First Report of Fusarium armeniacum Causing Seed Rot and Root Rot on Soybean (Glycine max) in the United States

In a survey for Fusarium root rot, soybean plants were sampled from eight counties across Iowa in 2008 to 2009. Fusarium isolates were recovered from surface-sterilized symptomatic and asymptomatic root tissue by culturing on peptone PCNB agar (2). Single-spore isolates were transferred to carnation leaf agar (CLA) and potato dextrose agar (PDA) for morphological identification; 11 isolates were identified as F. armeniacum (Forbes, Windels, and Burgess) Burgess and Summerell (previously F. acuminatum ssp. armeniacum) (2). Colonies on PDA produced white aerial mycelium, red to apricot pigment in agar, and bright orange sporodochia in the center of the culture. Some isolates produced a pionnotal form of slow-growing colonies with little aerial mycelium and abundant orange sporodochia. On CLA, macroconidia in orange sporodochia on carnation leaves and chlamydospores formed abundantly, but microconidia were absent (2). Species identity for the 11 isolates was confirmed by sequencing of the elongation factor gene (EF1-α) using ef1 and ef2 primers (4) (reference sequences deposited in GenBank JX101763 and JX101764). Pathogenicity of seven F. armeniacum isolates was tested using surface-sterilized soybean seed, cv. AG2403, in a petri dish assay with 3-day-old cultures on 2% water agar (1). Germination, seed rot, and lesion development were scored 7 dai using an ordinal scale (1). The experiment was a completely randomized design (CRD), had three replicate plates per isolate, and was conducted twice. All seven isolates were pathogenic on soybean, though variation in aggressiveness was observed among isolates (P < 0.0001) related to colony morphology on PDA. Seed germination was 0 to 40% when inoculated with four isolates showing white fluffy aerial mycelium on PDA. Seedlings were severely stunted with dark brown lesions covering a majority of the root system. When inoculated with three isolates showing the pionnotal form of slow-growing mycelium, germination was 70 to 100%, with few small brown lesions (~5 to 10 mm) on the roots. Noninoculated controls showed 100% germination and no symptoms. Pathogenicity was also tested in a growth chamber assay at 18°C using autoclaved soil mixed with an infested sand-cornmeal inoculum (3). Data for dry root and shoot weights and root rot severity (visually scored on a % scale) were collected at 6 weeks. The CRD experiment had five replications (single plant in a cone containing 150 ml infested soil), and was conducted twice. Root symptoms and similar variation in aggressiveness among isolates (based on colony morphology) was observed in inoculated plants. Isolates differed significantly for effects on root weight (P = 0.0125), shoot weight (P = 0.0035), and root rot severity (P = 0.0158). F. armeniacum was reisolated from infected root tissue, but not from noninoculated controls. Recovered isolates maintained their original colony morphology. F. armeniacum was previously reported in Minnesota on symptomless corn (2), but it has not been reported on soybean and its pathogenicity has not been established on any crop. To our knowledge, this is the first report of F. armeniacum as a pathogen on soybean in the United States. References: (1) K. E. Broders et al. Plant Dis. 91:727, 2007. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (3) G. P. Munkvold and J. K. O'Mara. Plant Dis. 86:143, 2002. (4) K. O'Donnell et al. Proc. Natl. Acad. Sci. 95:2044, 1998.

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First Report of Fusarium commune Causing Damping-off, Seed Rot, and Seedling Root Rot on Soybean (Glycine max) in the United States

Plant Disease ◽

10.1094/pdis-07-12-0644-pdn ◽

2013 ◽

Vol 97 (2) ◽

pp. 284-284 ◽

Cited By ~ 15

Author(s):

M. L. Ellis ◽

M. M. Díaz Arias ◽

D. R. Cruz Jimenez ◽

G. P. Munkvold ◽

L. F. Leandro

Keyword(s):

