First Report of Pythium Root Rot of Stevia Caused by Pythium myriotylum, P. irregulare, and P. aphanidermatum in North Carolina

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 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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Mefenoxam Sensitivity, Aggressiveness, and Identification of Pythium Species Causing Root Rot on Floriculture Crops in North Carolina

Plant Disease ◽

10.1094/pdis-02-15-0232-re ◽

2015 ◽

Vol 99 (11) ◽

pp. 1550-1558 ◽

Cited By ~ 16

Author(s):

E. C. Lookabaugh ◽

K. L. Ivors ◽

B. B. Shew

Keyword(s):

North Carolina ◽

Host Species ◽

Root Rot ◽

Internal Transcribed Spacer ◽

Ornamental Plants ◽

Pythium Species ◽

Selective Media ◽

Microtiter Plates ◽

Pythium Root Rot

Herbaceous ornamental plants exhibiting symptoms of Pythium root rot were collected from 26 greenhouses in 21 counties in North Carolina (NC) from 2010 to 2012. Plant symptoms ranged from mild stunting to severe wilting, root rot, and death. Roots were plated on selective media, and 356 isolates of Pythium were recovered from 34 host species. Selected isolates were identified by sequencing of the internal transcribed spacer (ITS) rDNA gene region. Seventeen Pythium species were identified, with P. aphanidermatum, P. irregulare, and P. myriotylum comprising 75% of the 320 isolates sequenced. Twelve of the 26 greenhouses had more than one species present. Mefenoxam sensitivity was tested in vitro by growing isolates in wells of microtiter plates containing clarified V8 agar amended with 100 µg a.i./ml mefenoxam. Colonization was scored after 24 to 48 h using a scale of 0 (no growth) to 5 (entire well colonized). Fifty-two percent of the isolates were resistant to mefenoxam (mean score ≥4). All 32 isolates of P. myriotylum were sensitive, whereas sensitivity varied among isolates of P. aphanidermatum and P. irregulare. Resistant and sensitive isolates of the same species were found within the same greenhouses. The aggressiveness of P. aphanidermatum and P. irregulare isolates was evaluated on poinsettia, Gerbera daisy, and petunia. P. aphanidermatum was more aggressive than P. irregulare on poinsettia and petunia; symptoms were mild and no differences in aggressiveness were observed on Gerbera daisy. Sensitivity to mefenoxam was not related to aggressiveness.

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First Report of Pythium myriotylum as a Causal Agent of Crown and Root Rot in Soilless Green Bean Cultivation in Italy

Plant Disease ◽

10.1094/pdis-07-17-0942-pdn ◽

2018 ◽

Vol 102 (3) ◽

pp. 688-688

Author(s):

S. Vitale ◽

L. Luongo ◽

E. Marinelli ◽

A. Belisario

Keyword(s):

Root Rot ◽

Causal Agent ◽

Green Bean ◽

Pythium Myriotylum ◽

First Report ◽

Crown And Root Rot

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First Report of Crown and Root Rot Caused by Pythium myriotylum on Hemp (Cannabis sativa) in Arizona

Plant Disease ◽

10.1094/pdis-12-20-2712-pdn ◽

2021 ◽

Author(s):

Jiahuai Hu

Keyword(s):

Root Rot ◽

Cannabis Sativa ◽

Morphological Characteristics ◽

Crown Rot ◽

Pathogenicity Test ◽

Light Cycle ◽

Pythium Myriotylum ◽

First Report ◽

Leaf Chlorosis ◽

Query Coverage

During August and September 2020, symptoms of leaf chlorosis, stunting, and wilting were observed on indoor hemp plants (Cannabis sativa L. cv. ‘Wedding Cake’) in a commercial indoor facility located in Coolidge, Arizona. Plants were grown in soilless coconut coir growing medium (Worm Factory COIR250G10), watered with 1.5 to 2.1 liters every 24 h through drip irrigation, and supplemented with 18 h of lighting. About 35% of plants displayed symptoms as described above and many symptomatic plants collapsed. To identify the causal agent, crown and root tissues from four symptomatic plants were harvested and rinsed with tap water. Tissue fragments (approx. 2 to 4 mm in size) were excised from the margins of the stem and root lesions, surface sterilized in 0.6% sodium hypochlorite for 1 min, rinsed well in sterile distilled water, blotted dry, and plated on potato dextrose agar (PDA) and on oomycete-selective clarified V8 media containing pimaricin, ampicillin, rifampicin, and pentachloronitrobenzene (PARP). Plates were incubated at room temperature (21-24 oC). Five isolates resembling Pythium were transferred after 3 days and maintained on clarified V8 media. Morphological characteristics were observed on grass blade cultures (Waterhouse 1967). Grass blades were placed on CV8 inoculated with the isolate. After a 1-day incubation at 25°C, the colonized blades were transferred to 8 ml of soil water extract in a Petri dish. Ten sporangia and oogonia were selected randomly and their diameters were measured under the microscope. Sporangia were mostly filamentous, undifferentiated or inflated lobulate, ranging from 7 to 17 µm in diameter. Knob-like appressoria were observed on branching clusters. Bulbous-like antheridia were formed on branched stalk with 1-8 antheridia per oogonium. Globose oogonia were terminal or intercalary and ranged from 21 to 33 µm in diameter. Globose oospores were mostly aplerotic and ranged from 15 to 21 μm in diameter. Based on these morphological characteristics, isolates were tentatively identified as Pythium myriotylum (Watanabe, 2002). Genomic DNA was extracted from mycelial mats of two isolates using DNeasy Plant Pro Kit (Qiagen Inc., Valencia, CA) according to the manufacturer’s instructions. The internal transcribed spacer (ITS) region of rDNA was amplified with primers ITS1/ITS4 and two identical nucleotide sequences were obtained and deposited under accession number MW380925. A BLASTn search revealed ≥ 98% query coverage and 100% match with sequences HQ237488.1, KY019264.1, and KM434129, which were isolates of P. myriotylum from palm, tobacco, and ginger, respectively. To fulfill Koch’s postulates, pathogenicity tests were conducted with 2 isolates using plants of ‘Wedding Cake’ grown in 12 1.9-liter pots filled with a steam-disinfested potting mix (Sungro Professional Growing Mix). Pots were placed in a plastic container and watered to flooding three times a week. Plants were maintained in a greenhouse with 18 h/10 h day/night supplemental light cycle (15-28 oC). Plants were fertilized weekly with Peters Professional fertilizer at 1mg/ml. Four plants were inoculated with each isolate at three weeks after seed sowing by placing two 5-mm mycelial plugs from active growing 4 days-old cultures on PDA media adjacent to the main root mass at an approximately 3 cm depth. Four plants were inoculated with blank PDA plugs as controls. Symptoms of leaf chlorosis, crown rot and wilting were observed after four weeks while control plants remained symptomless. P. myriotylum was re-isolated from necrotic roots of inoculated plants after surface-sterilization, but not from control plants. The pathogenicity test was repeated once. While P. myriotylum often occurs in warmer regions and has a wide host range of >100 host plant species including numerous economically important crops (Wang et al., 2003), there are only two reports of this pathogen on indoor hemp plants in a greenhouse in Connecticut (McGehee et al., 2019) and in Canada (Punja et al., 2019). This is the first report of P. myriotylum causing root and crown rot of indoor hemp in Arizona. A more careful water management in soilless growth medium to reduce periods of saturation would minimize the risk of Pythium root rot in indoor hemp production.

