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

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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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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Relationships Between Yield and Crown Disease of Sweet Corn Grown in the Willamette Valley of Oregon

Plant Health Progress ◽

10.1094/php-2009-0831-01-rs ◽

2009 ◽

Vol 10 (1) ◽

pp. 9

Author(s):

Nathan L. Miller ◽

Cynthia M. Ocamb

Keyword(s):

Zea Mays ◽

Image Analysis ◽

Regression Analysis ◽

Root Rot ◽

Zea Mays L ◽

Sweet Corn ◽

Analysis Program ◽

Willamette Valley ◽

Nodal Roots ◽

Corn Plants

Sweet corn (Zea mays L.) yields in the Willamette Valley of Oregon declined during the 1990s. Severe root rot affected some plants shortly before harvest, but was absent in other plants that showed secondary symptoms of reduced ear yield and leaf death; necrosis of stalk nodes and crown tissues was found instead. Studies were done to determine if there is a relationship among yield and necrosis of crowns, stalk nodes, nodal roots, radicles, or sub-crown internodes. An image analysis program was used to quantify the grayscale value of crown and node tissues. Regression analysis indicates that plants with darker crown tissues have lower ear weights. Rots of the nodal roots, radicle, or sub-crown internode were poor predictors of ear weight at harvest. When either Fusarium oxysporum or F. verticillioides were isolated from crowns of commercial sweet corn plants, these crowns had significantly darker grayscale values than those from which neither species was isolated; ear weights were also lower when F. oxysporum was isolated from the crown or a stalk node. Accepted for publication 13 July 2009. Published 31 August 2009.

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First report of Curvularia leaf spot of field corn, caused by Curvularia lunata, in Mississippi

Plant Disease ◽

10.1094/pdis-10-21-2189-pdn ◽

2022 ◽

Author(s):

Alejandra M. Jimenez Madrid ◽

Tom Allen ◽

Amilcar Vargas ◽

Adam Connor ◽

Tessie Wilkerson

Keyword(s):

Dna Sequences ◽

Leaf Spot ◽

Growth Chamber ◽

Tween 20 ◽

Curvularia Lunata ◽

Pathogenicity Test ◽

Commonwealth Mycological Institute ◽

Field Corn ◽

Foliar Symptoms ◽

Corn Plants

In July 2021, foliar symptoms characterized by small, circular, light brown to tan lesions (0.5 to 3 mm diameter) with reddish-brown margins were observed on field corn (Zea mays L.) in two commercial fields in Hinds and Marion counties, Mississippi. Disease severity ranged from 2 to 15% on observed leaves. Symptomatic leaves were sealed in plastic bags, stored on ice, and transferred to the laboratory. Lesions were cut into small sections (≈4 mm2) and surface-sterilized with 70% ethanol for 30 s then rinsed with sterile water. Sterilized sections were transferred to potato dextrose agar (PDA) amended with chloramphenicol (75 mg/liter) and streptomycin sulfate (125 mg/liter) and incubated at 25°C in the dark for 7 days. Gray to brown-black colonies with orange margins and melanized, curved conidia with three transverse septa were observed microscopically (Fig. 1; ×400). Conidia measurements ranged from 15 to 25 μm in length and 7.5 to 12.5 μm in width (x̄= 20 × 9.8 μm; n= 44). Colony and conidia morphology were consistent with previous descriptions of Curvularia lunata (Wakker) Boedijn (Mabadeje 1969; Ellis 1971). Pure cultures were obtained, and DNA was extracted from 9-day old cultures. Two isolates (TW003-21; TW008-21) were selected for sequencing of the internal transcribed spacer (ITS) region using ITS4 and ITS5 primers. The 530-bp consensus sequences were deposited in GenBank under the accession No. OK095277 and OK095278. BLASTn queries of NCBI GenBank showed that the sequences shared 100% identity with C. lunata isolate DMCC2087 from Louisiana (MG971304) and isolate CX-3 from China (KR633084). A pathogenicity test was performed on V4/V5 stage corn plants (Progeny 9114VT2P) grown in 10.2 cm pots in the greenhouse. Plants were transferred to a growth chamber one-week prior to inoculation. The two isolates were grown on amended PDA for 14 days at 25°C and an inoculum suspension was prepared for each isolate by rinsing culture plates with 2 ml of autoclaved reverse osmosis (RO) water amended with Tween 20 (0.01%) and re-suspended into 40 ml of RO water containing Tween 20. The final concentration was adjusted to 2.6×105 conidia/ml (TW003-21) and 2×105 conidia/ml (TW008-21). Ten corn plants were sprayed with 10 ml of inoculum suspension for each isolate using a Preval sprayer with a CO2 canister, and 10 plants were sprayed with water containing Tween 20 only. Plants were incubated in a growth chamber at ≈79% relative humidity and 25°C. Foliar symptoms including small, circular, and tan lesions, similar to those observed in the field, developed 3 days after inoculation. No symptoms were observed on control plants. Following incubation, symptomatic leaves were collected and C. lunata was re-isolated as described above. Colony, spore morphology and DNA sequences from inoculated plants were consistent with the original isolates as described above. The disease has been recently reported in Louisiana (Garcia-Aroca et al. 2018), Kentucky (Anderson et al. 2019), and Delaware (Henrickson et al. 2021). Although Curvularia leaf spot has been observed sporadically in MS corn fields since 2009 (Allen, personal communication), to our knowledge, this is the first official report of the disease in MS. While this disease has been more frequently encountered in MS, the economic impact associated with C. lunata is currently unknown. References Anderson, N. R., et al. 2019. Plant Dis. 103:2692. Chang, J., et al. 2020. J. Integr. Agr. 19:551-560. Ellis, M. B. 1971. Dematiaceous Hyphomycetes. Commonwealth Mycological Institute, Kew, England, p. 452-458. Garcia-Aroca T., et al. 2018. Plant Health Prog. 19:140. Henrickson M., et al. 2021. Plant Dis. First Look. Mabadeje, S. A. 1969. Trans. Br. Mycol. Soc. 52:267-271. † Indicates the corresponding author. E-mail: [email protected]

