First Report of Phytophthora nicotianae on Bulb Onion in the United States

Phytophthora nicotianae (synonym P. parasitica) Breda de Haan was isolated from recently harvested onion bulbs (Allium cepa) in cold storage from a commercial field in southern New Mexico. Deteriorating, water-soaked tissue from the center of four bulbs was plated onto water agar and incubated at room temperature. After 72 h, cultures of Phytophthora (identified by the presence of coenocytic hyphae and papillate sporangia) were isolated and transferred to V8 agar amended with ampicillin (250 mg/liter), rifampicin (10 mg/liter), and pimaricin (0.2% wt/vol). Isolates were identified as P. nicotianae based on morphological characteristics and DNA analysis. Sporangia were sharply papilliate, noncaducous, and ovoid to spherical. The average sporangium size was 45.9 × 39.9 μm with a length-to-width ratio of 1.15. Clamydospores, both terminal and intercalary, were spherical to ovoid and averaged 37.2 × 35.2 μm (2). PCR from whole-cell extracts was performed on four cultured isolates from the infected onion tissue using previously described primers ITS4 and ITS6, which amplify the 5.8S rDNA and ITS1 and ITS2 internal transcribed spacers (1,4). A band of approximately 890 bp was amplified and directly sequenced (GenBank Accession No. HQ398876). A BLAST search of the NCBI total nucleotide collection revealed a 100% similarity to multiple P. nicotianae isolates previously sequenced (1). To confirm the pathogenicity of the isolates, onion seedlings were inoculated with 25 ml of P. nicotionae zoospore solution (15,000 zoospores/ml). Necrosis of leaf tissue and seedling death was observed 5 days postinoculation. P. nicotianae was reisolated from the infected onion seedlings and the ITS region was sequenced to confirm its identity. P. nicotianae was previously reported in bulb onion from Australia, Taiwan (Formosa), and Zimbabwe (Rhodesia) (2). P. nicotianae was reported on bunching onions (A. fistulosum) in Hawaii in 1989 (3). Onions are an important crop in New Mexico with a total production value of 47 million dollars in 2008 (NM Agriculture Statistics 2008). This discovery of a potentially significant postharvest disease poses a threat to the onion industry in New Mexico. To our knowledge, this is the first report of P. nicotianae in bulb onion in the United States and the first report of P. nicotianae in New Mexico on any crop. References: (1) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (2) D. C. Erwin and O. K. Ribeiro. Page 56 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) R. D. Raabe et al. Information Text Series No. 22. University of Hawaii. Hawaii Inst. Trop. Agric. Human Resources, 1981. (4) T. J. White et al. Page 315 in: PCR Protocols: A Guide to Methods and Applications. M. A. Innis et al., eds. Academic Press, San Diego, 1990.

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First Report of Stem and Foliage Blight of Chrysanthemum Caused by Phytophthora drechsleri in the United States

Plant Disease ◽

10.1094/pdis-03-21-0631-pdn ◽

2021 ◽

Author(s):

Charles Krasnow ◽

Nancy Rechcigl ◽

Jennifer Olson ◽

Linus Schmitz ◽

Steven N. Jeffers

Keyword(s):

