First Report of Race 8 of Downy Mildew, Caused by Peronospora farinosa f. sp. spinaciae, of Spinach in the United States

Downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is the most economically important disease of spinach (Spinacia oleracea) in the United States and the European Union. In the United States, 23,000 ha of spinach, with a crop value of approximately $170 million, were grown during 2005 (1; http://www.nass.usda.gov/index.asp ). Additionally, per capita, fresh-market spinach consumption has increased 214% in the past decade (1; http://www.nass.usda.gov/index.asp ). Increased demand for fresh-market spinach has led to changes in spinach production practices such as higher planting densities and year-round production. There are currently 10 described races (races 1 to 10) of P. farinosa f. sp. spinaciae. Race 8 was recovered from the Netherlands in 2004 (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]), but has not been previously identified in the United States. In February 2007, several commercial fresh-market spinach fields in central Arizona were severely affected with downy mildew. Symptoms consisted of bright yellow leaf lesions ranging in size from 1 to 3 cm in diameter that supported dense purple sporulation of the pathogen on the corresponding abaxial leaf surface. Affected fields were primarily planted with spinach cv. Parrot, which is reported to be resistant to races 1 to 7 and 9. As much as 32 ha were affected and disease incidence reached as high as 25 to 30%. An isolate (PAR1) of the pathogen was obtained and used to inoculate a standard set of 10 differential spinach cultivars for race identification as previously described (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). Briefly, a spore suspension (1 × 105 sporangia per ml) was misted onto test plants; plants were then incubated in a dew chamber (20°C, 100% relative humidity) for 24 h and maintained in a greenhouse. Inoculation tests were conducted at least twice at each of two different locations (Arkansas and California), with each test including two replications of 15 plants per differential cultivar. The selective development of downy mildew on specific differentials indicated that the isolate was race 8 (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). To our knowledge, this is the first report of race 8 in the United States. Since there are a number of commercial spinach cultivars available with resistance to race 8, the economic impact of this race in the United States is expected to be low if resistant cultivars are grown (B. M. Irish, J. Correll, S. T. Koike, and T. Morelock. Plant Dis. [In press]). Reference: (1) R. N. Acharya and I. Molina. NFAPP Newsl. Second Quarter, 2005.

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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.

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First Report of Impatiens Downy Mildew Outbreaks Caused by Plasmopara obducens Throughout the Hawai'ian Islands

Plant Disease ◽

10.1094/pdis-10-13-1017-pdn ◽

2014 ◽

Vol 98 (5) ◽

pp. 696-696 ◽

Cited By ~ 7

Author(s):

J. A. Crouch ◽

M. P. Ko ◽

J. M. McKemy

Keyword(s):

