scholarly journals First Report of Petunia Blight Caused by Choanephora cucurbitarum in the United States

Plant Disease ◽  
2003 ◽  
Vol 87 (6) ◽  
pp. 751-751 ◽  
Author(s):  
G. E. Holcomb
Keyword(s):  
United States ◽  
Morphological Characteristics ◽  
The United States ◽  
Plant Diseases ◽  
Disease Spread ◽  
American Phytopathological Society ◽  
First Report ◽  
Whole Plant ◽  
Cloudy Weather ◽  
Choanephora Cucurbitarum

A blight (wet rot) of petunia (Petunia ×hybrida Hort. Vilm.-Andr.) was observed in a wholesale propagation nursery in Baton Rouge, LA in September 2002. The grower reported that plants wilted and then completely rotted. The disease occurred during a period of hot, humid, and cloudy weather. Approximately 100 flats of flowering-age plants of cvs. Rose and White Madness were destroyed. No fungal sporulation was noticed on dead plants, but occasional strands of white mycelium were observed. The grower's use of azoxystrobin, iprodione, and thiophanate methyl plus mancozeb fungicides during current and past outbreaks of this disease did not prevent disease spread, but disease activity stopped after temperature and humidity dropped in early October. A fungus that produced white aerial mycelia that later developed light yellow areas and also black aerial spore masses was consistently isolated from diseased tissue placed on acidified potato dextrose agar (APDA). The fungus was identified as Choanephora cucurbitarum (Berk. & Ravenel) Thaxt. on the basis of cultural and morphological characteristics (3). Sporangiola were ellipsoid, pale brown to reddish brown with distinct longitudinal striations and measured 15 to 20 × 9 to 14 μm. Sporangiospores were broadly ellipsoid, pale brown to reddish brown, indistinctly striate with fine, hyaline polar appendages, and measured 16 to 34 × 7 to 12 μm. Spore measurements were within the range previously given for C.cucurbitarum (3). Pathogenicity tests were performed by misting a mixture of sporangiola and sporangiospores (25,000 to 70,000 per ml of water taken from 7- to 10-day-old cultures grown on APDA) on flowering-age petunia plants (cvs. Rose Madness, White Madness, and Dreams Pink). Tests were repeated twice. Inoculated plants and uninoculated control plants (2 to 4 of each treatment in each test) were held in a dew chamber at 28°C for 48 h and then moved to a greenhouse. Within 48 h after inoculation, plants developed water-soaked lesions on flowers, leaves, and stems, then wilted and rotted. Uninoculated plants remained disease free except for several that developed disease symptoms in the first test, apparently from the presence of natural inoculum on healthy-appearing plants that were obtained from the nursery where the disease was found. Koch's postulates were completed by reisolation of the pathogen from diseased inoculated plants. C. cucurbitarum (1) and C. infundibulifera (Curr.) Sacc. (2) have been reported to cause flower blight of petunia in the United States and whole plant blight (wet rot) of petunia in Japan (4). To our knowledge, this is the first report of C. cucurbitarum causing whole plant blight of petunia in the United States. References: (1) M. L. Daughtrey et al. Choanephora wet rot of poinsettia. Page 15 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (3) P. M. Kirk. Mycological Paper 152:1, 1984. (4) J. Takeuchi and H. Horie. Jpn. J. Phytopathol. 66:72, 2000.

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

Plant Disease ◽  
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.

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

Plant Disease ◽  
2013 ◽  
Vol 97 (8) ◽  
pp. 1116-1116 ◽  
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.