United States ◽

South Carolina ◽

Sequence Similarity ◽

Morphological Characteristics ◽

The United States ◽

Universal Primers ◽

Broad Host Range ◽

Pathogenicity Test ◽

First Report ◽

Foliage Blight

Chrysanthemum (Chrysanthemum × morifolium) plants exhibiting stem and foliage blight were observed in a commercial nursery in eastern Oklahoma in June 2019. Disease symptoms were observed on ~10% of plants during a period of frequent rain and high temperatures (26-36°C). Dark brown lesions girdled the stems of symptomatic plants and leaves were wilted and necrotic. The crown and roots were asymptomatic and not discolored. A species of Phytophthora was consistently isolated from the stems of diseased plants on selective V8 agar (Lamour and Hausbeck 2000). The Phytophthora sp. produced ellipsoid to obpyriform sporangia that were non-papillate and persistent on V8 agar plugs submerged in distilled water for 8 h. Sporangia formed on long sporangiophores and measured 50.5 (45-60) × 29.8 (25-35) µm. Oospores and chlamydospores were not formed by individual isolates. Mycelium growth was present at 35°C. Isolates were tentatively identified as P. drechsleri using morphological characteristics and growth at 35°C (Erwin and Ribeiro 1996). DNA was extracted from mycelium of four isolates, and the internal transcribed spacer (ITS) region was amplified using universal primers ITS 4 and ITS 6. The PCR product was sequenced and a BLASTn search showed 100% sequence similarity to P. drechsleri (GenBank Accession Nos. KJ755118 and GU111625), a common species of Phytophthora that has been observed on ornamental and vegetable crops in the U.S. (Erwin and Ribeiro 1996). The gene sequences for each isolate were deposited in GenBank (accession Nos. MW315961, MW315962, MW315963, and MW315964). These four isolates were paired with known A1 and A2 isolates on super clarified V8 agar (Jeffers 2015), and all four were mating type A1. They also were sensitive to the fungicide mefenoxam at 100 ppm (Olson et al. 2013). To confirm pathogenicity, 4-week-old ‘Brandi Burgundy’ chrysanthemum plants were grown in 10-cm pots containing a peat potting medium. Plants (n = 7) were atomized with 1 ml of zoospore suspension containing 5 × 103 zoospores of each isolate. Control plants received sterile water. Plants were maintained at 100% RH for 24 h and then placed in a protected shade-structure where temperatures ranged from 19-32°C. All plants displayed symptoms of stem and foliage blight in 2-3 days. Symptoms that developed on infected plants were similar to those observed in the nursery. Several inoculated plants died, but stem blight, dieback, and foliar wilt were primarily observed. Disease severity averaged 50-60% on inoculated plants 15 days after inoculation. Control plants did not develop symptoms. The pathogen was consistently isolated from stems of symptomatic plants and verified as P. drechsleri based on morphology. The pathogenicity test was repeated with similar results. P. drechsleri has a broad host range (Erwin and Ribeiro 1996; Farr et al. 2021), including green beans (Phaseolus vulgaris), which are susceptible to seedling blight and pod rot in eastern Oklahoma. Previously, P. drechsleri has been reported on chrysanthemums in Argentina (Frezzi 1950), Pennsylvania (Molnar et al. 2020), and South Carolina (Camacho 2009). Chrysanthemums are widely grown in nurseries in the Midwest and other regions of the USA for local and national markets. This is the first report of P. drechsleri causing stem and foliage blight on chrysanthemum species in the United States. Identifying sources of primary inoculum may be necessary to limit economic loss from P. drechsleri.

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First Report of Alternaria Leaf Spot of Banana Caused by Alternaria alternata in the United States

Plant Disease ◽

10.1094/pdis-01-13-0007-pdn ◽

2013 ◽

Vol 97 (8) ◽

pp. 1116-1116 ◽

Cited By ~ 3

Author(s):

V. Parkunan ◽

S. Li ◽

E. G. Fonsah ◽

P. Ji

Keyword(s):

United States ◽

Alternaria Alternata ◽

Leaf Spot ◽

Morphological Characteristics ◽

The United States ◽

Its Sequencing ◽

Single Spore ◽

First Report ◽

Alternaria Leaf Spot ◽

Leaf Spots

Research efforts were initiated in 2003 to identify and introduce banana (Musa spp.) cultivars suitable for production in Georgia (1). Selected cultivars have been evaluated since 2009 in Tifton Banana Garden, Tifton, GA, comprising of cold hardy, short cycle, and ornamental types. In spring and summer of 2012, 7 out of 13 cultivars (African Red, Blue Torres Island, Cacambou, Chinese Cavendish, Novaria, Raja Puri, and Veinte Cohol) showed tiny, oval (0.5 to 1.0 mm long and 0.3 to 0.9 mm wide), light to dark brown spots on the adaxial surface of the leaves. Spots were more concentrated along the midrib than the rest of the leaf and occurred on all except the newly emerged leaves. Leaf spots did not expand much in size, but the numbers approximately doubled during the season. Disease incidences on the seven cultivars ranged from 10 to 63% (10% on Blue Torres Island and 63% on Novaria), with an average of 35% when a total of 52 plants were evaluated. Six cultivars including Belle, Ice Cream, Dwarf Namwah, Kandarian, Praying Hands, and Saba did not show any spots. Tissue from infected leaves of the seven cultivars were surface sterilized with 0.5% NaOCl, plated onto potato dextrose agar (PDA) media and incubated at 25°C in the dark for 5 days. The plates were then incubated at room temperature (23 ± 2°C) under a 12-hour photoperiod for 3 days. Grayish black colonies developed from all the samples, which were further identified as Alternaria spp. based on the dark, brown, obclavate to obpyriform catenulate conidia with longitudinal and transverse septa tapering to a prominent beak attached in chains on a simple and short conidiophore (2). Conidia were 23 to 73 μm long and 15 to 35 μm wide, with a beak length of 5 to 10 μm, and had 3 to 6 transverse and 0 to 5 longitudinal septa. Single spore cultures of four isolates from four different cultivars were obtained and genomic DNA was extracted and the internal transcribed spacer (ITS1-5.8S-ITS2) regions of rDNA (562 bp) were amplified and sequenced with primers ITS1 and ITS4. MegaBLAST analysis of the four sequences showed that they were 100% identical to two Alternaria alternata isolates (GQ916545 and GQ169766). ITS sequence of a representative isolate VCT1FT1 from cv. Veinte Cohol was submitted to GenBank (JX985742). Pathogenicity assay was conducted using 1-month-old banana plants (cv. Veinte Cohol) grown in pots under greenhouse conditions (25 to 27°C). Three plants were spray inoculated with the isolate VCT1FT1 (100 ml suspension per plant containing 105 spores per ml) and incubated under 100% humidity for 2 days and then kept in the greenhouse. Three plants sprayed with water were used as a control. Leaf spots identical to those observed in the field were developed in a week on the inoculated plants but not on the non-inoculated control. The fungus was reisolated from the inoculated plants and the identity was confirmed by morphological characteristics and ITS sequencing. To our knowledge, this is the first report of Alternaria leaf spot caused by A. alternata on banana in the United States. Occurrence of the disease on some banana cultivars in Georgia provides useful information to potential producers, and the cultivars that were observed to be resistant to the disease may be more suitable for production. References: (1) E. G. Fonsah et al. J. Food Distrib. Res. 37:2, 2006. (2) E. G. Simmons. Alternaria: An identification manual. CBS Fungal Biodiversity Center, Utrecht, Netherlands, 2007.

