Dicentra, Epimedium, and Heuchera: New Perennial Ornamental Hosts of Tobacco rattle virus in the United States

Yellow ringspotting and concentric line patterns in plants of Dicentra (bleeding heart), Epimedium (barrenwort), and Heuchera (coral bells) from commercial nurseries and home gardens in Minnesota, Michigan, and Massachusetts were associated with infection by Tobacco rattle virus (TRV), which was identified by particle morphology, enzyme-linked immunosorbent assay and immunosorbent electron microscopy. No other viruslike particles were observed by electron microscopy in partially purified preparations of TRV-infected leaf tissue, and TRV was not detected in asymptomatic plants. This is the first report of TRV occurrence in Dicentra in the United States and the first report of TRV occurrence in Epimedium and Heuchera. In previous reports (1,2) we have called attention to the increasing incidence of TRV in vegetatively propagated perennial ornamental plant species in the United States and to the potential for virus spread to crops such as potato, in which TRV has not been reported in the midwestern United States. It is possible that increased international trade in vegetatively propagated ornamental plants may be resulting in the introduction of TRV and other exotic viruses into the United States and elsewhere. It is also possible that the natural occurrence of TRV in North America may be actually more widespread than has been reported. References: (1) B. E. Lockhart et al. Plant Dis. 79:1249, 1995. (2) B. E. Lockhart and J. A. Westendorp. Plant Dis. 82:712, 1998.

Download Full-text

First Report of Alfalfa mosaic virus Occurrence in Hydrangea in the United States

Plant Disease ◽

10.1094/pdis-07-12-0618-pdn ◽

2013 ◽

Vol 97 (9) ◽

pp. 1258-1258 ◽

Cited By ~ 4

Author(s):

B. Lockhart ◽

D. Mollov ◽

M. Daughtrey

Keyword(s):

Electron Microscopy ◽

United States ◽

Mosaic Virus ◽

Alfalfa Mosaic Virus ◽

Leaf Tissue ◽

The United States ◽

Spherical Particles ◽

Genomic Sequences ◽

Rt Pcr ◽

First Report

In spring of 2012, a previously unrecorded virus-like disease characterized by conspicuous yellow leaf blotching (calico symptoms) was observed in plants of Hydrangea macrophylla in a single location in Southampton, NY. Bacilliform and spherical particles resembling those of Alfalfa mosaic virus (AMV) were observed by transmission electron microscopy (TEM) in partially purified extracts from symptomatic leaf tissue. The identity of the virus was confirmed by immunosorbent electron microscopy (ISEM) (4) using antiserum to AMV (ATCC PVAS 92) that both trapped and decorated the virions. Three primer pairs designed from available AMV RNA 1, RNA 2, and RNA 3 genomic sequences were used to generate amplicons from the hydrangea AMV isolate. Reverse-transcription (RT)-PCR was done using total RNA extracted from symptomatic hydrangea leaf tissue with a Qiagen RNeasy kit, and Ready-to-Go RT-PCR beads (GE Healthcare). Amplicons of 1,049, 1,013, and 658 bp were obtained using the primer pairs AMV1F (5′-ATCCACCGATGCCAGCCTTA)/AMV1R (5′-TTCCGCCTCACTGCTGTCTG), AMV2F (5′-GATCGCCGGAAGTGATCCAG)/AMV2R (5′-TCACCGGAAGCAACAACGAA), and AMV3F (5′-GCCGGTTCTCCAAAGGGTCT)/AMV3R (5′-CGCGTCGAAGTCCAGACAGA), respectively. The PCR products were cloned using a TOPO TA cloning kit (Invitrogen) and three clones of each were sequenced. The sequences obtained from the hydrangea AMV RNA 1 (JX154090), RNA 2 (JX154091), and RNA 3 (JX154092) had 95 to 98% nucleotide sequence identity to homologous genomic sequences of known AMV isolates. To our knowledge, this is the first report of AMV occurrence in H. macrophylla in the United States. This virus has been reported to occur in H. macrophylla in British Columbia (3), but in a previous survey its presence was not detected in hydrangeas in the United States (1). A report of possible AMV infection in H. macrophylla in Italy (2) was based solely on symptomatology and cross-protection tests and therefore cannot be verified. The AMV-infected hydrangea plants were found by ISEM to also contain low concentrations of Hydrangea ringspot virus (HRSV) and Hydrangea chlorotic mottle virus (HdCMV). However, based on previous evidence of single and mixed infections (3), it is unlikely that the calico symptoms observed were influenced by the presence of HRSV and HdCMV. This report is of interest both because AMV, unlike HRSV and HdCMV, causes foliar symptoms that would render hydrangea plant unmarketable, and because the disease can be spread by a number of common aphid species that transmit AMV. It will also serve to alert growers and diagnosticians to the potential threat posed by AMV infection. References: (1) T. C. Allen et al. Acta Hortic. 164:85, 1985. (2) G. Belli. Phytopathol. Mediterr. 7:70, 1968. (3) A. W. Chiko and S. E. Godkin. Plant Dis. 70:541, 1986. (4) B. E. L. Lockhart et al. Phytopathology 82:691, 1992.

