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1.
Plant Dis ; 90(10): 1361, 2006 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30780955

RESUMO

In 2001 and again in December 2005, an outbreak of leaf spots was observed on Guzmania sp. 'Gwendolyne' (Bromeliaceae) in a Belgian nursery. Typical disease symptoms were irregular spots with a grayish center and a narrow red-brown margin. Identification was based on morphological characteristics and molecular techniques. Isolations of diseased leaf tissues previously washed with sterile distilled water on potato dextrose agar (PDA) resulted in mycelial colonies after 7 to 8 days. Fungal mycelium grew at a linear rate of 30.4 mm per 24 h at 21°C in the dark. The pathogen produced aerial mycelium and sporulation was abundant. The color of the colonies on PDA was pale to dark brown and conidial characteristics similar to those of Cochliobolus sativus (anamorph Bipolaris sorokiniana) (1) were observed: brown ellipsoidal spores rounded at the top, 3 to 12 distoseptate, with average dimensions of 40 to 120 × 17 to 28 µm. The pathogen was also characterized with molecular tools. DNA was isolated from mycelium from a PDA plate. The ribosomal DNA region ITS1-5.8S-ITS2 was amplified and cloned. The ITS1 sequences (174 bp) of two independent clones were analyzed. The three highest similarity scores (E = 2e-71) obtained in BLAST were C. sativus (GenBank Accession Nos. AF158105 and AF071329) and B. sorokiniana strain BS11 (GenBank Accession No. AY372677). For these, pairwise alignments resulted in an identical score of 97.1% (169 identical bases, four indels, and one transversion). The new Genbank Accession No. of the ITS1 sequence is DQ 641269. To prove pathogenicity of the isolate, inoculations were done by spraying leaves of three young Guzmania sp. 'Gwendolyne' plants with a 20-ml spore suspension (106 spores/ml). Three plants were sprayed with sterile distilled water as controls. The plants were kept for 48 h under a humid chamber and subsequently at room temperature (20 to 25°C) on the laboratory bench. Three to four days after inoculation, leaf spots were observed and C. sativus (anamorph B. sorokiniana) was reisolated, completing Koch's postulates successfully. On the basis of symptoms, morphological characteristics, and pathogenicity tests, the pathogen was identified as C. sativus (anamorph B. sorokiniana). To our knowledge, this is the first record of C. sativus (anamorph B. sorokiniana) on Guzmania sp. in Belgium. References: (1) A. Sivanesan and P. Holliday. Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, UK, 1981.

2.
Plant Dis ; 90(3): 379, 2006 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30786576

RESUMO

Sunflower (Helianthus annuus) is widely used for cut flowers and decoration in Belgium. A serious outbreak of what was suspected to be white rust on sunflower was observed in an East Flemish nursery near the city of Ghent in August 2004. This disease has previously been reported in Europe (southwest of France) (1) and other parts of the world with losses as much as 70 to 80% (Australia, North and South America, and Africa) (2,3). In the Flemish nursery, only single diseased plants (cv. Sunrich) were found. Blister-like pustules containing sporangia were observed on infected leaves. Initially the blisters were pale green to yellow on the abaxial surface and white on the adaxial surface of the leaves. As the disease progressed, white pustules that formed on the adaxial surface of the leaves slowly turned yellow, and the blisters on the abaxial surface became yellow to orange and necrotic in the center. Finally, the pustules coalesced and the leaves withered. Stem lesions were not observed. Short, cylindrical to spherical-cuboid sporangia, recovered from the pustules on the adaxial surface of leaves, measured between 17.5 and 22.5 µm, with an average of 20.2 µm. Sporangial dimensions were similar to those of Albugo tragopogonis (Pers.) S.F. Gray (1). Inoculations were done by spraying a suspension of 1 × 105 sporangia per ml prepared by scraping pustules from naturally infected leaves. Leaves on three 2-month-old healthy plants were sprayed with this inoculum and three plants sprayed with distilled water served as controls. The plants were kept for 48 h under a humid chamber and subsequently at room temperature (20 to 25°C) on the laboratory bench. Initial symptoms of white rust were observed 12 to 14 days after inoculation. On the basis of symptoms, morphological characteristics, and pathogenicity tests, the pathogen was identified as A. tragopogonis. To our knowledge, this is the first record of A. tragopogonis on H. annuus in Belgium. References: (1) K. G. Mukerji. Description of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, England, UK, 1976. (2) A. Pernaud and A. Perny, Phytoma 471:43, 1995. (3) P. S. van Wyk et al. Helia 22:83, 1999.