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First Report of Fusarium proliferatum Causing Root Rot on Soybean (Glycine max) in the United States

Plant Disease ◽

10.1094/pdis-04-11-0346 ◽

2011 ◽

Vol 95 (10) ◽

pp. 1316-1316 ◽

Cited By ~ 18

Author(s):

M. M. Díaz Arias ◽

G. P. Munkvold ◽

L. F. Leandro

Keyword(s):

United States ◽

Root Rot ◽

Morphological Characteristics ◽

Dry Weight ◽

The United States ◽

Growth Stages ◽

Species Identity ◽

First Report ◽

Soybean Roots ◽

Soybean Diseases

Fusarium spp. are widespread soilborne pathogens that cause important soybean diseases such as damping-off, root rot, Fusarium wilt, and sudden death syndrome. At least 12 species of Fusarium, including F. proliferatum, have been associated with soybean roots, but their relative aggressiveness as root rot pathogens is not known and pathogenicity has not been established for all reported species (2). In collaboration with 12 Iowa State University extension specialists, soybean roots were arbitrarily sampled from three fields in each of 98 Iowa counties from 2007 to 2009. Ten plants were collected from each field at V2-V3 and R3-R4 growth stages (2). Typical symptoms of Fusarium root rot (2) were observed. Symptomatic and asymptomatic root pieces were superficially sterilized in 0.5% NaOCl for 2 min, rinsed three times in sterile distilled water, and placed onto a Fusarium selective medium. Fusarium colonies were transferred to carnation leaf agar (CLA) and potato dextrose agar and later identified to species based on cultural and morphological characteristics. Of 1,230 Fusarium isolates identified, 50 were recognized as F. proliferatum based on morphological characteristics (3). F. proliferatum isolates produced abundant, aerial, white mycelium and a violet-to-dark purple pigmentation characteristic of Fusarium section Liseola. On CLA, microconidia were abundant, single celled, oval, and in chains on monophialides and polyphialides (3). Species identity was confirmed for two isolates by sequencing of the elongation factor (EF1-α) gene using the ef1 and ef2 primers (1). Identities of the resulting sequences (~680 bp) were confirmed by BLAST analysis and the FUSARIUM-ID database. Analysis resulted in a 99% match for five accessions of F. proliferatum (e.g., FD01389 and FD01858). To complete Koch's postulates, four F. proliferatum isolates were tested for pathogenicity on soybean in a greenhouse. Soybean seeds of cv. AG2306 were planted in cones (150 ml) in autoclaved soil infested with each isolate; Fusarium inoculum was applied by mixing an infested cornmeal/sand mix with soil prior to planting (4). Noninoculated control plants were grown in autoclaved soil amended with a sterile cornmeal/sand mix. Soil temperature was maintained at 18 ± 1°C by placing cones in water baths. The experiment was a completely randomized design with five replicates (single plant in a cone) per isolate and was repeated three times. Root rot severity (visually scored on a percentage scale), shoot dry weight, and root dry weight were assessed at the V3 soybean growth stage. All F. proliferatum isolates tested were pathogenic. Plants inoculated with these isolates were significantly different from the control plants in root rot severity (P = 0.001) and shoot (P = 0.023) and root (P = 0.013) dry weight. Infected plants showed dark brown lesions in the root system as well as decay of the entire taproot. F. proliferatum was reisolated from symptomatic root tissue of infected plants but not from similar tissues of control plants. To our knowledge, this is the first report of F. proliferatum causing root rot on soybean in the United States. References: (1) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004. (2) G. L. Hartman et al. Compendium of Soybean Diseases. 4th ed. The American Phytopathologic Society, St. Paul, MN, 1999. (3) J. F. Leslie and B. A. Summerell. The Fusarium Laboratory Manual. Blackwell Publishing, Oxford, UK, 2006. (4) G. P. Munkvold and J. K. O'Mara. Plant Dis. 86:143, 2002.