Download Full-text

First Report of Soybean Rust Caused by Phakopsora pachyrhizi on Pachyrhizus erosus in the United States

Plant Disease ◽

10.1094/pdis-07-10-0483 ◽

2011 ◽

Vol 95 (8) ◽

pp. 1034-1034

Author(s):

M. A. Delaney ◽

E. J. Sikora ◽

D. P. Delaney ◽

M. E. Palm ◽

J. Roscoe ◽

...

Keyword(s):

United States ◽

Ribosomal Rna ◽

Agricultural Research ◽

The United States ◽

University Teaching ◽

Soybean Rust ◽

Infected Leaf ◽

Phakopsora Pachyrhizi ◽

First Report ◽

Pachyrhizus Erosus

Soybean rust, caused by the fungus Phakopsora pachyrhizi, was detected on jicama (Pachyrhizus erosus L. Urban) for the first time in the United States in November 2009. The pathogen was observed on leaves of a single, potted jicama plant grown outdoors in a residential area and on leaves of all plants in a 12-m2 demonstration plot located at the Auburn University Teaching Garden in Auburn, AL. Symptoms on the upper leaf surfaces were isolated chlorotic areas near the leaf edges in the lower part of the canopy. The abaxial surface was first observed to exhibit brown lesions and subsequently produced volcano-shaped uredinia. These symptoms are consistent with a rust previously described on jicama in Mexico (1). Representative symptomatic plant tissue was sent to the USDA National Identification Services (Mycology) Laboratory in Beltsville, MD for diagnostic confirmation at both the Urbana, IL lab and the USDA National Plant Germplasm and Biotechnology Laboratory for DNA testing. From an infected leaf, samples of approximately 5 mm2 were excised from a microscopically observed rust lesion and an apparently noninfected area. Total DNA was purified with the FastDNA Spin Kit (MP Biomedicals, Solon, OH) followed by the E.Z.N.A. MicroElute DNA Clean-Up Kit (Omega Bio-tek, Inc, Doraville, GA) per manufacturer's instructions. Detection of P. pachyrhizi and P. meibomiae DNA was achieved by quantitative PCR using the method of Frederick et al. (2) and a DNA standard of previously prepared P. pachyrhizi spores. The observed rust pustule was found to contain P. pachyrhizi DNA in excess of 28,000 genomes, while no P. pachyrhizi DNA was observed from the asymptomatic sample. Both samples were negative for P. meibomiae. The fungal structures present were confirmed to be Phakopsora spp. DNA was extracted from sori aseptically removed from leaves with a Qiagen (Valencia, CA) DNeasy Plant Mini Kit and amplified with primers Ppa1 and NL4. The resulting partial ITS2 and 28S ribosomal RNA sequences were 100% identical to GenBank entry DQ354537 P. pachyrhizi internal transcribed spacer 2 and 28S ribosomal RNA gene, partial sequence. Sequences from jicama from Alabama were deposited in GenBank. Voucher specimens were deposited in the USDA Agricultural Research Service, National Fungus Collection (BPI). To our knowledge, this is the first report of the disease on jicama in the United States. References: (1) A. Cárcamo Rodriguez et al. Plant Dis. 90:1260, 2006. (2) R. D. Frederick et al. Phytopathology 92:217, 2002.