Root Rot ◽

Petri Dish ◽

The United States ◽

Small Subunit ◽

Ordinal Scale ◽

Morphological Identification ◽

Single Spore ◽

First Report ◽

Significant Difference ◽

Seed Rot

During 2007 to 2009, symptomatic and asymptomatic soybean plants were collected from fields in 18 Iowa counties. Fusarium isolates were recovered from surface-sterilized root tissue on peptone PCNB agar (2). Single-spore isolates were transferred to synthetic low nutrient agar (SNA) overlain with pieces (1 × 2 cm) of sterile filter paper, and to potato dextrose agar (PDA), and placed in the dark for 10 to 14 days for morphological identification (4). Twenty-three isolates were identified as Fusarium commune K. Skovg., O'Donnell & Nirenberg, previously in the F. oxysporum species complex (4). Colonies on PDA had white, fluffy, aerial mycelium with magenta to violet pigmentation in the medium. On SNA, macroconidia, chlamydospores, and microconidia on monophialides and polyphialides were consistent with the species description (4). Identification of all 23 isolates was confirmed by DNA sequencing of the translation elongation factor (EF1-α) gene, using ef1 and ef2 primers, and the mitochondrial small subunit (mtSSU), using primers MS1 and MS2 (4) [GenBank accessions for two representative isolates: EF1-α (JX289892 and JX289893), and mtSSU (JX289894 and, JX289895)]. Pathogenicity of two representative isolates of F. commune was tested on soybean (cv. AG2403) in a greenhouse, in water baths set at 18°C, using autoclaved soil mixed with infested sand-cornmeal inoculum (3). The experiment entailed a completely randomized design (CRD) with five replications (single plant/150 ml cone) per treatment, and was conducted three times. Dry root and shoot weights, and root rot severity (visual estimate of percent root rot on the entire root system) were evaluated after 6 weeks. Mean seedling emergence in soil infested with F. commune was 47 and 40% for the two isolates; in contrast, non-inoculated control plants had 100% emergence. There were significant differences in root (P < 0.0001) and shoot (P < 0.0001) weights, and root rot severity (P < 0.0001), between inoculated and non-inoculated plants. Seedlings that emerged were severely stunted and had dark brown lesions. F. commune was reisolated from infected roots of inoculated plants, but not from non-inoculated plants. Pathogenicity of both isolates to soybean (cv. MN1805) was also tested using a petri dish assay, in which eight seeds were placed on a plate with a 4-day-old culture growing on 2% water agar (1). Plates were rated 7 days later for seed germination, seed rot, and lesion development, using an ordinal scale (1). The experiment entailed a CRD with three replicate plates/treatment, and was conducted three times. Germination of inoculated seeds ranged from 37.5 to 75.0%, and germinated seedlings had dark brown lesions on the taproots. There was a significant difference between isolates in the petri dish assay (P = 0.0030); one isolate was less aggressive, but both isolates resulted in significantly more disease than on the non-inoculated control plants, which had 100% germination and no symptoms (P < 0.0001). F. oxysporum is a known soybean pathogen (1), but isolates of F. commune may have been misidentified as F. oxysporum in previous studies. To our knowledge, this is the first report of F. commune as a pathogen on soybean in the U.S.A. References: (1) K. E. Broders et al. Plant Dis. 91:727, 2007. (2) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (3) G. P. Munkvold and J. K. O'Mara. Plant Dis. 86:143, 2002. (4) K. Skovgaard et al. Mycologia. 94:630, 2003.