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First Report of Leaf Blight on Fan Columbine (Aquilegia flabellata) Caused by Rhizoctonia solani AG 4 in Italy

Plant Disease ◽

10.1094/pdis-93-4-0433a ◽

2009 ◽

Vol 93 (4) ◽

pp. 433-433 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Rhizoctonia Solani ◽

Aqueous Suspension ◽

Morphological Characteristics ◽

The United States ◽

Leaf Blight ◽

Herbaceous Plant ◽

Pathogenicity Test ◽

First Report ◽

Leaf Petiole

Aquilegia flabellata (Ranunculaceae), fan columbine, is a perennial herbaceous plant with brilliant blue-purple flowers with white petal tips. It can also be grown for cut flower production. In April of 2008, in several nurseries located near Biella (northern Italy), a leaf blight was observed on 10 to 15% of potted 30-day-old plants grown on a sphagnum peat substrate at 15 to 20°C and relative humidity of 80 to 90%. Semicircular, water-soaked lesions developed on leaves just above the soil line at the leaf-petiole junction and later along the leaf margins. Lesions expanded over several days along the midvein until the entire leaf was destroyed. Blighted leaves turned brown, withered, and abscised. Severely infected plants died. Diseased tissue was disinfested for 10 s in 1% NaOCl, rinsed with sterile water, and plated on potato dextrose agar (PDA) amended with 25 mg/liter streptomycin sulfate. A fungus with the morphological characteristics of Rhizoctonia solani was consistently recovered, then transferred and maintained in pure culture. Ten-day-old mycelium grown on PDA at 22 ± 1°C appeared light brown, rather compact, and had radial growth. Sclerotia were not present. Isolates obtained from affected plants successfully anastomosed with tester isolate AG 4 (AG 4 RT 31, obtained from tobacco plants). Results were consistent with other reports on anastomosis reactions (2). Pairings were also made with tester isolates of AG 1, 2.1, 2.2, 3, 6, 7, 11, and BI with no anastomoses observed between the recovered and tester isolates. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 and sequenced. BLASTn analysis (1) of the 648-bp fragment showed a 100% homology with the sequence of R. solani AG-4 AB000018. The nucleotide sequence has been assigned GenBank Accession No. FJ 534555. For pathogenicity tests, the inoculum of R. solani was prepared by growing the pathogen on PDA for 10 days. Five plants of 30-day-old A. flabellata were grown in 3-liter pots. Inoculum consisting of an aqueous suspension of PDA and mycelium disks (5 g of mycelium + agar per plant) was placed at the collar of plants. Five plants inoculated with water and PDA fragments alone served as control treatments. Plants were maintained in a greenhouse at temperatures between 20 and 24°C. The first symptoms, similar to those observed in the nursery, developed 7 days after the artificial inoculation. R. solani was consistently reisolated from infected leaves and stems. Control plants remained healthy. The pathogenicity test was carried out twice with similar results. The presence of R. solani AG1-IB on A. flabellata has been reported in Japan (4), while in the United States, Rhizoctonia sp. is described on Aquilegia sp. (3). This is, to our knowledge, the first report of leaf blight of A. flabellata caused by R. solani in Italy as well as in Europe. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) D. E. Carling. Grouping in Rhizoctonia solani by hyphal anastomosis reactions. In: Rhizoctonia Species: Taxonomy, Molecular Biology, Ecology, Pathology and Disease Control. Kluwer Academic Publishers, The Netherlands, 1996. (3) D. F. Farr et al. Fungi on Plants and Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (4) E. Imaizumi et al. J. Gen. Plant Pathol. 66:210, 2000.

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First Report of Powdery Mildew Caused by Golovinomyces cichoracearum on Crotalaria juncea (‘Tropic Sun’ Sunn hemp)

Plant Disease ◽

10.1094/pdis-93-4-0427a ◽

2009 ◽

Vol 93 (4) ◽

pp. 427-427 ◽

Cited By ~ 4

Author(s):

A. J. Gevens ◽

G. Maia ◽

S. A. Jordan

Keyword(s):