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464 Distribution of Sugars in Sweet Corn

HortScience ◽

10.21273/hortsci.34.3.524d ◽

1999 ◽

Vol 34 (3) ◽

pp. 524D-524

Author(s):

V.M. Russo ◽

T. Smith

Keyword(s):

Zea Mays ◽

Correlation Analysis ◽

Plant Development ◽

Developmental Stages ◽

Sweet Corn ◽

Sugar Content ◽

The Other ◽

Fresh Market ◽

Leaf Stage ◽

Corn Plants

Sweet corn (Zea mays L.) kernels are sinks, and sugars found in kernels must be translocated from a source. Stalk tissues can act as a source and a sink as sweet corn plants age. Quantity and types of sugars present in various sweet corn tissues during plant development are not well documented. Concentrations of fructose, glucose, sucrose, and their total were determined in the ninth stalk internodes (I9) from the 12-leaf stage (V12) to fresh-market maturity (R3) in sweet corn cultivars carrying either the su1se1, su1, or sh2 endosperm genotype. Developing ears were sampled at tassel emergence (VN) and silking (R1). Kernels and cob tissue were sampled separately at blister stage (R2) and R3. Correlation analysis was performed on concentrations of sugars at all developmental stages. In I9, from V12 to R3, levels of fructose and glucose declined and sucrose increased. In developing ears, concentrations of fructose and glucose increased from VN to R1. Concentrations of sugars in cobs in all cultivars were generally the same at R2 and R3. In kernels from R2 to R3 in the su1se1 cultivar, glucose decreased while the other sugars were unchanged; in the su1 cultivar, fructose decreased while levels of the other sugars stayed the same; and in the sh2 cultivar, fructose decreased, glucose was unchanged and sucrose increased. Correlation analysis suggested that the cultivars moved sugars to the kernels differently. The pattern of movement of sugars to kernels was most complex in the su1se1 cultivar than in the su1, which was more comlex than in the sh2 cultivar. Knowing how sugar content changes in the plant may be used to predict sugar content in kernels.