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

Plant Disease ◽  
2004 ◽  
Vol 88 (8) ◽  
pp. 909-909 ◽  
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.

scholarly journals First Report of Powdery Mildew Caused by Erysiphe aquilegiae var. aquilegiae on Aquilegia flabellata in Italy

Plant Disease ◽  
2004 ◽  
Vol 88 (6) ◽  
pp. 681-681
Author(s):  
A. Garibaldi ◽  
D. Bertetti ◽  
M. L. Gullino
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
The United States ◽  
Northern Italy ◽  
American Phytopathological Society ◽  
First Report ◽  
Powdery Mildews ◽  
The Family ◽  
White Mycelium ◽  
The University

Aquilegia flabellata Sieb. and Zucc. (columbine) is a perennial garden species belonging to the family Ranunculaceae. During the summer of 2003, a severe outbreak of a previously unknown powdery mildew was observed in several gardens near Biella (northern Italy). Upper surfaces of leaves were covered with a white mycelium and conidia, and as the disease progressed infected leaves turned yellow and died. Foot cell was cylindric and appressorium lobed. Conidia were hyaline, ellipsoid, and measured 31.2 to 47.5 × 14.4 to 33 μm (average 38.6 × 21.6 μm). Fibrosin bodies were not present. Cleistothecia were globose, brown, had simple appendages, ranged from 82 to 127 (average 105) μm in diameter, and contained one to two asci. Ascocarp appendages measured five to eight times the ascocarp diameter. Asci were cylindrical (ovoidal) and measured 45.3 to 58.2 × 30.4 to 40.2 μm. Ascospores (three to four per ascus) were ellipsoid or cylindrical and measured 28.3 to 31.0 × 14.0 to 15.0 μ;m. On the basis of its morphology, the pathogen was identified as Erysiphe aquilegiae var. aquilegiae (1). Pathogenicity was confirmed by gently pressing diseased leaves onto leaves of five, healthy A. flabellata plants. Five noninoculated plants served as controls. Inoculated and noninoculated plants were maintained in a garden where temperatures ranged between 20 and 30°C. After 10 days, typical powdery mildew symptoms developed on inoculated plants. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of the presence of powdery mildew on Aquilegia flabellata in Italy. E. communis (Wallr.) Link and E. polygoni DC. were reported on several species of Aquilegia in the United States (2), while E. aquilegiae var. aquilegiae was previously observed on A. flabellata in Japan and the former Union of Soviet Socialist Republics (3). Specimens of this disease are available at the DIVAPRA Collection at the University of Torino. References: (1) U. Braun. Nova Hedwigia, 89:700, 1987. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St Paul, MN, 1989. (3) K. Hirata. Host Range and Geographical Distribution of the Powdery Mildews. Faculty of Agriculture, Niigata University, 1966.

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

Plant Disease ◽  
2011 ◽  
Vol 95 (10) ◽  
pp. 1316-1316 ◽  
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.

scholarly journals First Report of Bremia lactucae Causing Downy Mildew on Helichrysum bracteatum in Italy

Plant Disease ◽  
2003 ◽  
Vol 87 (3) ◽  
pp. 315-315 ◽  
Author(s):  
A. Garibaldi ◽  
A. Minuto ◽  
G. Gilardi ◽  
M. L. Gullino
Keyword(s):  
Downy Mildew ◽  
Morphological Characteristics ◽  
The United States ◽  
Northern Italy ◽  
Plant Diseases ◽  
Bremia Lactucae ◽  
First Report ◽  
Parasitic Fungi ◽  
Commercial Farms ◽  
Helichrysum Bracteatum