United States ◽

Powdery Mildew ◽

Cover Crop ◽

Morphological Characteristics ◽

The United States ◽

Universal Primers ◽

Crotalaria Juncea ◽

First Report ◽

Golovinomyces Cichoracearum ◽

Sunn Hemp

Crotalaria juncea L. (Fabaceae), commonly known as sunn hemp, is a subtropical annual legume grown in the United States as a cover crop that improves soil quality, provides nitrogen, suppresses weeds and nematodes, and adds organic matter to soils. In Florida, sunn hemp is a warm- and short-season cover crop that is typically planted in June and cut and incorporated into soil in September. In 2008, powdery mildew was observed on sunn hemp in a research field in Hastings, FL. This disease is important because it has the potential to impact the health and quality of sunn hemp, and this particular powdery mildew can infect cucurbits that are grown in north Florida from late summer to fall. Fungal growth appeared as typical white, powdery mildew colonies initially seen on upper leaf surfaces, especially along the midvein of infected leaves, but moving to undersides as disease progressed; petioles and floral parts were disease free. As disease progressed, colonies enlarged and coalesced to cover the entire leaf surface; heavily infected leaves senesced and abscised. Infection was primarily seen on the lower, more mature leaves of plants and not on the top 0.6 m (2 feet) of the plant. Mycelia produced white accumulations of conidiophores and conidia. Hyphae were superficial with papillate appressoria and produced conidiophores with cylindrical foot cells that measured 48.5 × 10.0 μm (mean of 100 foot cell measurements) and short chains of conidia. Conidia were hyaline, short-cylindrical to ovoid, lacked fibrosin bodies, borne in chains, had sinuate edge lines with other immature conidia, and measured 22.5 to 40.0 (mean = 29.85 μm) × 12.5 to 20.0 μm (mean = 15.55 μm). The teleomorph was not observed. The nuclear rDNA internal transcribed spacer (ITS) regions were amplified by PCR, using universal primers ITS1 and ITS4, and sequenced (GenBank Accession No. FJ479803). On the basis of morphological characteristics of the asexual, imperfect state that are consistent with published reports of Golovinomyces cichoracearum (2) and ITS sequence data that indicated 100% homology with G. cichoracearum from Helianthus annus (GenBank Accession No. AB077679), this powdery mildew was identified as caused by G. cichoracearum of the classification Golovinomyces Clade III (3). Pathogenicity was confirmed by gently pressing disease leaves onto leaves of healthy C. juncea plants. Inoculated plants were placed into plastic bags containing moist paper towels to maintain high humidity. The temperature was maintained at 24°C, and after 2 days, powdery mildew colonies developed in a manner consistent with symptoms observed under field conditions. A powdery mildew on Crotalaria was previously identified as caused by Microsphaera diffusa Cooke & Peck (1). To our knowledge, this is the first report of G. cichoracearum causing powdery mildew on C. juncea. References: (1) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (2) D. A. Glawe et al. Online publication. doi: 10.1094/PHP-2006-0405-01-BR. Plant Health Progress, 2006. (3) S. Takamatsu et al. Mycol. Res. 110:1093, 2006.

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First Report of Curvularia Blight of Zoysiagrass Caused by Curvularia lunata in the United States

Plant Disease ◽

10.1094/pdis-92-1-0173b ◽

2008 ◽

Vol 92 (1) ◽

pp. 173-173 ◽

Cited By ~ 2

Author(s):

J. A. Roberts ◽

L. P. Tredway

Keyword(s):

United States ◽

North Carolina ◽

Morphological Characteristics ◽

Microscopic Analysis ◽

The United States ◽

Curvularia Lunata ◽

One Pot ◽

Plastic Container ◽

First Report ◽

Initial Symptoms

Symptoms of an unknown foliar blight have been observed in zoysiagrass (Zoysia matrella, Z. japonica, and hybrids) landscapes in North Carolina since 2002. Disease activity is most common during spring and summer when temperatures are between 21 and 30°C. Affected leaves initially exhibit small, chocolate brown spots, followed by dieback of leaves from the tips, and eventually blighting of entire tillers. Symptoms appear in small, irregular patches as much as 15 cm in diameter, but numerous patches may coalesce to impact large sections of turf. Infected turf appears tan or brown from a distance, but often turns black during periods of wet or humid weather. Microscopic analysis revealed profuse sporulation of Curvularia spp. on the surface of symptomatic leaves. Leaf sections were surface disinfested in 10% Clorox for 1 to 2 min, blotted dry, then plated on potato dextrose agar (PDA) containing 50 mg/l of tetracycline, streptomycin, and chloramphenicol. Twenty-eight fungal isolates were obtained from six locations. Examination of conidia produced in culture revealed 21 isolates of Curvularia, two isolates of Drechslera, one isolate of Nigrospora, and four unidentified sterile fungi. Curvularia isolates were identified to species on the basis of morphological characteristics (1) and ITS-rDNA sequences. Known isolates of C. eragrostidis, C. geniculata, C. inequalis, C. lunata, C. pallescens, and C. trifolii were obtained from the American Type Culture Collection for comparison. All unknown isolates produced conidia that were characteristic of C. lunata (lacking a protuberant hilum, smooth walled, tri-septate, predominantly curved, and mid- or dark brown, average dimensions 17 to 25 × 8 to 12 μm). Colonies on PDA lacked stroma or the zonate appearance indicative of C. lunata var. aeria. The pathogenicity of C. lunata isolates was tested on zoysiagrass cvs. El Toro (Z. japonica) and Emerald (Z. japonica × matrella). Cores (11.4 cm in diameter) of established zoysiagrass were potted in calcined clay (Turface Allsport; Profile Products LLC, Buffalo Grove, IL), and transferred to a greenhouse where the average temperature was 26°C. Five isolates were selected to represent the geographic range of Curvularia blight in North Carolina, and conidia were produced on PDA under continuous fluorescent illumination. Each isolate was inoculated to one pot of each zoysiagrass variety by spraying with 25 ml of a suspension containing 2 × 105 conidia/ml with an airbrush. Inoculated pots were placed in a sealed, nontransparent plastic container for 48 h at 28°C to encourage infection and then transferred back to the greenhouse bench. Pathogenicity tests were repeated four times over time. Isolates ZFB3 and ZFB28 were most virulent with initial symptoms of foliar dieback appearing within 1 week after inoculation. Continued disease progress resulted in necrosis of the entire plant. Other isolates induced symptoms within 2 to 3 weeks after inoculation; however, disease severity was lower as compared with ZFB3 and ZFB28 throughout each experiment. Cvs. Emerald and El Toro were equally susceptible to infection by C. lunata. To our knowledge, this is the first report of Curvularia blight of zoysiagrass in the United States. This disease was previously described in Japan where it is commonly referred to as ‘dog footprint’ (3) and Brazil (2). References: (1) M. B. Ellis. Dematiaceous Hyphomycetes. CMI, Kew, Surrey, UK, 1971. (2) F. B. Rocha et al. Australas. Plant Pathol. 33:601, 2004. (3) T. Tani and J. B. Beard. Color Atlas of Turfgrass Diseases. Ann Arbor Press, Chelsea, MI, 1997.

