First Report of Leaf Spot Caused by Alternaria alternata on Hydrangea macrophylla in Italy

Hydrangea macrophylla is cultivated as an ornamental and also used in the landscape. During the fall of 2005, leaves and young stems on 12-month-old plants (cvs. Hanabi, Nigra, and Zaffiro) grown in pots in several gardens and commercial nurseries in the Piedmont (northern Italy) had extensive necrosis. In many cases, 4-mm-diameter spots on the upper side of the leaves were surrounded by a chlorotic halo, which turned progressively black. Lesions often coalesced into 3- to 8-cm-diameter necrotic areas. Initial necrosis developed mainly on the leaf margins and near the petioles. Severely affected plants were defoliated. Infected plants rarely died, but the presence of lesions reduced the aesthetic quality and subsequently the commercial value. The disease occurred on 30 to 50% of the plants. Leaf spots contained dark brown, multicellular, pear-shaped conidia. Conidia were 19.2 to 36.5 μm (average 26.3 μm) long and 7.7 to 11.5 μm (average 8.9 μm) wide, with 3 to 4 longitudinal cross walls and an average of 4.4 single cells. A fungus identified on the basis of its morphological characteristics as an Alternaria sp. was consistently isolated from symptomatic leaves onto potato dextrose agar. DNA was extracted from mycelium (Nucleospin Plant Kit, Macherey Nagel, Brockville, ON, Canada) and PCR was completed using Alt-for/Alt-rev primers (3), which amplified a part of the gene that encodes for the protein Alt a 1, the major allergen produced by the genus Alternaria. A 305-bp fragment was amplified, sequenced, and the sequence was subjected to BLASTn analysis (1), which confirmed that the isolate belonged to the genus Alternaria and to the alternata group (3). The nucleotide sequence has been deposited in GenBank (Accession No. EF446670). Pathogenicity tests were performed by spraying leaves of healthy potted H. macrophylla plants, cvs. Zaffiro (6-month-old) and Hanabi (12-month-old) with a spore suspension (105 conidia/ml). Plants sprayed with water only served as a control. Ten plants per cultivar were used for each treatment. Plants were covered with plastic bags for 5 days after inoculation and maintained at 20°C for an additional 7 days. Plants were transferred outdoors and kept at temperatures ranging from 19 to 25°C. The first foliar lesions developed on leaves 15 days after inoculation, whereas control plants remained healthy. Alternaria sp. was consistently reisolated from these lesions. The pathogenicity test was completed twice. The presence of Alternaria sp. on Hydrangea spp. was reported in the United States (2), whereas A. hortensiae was observed in Spain (4). To our knowledge, this is the first report of Alternaria sp. belonging to the alternata group infecting H. macrophylla in Italy. The disease is currently spreading in other Italian areas. References: (1) S. F. Altschud et al. Nucleic Acids Res. 25:3389, 1997. (2) M. L. Daughtrey et al. Page 9 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society, St. Paul, MN, 1995. (3) S. Gyu Hong et al. Fungal Genet. Biol. 42:119, 2005. (4) L. M. Unamuno. An. Jard. Bot. Madr. 4:145, 1944.

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Leaf Spot Caused by Alternaria sp. on Iberis sempervirens in Italy

