scholarly journals First Outbreak of Blackleg Caused by Phoma lingam in Commercial Canola Fields in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (4) ◽  
pp. 435-435 ◽  
Author(s):  
S. A. Gaetán
Keyword(s):  
Buenos Aires ◽  
Disease Incidence ◽  
Leptosphaeria Maculans ◽  
Leaf Tissue ◽  
Pathogenic Fungi ◽  
Buenos Aires Province ◽  
Conidial Suspension ◽  
Phoma Lingam ◽  
Current Time ◽  
Production Region

Canola (Brassica napus) was introduced as an alternative crop to wheat in Argentina. During 2004, typical symptoms of foliar blackleg disease were observed on canola plants in commercial and experimental fields in southern Buenos Aires Province. Average disease incidence was 32% on 2- to 4-month-old plants of canola cvs. Impulse, Master, Mistral, and Teddy. The range of incidence on these cultivars was 21 to 43%. Foliar symptoms were randomly distributed at seedling, rosette, and flowering stages. Symptoms included necrosis and chlorosis of the affected leaf tissue and defoliation. Foliar leaf spots were circular to irregularly oval, 5 to 12 mm in diameter, pale brown in the center, and grayish green at the margin. Small, black pycnidia formed in the center of the adaxial surface of diseased foliage. Under favorable temperature and moisture conditions, lesions enlarged and coalesced. Older lesions appeared chlorotic and desiccated with shredded tissue at the center. A severe defoliation of the lower leaves was observed. As the disease developed, basal stem cankers formed on these plants, although disease incidence in this phase was low. Pieces (0.5 cm long) were taken from leaves and stems of diseased plants, dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 2 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar (PDA). Plates were incubated in the dark at 26°C for 4 days, and then plates were incubated under 12 h of NUV light and 12-h dark for 7 days. Four fungal isolates were obtained. The fungi were examined microscopically and confirmed as Phoma lingam (Tode:Fr.) Desmaz. (Leptosphaeria maculans (Desmaz.) Ces. & De Not) (3,4). P. lingam was the only fungus isolated from the infected tissue. The teleomorph stage was not observed. Koch's postulates were completed for two isolates by spray-inoculating foliage of 3-week-old canola plants of cvs. Impulse, Master, Mistral, and Teddy with a conidial suspension (1 × 106 conidia per ml). The experiment, which included four inoculated plants per isolate and two noninoculated control plants for each cultivar, was performed in a greenhouse at 22 to 24°C and maintained at 75% relative humidity with no supplemental light. Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Plants developed small, pale brown lesions on leaves within 11 days for both isolates, and the pathogen was reisolated. Control plants, inoculated only with sterile distilled water, remained symptomless. The experiment was repeated once with similar results. Blackleg is the most important fungal disease affecting canola with a worldwide distribution (1,2). In 1995, the disease was first observed on canola in Argentina in northern Buenos Aires Province, but only in experimental field plots with a low disease incidence. Since that time, it has not been found in other areas where canola is produced. The results emphasize the importance of this pathogen in Argentina, since at the current time most commercial cultivars were susceptible to P. lingam. To our knowledge, this is the first report of an outbreak of P. lingam infection in commercial crops in the main canola-production region in Argentina. References: (1) H. A. Lamey and D. E. Hershman, Plant Dis. 77:1263, 1993. (2) G. A. Petri. Can. Plant Dis. Surv. 65:43, 1985. (3) E. Punithalingham and P. Holliday. No. 331 in: Descriptions of Pathogenic Fungi and Bacteria. CMI Kew, Surrey, UK, 1972. (4) B. C. Sutton. Fungi imperfecti with pycnidia, acervuli and stromata. Pages 386–388 in: The Coelomycetes. CMI, Kew, Surrey, England, 1980.

scholarly journals Occurrence of Charcoal Rot Caused by Macrophomina phaseolina on Canola in Argentina

Plant Disease ◽  
2006 ◽  
Vol 90 (4) ◽  
pp. 524-524 ◽  
Author(s):  
S. A. Gaetán ◽  
L. Fernandez ◽  
M. Madia
Keyword(s):  
United States ◽  
Buenos Aires ◽  
Vascular Tissue ◽  
Disease Incidence ◽  
Pathogenic Fungi ◽  
Macrophomina Phaseolina ◽  
The United States ◽  
Buenos Aires Province ◽  
Charcoal Rot ◽  
Experimental Plots