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

Plant Disease ◽

10.1094/pdis-09-16-1249-pdn ◽

2017 ◽

Vol 101 (6) ◽

pp. 1038 ◽

Cited By ~ 7

Author(s):

J. Beckerman ◽

H. Nisonson ◽

N. Albright ◽

T. Creswell

Keyword(s):

United States ◽

Root Rot ◽

The United States ◽

Pythium Aphanidermatum ◽

First Report ◽

Crown And Root Rot ◽

Industrial Hemp

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First Report of Fusarium proliferatum Causing Root Rot on Soybean (Glycine max) in the United States

Plant Disease ◽

10.1094/pdis-04-11-0346 ◽

2011 ◽

Vol 95 (10) ◽

pp. 1316-1316 ◽

Cited By ~ 18

Author(s):

M. M. Díaz Arias ◽

G. P. Munkvold ◽

L. F. Leandro

Keyword(s):

United States ◽

Root Rot ◽

Morphological Characteristics ◽

Dry Weight ◽

The United States ◽

Growth Stages ◽

Species Identity ◽

First Report ◽

Soybean Roots ◽

Soybean Diseases

Fusarium spp. are widespread soilborne pathogens that cause important soybean diseases such as damping-off, root rot, Fusarium wilt, and sudden death syndrome. At least 12 species of Fusarium, including F. proliferatum, have been associated with soybean roots, but their relative aggressiveness as root rot pathogens is not known and pathogenicity has not been established for all reported species (2). In collaboration with 12 Iowa State University extension specialists, soybean roots were arbitrarily sampled from three fields in each of 98 Iowa counties from 2007 to 2009. Ten plants were collected from each field at V2-V3 and R3-R4 growth stages (2). Typical symptoms of Fusarium root rot (2) were observed. Symptomatic and asymptomatic root pieces were superficially sterilized in 0.5% NaOCl for 2 min, rinsed three times in sterile distilled water, and placed onto a Fusarium selective medium. Fusarium colonies were transferred to carnation leaf agar (CLA) and potato dextrose agar and later identified to species based on cultural and morphological characteristics. Of 1,230 Fusarium isolates identified, 50 were recognized as F. proliferatum based on morphological characteristics (3). F. proliferatum isolates produced abundant, aerial, white mycelium and a violet-to-dark purple pigmentation characteristic of Fusarium section Liseola. On CLA, microconidia were abundant, single celled, oval, and in chains on monophialides and polyphialides (3). Species identity was confirmed for two isolates by sequencing of the elongation factor (EF1-α) gene using the ef1 and ef2 primers (1). Identities of the resulting sequences (~680 bp) were confirmed by BLAST analysis and the FUSARIUM-ID database. Analysis resulted in a 99% match for five accessions of F. proliferatum (e.g., FD01389 and FD01858). To complete Koch's postulates, four F. proliferatum isolates were tested for pathogenicity on soybean in a greenhouse. Soybean seeds of cv. AG2306 were planted in cones (150 ml) in autoclaved soil infested with each isolate; Fusarium inoculum was applied by mixing an infested cornmeal/sand mix with soil prior to planting (4). Noninoculated control plants were grown in autoclaved soil amended with a sterile cornmeal/sand mix. Soil temperature was maintained at 18 ± 1°C by placing cones in water baths. The experiment was a completely randomized design with five replicates (single plant in a cone) per isolate and was repeated three times. Root rot severity (visually scored on a percentage scale), shoot dry weight, and root dry weight were assessed at the V3 soybean growth stage. All F. proliferatum isolates tested were pathogenic. Plants inoculated with these isolates were significantly different from the control plants in root rot severity (P = 0.001) and shoot (P = 0.023) and root (P = 0.013) dry weight. Infected plants showed dark brown lesions in the root system as well as decay of the entire taproot. F. proliferatum was reisolated from symptomatic root tissue of infected plants but not from similar tissues of control plants. To our knowledge, this is the first report of F. proliferatum causing root rot on soybean in the United States. References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) G. L. Hartman et al. Compendium of Soybean Diseases. 4th ed. The American Phytopathologic Society, St. Paul, MN, 1999. (3) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (4) G. P. Munkvold and J. K. O'Mara. Plant Dis. 86:143, 2002.

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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.