3.
Plant Dis ; 89(1): 107, 2005 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-30795298

RESUMO

Laurus nobilis (laurel tree) is used as an herbal and ornamental tree in gardens in Belgium. During the summer of 2001, a serious outbreak of leaf spots was observed in some Belgian nurseries. Symptoms were large, irregular, brown leaf spots located primarily on the distal half of leaves and delimited by a black margin. As the disease progressed, the spots enlarged, coalesced, and finally led to leaf withering. The isolated fungus had morphological characteristics typical of Phytophthora citricola. On potato dextrose agar (PDA) it formed white, entire rosette colonies. Within 1 week, semipapillate sporangia were found abundantly in water at room temperature. They were mostly ovoid and highly variable in size (20 to 82 × 12 to 48 µm). The sporangial apex was broadly papillate. Oogonia were spherical (18 to 38 µm in diameter), and the antheridia were paragynous. Pathogenicity of the isolated fungus was confirmed by inoculating two visibly healthy L. nobilis plants. Five leaves per plant were wounded by a scalpel, subsequently inoculated with 5-mm-diameter mycelial plugs on PDA, and sealed with Parafilm. As a control, noncolonized agar plugs were placed on wounded leaves from a third L. nobilis plant. The inoculated plants and the control plant were kept for 1 day under a plastic cover (approximately 95% relative humidity) on the laboratory bench. Within 1 week, all inoculated leaves developed symptoms, whereas the control leaves remained symptomless. P. citricola was sucessfully re-isolated, satisfying Koch's postulates. The pathogen was also characterized using molecular tools. The ribosomal DNA regions, ITS1 and 5.8S rDNA-ITS2, were sequenced and highest similarity scores were obtained with corresponding Phytophthora citricola sequence regions (>99% identity for both sequences). The new GenBank Accession Nos. are AY525786 (ITS1) and AY525787 (5.8S rDNA-ITS2). On the basis of the symptoms, cultural and morphological characteristics, and positive results in pathogenicity and PCR tests, the isolate was considered to be P. citricola. To our knowledge, this is the first record of P. citricola on leaves of L. nobilis in Belgium.

4.
Plant Dis ; 88(4): 427, 2004 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-30812635

RESUMO

During late May and June of 2003, a fire blight epidemic occurred in southcentral Bulgaria on earlier reported hosts such as apple, pear, quince, and hawthorn (1). A new host was found when fire blight was also observed in mid-June on Pyracantha coccinea grown in the Plovdiv Region. Symptoms were necrotic flowers, shoots, petioles, and the presence of sticky ooze droplets mainly on the shoots. Isolations made from blighted Pyracantha coccinea flowers and shoots onto King's medium B (2 days at 25 to 26°C) yielded whitish, glistening, round bacterial colonies. Infiltration of the suspensions of three of the isolates into tobacco leaves resulted in a typical hypersensitive reaction. When Pyracantha coccinea and Cotoneaster sp. shoots were inoculated with these three isolates, typical fire blight symptoms were obtained. The pathogen was reisolated 2 weeks after inoculation from necrotic tissues (15 to 20 mm above and below the inoculation site), thereby fulfilling the Koch's postulates. No symptoms and bacteria were found within any of the shoots from the same plant species injected with sterile water. The identity of the isolates was also determined by conducting nested polymerase chain reaction (PCR) (2) and target-specific PCR (23S rDNA) (3). On the basis of the symptoms, cultural characteristics, and positive results in pathogenicity and PCR tests, the isolates were considered to be Erwinia amylovora. To our knowledge, this is the first report of fire blight on Pyracantha coccinea in Bulgaria. References: (1) S. G. Bobev et al. Plant Dis. 82:1283, 1998. (2) P. Llop et al. Appl. Environ. Microbiol. 66:2071, 2000. (3) M. Maes et al. Plant Pathol. 45:1139, 1996.

