First Report of Pythium polymastum on Broccoli and Cauliflower in California

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.

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

Plant Disease ◽

10.1094/pd-90-1552c ◽

2006 ◽

Vol 90 (12) ◽

pp. 1552-1552 ◽

Cited By ~ 4

Author(s):

S. P. Fernández-Pavía ◽

G. Rodríguez-Alvarado ◽

A. López-Ordaz ◽

Y. L. Fernández-Pavía

Keyword(s):

Root Rot ◽

Disease Incidence ◽

Phytophthora Capsici ◽

Corn Meal ◽

Corn Meal Agar ◽

American Phytopathological Society ◽

Hydroponic System ◽

First Report ◽

Pathogenicity Tests ◽

Stem Lesions

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.

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Damping-Off, Root Rot, and Lower Stem Rot of Seed-Propagated Geraniums Caused by Pythium ultimum

Plant Disease ◽

10.1094/pd-73-0625 ◽

1989 ◽

Vol 73 (8) ◽

pp. 625 ◽

Cited By ~ 4

Author(s):

M. K. Hausbeck

Keyword(s):

Root Rot ◽

Pythium Ultimum ◽

Stem Rot ◽

Damping Off ◽

Lower Stem

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First Report of Stem Rot and Wilt of Sunflower Caused by Sclerotinia minor in Spain

Plant Disease ◽

10.1094/pdis.2002.86.6.697d ◽

2002 ◽

Vol 86 (6) ◽

pp. 697-697

Author(s):

M. L. Molinero-Ruiz ◽

J. M. Melero-Vara

Keyword(s):

Helianthus Annuus ◽

Root Rot ◽

Mycelial Growth ◽

Disease Incidence ◽

Potato Dextrose Agar ◽

Stem Rot ◽

Sclerotinia Minor ◽

Stem Base ◽

First Report ◽

White Mycelium

In 2001, sunflower (Helianthus annuus L.) plants with symptoms of stem and root rot and wilt were observed in Soria, Spain. Light brown, water-soaked lesions developed on the collar of infected plants and extended along the stem, affecting the pith and causing early and sudden wilt. White mycelium and sclerotia (0.5 to 2 mm long) formed in the pith of stems. The sclerotia were disinfested in NaClO (10% vol/vol) for 1 min, transferred to potato dextrose agar (PDA), and incubated at 20°C. The fungus consistently obtained was identified as Sclerotinia minor Jagger (1). Pathogenicity was confirmed in a greenhouse experiment (15 to 25°C, 13 h light). Seven-week-old plants of six genotypes of sunflower (‘Peredovik’, HA89, HA821, HA61, RHA274, and HA337) were inoculated by placing one PDA disk with active mycelial growth adjacent to each basal stem just below the soil line and covering it with peat/sand/silt (2:2:1, vol/vol). Six plants of each genotype were inoculated without wounding, and another six were inoculated immediately after stem base wounding with a scalpel; six wounded and uninoculated plants were used as controls. First symptoms (wilting) appeared 4 days after inoculation in all genotypes. Two weeks after inoculation, the percentage of dead plants ranged from 33 to 92% (depending on cultivar), white mycelium was observed at the base of affected plants, and sclerotia were present in the pith of diseased plants. There was no effect of plant wounding on disease incidence or severity, and the fungus was reisolated from inoculated plants. To our knowledge, this is the first report of S. minor in Spain. Reference: (1) L. M. Kohn. Mycotaxon IX 2:365, 1979.

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First Report of Fusarium falciforme (FSSC 3+4) Causing Rot of Industrial Hemp (Cannabis sativa) in California

Plant Disease ◽

10.1094/pdis-08-21-1640-pdn ◽

2021 ◽

Author(s):

Kelley Rose Paugh ◽

Johanna Del Castillo Múnera ◽

Cassandra L Swett

Keyword(s):