Canola (Brassica napus) is an important oleaginous crop in Argentina. Approximately 16,000 ha are grown commercially in the southern region of Buenos Aires Province. In 2003, typical symptoms and signs of charcoal rot were observed on canola plants in experimental plots located at the School of Agricultural Sciences, University of Buenos Aires in Buenos Aires. Average disease incidence across three 5- to 6-month-old plants (cvs. Monty, Rivette, and Trooper) was 12% (range = 7 to 17%). Affected plants appeared in patches following the rows at pod-filling stage. Symptoms included wilted foliage, premature senescence, and death of plants. Black, spherical microsclerotia 78 to 95 μm in diameter were present in vascular tissue of basal stems and taproots. The affected plants were stunted and had unfilled pods. In advanced phases of the disease, areas of silver gray-to-black discoloration were observed in the stem cortex; many plants were killed during late-grain fill, and plants could be pulled easily from the ground because basal stems were shredded. Four samples consisting of five symptomatic plants per sample were randomly collected from experimental plots. Pieces (1-cm long) taken from taproots and basal stems of diseased plants were surface sterilized with 1% NaOCl for 2 min and then placed on potato dextrose agar (PDA). Plates were incubated in the dark at 26°C for 4 days and then exposed to 12-h NUV light/12-h dark for 6 days. Five resulting isolates were identified as Macrophomina phaseolina (Tassi) Goidanich (1) based on the gray color of the colony and the presence of microsclerotia 71 to 94 μm in diameter. Two colonies developed globose pycnidia with one-celled, hyaline, and elliptic conidia. Pathogenicity tests were conducted using four inoculated and three non-inoculated control plants potted in a sterilized soil mix (soil/sand, 3:1) in a greenhouse at 25°C and 75% relative humidity with no supplemental light. Crown inoculations were carried out by placing a disk taken from an actively growing culture of M. phaseolina into wounds made with a sterile scalpel. Control plants received disks of sterile PDA. Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Three isolates caused disease on 7-week-old canola plants (cvs. Master, Mistral, Rivette, and Trooper). Characteristic symptoms similar to the original observations developed for all three isolates within 21 days after inoculation on 80% of inoculated plants. The pathogen was successfully reisolated from diseased stem tissue in all instances. Symptoms included leaf necrosis, stunting, decay and collapse of seedlings, and plant death. Control plants remained asymptomatic. The experiment was repeated once with similar results. To our knowledge, this is the first report of the occurrence of M. phaseolina causing charcoal rot on canola in Argentina. This pathogen has been previously reported in the United States (2,3). The results demonstrate the potential importance of this pathogen in Argentina, since two commercial cultivars (Master and Mistral) were apparently susceptible to M. phaseolina. More studies are needed to determine the presence of charcoal rot in canola-growing areas of Argentina. References: (1) Anonymous. Macrophomina phaseolina. No. 275 in: Descriptions of Plant Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1970. (2) R. E. Baird et al. Plant Dis. 78:316, 1994. (3) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989.

scholarly journals First Report of Ascochyta rabiei Causing Ascochyta Blight of Chickpea in Argentina

Plant Disease ◽  
2012 ◽  
Vol 96 (9) ◽  
pp. 1375-1375 ◽  
Author(s):  
G. Viotti ◽  
M. A. Carmona ◽  
M. Scandiani ◽  
A. N. Formento ◽  
A. Luque
Keyword(s):  
Disease Incidence ◽  
Ascochyta Blight ◽  
Morphological Characteristics ◽  
Pathogenic Fungi ◽  
Ascochyta Rabiei ◽  
Infected Leaf ◽  
Buenos Aires Province ◽  
Conidial Suspension ◽  
First Report ◽  
Plastic Bags

In November 2011, lesions similar to those reported for Ascochyta blight (1) were observed on Cicer arietinum L. (chickpea) plants growing in three commercial fields located at Río Primero and Río Segundo (Cordoba Province) and Lobería (Buenos Aires Province), Argentina. Disease incidence (percentage of plants affected) was 100% in all fields surveyed. Plants showed leaves, petioles, stems, and pods with brown lesions. Symptoms on leaves and pods were circular to oval (2 to 14 mm) while in the stems the lesions were elongated (2 to 30 mm). Seeds appeared small and shriveled with brown discoloration. Morphology of the fungi was examined on infected tissues. Numerous black pycnidia measuring 94.6 to 217.9 μm (145.9 ± 28.8 μm), arranged in concentric rings, were observed within of all the lesions. Conidia were predominantly aseptate, straight, hyaline with blunt ends, and measured 9.3 to 12.9 (11.3 ± 1.12) × 3.3 to 5.0 μm (4.2 ± 0.51). Morphological characteristics of the pathogen were similar to those described for Ascochyta rabiei (Pass.) Labrousse (teleomorph Didymella rabiei (Kovacheski) v. Arx (= Mycosphaerella rabiei Kovacheski)) (2). Fungus from infected leaf tissues was isolated on potato dextrose agar. Pathogenicity tests were conducted on seedlings of the susceptible cultivar by spraying leaves of each of 100 seedling plants with 10 ml of a conidial suspension (2 × 104 conidia/ml) of the isolated pathogen with a handheld atomizer. Plants were covered with plastic bags and placed in a growing chamber at 20 to 25°C for 3 days. The plastic bags were removed and the plants were maintained in high humidity at the same temperature. Noninoculated plants were used as controls. After 5 days, all inoculated plants showed typical symptoms. Foliar and stem lesions symptoms were similar to those originally observed in the field. Control plants remained healthy. Koch's postulates were fulfilled by isolating A. rabiei from inoculated plants. The colonies and the morphology of conidia were the same as those of the original isolates. To our knowledge, this is the first report of A. rabiei infecting chickpeas in Argentina. The outbreak of Ascochyta blight in Argentina is of concern because of its severity and the possibility that the pathogen was introduced on seed. This report underscores the need for further research on effective management programs for Ascochyta blight. References: (1) B. Bayaa and W. Chen. Compendium of Chickpea and Lentil Diseases and Pests The American Phytopathological Society, St. Paul, MN, 2011. (2) E. Punithalingam and P. Holliday. Page 337 in: CMI Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1972.