Download Full-text

First report of Coleus blumei viroid 1 in commercial Coleus blumei in the United States

Plant Disease ◽

10.1094/pdis-05-21-0917-pdn ◽

2021 ◽

Author(s):

Gardenia Orellana ◽

Alexander V Karasev

Keyword(s):

United States ◽

Leaf Tissue ◽

The United States ◽

Universal Primers ◽

Rt Pcr ◽

Universal Primer ◽

Tissue Samples ◽

First Report ◽

Specific Pcr ◽

Coleus Blumei

Coleus scutellarioides (syn. Coleus blumei) is a widely grown evergreen ornamental plant valued for its highly decorative variegated leaves. Six viroids, named Coleus blumei viroid 1 to 6 (CbVd-1 to -6) have been identified in coleus plants in many countries of the world (Nie and Singh 2017), including Canada (Smith et al. 2018). However there have been no reports of Coleus blumei viroids occurring in the U.S.A. (Nie and Singh 2017). In April 2021, leaf tissue samples from 27 cultivars of C. blumei, one plant of each, were submitted to the University of Idaho laboratory from a commercial nursery located in Oregon to screen for the presence of viroids. The sampled plants were selected randomly and no symptoms were apparent in any of the samples. Total nucleic acids were extracted from each sample (Dellaporta et al. 1983) and used in reverse-transcription (RT)-PCR tests (Jiang et al. 2011) for the CbVd-1 and CbVd-5 with the universal primer pair CbVds-P1/P2, which amplifies the complete genome of all members in the genus Coleviroid (Jiang et al. 2011), and two additional primer pairs, CbVd1-F1/R1 and CbVd5-F1/R1, specific for CbVd-1 and CbVd-5, respectively (Smith et al. 2018). Five C. blumei plants (cvs Fire Mountain, Lovebird, Smokey Rose, Marrakesh, and Nutmeg) were positive for a coleviroid based on the observation of the single 250-nt band in the RT-PCR test with CbVds-P1/P2 primers. Two of these CbVd-1 positive plants (cvs Lovebird and Nutmeg) were also positive for CbVd-1 based on the presence of a single 150-nt band in the RT-PCR assay with CbVd1-F1/R1 primers. One plant (cv Jigsaw) was positive for CbVd-1, i.e. showing the 150-nt band in RT-PCR with CbVd1-F1/R1 primers, but did not show the ca. 250-bp band in RT-PCR with primers CbVds-P1/P2. None of the tested plants were positive for CbVd-5, either with the specific, or universal primers. All coleviroid- and CbVd-1-specific PCR products were sequenced directly using the Sanger methodology, and revealed whole genomes for five isolates of CbVd-1 from Oregon, U.S.A. The genomes of the five CbVd-1 isolates displayed 96.9-100% identity among each other and 96.0-100% identity to the CbVd-1 sequences available in GenBank. Because the sequences from cvs Lovebird, Marrakesh, and Nutmeg, were found 100% identical, one sequence was deposited in GenBank (MZ326145). Two other sequences, from cvs Fire Mountain and Smokey Rose, were deposited in the GenBank under accession numbers MZ326144 and MZ326146, respectively. To the best of our knowledge, this is the first report of CbVd-1 in the United States.

Download Full-text

First Report of Downy Mildew Caused by Plasmopara obducens on Impatiens in California

Plant Disease ◽

10.1094/pdis.2004.88.8.909b ◽

2004 ◽

Vol 88 (8) ◽

pp. 909-909 ◽

Cited By ~ 14

Author(s):

S. N. Wegulo ◽

S. T. Koike ◽

M. Vilchez ◽

P. Santos

Keyword(s):