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First Report of Fusarium brasiliense Causing Root Rot of Dry Bean in the United States

Plant Disease ◽

10.1094/pdis-02-18-0332-pdn ◽

2018 ◽

Vol 102 (10) ◽

pp. 2035 ◽

Cited By ~ 4

Author(s):

J. L. Jacobs ◽

K. Oudman ◽

H. Sang ◽

M. I. Chilvers

Keyword(s):

United States ◽

Root Rot ◽

The United States ◽

Dry Bean ◽

First Report

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

Plant Disease ◽

10.1094/pdis-12-17-1999-pdn ◽

2018 ◽

Vol 102 (10) ◽

pp. 2045-2045 ◽

Cited By ~ 3

Author(s):

J. Beckerman ◽

J. Stone ◽

G. Ruhl ◽

T. Creswell

Keyword(s):

United States ◽

Root Rot ◽

Pythium Ultimum ◽

The United States ◽

First Report ◽

Crown And Root Rot ◽

Industrial Hemp

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First Report of Root Rot and Wilt Caused by Pythium myriotylum on Hemp (Cannabis sativa) in the United States

Plant Disease ◽

10.1094/pdis-11-18-2028-pdn ◽

2019 ◽

Vol 103 (12) ◽

pp. 3288-3288 ◽

Cited By ~ 2

Author(s):

C. S. McGehee ◽

P. Apicella ◽

R. Raudales ◽

G. Berkowitz ◽

Y. Ma ◽

...

Keyword(s):

United States ◽

Root Rot ◽

Cannabis Sativa ◽

The United States ◽

Pythium Myriotylum ◽

First Report

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First Report of a Root and Crown Disease of the Invasive Weed Lepidium draba Caused by Phoma macrostoma

Plant Disease ◽

10.1094/pdis-02-11-0107 ◽

2012 ◽

Vol 96 (1) ◽

pp. 145-145 ◽

Cited By ~ 1

Author(s):

A. J. Caesar ◽

R. T. Lartey ◽

T.-C. Caesar-Ton-That

Keyword(s):

United States ◽

Biological Control ◽

Patent Application ◽

The United States ◽

Root Tissue ◽

Conidial Suspension ◽

Internal Transcribed Spacer Region ◽

First Report ◽

South Central ◽

Lepidium Draba

The exotic rangeland perennial Lepidium draba occurs as a noxious weed in 22 states, mostly in the western United States. Because chemical control measures against this invasive perennial, a member of the Brassicaceae, have not achieved adequate results, biological control is being pursued. While inventories of arthropods that feed on L. draba have been established, little is known of soilborne pathogens for possible use as biological control agents. To address this deficiency, we have surveyed for diseases of L. draba in the United States and Eurasia to identify and test potential biocontrol agents. In intensive surveys for soilborne diseases in a single infestation that is >20 years old in a cattle pasture in south-central Montana, several chlorotic, stunted plants were noted. Roots of chlorotic plants that exhibited elongated fissures from which other soilborne fungi were isolated also had numerous prominent pycnidia embedded in the crown tissue above the lesions. Examination with a dissecting microscope revealed large ostioles made evident by the wide concave inversions in the short necks of the pycnidia. Culture of root tissue on potato dextrose agar resulted in whitish, becoming pale gray colonies, with a dull peach-to-reddish tinge at the margins, with abundant single pycnidia. Conidia in vitro were mainly unicellular, variable shape, subglobose to ellipsoidal, with several guttules averaging 6 × 2.5 μm. These morphological traits are characteristic of Phoma macrostoma, which is regarded as a weak or wound pathogen. The internal transcribed spacer region of rDNA was amplified using primers ITS1 and ITS4 and sequenced. BLAST analysis of the 575-bp fragment showed a 100% homology with the sequence of an isolate of P. macrostoma that has been investigated extensively for commercialization as a biological control agent of various agricultural weeds (1), including wild mustard (GenBank No. DQ474091). The nucleotide sequence has been assigned GenBank No. HM755951. Pathogenicity tests consisted of making four 1.4-mm-diameter holes in five NaOCl (0.1%)-sterilized root sections of L. draba and pipetting ~50 to 100 μl of a 106 CFU/ml conidial suspension into the incisions, incubating the inoculated roots at 20 to 25°C overnight and planting the root sections, one per pot, in an artificial greenhouse potting mix and placing the pots in the greenhouse at 20 to 25°C. Controls were five root sections that were treated similarly except that sterile water was injected. The experiment was repeated. After 10 days, shoots that grew from inoculated roots were chlorotic and shorter than those produced from control roots. P. macrostoma was isolated from tissue of inoculated roots that became blackened distal to the inoculation points. To examine the host range of P. macrostoma on other brassica species, crowns of 2-week-old seedlings of radish, broccoli, cauliflower, broccoli raab, turnip, kohlrabi, cabbage, Chinese cabbage, mustard greens, and canola were injected with 0.5 ml of a 106 CFU/ml conidial suspension. Plants were grown in the greenhouse at 20 to 25°C for 4 weeks after inoculation and examined for symptoms. The experiment was repeated twice. Blackened root tissue with slight chlorosis occurred only on roots of radish and crowns of broccoli, from which P. macrostoma was reisolated. To our knowledge, this the first report of a disease of L. draba caused by P. macrostoma. Reference: (1) K. L. Bailey et al. U.S. Patent Application Serial No. 60/294,475, Filed May 20, 2001.