Plant Disease ◽

10.1094/pd-89-1243b ◽

2005 ◽

Vol 89 (11) ◽

pp. 1243-1243 ◽

Cited By ~ 1

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

Leaf Spot ◽

Single Cells ◽

Morphological Characteristics ◽

Weather Conditions ◽

The United States ◽

Plant Diseases ◽

Pathogenicity Test ◽

Aesthetic Quality ◽

Leaf Spots ◽

Alternaria Sp

Iberis sempervirens (candytuft) is increasingly grown in Liguria (northern Italy) as a potted plant for ornamental purposes, particularly under cool-weather conditions. At the end of the summer of 2003, extensive necrosis was observed on leaves and young stems of 4-month-old plants grown in 14-cm diameter pots outdoors at a commercial farm. In many cases, on the upper side of the leaves, necrotic spots were surrounded by a chlorotic halo that turned progressively black. The necrotic areas often coalesced, generating larger and irregularly shaped spots. On the lower side of the leaves, no chlorotic areas were observed. Severely affected plants were defoliated. Infected plants rarely died, but the presence of lesions on mature plants decreased aesthetic quality and subsequently market value. The disease occurred on 40% of plants at each of the two farms. Leaf spots contained dark brown, multicellular pear-shaped conidia. Conidia were 22.5 to 50.0 μm (average 32.8 μm) long and 7.5 to 15.0 μm (average 12.3 μm) wide, with 5 to 7 longitudinal cross walls and an average of 6 to 7 single cells. From infected leaves, a fungus identified on the basis of its morphological characteristics as Alternaria sp. was consistently isolated on potato dextrose agar. Pathogenicity tests were performed by spraying leaves of healthy 12-month-old potted I. sempervirens plants with a spore and mycelial suspension (105 CFU/ml). Plants without inoculation served as control. Ten plants were used for each treatment. Plants were covered with plastic bags for 10 days after inoculation and kept outdoors for 60 days at temperatures ranging from 0 to 32°C (average 12°C). The first lesions developed on leaves 45 days after inoculation, while control plants remained healthy. From such lesions, Alternaria sp. was consistently reisolated. The pathogenicity test was carried out twice. The presence of A. brassicae was reported in Tanganica on Iberis sp., I. umbellata in Denmark (2), and I. amara in the United States (4); A. matthiolae was observed on seeds of I. amara and I. umbellata (3). A leaf spot incited by Alternaria sp. on I. amara was observed in Florida (1). This is, to our knowledge, the first report of Alternaria sp. on I. sempervirens in Italy as well as worldwide. References: (1) S. A. Alfieri et al. Index of Plant Diseases in Florida. Bull. 11, 1984. (2) P. Neergaard. Rev. Appl. Micol. 18:572, 1939. (3) P. Neergaard. Rev. Appl. Micol. 25:382, 1946). (4) R. D. Raabe. Comb. Proc. Int. Plant Propagators Soc. 40:160, 1991.

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First Report of a Leaf Spot Caused by Alternaria compacta on Hydrangea anomala subsp. petiolaris in Italy

Plant Disease ◽

10.1094/pdis-92-1-0173c ◽

2008 ◽

Vol 92 (1) ◽

pp. 173-173 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

D. Bertetti ◽

M. L. Gullino

Keyword(s):