scholarly journals Occurrence of Fusarium Wilt Caused by Fusarium oxysporum on Common Sage in Argentina

Plant Disease ◽  
2006 ◽  
Vol 90 (6) ◽  
pp. 833-833
Author(s):  
S. A. Gaetán ◽  
M. Madia
Keyword(s):  
Fusarium Oxysporum ◽  
Fusarium Wilt ◽  
Buenos Aires ◽  
Disease Incidence ◽  
Wilt Disease ◽  
Buenos Aires Province ◽  
Conidial Suspension ◽  
Koch’S Postulates ◽  
Koch's Postulates ◽  
Open Fields

Common sage (Salvia officinalis L.) is being increasingly grown commercially in Argentina for its medicinal properties and as ornamental plants. Although the crop can be produced in greenhouses, most of the crop production is in open fields in Buenos Aires, Córdoba, and Santa Fe provinces. During the last 3 years, common sage has repeatedly shown decline symptoms in several production fields in the southern region of Buenos Aires Province. In the spring of 2004, a serious common sage wilt disease developed under field conditions resulting in as much as 15% loss of plants. The disease, affecting 10-month-old common sage plants, was observed in this region in two commercial fields located at Sierra de la Ventana. Affected plants appeared in irregular patches throughout the rows. Diseased plants exhibited symptoms of chlorosis, wilting, and death. Lower leaves on wilted plants showed gradual yellowing, apical necrosis, and premature defoliation. At advanced stages of the disease, irregular, brown, necrotic areas on the leaves occurred. The necroses on affected leaf parts occasionally expanded and coalesced to form large necrotic lesions that turned the entire leaf brown. Other symptoms included stunting, black streaking on stems, and rotting of roots. Longitudinal sections through stems and roots showed severely necrotic vascular tissue. Pieces taken from stems and roots of diseased plants were plated on potato dextrose agar after surface sterilization with 1% NaOCl for 3 min. The plates were incubated in the dark for 2 days and then kept under 12-h alternations of NUV light/dark for 8 days. On the basis of morphological and cultural characteristics, two fungal colonies were identified as Fusarium oxysporum Schlechtend.:Fr. (1) and used in the following studies. Pathogenicity tests were carried out on 4-month-old healthy common sage plants. Koch's postulates were completed for two isolates by dipping the roots of seedlings in a conidial suspension (2 × 105 conidia/ml) of a single-spore isolate for 25 min. Plants were repotted in a sterilized soil mix (soil/sand, 2:1). The experiment was conducted in a greenhouse at 23 to 25°C and 75% relative humidity with no supplemental light. Within 14 days, all inoculated plants showed typical Fusarium wilt symptoms similar to that observed in the field. Plants exhibited yellowing followed by wilting of foliage, rotting of roots, brown vascular discoloration, and then eventually collapsed. Four weeks postinoculation, 90% of the plants were dead. No symptoms were observed on control plants dipped only in distilled water. The fungus was successfully reisolated from the symptomatic plants, fulfilling Koch's postulates in all instances. F. oxysporum had been previously reported in 1995 to cause a wilt disease in clary sage (Salvia sclarea L.) fields in North Carolina; the disease was detected at seedling stage, reducing plant stand as much as 40 to 50% (2). In Argentina, the pathogen that caused wilt symptoms on common sage had also been observed in 2002 in greenhouses on the outskirts of Buenos Aires, although the disease incidence was low. At this time, the disease could become a limiting factor in common sage production and further information regarding this pathogen within the region is needed. To our knowledge, this is the first report of the occurrence of Fusarium wilt caused by F. oxysporum on commercial S. officinalis in open fields in Argentina. References: (1) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press. University Park, PA, 1983. (2) V. P. Subbiah et al. Plant Dis. 80:1080, 1996.