Root Rot ◽

Cannabis Sativa ◽

Negative Control ◽

Stem Rot ◽

Tween 20 ◽

Post Inoculation ◽

First Report ◽

Fusarium Falciforme ◽

Stem Lesions ◽

Industrial Hemp

Industrial hemp (Cannabis sativa) is a newly legal crop in California that is grown for cannabidiol oil, fiber and seed. In August 2019, whole plant decline and root rot were observed affecting <5% of plants in two industrial fields in Fresno County, CA. Symptoms included chlorotic, collapsed foliage, stem vascular discoloration, and root rot with abundant mycelial growth. Stem and root segments (1-2 cm) from three to five diseased plants were agitated in 0.1% tween-20 and soaked in 70% ethanol for 30 s and 1% NaOCl for 2 min. After incubating for 5 to 7 days on 1:10 potato dextrose agar (PDA) amended with tetracycline, Fusarium selective medium (FSM), and PARP (pimaricin + ampicillin + rifampicin + pentachloronitrobenzene [PCNB] agar) medium, white to pale cream aerial mycelium emerged from tissue of all plants on PDA and FSM but not PARP. Isolates cultured on 0.1% potassium chloride agar formed heads of microconidia on long monophialides consistent with the Fusarium solani species complex (FSSC) (Leslie and Summerell 2008). To obtain pure cultures of two isolates (CS529 and CS530), a single-hyphal tip was excised and grown on PDA. DNA was extracted from actively growing mycelium (PrepMan Ultra kit). The translation elongation factor gene (EF-1α) was amplified via PCR using EF1/EF2 primers (O’Donnell et al. 1998). Sequences of the two isolates were identical and deposited under accession number MW892973 in GenBank. The 599 bp sequence was 99.33% identical to FSSC 3 + 4 (Fusarium falciforme) accessions FD_01443_EF-1a based on FUSARIUM-ID BLAST analysis. To evaluate pathogenicity, stems of hemp plants (cv. ‘Berry Blossom’; n=8 plants per isolate) were wounded by penetrating the epidermis in an area about 0.5-cm square by 1-mm deep and 8-inches above the soil line. A 0.5 cm-diameter plug of 7-day old F. falciforme-colonized PDA was placed against the wound. Inoculation sites were loosely wrapped with parafilm for 2 days. A negative control consisted of a sterile PDA plug (n=3). Treatments were arranged in a completely randomized design in a greenhouse. The experiment was conducted once, due to regulatory restrictions at campus facilities. At 61 days post-inoculation, external stem lesions were significantly larger in diameter (P < 0.05; Tukey’s HSD) in plants inoculated with CS529 (8 ± 1 mm) compared to the control (2 ± 0 mm), and larger but not significant for CS530 (6 ± 1 mm). Internal stem lesions (i.e., rot in stele) were observed in plants inoculated with CS529 (9 ± 3 mm); stem rot was very minor in plants treated with CS530 (1 ± 1 mm) and nonexistent for control plants. No other disease symptoms were observed. F. falciforme was isolated from stems of CS529- and C530-inoculated plants. Sequences of re-isolates matched 100% with accession MW892973. These results suggest that F. falciforme causes rot in hemp in California. These studies specifically confirm stem rot abilities; field observations of root rot indicate root rotting abilities, but further tests are needed for confirmation. This is the first report of F. falciforme causing disease in industrial hemp. FSSC was described as causing foot rot in hemp in Italy (Sorrentino et al. 2019), but these isolates belonged to phylogenetic species 5 (F. solani) not F. falciforme. In addition, F. falciforme was reported as causing root rot in hydroponically grown cannabis (Punja and Rodriguez 2018). These studies provide the foundation for development of management tools for hemp disease.

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First Report of a Ceratobasidium sp. Causing Root Rot on Canola in Washington State

Plant Disease ◽

10.1094/pdis-12-11-1038-pdn ◽

2012 ◽

Vol 96 (4) ◽

pp. 591-591 ◽

Cited By ~ 5

Author(s):

K. L. Schroeder ◽

T. C. Paulitz

Keyword(s):