United States ◽

Downy Mildew ◽

The United States ◽

Molecular Data ◽

Economic Losses ◽

Voucher Specimen ◽

First Report ◽

Plastic Bags ◽

Leaf Surfaces ◽

Impatiens Walleriana

Downy mildew of impatiens (Impatiens walleriana Hook.f.) was first reported from the continental United States in 2004. In 2011 to 2012, severe and widespread outbreaks were documented across the United States mainland, resulting in considerable economic losses. On May 5, 2013, downy mildew disease symptoms were observed from I. walleriana ‘Super Elfin’ at a retail nursery in Mililani, on the Hawai'ian island of Oahu. Throughout May and June 2013, additional sightings of the disease were documented from the islands of Oahu, Kauai, Maui, and Hawai'i from nurseries, home gardens, and botanical park and landscape plantings. Symptoms of infected plants initially showed downward leaf curl, followed by a stippled chlorotic appearance on the adaxial leaf surfaces. Abaxial leaf surfaces were covered with a layer of white mycelia. Affected plants exhibited defoliation, flower drop, and stem rot as the disease progressed. Based on morphological and molecular data, the organism was identified as Plasmopara obducens (J. Schröt.) J. Schröt. Microscopic observation disclosed coenocytic mycelium and hyaline, thin-walled, tree-like (monopodial branches), straight, 94.0 to 300.0 × 3.2 to 10.8 μm sporangiophores. Ovoid, hyaline sporangia measuring 11.0 to 14.6 × 12.2 to 16.2 (average 13.2 × 14.7) μm were borne on sterigma tips of rigid branchlets (8.0 to 15.0 μm) at right angle to the main axis of the sporangiophores (1,3). Molecular identification of the pathogen was conducted by removing hyphae from the surface of three heavily infected leaves using sterile tweezers, then extracting DNA using the QIAGEN Plant DNA kit (QIAGEN, Gaithersburg, MD). The nuclear rDNA internal transcribed spacer was sequenced from each of the three samples bidirectionally from Illustra EXOStar (GE Healthcare, Piscataway, NJ) purified amplicon generated from primers ITS1-O and LR-0R (4). Resultant sequences (GenBank KF366378 to 80) shared 99 to 100% nucleotide identity with P. obducens accession DQ665666 (4). A voucher specimen (BPI892676) was deposited in the U.S. National Fungus Collections, Beltsville, MD. Pathogenicity tests were performed by spraying 6-week-old impatiens plants (I. walleriana var. Super Elfin) grown singly in 4-inch pots with a suspension of 1 × 104 P. obducens sporangia/ml until runoff using a handheld atomizer. Control plants were sprayed with distilled water. The plants were kept in high humidity by covering with black plastic bags for 48 h at 20°C, and then maintained in the greenhouse (night/day temperature of 20/24°C). The first symptoms (downward curling and chlorotic stippling of leaves) and sporulation of the pathogen on under-leaf surfaces of the inoculated plants appeared at 10 days and 21 days after inoculation, respectively. Control plants remained healthy. Morphological features and measurements matched those of the original inoculum, thus fulfilling Koch's postulates. To our knowledge, this is the first report of downy mildew on I. walleriana in Hawai'i (2). The disease appears to be widespread throughout the islands and is likely to cause considerable losses in Hawai'ian landscapes and production settings. References: (1) O. Constantinescu. Mycologia 83:473, 1991. (2) D. F. Farr and A. Y. Rossman. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved from http://nt.ars-grin.gov/fungaldatabases/ July 16, 2013. (3) P. A. Saccardo. Syllogue Fungorum 7:242, 1888. (4) M. Thines. Fungal Genet Biol 44:199, 2007.

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First Report of Iris yellow spot virus on Onion and Leek in Western Oregon

Plant Disease ◽

10.1094/pdis-91-4-0468a ◽

2007 ◽

Vol 91 (4) ◽

pp. 468-468 ◽

Cited By ~ 5

Author(s):

D. H. Gent ◽

R. R. Martin ◽

C. M. Ocamb

Keyword(s):