United States ◽

Downy Mildew ◽

Disease Incidence ◽

Leaf Tissue ◽

The United States ◽

Plant Diseases ◽

Single Type ◽

First Report ◽

Commercial Grower ◽

Impatiens Walleriana

During February 2004, diseased double impatiens (Impatiens walleriana) plants were received from a commercial grower in southern California. The upper surfaces of symptomatic leaves were pale yellow with no distinct lesions. Diseased leaves later wilted, and severely affected leaves abscised from the stem. At the nursery, only double impatiens plants in the Fiesta series were infected, and some cultivars were more heavily infected than others. Disease incidence in cv. Sparkler Hot pink was nearly 100%. The interior of infected leaves was colonized by coenocytic mycelium. A conspicuous white growth was observed only on the underside of leaves. Sporangiophores were hyaline, thin walled, emergent from stomata, and had slightly swollen bases. Sporangiophore branching was distinctly monopodial. Smaller sporangiophore branches were arranged at right angles to the supporting branches, and tips of branches measured 8 to 14 μm long. Sporangia were ovoid and hyaline with a single pore on the distal ends. Distal ends of sporangia were predominantly flat but occasionally had a slight papilla. Short pedicels were present on the attached ends. Sporangia measured 19.4 to 22.2 (-25.0) μm × 13.9 to 16.7 (-19.4) μm. Oospores were not observed in leaf tissue. On the basis of symptoms and morphology of the organism, the pathogen was identified as Plasmopara obducens J. Schröt. Pathogenicity tests were done on double type cvs. Fiesta, Tioga Red, and Tioga Cherry Red and on single type cvs. Cajun Watermelon and Accent Lilac. Plants were spray inoculated with sporangiospore suspensions (1 × 104 sporangiospores per milliliter), incubated for 24 h in a dew chamber (18 to 20°C), and then maintained in a greenhouse (22 to 24°C). Symptoms and signs of downy mildew developed after 12 days only on inoculated cv. Fiesta plants, and the pathogen morphology matched that of the originally observed pathogen. Nontreated control plants did not develop downy mildew. To our knowledge, this is the first report of downy mildew on impatiens in California. P. obducens is one of two causal agents of downy mildew of impatiens (2,4). The other pathogen, Bremiella sphaerosperma, has dichotomous sporangiophore branching and causes lesions with well-defined margins (2,4). In the United States, the disease has been recorded in the eastern and northeastern states and in Indiana, Minnesota, Mississippi, Montana, and Wisconsin (3). In Canada, the disease has been recorded in Manitoba and Quebec (1). References: (1) I. L. Conners. An Annotated Index of Plant Diseases in Canada and Fungi Recorded on Plants in Alaska, Canada, and Greenland. Research Branch, Canada Department of Agriculture, Publication 1251, 1967. (2) O. Constantinescu. Mycologia 83:473, 1991. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, 1989. (4) G. W. Wilson. Bull. Torrey Bot. Club 34:387, 1907.

Download Full-text

Alternanthera mosaic virus Found in Scutellaria, Crossandra, and Portulaca spp. in Florida

Plant Disease ◽

10.1094/pd-90-0833c ◽

2006 ◽

Vol 90 (6) ◽

pp. 833-833 ◽

Cited By ~ 11

Author(s):

C. A. Baker ◽

L. Breman ◽

L. Jones

Keyword(s):