Plant Height ◽

Root Rot ◽

Root Zone ◽

Dry Weight ◽

Washington State ◽

Infested Soil ◽

Damping Off ◽

Root Tips ◽

Hordeum Vulgare L ◽

First Report

Rhizoctonia root rot occurs commonly on canola (Brassica napus L.) in Washington State. Recently, isolates of an additional pathogen were found to be involved in this disease complex. Isolates of an AG-I-like Ceratobasidium sp. were collected from roots and root zone soil in central Washington near Ritzville. Identity of selected isolates was verified by sequencing the internal transcribed spacer (ITS) region of the rDNA (GenBank Accession Nos. JQ247570, JQ247571, and JQ247572), with a 90 to 93% identity to AG-I. All isolates also amplified with AG-I-like specific primers (1). Six isolates were included in pathogenicity assays conducted in the greenhouse. There were five replicates of three plants for each treatment and the experiment was conducted twice. Pasteurized soil was infested with ground oat inoculum (1%) and placed into containers (3.8 × 21 cm). Infested soils were seeded with canola, chickpea (Cicer arietinum L.), lentil (Lens culinaris Medik.), pea (Pisum sativum L.), barley (Hordeum vulgare L.), or wheat (Triticum aestivum L.). After 3 weeks of incubation at 15°C, the plants were destructively harvested. The emergence of canola was consistently reduced in soil infested with a Ceratobasidium sp., with reductions of 0 to 23% (average 11%). There was no postemergence damping-off, a symptom commonly associated with AG-2-1 (2). Plant height and top dry weights were significantly reduced for canola seeded into infested soil. Heights of plants growing in infested soil was reduced by 25 to 53% (average 42%) and top dry weight was reduced by 37 to 81% (average 61%) compared with the noninfested control. The legume hosts tested in this study were also affected by this Ceratobasidium sp., but to a lesser extent. Compared with the noninfested controls, there was evidence of preemergence damping-off in chickpea (0 to 27%, average 13%) and pea plants were consistently stunted (5 to 23%, average 12%). Chickpea and pea plants grown in infested soil also had reduced top dry weights of 9 to 28% (average 17%) and 13 to 35% (average 21%), respectively. The roots of all infected hosts had a characteristic brown discoloration with tapered, rotted root tips (spear tips). There was no reduction in emergence or plant height of wheat and barley; there was inconsistent reduction in dry weight of these plants. To our knowledge, this is the first report of a Ceratobasidium sp. causing disease on canola in Washington State. References: (1) P. A. Okubara et al. Phytopathology 98:837, 2008. (2) T. C. Paulitz et al. Plant Dis. 90:829, 2006.

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First Report of Damping-Off and Leaf Spot Caused by Cylindrocladium scoparium on Different Accessions of Bottlebrush Cuttings in Italy

Plant Disease ◽

10.1094/pdis-91-6-0769b ◽

2007 ◽

Vol 91 (6) ◽

pp. 769-769 ◽

Cited By ~ 6

Author(s):

G. Polizzi ◽

A. Vitale ◽

D. Aiello ◽

M. A. Dimartino ◽

G. Parlavecchio

Keyword(s):