United States ◽

Disease Incidence ◽

The United States ◽

Yellow Spot ◽

Onion Bulb ◽

Spot Virus ◽

First Report ◽

Seed Crop ◽

Onion Seed ◽

Seed Crops

Onion (Allium cepa) and leek (Allium porrum) are grown on approximately 600 ha in western Oregon annually for bulb and seed production. During July and August of 2006, surveys of onion bulb crops and onion and leek seed crops in western Oregon found plants with symptoms of elongated to diamond-shaped, straw-colored lesions characteristic of those caused by Iris yellow spot virus (IYSV) (1–4). Symptomatic plants were collected from fields of an onion bulb crop, an onion seed crop, and two leek seed crops located in Marion County. The onion bulb crop had been planted in the spring of 2006, and the onion and leek seed crops had been planted in the fall of 2005, all direct seeded. Cultivar names were not provided for proprietary purposes. Symptomatic plants in the onion bulb crop and leek seed crop generally were found near the borders of the field. Disease incidence was less than 5% and yield losses in these crops appeared to be negligible. In the onion seed crop, symptomatic plants were found throughout the field and disease incidence was approximately 20%. Approximately 1% of the onion plants in this field had large necrotic lesions that caused the seed stalks (scapes) to lodge. The presence of IYSV was confirmed from symptomatic leaves and scapes by ELISA (Agdia Inc., Elkhart, IN) using antiserum specific to IYSV. RNA was extracted from symptomatic areas of onion leaves and scapes, and a portion of the nucleocapsid gene was amplified by reverse transcription-PCR. The amplicons were sequenced and found to share more than 99% nucleotide and amino acid sequence identity with an onion isolate of IYSV from the Imperial Valley of California (GenBank Accession No. DQ233475). In the Pacific Northwest region of the United States, IYSV has been confirmed in the semi-arid regions of central Oregon (1), central Washington (2), and the Treasure Valley of eastern Oregon and southwest Idaho (3). To our knowledge, this is the first report of the disease on a host crop in the mild, maritime region west of the Cascade Mountain Range and the first report of IYSV on leek seed crops in the United States, which complements a simultaneous report of IYSV on commercial leek in Colorado. The presence of IYSV may have implications for the iris and other ornamental bulb industries in western Oregon and western Washington. This report underscores the need for further research to determine the impact of the disease on allium crops and other hosts and the development of effective management programs for IYSV and the vector, Thrips tabaci. References: (1) F. J. Crowe and H. R. Pappu. Plant Dis. 89:105, 2005. (2) L. J. du Toit et al. Plant Dis. 88:222, 2004. (3) J. M. Hall et al. Plant Dis. 77:952, 1993. (4) H. F. Schwartz et al. Plant Dis. 91:113, 2007.

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Three New Races of the Spinach Downy Mildew Pathogen Identified by a Modified Set of Spinach Differentials

Plant Disease ◽

10.1094/pdis-91-11-1392 ◽

2007 ◽

Vol 91 (11) ◽

pp. 1392-1396 ◽

Cited By ~ 22

Author(s):

B. M. Irish ◽

J. C. Correll ◽

S. T. Koike ◽

T. E. Morelock

Keyword(s):

United States ◽

European Union ◽

Downy Mildew ◽

The United States ◽

The European Union ◽

The Past ◽

Differential Cultivars ◽

Spinach Downy Mildew ◽

New Races ◽

Important Disease

Spinach downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is the most economically important disease of spinach worldwide. During the past few years, spinach cultivars resistant to the seven previously described races of P. farinosa f. sp. spinaciae were observed to be severely affected by downy mildew in both the United States and the European Union. Four new isolates of P. farinosa f. sp. spinaciae were collected from California and The Netherlands and characterized based on disease reactions on two modified sets of spinach differentials. The results led to the description of three new races of the downy mildew pathogen, designated races 8, 9, and 10. Four differential cultivars with resistance to races 1 to 7 were used to distinguish the three new races. Dolphin was susceptible to races 8 and 10 but resistant to race 9; Lion was susceptible to race 10 but resistant to races 8 and 9; Lazio was resistant to races 1 to 7 as well as races 8, 9, and 10; and Tarpy was susceptible to all three new races. The three new races also were used to evaluate the disease reactions on 43 contemporary commercial spinach cultivars in greenhouse trials. A survey of 58 isolates of P. farinosa f. sp. spinaciae collected in California and Arizona between 2004 and 2006 revealed that race 10 predominated in the areas sampled.

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First Report of Pseudoperonospora cubensis Causing Downy Mildew on Momordica balsamina and M. charantia in North Carolina

Plant Disease ◽

10.1094/pdis-03-14-0305-pdn ◽

2014 ◽

Vol 98 (9) ◽

pp. 1279-1279 ◽

Cited By ~ 10

Author(s):

E. Wallace ◽

M. Adams ◽

K. Ivors ◽

P. S. Ojiambo ◽

L. M. Quesada-Ocampo

Keyword(s):