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Host Specificity and Variations in Aggressiveness of North Carolina Isolates of Phytophthora cryptogea and P. drechsleri in Greenhouse Ornamental Plants

Plant Disease ◽

10.1094/pdis-02-12-0170-re ◽

2013 ◽

Vol 97 (1) ◽

pp. 74-80 ◽

Cited By ~ 7

Author(s):

H. A. Olson ◽

D. M. Benson

Keyword(s):

North Carolina ◽

Host Specificity ◽

Plant Species ◽

Root Rot ◽

Ornamental Plants ◽

Phytophthora Root Rot ◽

Phytophthora Cryptogea ◽

Foliar Symptoms ◽

Single Host ◽

African Marigold

Three isolates of Phytophthora cryptogea and three isolates of P. drechsleri were evaluated for host specificity and variations in aggressiveness on eight floriculture crops commonly grown in North Carolina. Plants were monitored for the development of foliar symptoms stemming from root rot caused by Phytophthora. No isolates of P. cryptogea or P. drechsleri had the same host range, though all P. cryptogea isolates caused foliar symptoms on gerbera daisy and annual stock, and all P. drechsleri isolates incited disease on osteospermum. No African marigold plants developed foliar symptoms of Phytophthora root rot. All P. cryptogea isolates caused foliar symptoms on at least three tested plant species. Isolates of P. drechsleri varied from highly specific and only causing disease on a single host species to relatively nonspecific and causing foliar symptoms on the majority of host plants. This is the first report of host specificity of ornamental isolates of P. drechsleri, and several of the tested plants are not reported hosts of P. drechsleri. Differences in isolate aggressiveness were found and depended on plant species; overall, isolates of P. drechsleri were more aggressive than P. cryptogea isolates. Isolations from nonsymptomatic inoculated plants suggest that these Phytophthora spp. could be moved between growers or from growers to consumers on nonsymptomatic infected ornamentals.

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First Report of Bacterial Root Rot, Caused by Dickeya dadantii, on Sweetpotato (Ipomoea batatas) in North Carolina

Plant Disease ◽

10.1094/pdis-03-20-0568-pdn ◽

2020 ◽

Vol 104 (10) ◽

pp. 2723-2723

Author(s):

M. N. Stahr ◽

S. Butler ◽

A. I. Huerta ◽

D. F. Ritchie ◽

L. M. Quesada-Ocampo

Keyword(s):

North Carolina ◽

Root Rot ◽

Ipomoea Batatas ◽

Dickeya Dadantii ◽

First Report

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First Report of Stem and Root Rot of Stevia Caused by Sclerotium rolfsii in North Carolina

Plant Disease ◽

10.1094/pdis-12-13-1238-pdn ◽

2014 ◽

Vol 98 (7) ◽

pp. 1005-1005 ◽

Cited By ~ 4

Author(s):

A. Koehler ◽

H. Shew

Keyword(s):

United States ◽

North Carolina ◽

Root Rot ◽

Mycelial Growth ◽

Sclerotium Rolfsii ◽

Pathogenic Fungi ◽

The United States ◽

Penicillin G ◽

Stem Tissue ◽

First Report

Stevia (Stevia rebaundia) is an emerging crop in the United States. Once established, the crop is grown for 3 to 5 years and is typically harvested twice per growing season. Stevia leaves contain multiple glycosides that are used as a natural noncaloric sweetener that was approved by the USDA in 2008 as a sugar substitute. In commercial plantings of Stevia in North Carolina, wilting and death of plants in first- and second-year plantings were observed in 2012 and 2013. Diseased plants were observed in multiple counties in the state, with first symptoms observed in May of each year and continuing through the summer months. Prior to Stevia, these fields had been planted primarily in a corn-soybean rotation. Symptoms began as moderate to severe wilting of young shoots and chlorosis of leaves, rapidly followed by death of stems and rotting of roots. White mycelial growth was frequently observed at the base of stem tissue. Theses characteristic hyphae of Sclerotium rolfsii were often accompanied by the presence of abundant white to brown sclerotia. Isolations from infected root and stem tissue were made on potato dextrose agar amended with 50 μg/ml of streptomycin sulfate and penicillin G. Isolations from diseased tissue yielded characteristic white hyphae of S. rolfsii (1,3). Numerous sclerotia 0.5 to 2 mm in diameter developed following 4 to 7 days of mycelial growth. Sclerotia were initially white and melanized turning brown with age. To verify pathogenicity, 10-week-old Stevia seedlings were transplanted in 10-cm diameter pots containing sterile 1:1:1 sand, loam, media mix. Inoculum consisted of oat grains infested with one isolate obtained from the field plants. Oats were sterilized on three consecutive days and then inoculated with colonized agar plugs of S. rolfsii. Oats were incubated at room temperature to allow the fungus to thoroughly colonize the oats. Three infested oat grains were added to each test pot and plants were then observed over a 3-week period. Symptoms were observed within 5 days on most plants and included chlorotic leaves, bleached stems, wilting, and necrotic roots. White mycelium and abundant sclerotia were found at the base of plants. Uninoculated plants did not develop any symptoms. This is the first report of S. rolfsii on Stevia in the United States. Kamalakannan et al. (2) reported a root rot disease of Stevia in India and confirmed S. rolfsii as the causal agent. References: (1) R. Aycock. N.C. Agr. Exp. St. Tech. Bull. No. 174, 1966. (2) A. Kamalakannan et al. Plant Pathol. 56:350, 2007. (3) J. E. M. Mordue. Corticium rolfsii. CMI Descriptions of Pathogenic Fungi and Bacteria No. 410. CAB International, Wallingford, UK, 1974.