Morphological Characteristics ◽

The United States ◽

Plant Diseases ◽

Spore Suspension ◽

Pathogenicity Test ◽

Aesthetic Quality ◽

First Report ◽

Plastic Bags ◽

Alternaria Sp ◽

The Aesthetic

Hydrangea anomala subsp. petiolaris (synonym H. petiolaris and H. scandens), also known as climbing hydrangea, is cultivated as an ornamental for landscaping in parks and gardens. This species, belonging to the Hydrangeaceae and native to the woodlands of Japan and coastal China, is widely appreciated for its abundant, creamy white flowers with a sweet aroma, particularly in shade gardens. During the summer of 2006, extensive necroses were observed on leaves and young stems of 3-year-old plants grown outdoors in several gardens of Piedmont of northern Italy. In many cases, on the upper side of the leaves, necrotic spots (4 to 10 mm in diameter) turned progressively black. Lesions often coalesced, generating larger (2 to 6 cm in diameter) necrotic areas. Necroses initially developed mainly at leaf margins and near petioles, and severely affected plants were defoliated. Infected plants rarely died, but the presence of lesions reduced the aesthetic quality and subsequently the commercial value. The disease occurred on 50 of 100 plants. A fungus was consistently isolated from infected leaves on potato dextrose agar (PDA) and identified on the basis of its morphological characteristics as an Alternaria sp. Conidia were dark gray, multicellular, clavate to pear shaped, measuring 23 to 54 × 10 to 13 μm (average 38 × 12 μm), with five longitudinal crosswalls and a relatively short apical beak. DNA was extracted with a Nucleospin Plant Kit (Macherey Nagel, Brockville, ON, Canada) and PCR was carried out with ITS 6/ITS 4 primer (2). A 557-bp PCR product was sequenced, and a BLASTn search (1) confirmed that the sequence corresponded to Alternaria compacta (99% homology). The nucleotide sequence has been assigned GenBank Accession No. EU 128529. Pathogenicity tests were performed by spraying leaves of healthy 1-year-old potted H. anomala plants with an aqueous 105 CFU/ml spore suspension. The inoculum was obtained from cultures of the fungus grown on sterilized host leaves placed on PDA for 20 days in light/dark at 23 ± 1°C. Plants sprayed only with water served as controls. Five plants were used for each treatment. Plants were covered with plastic bags for 3 days after inoculation and maintained between 12 and 22°C. Lesions developed on leaves 8 days after inoculation with the spore suspension, whereas control plants remained healthy. A. compacta was consistently reisolated from these lesions. The pathogenicity test was repeated twice. The presence of an Alternaria sp. on H. macrophylla was reported in the United States (3), whereas A. hortensiae was observed in Spain on H. hortensis. Recently, A. alternata belonging to the alternata group was reported on H. macrophylla in Italy (4). This is, to our knowledge, the first report of A. compacta on H anomala subsp. petiolaris in Italy. References: (1) S. F. Altschud et al. Nucleic Acids Res. 25:3389, 1997. (2) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (3) M. L. Daughtrey et al. Page 9 in: Compendium of Flowering Potted Plant Diseases. American Phytopathological Society. St. Paul, MN, 1995. (4) A. Garibaldi et al. Plant Dis. 91:767, 2007.

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First Report of Alternaria Leaf Spot on Camellia in Italy

Plant Disease ◽

10.1094/pdis-91-3-0324c ◽

2007 ◽

Vol 91 (3) ◽

pp. 324-324 ◽

Cited By ~ 2

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

M. L. Gullino

Keyword(s):