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First Report of Root Rot Caused by Fusarium solani on Benincasa hispida in the United States

Plant Disease ◽

10.1094/pdis-06-11-0494 ◽

2012 ◽

Vol 96 (2) ◽

pp. 294-294 ◽

Cited By ~ 2

Author(s):

P. Ji ◽

J. Yin ◽

K. L. Jackson

Keyword(s):

United States ◽

Dna Sequences ◽

Root Rot ◽

Morphological Characteristics ◽

The United States ◽

First Report ◽

Benincasa Hispida ◽

Field Samples ◽

Vegetable Farm ◽

Wax Gourd

Root rot was observed on wax gourd (Benincasa hispida (Thunb.) Cogn.) cv. Black Giant in August 2010 in a commercial vegetable farm in southern Georgia. Approximately 5% of the plants were affected and infected roots turned light to dark brown with partial or entire roots affected and the lower leaves became wilted. Symptomatic roots from six plants were surface sterilized with 0.6% sodium hypochlorite and plated on potato dextrose agar (PDA) medium. Pure cultures had white mycelia and spore masses and were obtained from all six plants by subculturing hyphal tips onto PDA. One- to two-celled, oval- to kidney-shaped microconidia and cylindrical macroconidia with two or three cells plus apical and basal cell were produced, which averaged 12.5 × 4 μm and 28 × 4.5 μm, respectively. Microconidia were abundant and macroconidia were sparse on PDA. Single-spore isolates were obtained and identified as a Fusarium sp. by PCR analysis with primers ITS-Fu-f and ITS-Fu-r (1). Genomic DNA of two isolates obtained from different plants was extracted and a portion of the translation elongation factor 1-α (TEF) gene of the isolates was amplified and sequenced (3). When compared with sequences available in the GenBank database, DNA sequences of the two isolates (GenBank Accession No. JF928376) shared 100% sequence identity with F. solani strain FRC S1734 (GenBank Accession No. DQ247527). The fungus was identified as F. solani (Mart.) Sacc. based on molecular analysis and morphological characteristics (2). Oat grains were separately infected with two isolates, BG2a and BG6, and used to inoculate healthy, 3-week-old wax gourd seedlings (cv. Black Giant) under greenhouse conditions (14-h photoperiod, 24 to 30°C). Each seedling was grown in a 10-cm pot containing a commercial potting mix, and five healthy plants were inoculated with each isolate by placing 15 infected oat grains around each plant at a depth of 5 cm in the soil. Five plants treated with noninfected oat grains served as controls. Symptoms identical to those on field samples developed on all inoculated plants 3 weeks after inoculation but not on the control plants. F. solani was reisolated from inoculated symptomatic plants and the identity was confirmed, which completed Koch's postulates. The experiment was repeated one more time under similar conditions. To our knowledge, this is the first report of root rot caused by F. solani on wax gourd in the United States. Wax gourd is an important specialty crop in the southeastern United States and the occurrence of this disease needs to be taken into account in wax gourd production. References: (1) K. A. Abd-Elsalam et al. Afr. J. Biotechnol. 2:82, 2003. (2) C. Booth. Fusarium Laboratory Guide to the Identification of the Major Species. CMI, Kew, England, 1977. (3) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004.