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Agronomic performance of super-sweet corn genotypes in the north of Rio de Janeiro

Cropp Breeding and Applied Biotechnology ◽

10.1590/s1984-70332014000100002 ◽

2014 ◽

Vol 14 (1) ◽

pp. 8-14 ◽

Cited By ~ 9

Author(s):

Pedro Henrique Araújo Diniz Santos ◽

Messias Gonzaga Pereira ◽

Roberto dos Santos Trindade ◽

Keila Silva da Cunha ◽

Geovana Cremonini Entringer ◽

...

Keyword(s):

Rio De Janeiro ◽

Sweet Corn ◽

Northern Region ◽

Agronomic Performance ◽

Corn Hybrids ◽

Breeding Lines ◽

The North ◽

Field Corn ◽

Genetic Value ◽

Single Cross Hybrids

We investigated the agronomic performance of super-sweet corn genotypes. Super-sweet corn genotypes were backcrossed with regionally adapted field varieties (CIMMYT 8 and Piranão 8). Eight morphological and yield-related traits were evaluated. A significant effect of interaction was observed between the five groups of genotypes (donor parents; super-sweet backcrossed parents; super-sweet intervarietal hybrids; common intervarietal corn hybrids; and field corn populations). Despite the low yield of genotype SH2Piranão, the hybrids resulting from interbreeding of the backcrossed parents for the improvement of super-sweet corn were promising. The agronomic performance of the super-sweet parents and their hybrids indicates the possibility of breeding lines with high genetic value to obtain single-cross hybrids and cultivars of super-sweet corn adapted to the northern region of the State of Rio de Janeiro.

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First Report of Phakopsora pachyrhizi on Kudzu (Pueraria montana var. lobata) in North Carolina and Increased Incidence of Soybean Rust on Soybean in 2006

Plant Disease ◽

10.1094/pdis-91-5-0637a ◽

2007 ◽

Vol 91 (5) ◽

pp. 637-637 ◽

Cited By ~ 3

Author(s):

S. R. Koenning ◽

J. W. Frye ◽

S. C. Butler ◽

T. C. Creswell

Keyword(s):

North Carolina ◽

Leaf Tissue ◽

Diagnostic Techniques ◽

Soybean Rust ◽

Phakopsora Pachyrhizi ◽

Tissue Samples ◽

First Report ◽

The North ◽

Two Samples ◽

Pueraria Montana

Asian soybean rust, caused by Phakopsora pachyrhizi H. Sydow & Sydow, was first detected in the continental United States in soybean (Glycine max (L.) Merr.) in Louisiana on 6 November 2004 (3) and in kudzu (Pueraria montana var. lobata) in Florida during February 2005 (1). Soybean rust was first confirmed in North Carolina in commercial soybean fields in Brunswick, Columbus, and Robeson counties on 25 October 2005 (2). Subsequently, the disease was detected in soybean in 18 counties, but not in kudzu, even when it was growing adjacent to infected soybean. During 2006, soybean rust was first detected in North Carolina in soybean on 14 September 2006 from a sample from Columbus County that was submitted to the North Carolina State University Plant Disease and Insect Clinic (NCSU-PDIC). Thus, the first detection of soybean rust in North Carolina occurred almost 6 weeks earlier in 2006 than in 2005. Subsequently, in 2006, soybean rust was found in soybean in 42 counties in North Carolina through survey, sentinel plot monitoring, and samples submitted to the NCSU-PDIC. In addition, what appeared to be soybean rust was observed in two samples of kudzu collected on 3 and 6 November 2006 from Moore (35.28313°N, 79.38020°W) and Johnston (35.42742°N, 78.18154°W) counties of North Carolina. The diagnosis of P. pachyrhizi in kudzu was confirmed visually and by ELISA protocol supplied with the EnviroLogix QualiPlate kit (Portland, ME). ELISA tests for each kudzu sample were run in triplicate. PCR was also conducted on infected kudzu samples with a protocol previously reported (1). The PCR master mix that was used came from a dilution scheme based on previous PCR work completed by G. Z. Abad. A total of 24 reactions were run, including four 1-kb molecular markers, four positive controls, four negative controls, and four infected kudzu leaf tissue samples. The results of all diagnostic techniques confirmed the presence of P. pachyrhizi in diseased kudzu. To our knowledge, this is the first report of P. pachyrhizi in kudzu in North Carolina. References: (1) P. F. Harmon et al. Online publication. doi:10.1094/PHP-2005-0613-01-RS. Plant Health Progress, 2005. (2) S. R. Koenning et al. Plant Dis. 90:973, 2006. (3) R. W. Schneider et al. Plant Dis. 89:774, 2005.