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First Report of Phoma terrestris Causing Red Root Rot on Sweet Corn (Zea mays) in North Carolina

Plant Disease ◽

10.1094/pdis-91-8-1054c ◽

2007 ◽

Vol 91 (8) ◽

pp. 1054-1054 ◽

Cited By ~ 5

Author(s):

S. R. Koenning ◽

J. W. Frye ◽

J. K. Pataky ◽

M. Gibbs ◽

D. Cotton

Keyword(s):

North Carolina ◽

Root Rot ◽

Sweet Corn ◽

Adventitious Shoot ◽

Fresh Market ◽

First Report ◽

The North ◽

Field Corn ◽

Foliar Symptoms ◽

Corn Plants

Red root rot, caused by Phoma terrestris E. M. Hansen, caused premature senescence and yield reductions to fresh-market sweet corn in Hyde County, North Carolina in July 2006. Foliar symptoms developed over a period of 5 to 8 days approximately 1 to 2 weeks after anthesis and included desiccation of leaves and poor development of ears. By 3 weeks after pollination, when the sweet corn was harvested, crowns and the first aboveground internode of affected plants were rotted and reddish colored, but roots appeared normal. The root mass of affected plants tended to be greater than that of unaffected plants. Incidence of symptomatic plants was greater than 30% in some fields and was lower on crops planted and harvested early. Symptomatic and asymptomatic plants were adjacent in affected fields. Diseased plants were more common in fields of sweet corn that followed soybean (Glycine max) or a double-crop of onions (Allium cepa) than in fields that followed corn. Incidence of symptomatic plants also differed among adjacent plantings of different sweet corn hybrids. Hybrids ‘173A’, ‘182A’, ‘378a’, and ‘XTH1178’ had a high incidence of symptomatic plants and ‘372A’, ‘278A’, ‘8101’, and ‘8102’ were less affected. Samples of symptomatic plants of the hybrid ‘182A’ were examined at the North Carolina Plant Disease and Insect Clinic during August. Olivaceous black pycnidia with long setae around the ostioles were imbedded in the stalk near the first node aboveground. Numerous conidia (1.8 to 2.3 × 4.5 to 5.5 μm) were released in cirri from pycnidia. When cultured on potato dextrose agar (PDA), the fungus produced a red pigment and intercalary and terminal chlamydospores. Pathogenicity was demonstrated in the greenhouse by transplanting corn seedlings or direct-seeding corn into pots of soil infested with plates of PDA containing chlamydospores and hyphae. A suspension of chlamydospores and hyphae also was injected into the stems of plants 28 days after transplanting. Five replicates of the pathogenicity experiments were repeated twice with noninoculated controls. After 8 weeks, P. terrestris was recovered from the roots of all inoculated plants. Soil inoculation resulted in necrotic root tissue in approximately 25% of inoculated plants. Approximately 90% of inoculated plants had discolored crowns that resembled symptoms from field infected plants. Stem inoculations resulted in necrosis extending 2 to 5 cm from the point of injection and resulted in shoot death of 40% of inoculated plants that resulted in the development of an adventitious shoot. Red root rot was prevalent on field corn in the Delmarva Peninsula throughout the late 1980s and 1990s (1). To our knowledge, this is the first report of this disease causing damage to sweet corn in North Carolina. Foliar symptoms and discoloration of crowns of diseased sweet corn plants were similar to previously described symptoms of red root rot on field corn (2), however, roots of affected sweet corn plants were not substantially rotted and did not have a symptomatic reddish pink or dark carmine color, presumably because sweet corn is harvested prior to the development of root symptoms. References: (1) K. W. Campbell et al. Plant Dis. 75:1186, 1991. (2) D. G. White, ed. Compendium of Corn Diseases. The American Phytopathological Society, St Paul, MN, 1999.

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