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First Report of Collar and Root Rot Caused by Phytophthora nicotianae on Daphne odora in Italy

Plant Disease ◽

10.1094/pdis-93-8-0848a ◽

2009 ◽

Vol 93 (8) ◽

pp. 848-848

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Root Rot ◽

The United States ◽

Phytophthora Nicotianae ◽

Control Treatment ◽

Peat Moss ◽

Late Winter ◽

American Phytopathological Society ◽

First Report ◽

Daphne Odora

Daphne odora is becoming popular in gardens because of its variegated foliage and fragrant flowers in late winter and early spring. During October of 2008 in a commercial nursery near Maggiore Lake (Verbano-Cusio-Ossola Province) in northwestern Italy, plants of D. odora showed extensive chlorosis and root rot. Diseased plants eventually wilted and died, dropping leaves in some cases. Most frequently, wilted leaves persisted on stems. At the soil level, dark brown-to-black water-soaked lesions that coalesced often girdled the stem. All of the crown and root system was affected. Disease was widespread and severe with 70% of 2,500 potted plants being affected. A Phytophthora-like organism was isolated consistently on a medium selective for oomycetes (4) after disinfestation of lower stem and root pieces of D. odora for 1 min in a solution containing 1% NaOCl. Tissue fragments of 1 mm2 were excised from the margins of the lesions and plated. The pathogen was identified based on morphological and physiological features as Phytophthora nicotianae (= P. parasitica) (2). Sporangia were produced for identification by growing a pure culture in sterilized soil extract solution at neutral pH (obtained by shaking and then centrifuging 300 g of soil in 1 liter of distilled water). They were spherical to ovoid, papillate, and measured 39.2 to 54.5 × 31.7 to 41.7 μm (average 44.8 × 34.5 μm). Papillae measured 2.4 to 4.9 μm (average 3.7 μm). Chlamydospores were spherical with a diameter ranging from 15.8 to 36.1 μm (average 25.4 μm). The internal transcribed spacer (ITS) region of rDNA of a single isolate was amplified using primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 804-bp segment showed a 100% homology with the sequence of P. nicotianae EF140988. The nucleotide sequence has been assigned GenBank No. FJ843100. Pathogenicity of two isolates obtained from infected plants was confirmed by inoculating 12-month-old plants of D. odora. Both isolates were grown for 15 days on a mixture of 70:30 wheat/hemp kernels and then 80 g/liter of the inoculum was mixed into a substrate containing sphagnum peat moss/pumice/pine bark/clay (50:20:20:10 vol/vol). One plant per 3-liter pot was transplanted into the substrate and constituted the experimental unit. Three replicates were used for each isolate and noninoculated control treatment; the trial was repeated once. All plants were kept in a greenhouse at temperatures from 20 to 25°C. Plants inoculated with isolate no. 1 developed symptoms of chlorosis and root rot within 14 days and then a wilt rapidly followed. Isolate no. 2 was less aggressive causing the same symptoms within 20 days. Control plants remained symptomless. P. nicotianae consistently was reisolated from inoculated plants. Previously, P. nicotianae (= P. parasitica) has been reported in several states of the United States on D. odora (3). To our knowledge, this is the first report of P. nicotianae on D. odora in Italy. The economic importance of the disease is low because of the limited number of farms that grow this crop in Italy, although spread could increase as the popularity of plantings expand. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997 (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) D. F. Farr et al. Fungi on Plants and Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (4) H. Masago et al. Phytopathology, 67:425, 1977.

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