United States ◽

North Carolina ◽

Downy Mildew ◽

Leaf Surface ◽

The United States ◽

Pseudoperonospora Cubensis ◽

Post Inoculation ◽

Bitter Melon ◽

First Report ◽

C Cycle

Momordica balsamina (balsam apple) and M. charantia L. (bitter melon/bitter gourd/balsam pear) commonly grow in the wild in Africa and Asia; bitter melon is also cultivated for food and medicinal purposes in Asia (1). In the United States, these cucurbits grow as weeds or ornamentals. Both species are found in southern states and bitter melon is also found in Pennsylvania and Connecticut (3). Cucurbit downy mildew (CDM), caused by the oomycete Pseudoperonospora cubensis, was observed on bitter melon and balsam apple between August and October of 2013 in six North Carolina sentinel plots belonging to the CDM ipmPIPE program (2). Plots were located at research stations in Johnston, Sampson, Lenoir, Henderson, Rowan, and Haywood counties, and contained six different commercial cucurbit species including cucumbers, melons, and squashes in addition to the Momordica spp. Leaves with symptoms typical of CDM were collected from the Momordica spp. and symptoms varied from irregular chlorotic lesions to circular lesions with chlorotic halos on the adaxial leaf surface. Sporulation on the abaxial side of the leaves was observed and a compound microscope revealed sporangiophores (180 to 200 μm height) bearing lemon-shaped, dark sporangia (20 to 35 × 10 to 20 μm diameter) with papilla on one end. Genomic DNA was extracted from lesions and regions of the NADH dehydrogynase subunit 1 (Nad1), NADH dehydrogynase subunit 5 (Nad5), and internal transcribed spacer (ITS) ribosomal RNA genes were amplified and sequenced (4). BLAST analysis revealed 100% identity to P. cubensis Nad1 (HQ636552.1, HQ636551.1), Nad5 (HQ636556.1), and ITS (HQ636491.1) sequences in GenBank. Sequences from a downy mildew isolate from each Momordica spp. were deposited in GenBank as accession nos. KJ496339 through 44. To further confirm host susceptibility, vein junctions on the abaxial leaf surface of five detached leaves of lab-grown balsam apple and bitter melon were either inoculated with a sporangia suspension (10 μl, 104 sporangia/ml) of a P. cubensis isolate from Cucumis sativus (‘Vlaspik' cucumber), or with water as a control. Inoculated leaves were placed in humidity chambers to promote infection and incubated using a 12-h light (21°C) and dark (18°C) cycle. Seven days post inoculation, CDM symptoms and sporulation were observed on inoculated balsam apple and bitter melon leaves. P. cubensis has been reported as a pathogen of both hosts in Iowa (5). To our knowledge, this is the first report of P. cubensis infecting these Momordica spp. in NC in the field. Identifying these Momordica spp. as hosts for P. cubensis is important since these cucurbits may serve as a source of CDM inoculum and potentially an overwintering mechanism for P. cubensis. Further research is needed to establish the role of non-commercial cucurbits in the yearly CDM epidemic, which will aid the efforts of the CDM ipmPIPE to predict disease outbreaks. References: (1) L. K. Bharathi and K. J. John. Momordica Genus in Asia-An Overview. Springer, New Delhi, India, 2013. (2) P. S. Ojiambo et al. Plant Health Prog. doi:10.1094/PHP-2011-0411-01-RV, 2011. (3) PLANTS Database. Natural Resources Conservation Service, USDA. Retrieved from http://plants.usda.gov/ , 7 February 2014. (4) L. M. Quesada-Ocampo et al. Plant Dis. 96:1459, 2012. (5) USDA. Index of Plant Disease in the United States. Agricultural Handbook 165, 1960.

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First Report of Tomato chlorotic dwarf viroid in Petunia hybrida from the United States of America

Plant Disease ◽

10.1094/pdis-91-3-0324b ◽

2007 ◽

Vol 91 (3) ◽

pp. 324-324 ◽

Cited By ~ 24

Author(s):

J. Th. J. Verhoeven ◽

C. C. C. Jansen ◽

A. W. Werkman ◽

J. W. Roenhorst

Keyword(s):