South African ◽

Root Rot ◽

Severe Disease ◽

Damping Off ◽

Single Spore ◽

Centraalbureau Voor ◽

First Report ◽

Leaf Spots ◽

Plastic Bags ◽

Collar And Root Rot

In May of 2006, approximately 10,000 cuttings of bottlebrushes (Callistemon cvs. Laevis, Hannah Ray, Kings Park Special, Masotti Mini Red, and Rose Opal with either C. viminalis (Soland. ex Gaertn.) Cheel. [excluded] or C. citrinus (Curtis) Skeels as one parent) grown in a nursery in eastern Sicily (Italy) exhibited severe disease symptoms including damping-off, leaf spots, and collar and root rot. Initially, the infections were detected on approximately 30% of the cuttings, but by late September 2006, 70% of the plants had symptoms. A Cylindrocladium sp. was consistently isolated from the diseased portions of plants onto potato dextrose agar. To determine the species, single-conidial isolates of the fungus were cultured on carnation leaf agar (CLA) for 7 days at 25°C with 12 h of light/dark conditions. Only the mycelia and spores growing on the carnation leaves were examined with a light microscope, and the isolates were identified as Cylindrocladium scoparium Morgan (teleomorph Calonectria morganii Crous, Alfenas & M.J. Wingf.) on the basis of their pyriform to broadly ellipsoidal terminal vesicles, conidiophore branching pattern, and conidia (1). In addition, the ability of the colonies to mate with South African tester strains of C. scoparium (2,3) confirmed the identification. Koch's postulates were fulfilled by inoculating 10 cuttings for each bottlebrush accession with a spore suspension (105 conidia per ml) of one isolate of the pathogen (DISTEF-GCs7) obtained from 14-day-old single-spore colonies grown on CLA at 24°C under fluorescent cool white lights with 12 h of light/dark. Following inoculation, all plants were maintained in plastic bags in a growth chamber at 25 ± 1°C and 90 to 95% relative humidity. The same number of cuttings was used as a control. Damping-off, crown root rot, and leaf spots symptoms identical to those observed in the nursery appeared within 5 to 20 days. No symptoms were detected on the control plants. C. scoparium was reisolated from the artificially infected tissues. The isolate, used in the pathogenicity proof, was deposited at the Fungal Biodiversity Centre, Centraalbureau voor Schimmelcultures (Accession No. CBS 120930). The presence of C. scoparium was detected for the first time in Italy on mastic tree in 2005 (3). To our knowledge, this is the first report of C. scoparium on bottlebrush in Italy and it represents the first information about the susceptibility of these Callistemon cultivar accessions to the fungus and confirms the spread of the pathogen in Sicilian ornamental nurseries. References: (1) P. W. Crous. Taxonomy and Pathology of Cylindrocladium (Calonectria) and Allied Genera. The American Phytopathological Society, St. Paul MN, 2002. (2) P. W. Crous and M. J. Wingfield. Mycotaxon 51:341, 1994. (3) G. Polizzi et al. Plant Dis. 90:1110, 2006.

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First Report of Macrophomina phaseolina Causing Pre-harvest Cassava Root Rot in Benin and Nigeria

Plant Disease ◽

10.1094/pdis.1998.82.12.1402c ◽

1998 ◽

Vol 82 (12) ◽

pp. 1402-1402 ◽

Cited By ~ 7

Author(s):

W. Msikita ◽

B. James ◽

H. T. Wilkinson ◽

J. H. Juba

Keyword(s):

Plant Height ◽

Root Rot ◽

Macrophomina Phaseolina ◽

Hot Water ◽

Stem Rot ◽

Rice Seed ◽

First Report ◽

Cassava Root ◽

Number Of Leaves ◽

Lower Stem

In diagnostic surveys conducted in parts of Benin and Nigeria to determine the incidence of pre-harvest cassava root and stem rot during the dry season, Macrophomina phaseolina (Tassi) Goidanich constituted 14.2 and 18.7% of the total fungi (n = 201) associated with cassava root and stem rot from Benin and Nigeria (1). Pathogenicity of M. phaseolina on cassava was tested with cv. Agric. Inocula for pathogenicity tests were prepared by incubating 5-mm-diameter mycelial plugs for each of five isolates (Mp 1 to Mp 5, all collected from Benin) with 500 ml of autoclaved, sterilized, dehusked rice seed for 14 days at 30°C. Five 30-cm-long stem portions per isolate were cut from healthy cassava, surface disinfested in hot water (52°C, 5 min), and planted into 1-liter pots containing autoclaved, sterilized sand mixed with 10 ml of air-dried inoculum. Five plants per isolate similarly treated but not inoculated served as controls. Plants were watered once a week, and maintained in a greenhouse under natural light at 28 to 30°C. Lower leaves of inoculated plants gradually wilted, usually preceded by chlorosis, and brown to black lesions formed on the lower stem portions of some roots. Control plants remained asymptomatic. Plant height and percentage of leaf wilt (determined by counting the number of leaves wilted per plant and dividing by the total number of leaves per plant) were measured on a weekly basis for 8 weeks for each of the control and inoculated plants. At the end of 8 weeks, lesion length on the lower stem was measured. There were significant differences (P < 0.05) in length of the lesions and percentage of leaf wilt induced by the different isolates of M. phaseolina. Isolate Mp 1 induced the longest lesion (7.2 cm), followed by Mp 4 (4.1 cm), Mp 3 and Mp 5 (3.8 cm each), and Mp 2 (1.2 cm). Mp 4 induced the highest percentage of wilted leaves (53%), followed by Mp 1, Mp 3, and Mp 5 (30%), and Mp 2 (10%). All five M. phaseolina isolates (except Mp 3) reduced plant height, compared with control treatments. M. phaseolina was isolated from all infected plants, and the identification was independently confirmed by the International Mycological Institute, Surrey, UK. This is the first report of M. phaseolina causing pre-harvest cassava root rot in Benin and Nigeria. Reference: (1) W. Msikita et. al. Plant Dis. 81:1332, 1997.