Electron Microscopy ◽

United States ◽

Mosaic Virus ◽

Plant Species ◽

The United States ◽

Enzyme Linked Immunosorbent Assay ◽

Rt Pcr ◽

Indicator Plants ◽

Partial Identity ◽

Pcr Products

In the fall of 1998, the Division of Plant Industry (DPI) received vegetative propagations of Scutellaria longifolia (skullcap) with symptoms of foliar mosaic, chlorotic/necrotic ringspots, and wavy line patterns from a nursery in Manatee County. Flexuous particles approximately 500 nm long were found with electron microscopy. The plants tested positive for Papaya mosaic virus (PaMV) in an enzyme-linked immunosorbent assay (ELISA) test with antiserum to PaMV (Agdia, Elkhart, IN). However, in immunodiffusion tests (antiserum from D. Purcifull, University of Florida), this virus gave a reaction of partial identity indicating it was related but not identical to PaMV (1). The original infected plants were kept in a greenhouse. In January 2005, a specimen of Crossandra infundibuliformis (firecracker plant) with mosaic symptoms was submitted to the DPI from a nursery in Alachua County. Inclusions found with light microscopy and particles found with electron microscopy indicated that this plant was infected with a potexvirus. This was confirmed by reverse transcription-polymerase chain reaction (RT-PCR) with primers designed to detect members of the virus family Potexviridae (3). These plants reacted positive to PaMV antiserum in ELISA and gave a reaction of partial identity to PaMV in immunodiffusion. A specimen of Portulaca grandiflora (moss rose) with distorted leaves found at a local retail store was also tested and gave the same results. Leaves from each of the three plant species were rubbed onto a set of indicator plants using Carborundum and potassium phosphate buffer. Total RNA was extracted from symptomatic indicator plants of Nicotiana benthamiana. RT-PCR (3) was performed, and PCR products were sequenced directly. Sequences of approximately 700 bp were obtained for all three plant species and showed 98% identity with each other. BLAST search results showed that these sequences were 93% identical to an Alternanthera mosaic virus (AltMV) sequence at the nucleotide level but only 76% identical to PaMV. The amino acid sequences were 98 and 82% identical to AltMV and PaMV, respectively. The PCR products of the virus from Scutellaria sp. were cloned, resequenced, and the sequence was entered into the GenBank (Accession No. DQ393785). The bioassay results matched those found for AltMV in Australia (2) and the northeastern United States (4), except that the Florida viruses infected Datura stramonium and Digitalis purpurea (foxglove). The virus associated with the symptoms of these three plants appears to be AltMV and not PaMV. AltMV has been found in ornamental plants in Australia, Italy, and the United States (Pennsylvania, Maryland, and now Florida). Since this virus is known to infect several plants asymptomatically and can be easily confused with PaMV serologically, it is likely that the distribution of this virus is much wider than is known at this time. References: (1) L. L. Breman. Plant Pathology Circular No. 396. Fla. Dept. Agric. Consum. Serv. DPI, 1999. (2) A. D. W. Geering and J. E. Thomas. Arch Virol 144:577, 1999. (3) A. Gibbs et al. J Virol Methods 74:67, 1998. (4) J. Hammond et al. Arch Virol. 151:477, 2006.

Download Full-text

First Report of Alternanthera mosaic virus Infection in Angelonia in the United States

Plant Disease ◽

10.1094/pdis-92-10-1473b ◽

2008 ◽

Vol 92 (10) ◽

pp. 1473-1473 ◽

Cited By ~ 7

Author(s):

B. E. Lockhart ◽

M. L. Daughtrey

Keyword(s):

United States ◽

Nucleotide Sequence ◽

Mosaic Virus ◽

Genomic Sequence ◽

Nutrient Deficiency ◽

Leaf Tissue ◽

The United States ◽

Nucleotide Sequence Analysis ◽

Degenerate Primers ◽

First Report

Stunting, chlorosis, and light yellow mottling resembling symptoms of nutrient deficiency were observed in angelonia (Angelonia angustifolia) in commercial production in New York. Numerous, filamentous particles 520 to 540 nm long and spherical virus particles 30 nm in diameter were observed by transmission electron microscopy (TEM) in negatively stained partially purified extracts of symptomatic Angelonia leaf tissue. Two viruses, the filamentous potexvirus Alternanthera mosaic virus (AltMV) and the spherical carmovirus Angelonia flower break virus (AnFBV) were subsequently identified on the basis of nucleotide sequence analysis of amplicons generated by reverse transcription (RT)-PCR using total RNA isolated from infected leaf tissue. A 584-bp portion of the replicase-encoding region of the AltMV genome was obtained with the degenerate primers Potex 2RC (5′-AGC ATR GNN SCR TCY TG-3′) and Potex 5 (5′-CAY CAR CAR GCM AAR GAT GA-3′) (3). Forward (AnFBV CP 1F-5′-AGC CTG GCA ATC TGC GTA CTG ATA-3′) and reverse (AnFBV CP 1R-5′-AAT ACC GCC CTC CTG TTT GGA AGT-3′) primers based on the published AnFBV genomic sequence (GenBank Accession No. NC_007733) were used to amplify a portion of the viral coat protein (CP) gene. The nucleotide sequence of the amplicon generated using the potexvirus-specific primers (GenBank Accession No. EU679362) was 99% identical to the published AltMV (GenBank Accession No. NC_007731) sequence and the nucleotide sequence of the amplicon obtained using the AnFBV CP primers was 99% identical to the published AnFBV genomic sequence (GenBank Accession No. EU679363). AnFBV occurs widely in angelonia (1) and AltMV has been identified in phlox (2). These data confirm the presence of AltMV and AnFBV in diseased angelonia plants showing stunting and nutrient deficiency-like symptoms and substantiates, to our knowledge, this first report of AltMV in angelonia in the United States. References: (1) S. Adkins et al. Phytopathology 96:460, 2006. (2) J. Hammond et al. Arch. Virol. 151:477, 2006. (3) R. A. A. van der Vlugt and M. Berendeson. Eur. J. Plant Pathol. 108:367, 2002.

