenced. The sequences were deposited into GenBank with accessions MT904003, MT904004, and MT898650 to MT898659. BLASTN analyses against the GenBank database showed that they all had over 99% identity to the type strain of Colletotrichum siamense isolate ICMP 18642 (GenBank accession numbers JX010278, GQ856775, JX009709, GQ856730, JX010410, JX010019) (Weir et al., 2012). A phylogenetic tree based on the combined ITS, ACT, CAL, CHS, TUB2 and GAPDH sequences using the Neighbor-joining algorithm also showed that the isolates were C. siamense. Pathogenicity tests were conducted on 24 mature, healthy and surface-sterilized papaya fruits. On 12 papaya fruits, three well separated wounded sites were made for inoculation, and for each wounded site, six adjacent pinhole wounds were made in a 5-mm-diameter circular area using a sterilized needle. A 10 µl aliquot of 1 × 106 conidia/ml suspension of each of the isolates (MG2-1 and MG3-1) was inoculated into each wound. For each isolate, there were six replicate fruits. The control fruits were inoculated with sterile distilled water. The same inoculation was applied to 12 non-wound papaya fruits. Fruits were then placed in boxes which were first washed with 75% alcohol and lined with autoclaved filter paper moistened with sterilized distilled water to maintain high humidity. The boxes were then sealed and incubated at 28°C. After 10 days, all the inoculated fruits showed symptoms, while the fruits that were mock inoculated were without symptoms. Koch's postulates were fulfilled by re-isolation of C. siamense from diseased fruits. To our knowledge, this is the first report of C. siamense causing anthracnose of papaya in China. This finding will enable better control of anthracnose disease caused by C. siamense on papaya.

Download Full-text

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.

Download Full-text

First Report of Stem Blight Caused by Calonectria colhounii (Anamorph Cylindrocladium colhounii) on Greenhouse-Grown Blueberries in the United States

Plant Disease ◽

10.1094/pdis-02-11-0117 ◽

2011 ◽

Vol 95 (9) ◽

pp. 1187-1187

Author(s):

J. J. Sadowsky ◽

T. D. Miles ◽

A. M. C. Schilder

Keyword(s):

United States ◽

North Carolina ◽

Root Rot ◽

The United States ◽

Vaccinium Corymbosum ◽

Conidial Suspension ◽

Centraalbureau Voor ◽

First Report ◽

Stem Lesions ◽

Β Tubulin

Necrotic stems and leaves were observed on 2- to 4-month-old, rooted microshoot plants (Vaccinium corymbosum L. ‘Liberty’ and ‘Bluecrop’, V. angustifolium Aiton ‘Putte’, and V. corymbosum × V. angustifolium ‘Polaris’) in a Michigan greenhouse in 2008 and 2009. As the disease progressed, leaves fell off and 80 to 100% of the plants died in some cases. Root rot symptoms were also observed. A fungus was isolated from stem lesions. On potato dextrose agar (PDA), cultures first appeared light tan to orange, then rusty brown and zonate with irregular margins. Chains of orange-brown chlamydospores were abundant in the medium. Macroconidiophores were penicillately branched and had a stipe extension of 220 to 275 × 2.5 μm with a narrowly clavate vesicle, 3 to 4 μm wide at the tip. Conidia were hyaline and cylindrical with rounded ends, (1-)3-septate, 48 to 73 × 5 to 7 (average 60 × 5.5) μm and were held together in parallel clusters. Perithecia were globose to subglobose, yellow, 290 to 320 μm high, and 255 to 295 μm in diameter. Ascospores were hyaline, 2- to 3-septate, guttulate, fusoid with rounded ends, slightly curved, and 30 to 88 × 5 to 7.5 (average 57 × 5.3) μm. On the basis of morphology, the fungus was identified as Calonectria colhounii Peerally (anamorph Cylindrocladium colhounii Peerally) (1,2). The internal transcribed spacer region (ITS1 and ITS2) of the ribosomal DNA and the β-tubulin gene were sequenced (GenBank Accession Nos. HQ909028 and JF826867, respectively) and compared with existing sequences using BLASTn. The ITS sequence shared 99% maximum identity with that of Ca. colhounii CBS 293.79 (GQ280565) from Java, Indonesia, and the β-tubulin sequence shared 97% maximum identity with that of Ca. colhounii CBS 114036 (DQ190560) isolated from leaf spots on Rhododendron sp. in North Carolina. The isolate was submitted to the Centraalbureau voor Schimmelcultures in the Netherlands (CBS 129628). To confirm pathogenicity, 5 ml of a conidial suspension (1 × 105/ml) were applied as a foliar spray or soil drench to four healthy ‘Bluecrop’ plants each in 10-cm plastic pots. Two water-sprayed and two water-drenched plants served as controls. Plants were misted intermittently for 2 days after inoculation. After 7 days at 25 ± 3°C, drench-inoculated plants developed necrotic, sporulating stem lesions at the soil line, while spray-inoculated plants showed reddish brown leaf and stem lesions. At 28 days, three drench-inoculated and one spray-inoculated plant had died, while others showed stem necrosis and wilting. No symptoms were observed on control plants. Fungal colonies reisolated from surface-disinfested symptomatic stem, leaf, and root segments appeared identical to the original isolate. Cy. colhounii was reported to cause a leaf spot on blueberry plants in nurseries in China (3), while Ca. crotalariae (Loos) D.K. Bell & Sobers (= Ca. ilicicola Boedijn & Reitsma) causes stem and root rot of blueberries in North Carolina (4). To our knowledge, this is the first report of Ca. colhounii causing a disease of blueberry in Michigan or the United States. Because of its destructive potential, this pathogen may pose a significant threat in blueberry nurseries. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul, MN, 2002. (2) L. Lombard et al. Stud. Mycol. 66:31, 2010. (3) Y. S. Luan et al. Plant Dis. 90:1553, 2006. (4) R. D. Milholland. Phytopathology 64:831, 1974.

Download Full-text