5.
Plant Dis ; 87(12): 1539, 2003 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-30812407

RESUMO

In the fall of 2000, a new blight disease was observed on Buxus spp. in private gardens in Belgium. Since then, more and similar disease samples from other Belgian sites, nurseries, and several garden centers have been received, indicating that this disease is spreading. Similar observations have been made in the U.K. and France, where the disease is widespread and losses are sometimes dramatic (1). Diseased plants have dark brown-to-black leaf spots and streaky, black stem lesions which lead, in some cases, to complete defoliation. On some infected plants new leaves grew in defoliated areas, hiding the original blight symptoms. Infection was mainly observed on Buxus sempervirens cv. Suffruticosa, but B. sempervirens cv. Latifolia raculata, B. microphylla cv. Compacta, and B. microphylla var. japonica cv. Faulkner were also infected. In the U.K., infections have additionally been reported on varieties of B. sempervirens, B. sinica, and B. microphylla (1). On the basis of observed symptoms and comparison of the symptoms with descriptions by Henricot and Culham (2), we identified that this new form of Buxus blight in Belgium is caused by Cylindrocladium buxicola. Sporulating cultures on potato dextrose agar (PDA) had macroconidiophores with stipe extensions terminating in broadly ellipsoidal vesicles with pointed or papillate apices (6.5 to 11 µm in diameter) and a penicillate arrangement of fertile branches each terminating in two to five phialides. Phialides produced clusters of cylindrical conidia (42 to 68 × 4 to 6 µm) that were rounded at both ends and had a single septum. Pathogenicity of the isolate was demonstrated by inoculation of healthy stems and leaves of four 3-year-old plants of B. sempervirens cv. Suffruticosa. On each plant, agar pieces of 1-week-old cultures grown on PDA were placed on five stems and five leaves that had been wounded with a sterile scalpel, then sealed with Parafilm. As a control, five wounded stems and leaves from another B. sempervirens cv. Suffruticosa plant were inoculated with sterile agar plugs. Inoculated plants were incubated in humid chambers (approximately 95% relative humidity) on the laboratory bench. Two weeks after inoculation, no symptoms were visible on the control plant. The inoculated plants showed symptoms as previously described, and C. buxicola was successfully reisolated from diseased tissue completing Koch's postulates. To our knowledge, this is the first record of C. buxicola on Buxus spp. in Belgium. References: (1) B. Henricot et al. Plant Pathol. 49:805, 2000. (2) B. Henricot and A. Culham. Mycologia 94(6):980, 2002.

6.
Plant Dis ; 87(10): 1266, 2003 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-30812743

RESUMO

Plasmopara petroselini (Oomycetes) was identified on parsley (Petroselinum crispum subsp. crispum cv.Petra) (Apiaceae) in Belgium during the winters of 2001 and 2002. The fungus was present in numerous fields, especially on parsley grown in plastic tunnels. Losses were sometimes dramatic and similar to disease problems in France and Switzerland where 80 and 50 ha, respectively, were found infected (1). Initial symptoms consisted of white spots on the upper leaf surface. As the disease progressed, the spots enlarged, became angular, and turned yellow. At the location of leaf spots, white-to-grayish white mycelium developed on the lower surface of the leaves. Eventually the leaves and leaf stalks rotted. The pathogen was identified at the Centraalbureau voor Schimmelcultures (CBS) (Utrecht, the Netherlands) as the downy mildew organism P. petroselini (= P. umbelliferarum pro parte = P. nivea pro parte = P. crustosa), based on morphological characteristics. Sporangia were papillate, lemon-shaped, almost hyaline, and 9 to 20 µm long, and produced on tree-like sporangiophores (100 to 420 × 6 to 8.5 µm) that were monopodially branched at approximately right angles. The sporangiophores usually bear three sterigma (4 to 19 × 2 to 3 µm) that narrow toward the tip (2). Prophylactic actions are the primary method to prevent the disease. Fungicides based on propamocarb can be used as a curative control method. To our knowledge, this is the first report of P. petroselini on parsley in Belgium. References: (1) E. Béliard and J. Thibault. Phytoma 554:2, 2002. (2) M. Brandenburger. Page 451 in: Parastische Pilze an Gefässpflanzen in Europa. Fischer Verlag, Stuttgart, Germany, 1985.