Single Cells ◽

Morphological Characteristics ◽

The United States ◽

Tea Plant ◽

Northern Italy ◽

Plant Diseases ◽

Pathogenicity Test ◽

Camellia Japonica ◽

Aesthetic Quality ◽

First Report

Camellia cultivation has a long history in the Lake Maggiore area of northern Italy where a wide selection of varieties is present. Camellias are appreciated for their large, colorful flowers that bloom from late fall through early spring. In July 2005, a previously unknown foliar disease was observed on a collection of 2- to 12-month-old camellia cultivars (Camellia japonica) grown in several nurseries located in the Verbania Province (northern Italy). The disease was observed on plants grown in pots (10 to 24 cm in diameter) that were maintained either in the open or in a greenhouse and was present for the entire growing season. However, symptoms were more severe during the summer with temperatures ranging between 25 and 30°C with high relative humidity values. During the months of June and July of 2005, severe attacks involving as much as 70% of plants were observed on C. japonica cvs. Mrs. Tingley, Burnside, Hagoromo (synonym Magnoliaeflora), and Giuseppe Traverso. The disease was again observed in 2006. On the upper side of the younger leaves, small necrotic spots (3 to 8 mm in diameter) initially developed mainly at the margin of the leaves and near the petioles. Necrotic areas were surrounded by a chlorotic halo that turned progressively black. The necrotic areas often coalesced, generating larger spots with a diameter ranging from 15 to 30 mm. Severely affected plants were defoliated. Infected plants sometimes died. The presence of lesions on mature plants decreased aesthetic quality and market value. Leaf spots contained dark brown, multicellular, pyriform conidia. Conidia, generally in short chains, were 20.5 to 34.8 μm (average 29.3 μm) long, 6.9 to 12.2 μm (average 9.9 μm) wide, with 3 to 4 longitudinal cross walls, and an average of 5.7 single cells. From 15 samples of infected leaves, several isolates of a fungus identified on the basis of its morphological characteristics as belonging to the Alternaria alternata complex (2) were consistently isolated on potato dextrose agar containing 25 mg/l of streptomycin sulfate. Pathogenicity tests were performed by spraying leaves of healthy 6-month-old potted C. japonica cv. Burnside plants with a spore and mycelial suspension (1 × 105 CFU/ml) prepared by using a mixture of three isolates obtained in 2005 grown on PDA for 30 days at 23 ± 2°C in a growth chamber (12 h of light per day). Plants without inoculation served as a control. Five plants were used for each treatment. Plants were covered with plastic bags for 3 days after inoculation and maintained at 25°C in growth chambers. The first lesions developed on leaves 3 days after inoculation, while control plants remained healthy. Sixty days after artificial inoculation, 25% of the inoculated plants were dead, while the control plants remained healthy. From lesions of infected plants, a fungus belonging to the A. alternata complex was consistently reisolated. The pathogenicity test was carried out twice. The presence of A. alternata on C. sinensis, the commercial tea plant, was reported in India (1). Previously, a flower blight caused by A. tenuis was reported in the United States (3). This is, to our knowledge, the first report of A. alternata on C. japonica in Italy and probably in the world. The disease was present in 2005 and 2006 in several commercial nurseries affecting 50% of plants of susceptible cultivars. References: (1) B. N. Chakraborty et al. Plant Pathol. 55:303, 2006. (2) E. G. Simmons. Pages 1–35 in: Alternaria Biology, Plant Diseases and Metabolites. J. Chelchowski and A. Visconti, eds. Elsevier, Amsterdam, 1992. (3) A. J. Watson. Plant Dis. Rep. 34:186, 1950.

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First Report of Alternaria Leaf Blight of Aralia japonica Caused by Alternaria panax in Europe

Plant Disease ◽

10.1094/pdis.2004.88.1.82b ◽

2004 ◽

Vol 88 (1) ◽

pp. 82-82 ◽

Cited By ~ 4

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

M. L. Gullino

Keyword(s):