Helichrysum bracteatum, also known as strawflower, is commonly grown for the production of dried flowers and, more recently, as a potted plant. This latter cultivation system is becoming increasingly important on the Liguria Coast in northern Italy. During the spring of 2002, severe oubreaks of a previously unknown disease were observed in commercial farms in the area of Albenga (northern Italy) on several cultivars of H. bracteatum. Leaves of infected plants appeared curled and blistered; the infected portions of leaves turned chlorotic. On the lower leaf surface of chlorotic areas, a dense, whitish growth was evident. Infected leaves eventually wilted without dropping. Basal leaves with poor air circulation were the most severely affected. Certain cultivars of H. bracteatum (such as ‘Florabella Pink’) were most seriously affected, while others (‘Florabella Gold’ and ‘Florabella White’) had less disease. Microscopic observations revealed sporangiophores emerging from the stomata that were dichotomically branched, ending with 4 to 7 sterigmata. The sporangia were globose and measured 15.5 to 16.8 μm in diameter. The pathogen was identified as Bremia lactucae based on the morphological characteristics. Pathogenicity was confirmed by inoculating healthy H. bracteatum (100-day-old ‘Florabella Gold’) as well as Lactuca sativa (25-day-old ‘Salad bowl’) plants with a sporangial suspension (1 × 105 sporangia/ml). Five plants of H. bracteatum and 10 of lettuce were used as replicates. Noninoculated plants served as controls. Inoculated and uninoculated plants were maintained in a growth chamber at 20°C and 90 to 95% relative humidity. After 7 to 10 days, typical symptoms of downy mildew developed on H. bracteatum and lettuce plants artificially inoculated. Bremia lactucae was observed on infected leaves. Uninoculated plants did not show symptoms. To our knowledge, this is the first report of Bremia lactucae on H. bracteatum in Italy. B lactucae was previously reported as the causal agent of downy mildew on H. bracteatum in several countries including the United Kingdom (3), the United States (1), and Egypt (2). References: (1) S. A. Alfieri et al. Index of plant diseases in Florida. Bull No. 11, 1984. (2) H. Elarosi and M. W. Assawah. Rev. Plant Prot. Res., 39:583, 1959. (3) W. C. Moore. British Parasitic Fungi. Cambridge University Press, Cambridge, 1959.

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

Plant Disease ◽  
2009 ◽  
Vol 93 (4) ◽  
pp. 433-433 ◽  
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.

scholarly journals First Report of Myrothecium roridum Causing Myrothecium Leaf Spot on Salvia spp. in the United States

Plant Disease ◽  
2007 ◽  
Vol 91 (6) ◽  
pp. 772-772 ◽  
Author(s):  
J. A. Mangandi ◽  
T. E. Seijo ◽  
N. A. Peres
Keyword(s):  
United States ◽  
Leaf Spot ◽  
Pathogenic Fungi ◽  
Lower Surface ◽  
The United States ◽  
Plant Diseases ◽  
Control Measures ◽  
Conidial Suspension ◽  
First Report ◽  
Myrothecium Roridum

The genus Salvia includes at least 900 species distributed worldwide. Wild species are found in South America, southern Europe, northern Africa, and North America. Salvia, commonly referred to as sage, is grown commercially as a landscape plant. In August 2006, pale-to-dark brown, circular leaf spots 5 to 20 mm in diameter with concentric rings were observed on Salvia farinacea ‘Victoria Blue’. Approximately 5% of the plants in a central Florida nursery were affected. Lesions were visible on both leaf surfaces, and black sporodochia with white, marginal hyphal tuffs were present mostly on the lower surface in older lesions. Symptoms were consistent with those of Myrothecium leaf spot described on other ornamentals such as gardenia, begonia, and New Guinea impatiens (4). Isolations from lesions on potato dextrose agar produced white, floccose colonies with sporodochia in dark green-to-black concentric rings. Conidia were hyaline and cylindrical with rounded ends and averaged 7.4 × 2.0 μm. All characteristics were consistent with the description of Myrothecium roridum Tode ex Fr. (2,3). The internal transcribed spacer regions ITS1, ITS2, and the 5.8s rRNA genomic region of one isolate were sequenced (Accession No. EF151002) and compared with sequences in the National Center for Biotechnology Information (NCBI) database. Deposited sequences from M. roridum were 96.3 to 98.8% homologous to the isolate from salvia. To confirm pathogenicity, three salvia plants were inoculated by spraying with a conidial suspension of M. roridum (1 × 105 conidia per ml). Plants were covered with plastic bags and incubated in a growth chamber at 28°C for 7 days. Three plants were sprayed with sterile, distilled water as a control and incubated similarly. The symptoms described above were observed in all inoculated plants after 7 days, while control plants remained symptomless. M. roridum was reisolated consistently from symptomatic tissue. There are more than 150 hosts of M. roridum, including one report on Salvia spp. in Brunei (1). To our knowledge, this is the first report of Myrothecium leaf spot caused by M. roridum on Salvia spp. in the United States. Even the moderate level disease present caused damage to the foliage and reduced the marketability of salvia plants. Therefore, control measures may need to be implemented for production of this species in ornamental nurseries. References: (1) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory. Online publication. ARS, USDA, 2006, (2) M. B. Ellis. Page 449 in: Microfungi on Land Plants: An Identification Handbook. Macmillan Publishing, NY, 1985. (3) M. Fitton and P. Holliday. No. 253 in: CMI Descriptions of Pathogenic Fungi and Bacteria. The Eastern Press Ltd. Great Britain, 1970. (4) M. G. Daughtrey et al. Page 19 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society. St. Paul, MN, 1995.