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First Report of Myrothecium roridum Causing Leaf Spot on Garden Hydrangea in the United States

Plant Disease ◽

10.1094/pdis-04-10-0264 ◽

2010 ◽

Vol 94 (10) ◽

pp. 1266-1266 ◽

Cited By ~ 7

Author(s):

M. T. Mmbaga ◽

Y. Li ◽

M.-S. Kim

Keyword(s):

United States ◽

Leaf Spot ◽

Incubation Temperature ◽

Morphological Characteristics ◽

The United States ◽

Control Treatment ◽

Medium Size ◽

First Report ◽

Detached Leaves ◽

Myrothecium Roridum

Garden hydrangea (Hydrangea macrophylla) is a popular flowering shrub that grows well in Tennessee but foliar diseases impact their appearance, health, and market value. Leaves of garden hydrangea showed necrotic lesions with concentric rings of brown and dark brown at the Tennessee State University Research Center in McMinnville. A fungus was recovered from June and July leaf samples with 20% frequency of isolation from approximately 40 leaf pieces that were surface sterilized and plated in potato dextrose agar (PDA). Isolates developed white colonies and dark gray-to-black, spore-bearing mycelial cushions (sporodochia) that formed on older colonies (30 to 45 days old) at 25 ± 2°C. Conidia were hyaline to slightly dark, one-celled, ovoid to elongate with rounded ends, and 2.0 to 2.5 × 5.5 to 6.5 μm. These morphological characteristics were consistent with those described for Myrothecium roridum Tode ex Fr. (1). DNA sequence for three isolates of this fungus showed identical internal transcribed spacer (ITS) region sequences (GenBank Accession No. HM215150) with 99% maximum sequence identity to M. roridum isolates (GenBank Accession Nos. AJ301994.1 and AJ608978). Another close match (97%) was with M. gramineum (GenBank Accession No. FJ235084) and M. tongaense (GenBank Accession No. AY254157). Pathogenicity of M. roridum was evaluated on detached leaves from three hydrangea cultivars, Nikko Blue, All Summer Beauty, and Blue bird. Four, medium-size, detached leaves were placed in moist chambers and inoculated with 5-mm mycelial plugs from 14-day-old cultures; sterile PDA was used as the control treatment. A randomized, complete-block experimental design was used with a replication of four leaves per cultivar. Incubation temperature was 26 ± 2°C. Necrotic lesions started 4 to 5 days after inoculation in all inoculated leaves; lesions expanded to cover 10 to 25% of the leaf surface and formed concentric rings; sterile PDA plugs did not produce leaf lesions. This experiment was repeated twice and similar symptoms were produced; M. roridum was reisolated from all inoculated leaves. Spray inoculation of detached leaves of hydrangea cv. Pretty Maiden with 5 × 104 spores/ml produced similar symptoms; leaves sprayed with water remained symptom free. M. roridum has a wide host range and similar symptoms have been reported on other ornamentals including salvia (2), begonia ( http://mrec.ifas.ufl.edu/foliage/folnotes/begonias.htm ), gardenia ( http://cfextension.ifas.ufl.edu/agriculture/ nursery_production/ documents/Gardenia.pdf ), and cotton (3). To our knowledge, this is the first report of M. roridum causing leaf spot on H. macrophylla in the United States. References: (1) M. B. Ellis. Page 465 in: More Damatacous Hyphomycetes. CABI, Wallingford, UK. 1993. (2) J. A. Mangandi et al. Plant Dis. 91:772, 2007. (3) R. L. Munjal. Indian Phytopathol. New Delhi, 13:150, 1960.