Central Italy ◽

The United States ◽

Leaf Blight ◽

Plant Diseases ◽

Fluorescent Light ◽

Pathogenicity Test ◽

Single Spore ◽

Aesthetic Quality ◽

First Report ◽

Alternaria Panax

Aralia japonica (synonym Fatsia japonica), belonging to the Araliaceae family, is a foliage plant highly valued in Italy for landscape and interior decoration. In the fall of 2002, a leaf blight disease was observed on plants grown in pots that were maintained under shade at a density of 15 to 20 pots per m2 at a nursery located in central Italy (Teramo Province). Typical symptoms were tan-to-dark brown leaf spots and rapid blighting of foliage under moist conditions. Chlorotic zones around necrotic lesions were common, and considerable leaf drop was associated with the disease. Affected plants were rarely killed, but the presence of lesions on mature plants reduced aesthetic quality and market value. The disease occurred on 70% of the plants. A fungus identified morphologically as Alternaria panax (2) was consistently isolated from infected leaves on potato dextrose agar (PDA). The fungus grows slowly and sparsely on PDA and produces a light brown mycelium, a characteristic red diffusible pigment in the agar medium, and rare conidia under 12-hr photoperiods. Measurements were carried out on conidia formed from single-spore isolates grown on autoclavated host tissue on water agar (LWA) at 24°C for 10 days. In LWA culture, conidia were borne singly or in chains of two to four conidia. Conidia produced in culture were smaller than those formed on the host and were highly variable in shape. They appeared obclavate, ellipsoidal, and obpyriform and pale to dark brown with relatively short or false beaks. Conidial bodies were 14.4 to 48.0 μm long (average 30.5 μm) and 7.2 to 12.0 μm wide (average 9.9 μm) with 3 to 10 transverse and a few longitudinal septa. Length of appendages was 9.6 to 26.0 μm (average 16.0 μm). Pathogenicity tests were performed by inoculating leaves of healthy Aralia japonica and Schefflera actinophylla plants by placing mycelial disks (5 mm in diameter) directly on wounded leaf tissues. Uninoculated, wounded plants served as controls. Four plants of each species were used. Plants were covered for 72 h with plastic bags and maintained in a growth chamber at 20°C (12 hours per day of fluorescent light). Control plants were maintained similarly. The first lesions developed on leaves of inoculated plants of both species after 7 days. A. panax was consistently reisolated from the lesions. The pathogenicity test was carried out twice. The presence of A. panax on Aralia japonica has been reported in Japan, Korea (2), and the United States (1) but to our knowledge, this is the first report of A. panax on Aralia japonica in Europe. References: (1) S. Alfieri et al. Index of plant diseases in Florida. Bull. 11:52, Florida Department of Agriculture and Consumer Services, 1984 (2) S. H. Yu et al. Ann. Phytopathol. Soc. Jpn. 50:313, 1984.

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First Report of Leaf Spot Caused by Phoma exigua on Hydrangea macrophylla in Italy

Plant Disease ◽

10.1094/pd-90-1113b ◽

2006 ◽

Vol 90 (8) ◽

pp. 1113-1113 ◽

Cited By ~ 4

Author(s):

A. Garibaldi ◽

G. Gilardi ◽

D. Minerdi ◽

M. L. Gullino

Keyword(s):

Relative Humidity ◽

The United States ◽

Plant Diseases ◽

Limited Area ◽

Pathogenicity Test ◽

Internal Transcribed Spacer Region ◽

Aesthetic Quality ◽

Phoma Exigua ◽

Hydrangea Macrophylla ◽

Potted Plant

Hydrangea macrophylla is grown in Italy as a potted plant and also for landscaping. During the fall of 2005 in a nursery located in Lazio (central Italy), a severe foliar disease was observed on 12-month-old potted plants of cv. Hanabi. Small necrotic spots surrounded by chlorotic haloes were observed on the upper side of infected leaves. At temperatures near 20°C and relative humidity ranging between 80 to 90%, spots enlarged to form round areas 2 to 7 cm in diameter that were well defined by a brown margin. Severely infected leaves became chlorotic and abscised. Heavily affected plants were defoliated. Infected plants rarely died, but the presence of lesions on mature plants decreased aesthetic quality and subsequent market value. The disease occurred on 30% of the plants in one nursery. Stems and flowers were not affected by the disease. From infected leaves, a fungus was consistently isolated on potato dextrose agar with 25 mg/liter of streptomycin added. The fungus was grown on leaf extract agar, 30 g of leaves per liter, and maintained at 22°C (12 h of light and 12 h of dark). After 30 days, black pycnidia 275 to 255 μm in diameter developed, releasing conidia that were hyaline, elliptical, nonseptate, and measuring 4.6 to 7.6 (average 6.0) × 1.4 to 4.2 (average 2.6) μm. On oatmeal agar, the addition of a drop of concentrated NaOH caused a positive reaction, turning the medium red (2). On the basis of its morphological characteristics, the fungus was identified as a Phoma sp. The ITS (internal transcribed spacer) region of rDNA was amplified using the primers ITS4/ITS6 (3) and sequenced. BLASTn analysis (1) of the 560 bp obtained showing an E-value of 0.0 with Phoma exigua. The nucleotide sequence has been assigned GenBank Accession No. DQ384612. Pathogenicity tests were performed by spraying leaves of healthy 6-month-old potted H. macrophylla (cvs. Hanabi and Zaffiro) plants with a spore and mycelial suspension (105 CFU/ml). Plants without inoculation served as controls. Five plants were used for each treatment. Plants were covered with plastic bags for 5 days after inoculation and kept in a growth chamber at 20°C with relative humidity at 80 to 90%. The first lesions developed on leaves of cv. Hanabi 12 days after inoculation, while control plants remained healthy. Lesions did not develop on inoculated cv. Zaffiro plants. The fungus was consistently reisolated from the lesions of cv. Hanabi. The pathogenicity test was carried out twice. The presence of P. exigua on H. macrophylla has been reported in the United States (4). In Italy, the disease can be found in a limited area. References: (1) S. F. Altschud et al. Nucleic Acids Res. 25:3389, 1997. (2) G. H. Boerema and L. H. Howeler. Persoonia 5:15, 1967. (3) D. E. L. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997. (4) M. L. Daughtrey et al. Page 26 in: Compendium of Flowering Potted Plant Diseases. The American Phytopathological Society. St. Paul, MN, 1995.