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First Report of Erwinia carotovora subsp. carotovora Causing Bacterial Root Rot of Sweetpotato (Ipomoea batatas) in Louisiana

Plant Disease ◽

10.1094/pdis.1998.82.1.129a ◽

1998 ◽

Vol 82 (1) ◽

pp. 129-129 ◽

Cited By ~ 4

Author(s):

C. A. Clark ◽

M. W. Hoy ◽

J. P. Bond ◽

C. Chen ◽

Y.-K. Goh ◽

...

Keyword(s):

Root Rot ◽

Ipomoea Batatas ◽

Disease Incidence ◽

Erwinia Carotovora ◽

Soft Rot ◽

Stem Rot ◽

Identification System ◽

Natural Occurrence ◽

Storage Roots ◽

First Report

Bacterial root and stem rot of sweetpotato (Ipomoea batatas (L.) Lam.) was first fully characterized in the U.S. in 1977 (2). It was thought to be caused exclusively by Erwinia chrysanthemi. Although a previous report described sweetpotato as a host for E. carotovora subsp. carotovora, based on artificial inoculations, others have reported that neither E. carotovora subsp. carotovora nor E. carotovora subsp. atroseptica decay sweetpotato storage roots (1). In October 1995, storage roots of sweetpotato cv. Beauregard were received from St. Landry Parish, LA, that displayed typical bacterial root rot. Isolations from these roots yielded bacteria that showed a similarity of 0.945 to E. carotovora subsp. carotovora with the Biolog GN Bacterial Identification System (version 3.50). This isolate (Ecc-LH) also differed from isolates of E. chrysanthemi (Ech) from sweetpotato and other hosts in that it was insensitive to erythromycin, did not produce phosphatase or lecithinase, and did not produce gas from glucose. Ecc-LH differed from known strains of E. carotovora subsp. atroseptica in that it did not produce reducing substances from sucrose or acid from palatinose. When Beauregard storage roots were inoculated by inserting micropipette tips containing 50 μl of 1.0 × 108 CFU/ml, both Ecc-LH and Ech-48 produced typical bacterial root rot symptoms. However, when they were compared by infectivity titrations at 28 to 32°C, Ecc-LH was less virulent than Ech-48. Ecc-LH had an ED50 of approximately 1.0 × 106 CFU/ml and did not cause appreciable disease below inoculum concentrations of 1.0 × 105, whereas Ech-48 had an ED50 of approximately 1.0 × 108 and caused soft rot at the lowest concentration tested, 1.0 × 103. Similar disease incidence was observed in infectivity titrations at 22 to 24°C, but Ech-48 caused less severe soft rot. E. carotovora subsp. carotovora was reisolated from inoculated storage roots and its identity was reconfirmed by Biolog. When terminal vine cuttings of Beauregard were dipped in 1.0 × 108 CFU/ml and planted in a greenhouse, bacterial stem rot symptoms developed on plants inoculated with Ech-48 at about 4 weeks postinoculation, or when new growth began. However, no symptoms developed on plants inoculated with Ecc-LH. This is the first report of natural occurrence of E. carotovora subsp. carotovora causing bacterial root rot of sweetpotato in Louisiana. E. chrysanthemi remains the most important pathogen causing bacterial soft rot in sweetpotato since it is widely associated with sweetpotato, is more virulent on storage roots and also causes a stem rot. E. carotovora subsp. carotovora can cause root rot, but has been isolated in only one location to date, is less virulent on storage roots, and apparently does not cause stem rot on the predominant cultivar in U.S. sweetpotato production, Beauregard. References: (1) C. A. Clark and J. W. Moyer. 1988. Compendium of Sweet Potato Diseases. American Phytopathological Society, St. Paul, MN. (2) N. W. Schaad and D. Brenner. Phytopathology 67:302, 1977.