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First Report of Root Rot Caused by Fusarium solani on Benincasa hispida in the United States

Plant Disease ◽

10.1094/pdis-06-11-0494 ◽

2012 ◽

Vol 96 (2) ◽

pp. 294-294 ◽

Cited By ~ 2

Author(s):

P. Ji ◽

J. Yin ◽

K. L. Jackson

Keyword(s):

United States ◽

Dna Sequences ◽

Root Rot ◽

Morphological Characteristics ◽

The United States ◽

First Report ◽

Benincasa Hispida ◽

Field Samples ◽

Vegetable Farm ◽

Wax Gourd

Root rot was observed on wax gourd (Benincasa hispida (Thunb.) Cogn.) cv. Black Giant in August 2010 in a commercial vegetable farm in southern Georgia. Approximately 5% of the plants were affected and infected roots turned light to dark brown with partial or entire roots affected and the lower leaves became wilted. Symptomatic roots from six plants were surface sterilized with 0.6% sodium hypochlorite and plated on potato dextrose agar (PDA) medium. Pure cultures had white mycelia and spore masses and were obtained from all six plants by subculturing hyphal tips onto PDA. One- to two-celled, oval- to kidney-shaped microconidia and cylindrical macroconidia with two or three cells plus apical and basal cell were produced, which averaged 12.5 × 4 μm and 28 × 4.5 μm, respectively. Microconidia were abundant and macroconidia were sparse on PDA. Single-spore isolates were obtained and identified as a Fusarium sp. by PCR analysis with primers ITS-Fu-f and ITS-Fu-r (1). Genomic DNA of two isolates obtained from different plants was extracted and a portion of the translation elongation factor 1-α (TEF) gene of the isolates was amplified and sequenced (3). When compared with sequences available in the GenBank database, DNA sequences of the two isolates (GenBank Accession No. JF928376) shared 100% sequence identity with F. solani strain FRC S1734 (GenBank Accession No. DQ247527). The fungus was identified as F. solani (Mart.) Sacc. based on molecular analysis and morphological characteristics (2). Oat grains were separately infected with two isolates, BG2a and BG6, and used to inoculate healthy, 3-week-old wax gourd seedlings (cv. Black Giant) under greenhouse conditions (14-h photoperiod, 24 to 30°C). Each seedling was grown in a 10-cm pot containing a commercial potting mix, and five healthy plants were inoculated with each isolate by placing 15 infected oat grains around each plant at a depth of 5 cm in the soil. Five plants treated with noninfected oat grains served as controls. Symptoms identical to those on field samples developed on all inoculated plants 3 weeks after inoculation but not on the control plants. F. solani was reisolated from inoculated symptomatic plants and the identity was confirmed, which completed Koch's postulates. The experiment was repeated one more time under similar conditions. To our knowledge, this is the first report of root rot caused by F. solani on wax gourd in the United States. Wax gourd is an important specialty crop in the southeastern United States and the occurrence of this disease needs to be taken into account in wax gourd production. References: (1) K. A. Abd-Elsalam et al. Afr. J. Biotechnol. 2:82, 2003. (2) C. Booth. Fusarium Laboratory Guide to the Identification of the Major Species. CMI, Kew, England, 1977. (3) D. M. Geiser et al. Eur. J. Plant Pathol. 110:473, 2004.

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First Report of Collar and Root Rot Caused by Phytophthora nicotianae on Daphne odora in Italy