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First Report of Downy Mildew Caused by Peronospora parasitica on Iberis sempervirens in Italy

Plant Disease ◽

10.1094/pd-90-1261c ◽

2006 ◽

Vol 90 (9) ◽

pp. 1261-1261

Author(s):

A. Garibaldi ◽

A. Minuto ◽

M. L. Gullino

Keyword(s):

New York ◽

Downy Mildew ◽

Morphological Characteristics ◽

Sprinkler Irrigation ◽

The United States ◽

Plant Diseases ◽

Pathogenicity Test ◽

Peronospora Parasitica ◽

First Report ◽

Downy Mildews

Iberis sempervirens (evergreen candytuft) is a garden species belonging to the Brassicaceae family. During June 2004, a damaging foliar disease was observed in several commercial farms near Albenga (northern Italy) on I. sempervirens plants grown outdoors in containers. More than 30% of the plants were affected. Symptoms appeared on both sides of leaves, buds, flowers, and fruits. Initially, leaves were slightly chlorotic, but within 5 to 7 days a characteristic whitish furry growth developed on the lower and upper leaf surfaces. The efflorescence was particularly evident on the lower surfaces of leaves and consisted of sporangiophores and sporangia. The appearance and severity of the disease increased because of overhead sprinkler irrigation. Microscopic observations revealed dichotomously branched sporangiophores with slender curved tips. Sporangiophores with a length of 115 to 410 μm (average 295 μm) ended with sterigmata bearing single sporangia. Sporangia were ovoid and measured 18 to 28 × 25 to 45 μm (average 22 × 35 μm). The pathogen was identified as Peronospora parasitica on the basis of its morphological characteristics (3). Pathogenicity was confirmed by inoculating leaves of 10 45-day-old healthy plants grown in 14-cm-diameter pots with a sporangial suspension (1 × 103 conidia/ml). Ten noninoculated plants served as controls. Plants were maintained outdoors at 50% light intensity with temperatures ranging between 16 and 25°C (average 18°C) and 85 to 100% relative humidity. The pathogenicity test was carried out twice. After 18 days, typical symptoms of downy mildew developed on the inoculated plants and P. parasitica was observed on the leaves. Noninoculated plants did not show symptoms. To our knowledge, this is the first report of P. parasitica on evergreen candytuft in Italy. P. parasitica was previously reported on I. sempervirens in the United Kingdom (1) and on I. amara in California (2). Voucher specimens are available at the AGROINNOVA Collection, University of Torino, Italy. References: (1) S. Francis and G. Waterhouse. Trans. Br. Mycol. Soc. 91:1, 1988. (2) P. R. Muller et al. Index of Plant Diseases in the United States. USDA Handbook No. 165, 1960. (3) D. M. Spencer. The Downy Mildews. Academic Press, New York, 1981.