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First Report of Root Rot and Crown Necrosis Caused by Pythium aphanidermatum on Phaseolus vulgaris in Oman

Plant Disease ◽

10.1094/pdis-08-14-0795-pdn ◽

2015 ◽

Vol 99 (3) ◽

pp. 419-419 ◽

Cited By ~ 4

Author(s):

I. H. Al-Mahmooli ◽

A. R. Al-Fahdi ◽

A. M. Al-Sadi ◽

M. L. Deadman

Keyword(s):

Phaseolus Vulgaris ◽

Root Rot ◽

Pythium Aphanidermatum ◽

Phaseolus Vulgaris L ◽

Management Options ◽

First Report ◽

The North ◽

Bean Plants ◽

Hand Control ◽

Terminal Complexes

In March 2013, 90% of mature bean plants (Phaseolus vulgaris L. cv. Kendo) grown on a commercial farm in the north of Oman (Barka) developed symptoms of root rot and necrotic streaks on the crown area of the stem and wilted. A Pythium spp. was isolated consistently from roots and basal stems on 2.5% potato dextrose agar (PDA) and V8 (100% vegetable juice) plus 1.5% agar technical. Colonies of Pythium spp. on PDA and V8 plus agar developed abundant aerial mycelia, with the main hyphae being up to 10 μm wide. Zoosporangia were made up of terminal complexes of swollen hyphal branches of different lengths and up to 22 μm wide. Oogonia were terminal, globose, and smooth with a 26-μm diameter (average of 20). Antheridia were mostly intercalary, sometimes terminal, and broadly sac-shaped, 15 μm long and 11 μm wide (average of 20). Oospores were aplerotic, 23 μm in diameter (average of 24), with walls 1 to 2 μm thick at 25°C (ambient temperature). The internal transcribed spacer of the ribosomal DNA (ITS1 and ITS4) sequence of the isolates matched the sequence of Pythium aphanidermatum (Edson) Fitzp. in GenBank. The sequence of isolate Py1 was deposited in GenBank as Accession No. KM102739. This isolate was identified as P. aphanidermatum on the basis of morphological and cultural characteristics (1) and the ITS rDNA sequence. The ITS was found to share 100% nucleotide similarity to previously published sequences of the ITS (KJ755088). To fulfill Koch's postulate, a 5-mm plug of 5-day-old mycelium of isolate Py1 grown on 2.5% PDA was used to inoculate healthy seedlings of beans cv. Kendo. The plug was placed adjacent to the bean stem; PDA served as a control. Five replicate plants were used for the treatment and the control. The plants were maintained in a glasshouse at a temperature of 23 to 25°C. The plants were watered every day. The irrigation water had an electrical conductivity value of 0.2 dSm−1. Eleven days after inoculation, 90% of the plants developed root rot, crown necrosis, and wilt symptoms similar to those observed in the field. On the other hand, control plants did not show any symptoms. The pathogen was re-isolated from roots and basal stems of symptomatic plants. To our knowledge, this is the first report of P. aphanidermatum as the causal agent of root and crown necrosis of mature bean plants in Oman. Future studies should focus on evaluating management options for this disease to avoid possible losses in a crop that has a high export value in Oman. Reference: (1) Y. Serrano et al. Plant Dis. 92:174, 2008.

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