Download Full-text

Biological and Molecular Characterization of a Novel Carmovirus Isolated from Angelonia

Phytopathology ◽

10.1094/phyto-96-0460 ◽

2006 ◽

Vol 96 (5) ◽

pp. 460-467 ◽

Cited By ~ 14

Author(s):

Scott Adkins ◽

John Hammond ◽

Abed Gera ◽

Clarissa J. Maroon-Lango ◽

Irena Sobolev ◽

...

Keyword(s):

United States ◽

Polyacrylamide Gel Electrophoresis ◽

Sodium Dodecyl ◽

Particle Morphology ◽

The United States ◽

Open Reading Frames ◽

Enzyme Linked Immunosorbent Assay ◽

Major Protein ◽

Thin Sections ◽

Phlox Drummondii

A new carmovirus was isolated from Angelonia plants (Angelonia angustifolia), with flower break and mild foliar symptoms, grown in the United States and Israel. The virus, for which the name Angelonia flower break virus (AnFBV) is proposed, has isometric particles, ≈30 nm in diameter. The experimental host range was limited to Nicotiana species, Schizanthus pinnatus, Myosotis sylvatica, Phlox drummondii, and Digitalis purpurea. Virions were isolated from systemically infected N. benthamiana leaves, and directly from naturally infected Angelonia leaves, using typical carmovirus protocols. Koch's postulates were completed by mechanical inoculation of uninfected Angelonia seedlings with purified virions. Isometric particles were observed in leaf dips and virion preparations from both Angelonia and N. benthamiana, and in thin sections of Angelonia flower tissue by electron microscopy. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis of dissociated purified virus preparations, a major protein component with a molecular mass of 38 kDa was observed. Virion preparations were used to produce virus-specific polyclonal antisera in both Israel and the United States. The antisera did not react with Pelargonium flower break virus (PFBV), Carnation mottle virus (CarMV), or Saguaro cactus virus (SgCV) by either enzyme-linked immunosorbent assay or immunoblotting. In reciprocal tests, antisera against PFBV, CarMV, and SgCV reacted only with the homologous viruses. The complete nucleotide sequence of a Florida isolate of AnFBV and the coat protein (CP) gene sequences of Israeli and Maryland isolates were determined. The genomic RNA is 3,964 nucleotides and contains four open reading frames arranged in a manner typical of carmoviruses. The AnFBV CP is most closely related to PFBV, whereas the AnFBV replicase is most closely related to PFBV, CarMV, and SgCV. Particle morphology, serological properties, genome organization, and phylogenetic analysis are all consistent with assignment of AnFBV to the genus Carmovirus.

Download Full-text

First Report of Leaf Blight and Stem Dieback of St. John's-Wort Caused by Diploceras hypericinum in Oregon

Plant Disease ◽

10.1094/pdis.2000.84.11.1250b ◽

2000 ◽

Vol 84 (11) ◽

pp. 1250-1250 ◽

Cited By ~ 1

Author(s):

M. L. Putnam

Keyword(s):