United States ◽

Sequence Analysis ◽

United States Of America ◽

Petunia Hybrida ◽

Plant Protection ◽

Polyacrylamide Gel Electrophoresis ◽

The United States ◽

The European Union ◽

First Report ◽

Tomato Chlorotic Dwarf Viroid

In November 2005, 13 accessions of Petunia hybrida from the United States of America entered the post-entry quarantine station of the Plant Protection Service in the Netherlands. The plants were inspected and tested for quarantine organisms according to Directives 95/44 and 97/46 of the European Union. No virus and viroid symptoms were observed in the imported plants or in mechanically inoculated plants of Chenopodium quinoa, Nicotiana benthamiana, and N. occidentalis-P1 (3). Testing for pospiviroids by return-polyacrylamide gel electrophoresis (1) and reverse transcriptase-PCR with universal pospiviroid primers Pospi1-RE/FW (2) indicated the presence of pospiviroids in 3 and 11 P. hybrida accessions, respectively. The 196-bp amplicons of six accessions were sequenced. Sequence analysis showed the highest identity for all amplicons to both isolates of Tomato chlorotic dwarf viroid (TCDVd) in NCBI GenBank, Accession Nos. AF162131and AY372399, from Canada and the United States, respectively. Additional RT-PCRs with the Pospi1-RE/FW primers in opposite order and the semi-universal pospiviroid primers Vid-RE/FW (2) for one isolate, followed by sequence analysis, confirmed the identity as TCDVd. The isolate consisted of 359 nucleotides (GenBank Accession No. DQ859013) and showed sequence identities of 98.6 and 96.1% to the Canadian and American tomato isolates of this viroid, respectively. The next highest sequence identity was 90.0% to two accessions of Potato spindle tuber viroid (GenBank Accession Nos. AJ593449 and AY962324). On the basis of these results, the viroid from P. hybrida was identified as TCDVd. To our knowledge, this is the first report of TCDVd in this plant species. Reference: (1) J. W. Roenhorst et al. EPPO Bull. 30:453, 2000. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004. (3) J. Th. J. Verhoeven and J. W. Roenhorst. EPPO Bull. 33:305, 2003.

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First Report of Downy Mildew Caused by Peronospora sp. on Agastache sp. in the United States

Plant Disease ◽

10.1094/pdis-10-15-1119-pdn ◽

2016 ◽

Vol 100 (6) ◽

pp. 1249 ◽

Cited By ~ 4

Author(s):

Y. Rivera ◽

C. Salgado-Salazar ◽

T. C. Creswell ◽

G. Ruhl ◽

J. A. Crouch

Keyword(s):

United States ◽

Downy Mildew ◽

The United States ◽

First Report

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First Report of Downy Mildew Caused by Plasmopara halstedii on Ageratum houstonianum in the United States

Plant Disease ◽

10.1094/pdis-06-19-1331-pdn ◽

2019 ◽

Vol 103 (11) ◽

pp. 2968-2968

Author(s):

C. Pisani ◽

P. C. Patel ◽

E. N. Rosskopf ◽

M. Abbasi ◽

M. C. Aime

Keyword(s):

United States ◽

Downy Mildew ◽

The United States ◽

Plasmopara Halstedii ◽

First Report

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First Report of Peronospora farinosa f. sp. spinaciae Race 5 Causing Downy Mildew on Spinach in Florida

Plant Disease ◽

10.1094/pdis.2004.88.1.84c ◽

2004 ◽

Vol 88 (1) ◽

pp. 84-84 ◽

Cited By ~ 3

Author(s):

B. M. Irish ◽

J. C. Correll ◽

R. N. Raid ◽

T. E. Morelock

Keyword(s):