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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 Bremia lactucae Causing Downy Mildew on Helichrysum bracteatum in Italy

Plant Disease ◽

10.1094/pdis.2003.87.3.315a ◽

2003 ◽

Vol 87 (3) ◽

pp. 315-315 ◽

Cited By ~ 1

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.

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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 Passalora Leaf Spot Caused by Passalora bougainvilleae on Bougainvillea in Mexico

Plant Disease ◽

10.1094/pdis-11-10-0787 ◽

2011 ◽

Vol 95 (6) ◽

pp. 775-775 ◽

Cited By ~ 1

Author(s):

V. Ayala-Escobar ◽

V. Santiago-Santiago ◽

A. Madariaga-Navarrete ◽

A. Castañeda-Vildozola ◽

C. Nava-Diaz

Keyword(s):

Uv Light ◽

Disease Incidence ◽

Morphological Characteristics ◽

The United States ◽

Pathogenicity Test ◽

Commonwealth Mycological Institute ◽

Conidial Suspension ◽

Single Spore ◽

First Report ◽

Bougainvillea Spectabilis

Bougainvillea (Bougainvillea spectabilis Willd) growing in 28 gardens during 2009 showed 100% disease incidence and 3 to 7% disease severity. Bougainvilleas with white flowers were the most affected. Symptoms consisted of light brown spots with dark brown margins visible on adaxial and abaxial sides of the leaves. Spots were circular, 2 to 7 mm in diameter, often surrounded by a chlorotic halo, and delimited by major leaf veins. Single-spore cultures were incubated at 24°C under near UV light for 7 days to obtain conidia. Pathogenicity was confirmed by spraying a conidial suspension (1 × 104 spores/ml) on leaves of potted bougainvillea plants (white, red, yellow, and purple flowers), incubating the plants in a dew chamber for 48 h and maintaining them in a greenhouse (20 to 24°C). Identical symptoms to those observed at the residential gardens appeared on inoculated plants after 45 to 60 days. The fungus was reisolated from inoculated plants that showed typical symptoms. No symptoms developed on control plants treated with sterile distilled water. The fungus produced distinct stromata that were dark brown, spherical to irregular, and 20 to 24 μm in diameter. Conidiophores were simple, born from the stromata, loose to dense fascicles, brown, straight to curved, not branched, zero to two septate, 14 × 2 μm, with two to four conspicuous and darkened scars. The conidia formed singly, were brown, broad, ellipsoid, obclavate, straight to curved with three to four septa, 40 × 4 μm, and finely verrucous with thick hilum at the end. Fungal DNA from the single-spore cultures was obtained using a commercial DNA Extraction Kit (Qiagen, Valencia, CA); ribosomal DNA was amplified with ITS5 and ITS4 primers and sequenced. The sequence was deposited at the National Center for Biotechnology Information Database (GenBank Accession Nos. HQ231216 and HQ231217). The symptoms (4), morphological characteristics (1,2,4), and pathogenicity test confirm the identity of the fungus as Passalora bougainvilleae (Muntañola) Castañeda & Braun (= Cercosporidium bougainvilleae Muntañola). This pathogen has been reported from Argentina, Brazil, Brunei, China, Cuba, El Salvador, India, Indonesia, Jamaica, Japan, Thailand, the United States, and Venezuela (3). To our knowledge, this is the first report of this disease on B. spectabilis Willd in Mexico. P. bougainvilleae may become an important disease of bougainvillea plants in tropical and subtropical areas of Mexico. References: (1) U. Braun and R. R. Castañeda. Cryptogam. Bot. 2/3:289, 1991. (2) M. B. Ellis. More Dematiaceous Hypomycetes. Commonwealth Mycological Institute, Kew, Surrey, UK, 1976. (3) C. Nakashima et al. Fungal Divers. 26:257, 2007. (4) K. L. Nechet and B. A. Halfeld-Vieira. Acta Amazonica 38:585, 2008.

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