Plant Disease ◽

10.1094/pdis-93-8-0848a ◽

2009 ◽

Vol 93 (8) ◽

pp. 848-848

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

United States ◽

Root Rot ◽

The United States ◽

Phytophthora Nicotianae ◽

Control Treatment ◽

Peat Moss ◽

Late Winter ◽

American Phytopathological Society ◽

First Report ◽

Daphne Odora

Daphne odora is becoming popular in gardens because of its variegated foliage and fragrant flowers in late winter and early spring. During October of 2008 in a commercial nursery near Maggiore Lake (Verbano-Cusio-Ossola Province) in northwestern Italy, plants of D. odora showed extensive chlorosis and root rot. Diseased plants eventually wilted and died, dropping leaves in some cases. Most frequently, wilted leaves persisted on stems. At the soil level, dark brown-to-black water-soaked lesions that coalesced often girdled the stem. All of the crown and root system was affected. Disease was widespread and severe with 70% of 2,500 potted plants being affected. A Phytophthora-like organism was isolated consistently on a medium selective for oomycetes (4) after disinfestation of lower stem and root pieces of D. odora for 1 min in a solution containing 1% NaOCl. Tissue fragments of 1 mm2 were excised from the margins of the lesions and plated. The pathogen was identified based on morphological and physiological features as Phytophthora nicotianae (= P. parasitica) (2). Sporangia were produced for identification by growing a pure culture in sterilized soil extract solution at neutral pH (obtained by shaking and then centrifuging 300 g of soil in 1 liter of distilled water). They were spherical to ovoid, papillate, and measured 39.2 to 54.5 × 31.7 to 41.7 μm (average 44.8 × 34.5 μm). Papillae measured 2.4 to 4.9 μm (average 3.7 μm). Chlamydospores were spherical with a diameter ranging from 15.8 to 36.1 μm (average 25.4 μm). The internal transcribed spacer (ITS) region of rDNA of a single isolate was amplified using primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 804-bp segment showed a 100% homology with the sequence of P. nicotianae EF140988. The nucleotide sequence has been assigned GenBank No. FJ843100. Pathogenicity of two isolates obtained from infected plants was confirmed by inoculating 12-month-old plants of D. odora. Both isolates were grown for 15 days on a mixture of 70:30 wheat/hemp kernels and then 80 g/liter of the inoculum was mixed into a substrate containing sphagnum peat moss/pumice/pine bark/clay (50:20:20:10 vol/vol). One plant per 3-liter pot was transplanted into the substrate and constituted the experimental unit. Three replicates were used for each isolate and noninoculated control treatment; the trial was repeated once. All plants were kept in a greenhouse at temperatures from 20 to 25°C. Plants inoculated with isolate no. 1 developed symptoms of chlorosis and root rot within 14 days and then a wilt rapidly followed. Isolate no. 2 was less aggressive causing the same symptoms within 20 days. Control plants remained symptomless. P. nicotianae consistently was reisolated from inoculated plants. Previously, P. nicotianae (= P. parasitica) has been reported in several states of the United States on D. odora (3). To our knowledge, this is the first report of P. nicotianae on D. odora in Italy. The economic importance of the disease is low because of the limited number of farms that grow this crop in Italy, although spread could increase as the popularity of plantings expand. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997 (2) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. The American Phytopathological Society, St Paul, MN, 1996. (3) D. F. Farr et al. Fungi on Plants and Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (4) H. Masago et al. Phytopathology, 67:425, 1977.

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First Report of Septoria Leaf Spot of Pistachio in New Mexico

Plant Disease ◽

10.1094/pdis-93-7-0762c ◽

2009 ◽

Vol 93 (7) ◽

pp. 762-762

Author(s):

J. M. French ◽

R. J. Heerema ◽

E. A. Gordon ◽

N. P. Goldberg

Keyword(s):

New Mexico ◽

Leaf Spot ◽

Morphological Characteristics ◽

The United States ◽

The State ◽

Department Of Agriculture ◽

Widespread Occurrence ◽

Agricultural Industry ◽

First Report ◽

Septoria Leaf Spot

In September of 2008, a Septoria sp., the causal agent of Septoria leaf spot of pistachio (Pistacia vera L.) was isolated from leaf lesions in an orchard in southern New Mexico. Tree fruit and nut crops including pistachios are becoming an increasingly important part of New Mexico's agricultural industry with total cash receipts of $103 million in 2007 (3). This preliminary positive for Septoria prompted a survey of pistachio-growing counties in the state. The surveyed orchards accounted for approximately 30% of the pistachio acreage in New Mexico. Results indicated that all five pistachio-growing counties had orchards infected with a Septoria sp. Isolates of Septoria from leaf lesions were identified as Septoria pistaciarum Caracc. based on the following symptoms and morphological characteristics of the fungus: leaf lesions were usually circular, 0.5 to 3 mm in diameter, and contained many pycnidia per lesion; pycnidia were dark, ostiolate, and measured 101 to 255 × 69 to 133 μm; and conidia were hyaline, filiform, contained 3 to 9 septa, and measured 3 to 4 × 60 to 149 μm. Most orchards were only mildly affected. In severe cases, hundreds of leaf lesions were present on diseased leaves; large sections of the leaves turned tan and some trees defoliated prematurely. This widespread occurrence of Septoria leaf spot in New Mexico in 2008 suggests that the disease had already been present in the state for several years. A higher average rainfall in the summer of 2008 provided excellent conditions for disease development. Because of the high amounts of inoculum currently present in New Mexico orchards, Septoria leaf spot may emerge as a recurring disease problem for pistachio producers. This disease was first reported in the United States in Texas in 1971 and was also reported in Arizona in 1989 (1,2,4). To our knowledge, this is the first report of Septoria leaf spot of pistachio in New Mexico. References: (1) A. Chitzandis. Ann. Inst. Phytopathol. Benaki 10:29, 1956. (2) J. L. Maas et al. Plant Dis. Rep. 55:72, 1971. (3) New Mexico Agricultural Statistics, Department of Agriculture, 2007. (4) D. J. Young and T. Michailides. Plant Dis. 73:775, 1989.

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