United States ◽

Pacific Northwest ◽

Leaf Tissue ◽

The United States ◽

Leaf Blight ◽

Jefferson County ◽

Single Spore ◽

First Report ◽

St John’S Wort ◽

St John's Wort

St. John's-wort, Hypericum perforatum L., was formerly considered a noxious weed in the Pacific Northwest and is now grown commercially for its medicinal properties. In May 1999, plants from a 5-ha field in Jefferson County, OR, were observed with yellowing leaves and stem dieback. Lower leaves showed marginal necrosis or circular, expanding, uniformly brown, unremarkable leaf lesions that appeared randomly over the lamina and consumed from a quarter to nearly the entire leaf area. Remaining leaf tissue was chlorotic, and affected leaves eventually abscised. Infection of the stems resulted in girdling lesions 0.5 to 1.0 cm in length that caused chlorosis, wilting, and eventual dieback of tissues distal to the lesion. Diploceras hypericinum (Cesati) Diedicke was sporulating on affected stems and leaves. The fungus was isolated from surface-disinfested tissue onto 1.5% water agar. A single-spore isolate was used to inoculate 10-month-old plants raised from seed in sand. Spores from 6-week-old cultures grown on 50% potato-dextrose agar were harvested, suspended in phosphate buffer with 0.2% gelatin (PBG), and sprayed onto three plants using a DeVilbiss atomizer. Inoculum concentration was 7 × 103 and 3 ml per plant were used (plants were 8 to 10 cm tall). Three control plants were sprayed with sterile PBG. Inoculated and control plants were separately bagged to retain moisture and maintained at 22 to 25°C. Four days later, inoculated plants exhibited leaf spots similar to those originally observed, followed by stem dieback. D. hypericinum was isolated from all inoculated plants but not from control plants. The known distribution of D. hypericinum is France, Germany, Portugal, Sweden, Greece, and Ontario, Canada (1,2). This is the first report of D. hypericinum causing leaf blight and stem dieback of St. John's-wort in the United States. References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN. (2) T. R. Nag Raj. 1993. Coelomycetous Anamorphs with Appendage-bearing Conidia. Mycologue Publications, Waterloo, Canada.

Download Full-text

First Report of Downy Mildew Caused by Peronospora trigonellae on Fenugreek in the United States

Plant Disease ◽

10.1094/pdis-93-12-1349a ◽

2009 ◽

Vol 93 (12) ◽

pp. 1349-1349 ◽

Cited By ~ 1

Author(s):

S. Rooney-Latham ◽

C. L. Blomquist ◽

J. Turney

Keyword(s):

United States ◽

Los Angeles ◽

Sequence Data ◽

Leaf Tissue ◽

The United States ◽

Grocery Store ◽

Diagnostic Laboratory ◽

First Report ◽

Severe Stunting ◽

The United Kingdom

Fenugreek (Trigonella foenum-graecum) is a member of the Fabaceae family and is grown worldwide for culinary and medicinal purposes. The leaves are used as an herb while the seeds are used whole, ground as a spice, or germinated and used as sprouts. In November 2008, a fenugreek plant exhibiting leaf spotting and severe stunting was submitted to the CDFA Plant Pest Diagnostics Laboratory from the Los Angeles County Plant Diagnostic Laboratory. The county had received the sample from a homeowner who reported severe dieback of the fenugreek in his backyard planting. The fenugreek is grown by the resident as an annual and is propagated each year from the previous crop's seed. The seed was originally obtained from a local ethnic grocery store in Lakewood, CA. The homeowner stated that he had noticed symptoms for a number of years and that they seemed especially severe during the winter months. The adaxial surfaces of the leaves exhibited small chlorotic spots often at the leaf margins, while the abaxial surfaces exhibited a grayish violet, felty growth. Conidiophores found on the underside of the leaves branched dichotomously 6 to 10 times and were terminally forked. Conidiophores measured 280 to 525 μm (average 420 μm) with slightly swollen bases (7.5 to 10 μm broad). Conidia were slightly pigmented, oblong to ellipsoid, and measured 23 to 33 × 18 to 23 μm (average 27.8 × 20.3 μm). Globose oospores with verruculose walls measured 30 to 40 μm in diameter (average 36.1 μm) and were found embedded in the leaf tissue of older lesions. The pathogen was identified morphologically as Peronospora trigonellae Gaum. (3). Sequences of a portion of the rDNA, including the internal transcribed spacer regions, were obtained using primers DC6 and ITS6 (1). Sequence data for P. trigonellae had not previously been entered into GenBank and no identity was obtained. Pathogenicity experiments attempted by spraying healthy fenugreek seedlings with conidial suspensions were unsuccessful, presumably because of the age of the inoculum. Since fenugreek is not commercially grown in California, the economic importance of this disease is limited. Although P. trigonellae has been reported on fenugreek in Algeria, India, Pakistan, and the United Kingdom (2–4), to our knowledge, this is the first report of its occurrence in California and the United States. A specimen of P. trigonellae has been deposited in the U.S. National Fungus Collection (BPI 879153). References: (1) D. E. L. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (2) D. F. Farr et al. Fungal Databases. Systematic Mycology and Microbiology Laboratory. Online publication. ARS, USDA, 2009, (3) E. A. Gaumann. Beitr. Kryptogamenflora Schweiz 5:216, 1923. (4) D. R. Jones et al. Plant Pathol. 56:891, 2007.