7.
Plant Dis ; 87(6): 752, 2003 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-30812881

RESUMO

American ginseng (Panax quinquefolius) is a recently introduced crop in Bulgaria. In autumn 2001, several 2-year-old plants from Stara Zagora County exhibited symptoms of wilting and dying. Laboratory analysis also revealed some browning of the ginseng root surface and discoloration of the vascular tissues. During later stages of the disease, roots became soft, rubbery, and disintegrated. After storage in a humid chamber for 3 to 5 days, roots were covered with a white, cottony mycelium. Following the transfer onto potato dextrose agar, this fungus formed rounded colonies of white, aerial mycelium. Pathogenicity of the isolate was demonstrated by inoculation of roots that were surface-disinfected with alcohol (70%) for 30 s and rinsed with sterile water. Roots were wounded with a scalpel, and agar pieces from a 1-week-old culture were placed under the cortical tissue. Five inoculated root pieces were kept in a humid chamber at 24 to 25°C, and the pathogen was reisolated subsequently from necrotic lesions that developed from wounds. No symptoms were found in the five wounded but noninoculated control roots. The pathogen was reisolated from the diseased tissue to fulfill Koch's postulates. Microscopic examination showed that the pathogen had an aseptate mycelium (mean diameter of 5.3 µm), did not form hyphal swellings or chlamydospores, and had simple sympodial branching of the sporangiophores. Sporangia had a caducous nature with a pedicel length of 4.7 µm (1.7 to 6.7 µm). Sporangia were ovoid to obpyriform in shape, papillate, and nonproliferating measuring 30.6 (26.6 to 40.0) µm × 24.3 (23.3 to 30.0) µm. The length/width ratio varied between 1.25 and 1.3. The fungus was homothallic and produced paragynous antheridia and spherical oogonia with a diameter of 30.6 µm (26.6 to 33.3 µm) on V8 agar and in petri solution. Oospores were aplerotic and spherical (25 to 30 µm in diameter). Based on symptoms and pathogen characteristics (2), the disease was identified as Phytophthora root rot caused by Phytophthora cactorum. Additionally, the identity of the isolate was verified by sequence determination of the ribosomal internal transcribed spacer I region and alignment to the GenBank-EMBL DNA database (1), which revealed 100% sequence similarity with P. cactorum. To our knowledge, this is the first report of P. cactorum on American ginseng in Bulgaria. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389,1997. (2) D. C. Erwin and O. K. Ribeiro. Morphology and identification of Phytophthora species. Pages 96-125 in: Phytophthora Diseases Worldwide. The American Phytopathological Society, St. Paul, MN, 1996.

8.
Commun Agric Appl Biol Sci ; 68(4 Pt B): 589-97, 2003.
Artigo em Inglês | MEDLINE | ID: mdl-15151294

RESUMO

Phytophthora ramorum is a new and aggressive Phytophthora species that causes leaf blight and dieback symptoms on Viburnum and Rhododendron plants in Europe. A variant of this fungus is responsible for Sudden Oak Death (SOD) in California and Oregon. In Europe, problems so far are mostly restricted to nursery plants of Rhododendron and Viburnum while in the US, the fungus has been isolated from over 20 host species and is responsible for massive killing of oak trees (mostly Quercus agrifolia and Lithocarpus densiflorus) in forest and park settings. The potential for infection of native tree species in Europe and the recent detection of the fungus in nurseries of several European countries has lead to the implementation of EU emergency phytosanitary measures. As a result, most European countries have conducted surveys and are doing research as part of risk assessment efforts. The first part of this paper focuses on the plant diagnoses of the 2002 survey of P. ramorum in Belgian nurseries. The data from the survey indicates P. ramorum is present in Belgium at similar rates as in the neighbouring countries, in an apparent random distribution. The second part of this paper describes research results relating to the in vitro effect of oomycete fungicides on P. ramorum, Rhododendron cultivar susceptibility, the determination of the leaf infection site, and pathogen survival. Some fungicides had excellent in vitro activity against P. ramorum and should be tested further on plants. Use of host resistance as a control strategy may be limited as little difference in cultivar sensitivity was observed. Infection studies showed that wounds and the lower sides of the leaves are most susceptible to infection. Once the pathogen gets inside, it can survive well on detached leaves, especially when they are kept cool and moist. These data can contribute to management decisions of P. ramorum at the level of nurseries as well as the government.