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First report of root rot caused by (Pythium dissotocum) on hydroponically grown collard greens (Brassica oleracea var. acephala)

Plant Disease ◽

10.1094/pdis-07-21-1584-pdn ◽

2021 ◽

Author(s):

Noah Carr Luecke ◽

Kerri Crawford ◽

Hanane Stanghellini ◽

Alyssa Burkhard ◽

Steve Koike

Keyword(s):

Brassica Oleracea ◽

Cytochrome Oxidase ◽

Root Rot ◽

Soil Extract ◽

Coi Gene ◽

Ambient Light ◽

Light Conditions ◽

Base Pairs ◽

First Report ◽

Pythium Dissotocum

Collards (Brassica oleracea var. acephala) are grown throughout the United States. Hydroponic greens are more common now due to technological advances lowering the cost and increasing the efficacy of production. In January 2021, a 325 m2 indoor hydroponic farm opened to provide fresh produce for a school in Los Angeles County, CA. Three week old collard seedlings were purchased from a local nursery, rinsed of their rooting media, and transplanted into deep water culture beds (1.2 m x 2.5 m x 0.3 m). Two weeks later, symptoms including plant stunting, chlorosis, leaf curling and wilting, and brown necrotic roots appeared. By and by 80-100% of usable plants were lost to disease. Symptomatic roots were plated on corn meal agar (CMA) amended with 2 ml of 25% lactic acid and CMA amended with pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP) (Kannwischer et al. 1978). After 2 days a single colony type emerged on PARP but no growth occurred on acidified CMA. Representative isolates were transferred to CMA and to filtered (0.02 µm) soil extract solution with boiled grass blades (Martin 1992), both of which were incubated at 22 C and ambient light conditions. On CMA, isolates produced coenocytic mycelium with minimal aerial hyphae. After 24 h in soil extract, isolates developed filamentous sporangia, elongated discharge tubes with slightly inflated tips, and zoospores. Oospores were not observed. Pathogenicity was confirmed by soaking the roots of five day old collard seedlings in beakers containing zoospores (1 x 102 zoospores/ml) in filtered soil extract. Four isolates were tested on 15 seedlings each. After 24 h at 22 C in ambient light conditions, plants were transferred to new beakers with roots placed on filter paper at the bottom and saturated with sterile distilled water. Three days after this transfer, leaves on all plants turned chlorotic and roots developed brown lesions from which morphologically identical colonies were isolated. Control plants, soaked in filtered soil extract, developed no root or foliar symptoms. To molecularly identify the collard isolates, DNA was extracted from mycelial original and re-isolated isolates and was amplified by PCR using mitochondrial primers for the cytochrome oxidase I (COI) gene (Robideau et al. 2011) and the cytochrome oxidase II (COX2) gene (Martin 2000). The only species that matched both loci from the original and re-isolated isolates with a high percent identity was Pythium dissotocum. The COI locus from the original isolate (MZ027311) matched P. dissotocum with 99% identity and with 332/334 base pairs matching the isolate with Sequence ID MT981134.1. From the re-isolated isolate (MZ027313), the COIequence perfectly matched 657/657 base pairs of P. dissotocum (Sequence ID MT981147.1). The COX2 locus from the original isolate (MZ027312) matched P. dissotocum (Sequence ID MG719859.1) with a 99% identity and 517/518 matching base pairs and the re-isolated isolate (MZ027314) perfectly matched P. dissotocum (Sequence ID MG719859.1) with 515/515 matching base pairs. Based on these molecular and morphological data, the isolates were identified as Pythium dissotocum. To our knowledge, this is the first report of P. dissotocum causing root rot on collards. At this same facility, P. dissotocum was also confirmed as the cause of declining bean (Phaseolus vulgaris) plants. As hydroponics will be necessary to feed a growing population – especially in urban areas -- and because leafy greens are a main crop of the hydroponics industry, we anticipate this issue may become common. Hydroponic systems are highly conducive to the persistence of Oomycetes and a record of infection and plan of action will be necessary to preserve crop health.

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