Download Full-text

First Report of Quinoa Downy Mildew Caused by Peronospora variabilis in the United States

Plant Disease ◽

10.1094/pdis-09-11-0728 ◽

2012 ◽

Vol 96 (1) ◽

pp. 146-146 ◽

Cited By ~ 9

Author(s):

A. L. Testen ◽

J. M. McKemy ◽

P. A. Backman

Keyword(s):

United States ◽

Relative Humidity ◽

Downy Mildew ◽

Leaf Tissue ◽

The United States ◽

Voucher Specimen ◽

First Report ◽

Mean Width ◽

Field Samples ◽

Pink Discoloration

Quinoa, Chenopodium quinoa Willd., is an Andean crop prized for its high nutritional value and adaptability to harsh environments. Quinoa is plagued by downy mildew caused by Peronospora variabilis Gäum (formerly Peronospora farinosa f. sp. chenopodii Byford) (1). Quinoa production has spread beyond native Andean ranges and quinoa downy mildew has been reported in India, Canada, and Denmark (1). During the summer of 2011, quinoa trials were established to determine the ability of quinoa to grow under Mid-Atlantic conditions and monitor for regional disease problems. In July, after cool, rainy conditions, downy mildew-like symptoms were observed on quinoa at research plots in Centre and Lancaster counties of Pennsylvania. Symptoms and signs consisted of irregularly shaped areas of foliar chlorosis or pink discoloration accompanied by dense, gray sporulation on both leaf surfaces. Sporangia were tan to gray-brown, semi-ovoid, often with a pedicel, mean length of 31 μm, and mean width of 23 μm. Sporangiophores branched dichotomously, and the terminal branchlets curved and tapered to a point. Orange oospores were present in field samples of leaf tissue. DNA was extracted from infected foliar tissue and sporangial suspensions. A seminested PCR protocol (2) was used to obtain partial internal transcribed spacer (ITS) sequences of six Peronospora isolates. The sequences shared 99% maximum identity to a known P. variabilis accession (FM863721.2) in GenBank. A voucher specimen was deposited into the U.S. National Fungus Collections (BPI 882064). Pathogenicity of each of two strains of P. variabilis was confirmed by inoculating quinoa with sporangia (4). Sporangia were shaken from leaves in sterile distilled water and the suspension was filtered through cheesecloth. A 0.01% Tween solution was added and the suspension diluted to 103 sporangia/ml. With an atomizer, a 10-ml sporangial suspension (or sterile water for noninoculated control plants) was sprayed onto one flat of 18 2-week-old quinoa plants, and relative humidity was increased to saturation using a humidity dome for 24 h. After 1 week, chlorosis and pink discoloration were noted on leaves of inoculated quinoa, and after 18 h of subsequent increased humidity (>95% relative humidity), dense gray sporulation was observed. No symptoms were noted on noninoculated control plants. Sporangia and sporangiophores were examined morphologically and confirmed to be P. variabilis, confirming Koch's postulates. For culture maintenance, 2-week-old quinoa leaves were placed onto a sporangial suspension on top of 1% water agar and maintained in a growth chamber at 20°C with 16 h of light per day. Quinoa downy mildew is seedborne (3) and initial infections may have occurred from oospores in the pericarp, despite intensive processing of consumable quinoa seeds to remove saponins. To our knowledge, this is the first report of quinoa downy mildew in the United States and also the first report of P. variabilis in the United States. References: (1) Y. Choi et al. Mycopathologia 169:403, 2010. (2) D. Cooke et al. Fungal Genet. Biol. 30:17, 2000. (3) S. Danielson et al. Seed Sci. Technol. 32:91, 2004. (4) J. Ochoa et al. Plant Pathol. 48:425, 1999.

Download Full-text