Assuntos
Controle de Pragas/métodos , Phytophthora/crescimento & desenvolvimento , Doenças das Plantas/microbiologia , Rhododendron/microbiologia , Bélgica , Fungicidas Industriais/farmacologia , Controle Biológico de Vetores/métodos , Phytophthora/efeitos dos fármacos , Phytophthora/patogenicidade , Folhas de Planta/microbiologia , Quercus/microbiologia , Medição de Risco , Viburnum/microbiologia
9.
Plant Dis ; 86(5): 563, 2002 May.
Artigo em Inglês | MEDLINE | ID: mdl-30818698

RESUMO

In fall 2000 and 2001, large leaf spots were observed on Prunus laurocerasus. Two different plant pathogens proved to be the cause. Based on morphological characteristics they were identified as Peronospora sparsa (downy mildew) and Phytophthora cactorum. The P. cactorum isolate (CBS 110121) was identified at the Centraalbureau voor Schimmelcultures (Utrecht, the Netherlands). Sporangia were papillate, ovoid, and deciduous, with a short pedicel. The isolate was homothallic. Chlamydospores were present and approximately 40 µm in diameter. Oogonia were 25 to 31 µm in diameter, and the antheridia were paragynous. Peronospora sparsa had been reported to infect Prunus laurocerasus in the United Kingdom (1). In Belgium, cv. Etna was very susceptible, but cvs. Rotundifolia and Marbled White were also infected. Rotundifolia was susceptible to P. cactorum. At first inspection, the two pathogens caused similar leaf symptoms: large, irregular, brown, necrotic spots on the tips, margins, and center of leaves. However, the undersides of leaves infected with Peronospora sparsa were covered with typical gray mycelium, which was absent on leaves infected with P. cactorum. P. cactorum caused concentric circles in the brown spots. Leaf spots caused by P. cactorum developed quickly in a moist chamber. Spots caused by Peronospora sparsa did not enlarge significantly on detached leaves, but in the field it caused serious losses within a few days. To prove the pathogenicity of P. cactorum, Koch's postulates were satisified on five Prunus laurocerasus Etna plants. The fungus was grown on corn meal agar for 1 week until sporangia formed. An agar plug was placed on five wounded leaves per plant and sealed with Parafilm. Inoculated plants were kept under a plastic cover for 1 day at 22°C, then the cover was removed, and the plants were kept at 20°C. Symptom development was visible after 3 days, and P. cactorum was successfully reisolated. This is the first record of P. cactorum and Peronospora sparsa leaf infection on Prunus laurocerasus in Belgium. Reference: (1) G. Hall et al. Plant Pathol. 41:224, 1992.

10.
Plant Dis ; 82(11): 1283, 1998 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-30845429

RESUMO

Typical symptoms of fire blight, caused by Erwinia amylovora, were observed in late June of 1998 on Crataegus monogyna Jacq. (hawthorn) and Pyrus pyraster Burgsd. (syn. P. caucasia, wild or thorny pear) in the region of Plovdiv. Symptoms observed on hawthorn were shepherd's-crook shoots, necrotic flowers and fruitlets, and dried amber ooze droplets. On thorny pear, only infected shoots were detected. Isolation on King's B medium (2 days, 26°C) resulted in the appearance of whitish, glistening, rounded colonies. Based on their cultural characteristics, positive hypersensitive response (HR) on tobacco leaves, successful laboratory inoculations of hosts' shoots and pear fruitlets, positive serological reaction (slide agglutination), and target-specific polymerase chain reaction (PCR; 23S rDNA), the isolates from both species were placed in the E. amylovora group. The bacterium has also been isolated by the first author from Cydonia oblonga, Pyrus communis, Mespilus germanica, and Malus sylvestris within the 5-year period of 1989-1993 (1). To our knowledge this is the first official report of fire blight on C. monogyna and P. pyraster in Bulgaria. Reference: (1) S. G. Bobev. 1995. Pages 121-126 in: Jubilee Scientific Session, Higher Agricultural Institute of Plovdiv, vol. 3, bk. 1. (In Bulgarian.).

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