Downy Mildew ◽

Disease Incidence ◽

Field Isolate ◽

The United States ◽

Economic Losses ◽

Palm Beach County ◽

First Report ◽

Leaf Spots ◽

Plant Densities ◽

Production Area

Downy mildew, caused by Peronospora farinosa f. sp. spinaciae, is an economically important disease in most areas where spinach is grown. This disease has become increasingly important in production fields for prepackaged salad mixes where plant densities typically are very high. In Florida, spinach production for these markets has reached approximately 200 ha. Currently, seven physiological races of the downy mildew pathogen have been described (1). Downy mildew was observed in several commercial spinach fields in the Everglades agricultural area of Palm Beach County, Florida in January 2003 on cvs. Unipak 151 and Merlo Nero. Symptoms appeared as chlorotic and necrotic leaf spots. Disease incidence reached approximately 25% in some field locations. Economic losses were significant, since entire plantings in several fields were not harvested as a result of diminished quality. The race of a field isolate recovered from the cv. Unipak 151 was determined following greenhouse inoculation procedures and using differentials outlined by Irish et al (1). Greenhouse inoculation tests were conducted twice. Disease reactions on a U.S. and international set of differentials indicated that the isolate was race 5. To our knowledge, this is the first report of race 5 occurring outside of the California/Arizona spinach production area in the United States. There are commercial spinach lines with resistance to race 5, as well as the other described races (1). References: (1) B. M. Irish et al. Plant Dis. 87:567, 2003.

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First Report of Downy Mildew Caused by a Peronospora sp. on Basil in Florida and the United States

Plant Disease ◽

10.1094/pdis-93-2-0199b ◽

2009 ◽

Vol 93 (2) ◽

pp. 199-199 ◽

Cited By ~ 26

Author(s):

P. D. Roberts ◽

R. N. Raid ◽

P. F. Harmon ◽

S. A. Jordan ◽

A. J. Palmateer

Keyword(s):

United States ◽

Downy Mildew ◽

Leaf Surface ◽

Sequence Data ◽

Consensus Sequence ◽

Morphological Characteristics ◽

The United States ◽

South Florida ◽

Ambient Conditions ◽

Fresh Market

Basil is grown as a specialty crop in greenhouse and field production in Florida and other regions of the United States. Downy mildew on basil (Ocimum basilicum) was detected from four production sites (Collier, Hendry, Miami-Dade, and Palm Beach counties) in south Florida in the fall of 2007, and within months, it was also found in west-central north Florida (Hillsborough County). Incidence reached nearly 100% on some of the affected crops and caused complete yield losses on basil grown both in the field for fresh market and potted herbs market. Symptoms developed during transit on basil that appeared symptomless at harvest. Symptoms initially appeared as yellowing on the lower leaves that was typically delineated by the veins, although in some cases the entire leaf area of the leaf surface was affected. A gray, fuzzy growth was apparent on the abaxial leaf surface. Microscopic observation detected dichotomous branching, hyaline sporangiophores (220 to 750 × 4 to 9 μm) bearing single sporangia. Sporangia were light brown, ovoid to slightly ellipsoid, and measured 14 to 15 × 15 to 18 μm. Oospores were not observed. Leaves of potted basil plants and coleus (Solenostemon scutellarioides) were inoculated with a suspension containing 1 × 105 sporangia/ml and sprayed till runoff (approximately 15 ml per plant) with a hand-held pressurized aerosol canister. Plants were covered with a plastic bag for 24 h and maintained in the greenhouse under ambient conditions. Noninoculated plants served as controls. After 7 days, symptoms typical of downy mildew occurred only on the inoculated basil plants and sporulation was confirmed microscopically. The internal transcribed spacer regions of an isolate collected in Hendry County were sequenced bidirectionally. The consensus sequence was deposited into GenBank (Accession No. FJ346561). Sequence data matched (100% homology) with a Peronospora sp. reported on sweet basil in Switzerland (GenBank Accession No. AY884605) and was similar (99% homology) to an isolate (GenBank Accession No. DQ523586) reported on coleus, although inoculation to coleus failed to confirm pathogenicity on this host. The sequence data also distinguished the isolate from P. lamii (87% homology) previously reported to occur on basil. The pathogen was identified as a Peronospora sp. based on morphological characteristics and sequencing homology (1–3). References: (1) L. Belbahri et al. Mycol. Res. 109:1276, 2005. (2) S. Francis. CMI Descriptions of Pathogenic Fungi and Bacteria. No. 688. CMI, Kew, England, 1981. (3) A. McLeod et al. Plant Dis. 90:1115, 2006.

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