scholarly journals First Report of Powdery Mildew, Caused by an Oidium sp., on Poinsettia in California

Plant Disease ◽  
1998 ◽  
Vol 82 (1) ◽  
pp. 128-128 ◽  
Author(s):  
S. T. Koike ◽  
G. S. Saenz
Keyword(s):  
United States ◽  
Powdery Mildew ◽  
Pacific Northwest ◽  
The United States ◽  
Euphorbia Pulcherrima ◽  
American Phytopathological Society ◽  
First Report ◽  
The Pacific ◽  
Uninoculated Control ◽  
Alternative Identification

In December 1996 and January 1997, powdery mildew was observed on potted poinsettia (Euphorbia pulcherrima Willd. ex Klotzsch) plants in Monterey County, CA. Mycelia were observed on stems, petioles, mature and immature leaves, and bracts. Severely diseased leaves became twisted and bent and senesced prematurely. The white mycelia were conspicuous, epiphytic, and amphigenous; hyphae measured 4.6 to 6.9 μm in diameter. Growth initially was in patches but eventually became effused. Appressoria were slightly lobed to lobed and sometimes opposite. Conidiophore foot cells were cylindrical, sometimes bent at the base, and slightly flexuous to flexuous. Foot cells measured 30.0 to 46.2 μm × 5.8 to 6.9 μm and were followed by one to two shorter cells. Conidia were cylindrical to slightly doliform and measured 25.4 to 32.3 μm × 11.6 to 18.5 μm. The length-to-width ratios of conidia generally were greater than 2.0. Conidia were produced singly, placing the fungus in the Pseudoidium-type powdery mildew group. Conidia germinated at the ends, and no fibrosin bodies were observed. Cleistothecia were not found. The fungus was identified as an Oidium species. Pathogenicity was demonstrated by gently pressing infected leaves having abundant sporulation onto leaves of potted poinsettia plants (cvs. Freedom Red, Peter Star Marble, and Nutcracker White), incubating the plants in a moist chamber for 48 h, and then maintaining plants in a greenhouse. After 12 to 14 days, powdery mildew colonies developed on the inoculated plants, and the pathogen was morphologically identical to the original isolates. Uninoculated control plants did not develop powdery mildew. This is the first report of powdery mildew on poinsettia in California. This fungus appears similar to Microsphaera euphorbiae but has longer, slightly flexuous foot cells that do not match the description for M. euphorbiae (1,2). An alternative identification would be Erysiphe euphorbiae; however, there are no available mitosporic descriptions for morphological comparisons (1,2). In the United States, powdery mildew of poinsettia previously has been reported in various states in the Pacific Northwest, Midwest, and Northeast. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. American Phytopathological Society, St. Paul, MN.

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

Plant Disease ◽  
2009 ◽  
Vol 93 (4) ◽  
pp. 427-427 ◽  
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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