scholarly journals First Report of Gray Leaf Spot Caused by Alternaria brassicae on Canola in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (2) ◽  
pp. 207-207 ◽  
Author(s):  
S. Gaetán ◽  
M. Madia
Keyword(s):  
Leaf Spot ◽  
Buenos Aires ◽  
Disease Incidence ◽  
Leaf Tissue ◽  
Climatic Conditions ◽  
Gray Leaf Spot ◽  
Conidial Suspension ◽  
Alternaria Brassicae ◽  
First Report ◽  
And Control

Canola (Brassica napus) is a developing oleaginous crop grown commercially in Argentina. During 2003, typical symptoms of a foliar disease were observed on canola plants in experimental field plots in Buenos Aires. Average disease incidence across 14 6-month-old canola cultivars was 27% (range 12 to 42%). Climatic conditions in Buenos Aires during August 2003 included moderate temperatures and periods with high humidity, which were apparently favorable for disease development. Symptoms were observed on leaves, stems, and pods. Leaf symptoms were randomly distributed on the adaxial surfaces and consisted of zonate lesions of alternating light gray and dark brown areas that were 6 to 10 mm in diameter. Remaining leaf tissue was chlorotic and affected leaves abscised. Stem infections appeared as irregular and elongated black lesions, 0.7 to 1.2 cm long. Pods lesions were circular, 6 to 8 mm in diameter, gray in the center, and surrounded by a diffuse dark brown margin. The disease developed progressively from the lower leaves to the pods, resulting in premature senescence of the tissues, chlorosis, and defoliation. Conidiophores bearing conidia colonized the lesions as a dark gray growth of spore masses. Segments (0.5 cm long) taken from leaves, stems, and pods of diseased plants were dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 2 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar. Plates were incubated in the dark at 25°C for 2 to 3 days, followed by incubation under NUV light and a 12-h light/dark photoperiod for 6 to 8 days. Six fungal isolates were obtained. Fungal colonies were pale gray with dark concentric rings. Conidia were yellow to pale brown, ellipsoid to ovoid, produced singly or in short chains, with 8 to 10 transverse septa and 2 to 6 longitudinal septa. The spore body measured 13 to 22 × 68 to 135 µm with a beak cell 42 to 101 µm long. On the basis of conidial and cultural characteristics, the fungus was identified as Alternaria brassicae (Berk.) Sacc (1). Koch's postulates were completed for three isolates by spray-inoculating foliage of 6-week-old canola plants of cvs. Caviar, Dunkeld, Eclipse, Impulse, Mistral, and Sponsor with a conidial suspension (1 × 105 conidia per ml). The experiment, which included four inoculated plants and two noninoculated control plants for each cultivar per isolate, was conducted in the greenhouse at 22 to 24°C and maintained at 75% relative humidity with no supplemental light. Inoculated and control plants were covered with polyethylene bags for 48 h after inoculation. Within 12 days, inoculated plants developed small, brown lesions on leaves and stems for all three isolates; the pathogen was successfully reisolated in all instances. Control plants, inoculated only with sterile distilled water, remained symptomless. The experiment was repeated with similar results. The results suggest that A. brassicae may be a threat to the main cultivars being grown in Argentina. To our knowledge, this is the first report of A. brassicae causing gray leaf spot of canola in Argentina. Reference: (1) J. Joly. Le genre Alternaria. Recherches Physiologiques, Biologiques, et Systématiques. Paul Lechevalier, ed. Paris, France, 1964.

scholarly journals Occurrence of Stem Rot on Canola Caused by Sclerotinia sclerotiorum in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (5) ◽  
pp. 530-530 ◽  
Author(s):  
S. Gaetán ◽  
M. Madia
Keyword(s):  
United States ◽  
Sclerotinia Sclerotiorum ◽  
Buenos Aires ◽  
Disease Incidence ◽  
Fungal Growth ◽  
Ground Level ◽  
The United States ◽  
Stem Rot ◽  
Buenos Aires Province ◽  
Rot Disease

Canola (Brassica napus) was introduced as an alternative crop for wheat in Argentina. During 2003, typical symptoms of stem rot disease were observed on canola plants in two commercial fields located at Bragado, in northern Buenos Aires Province in Argentina. Average disease incidence across four canola cultivars was 21% (range = 13 to 29%). Symptoms included chlorosis and wilting of foliage and necrosis of basal stems. The disease appeared singly or in patches consisting of 4- to 5-month-old plants. The first visible symptom noticed was chlorosis and wilting of the foliage beginning from the basal leaves. Infection of the main stem at ground level typically was followed by a grayish white discoloration that progressed above the soil line to the apex. In advanced stages of the disease, stems and branches became bleached and eventually died. Black and irregularly shaped sclerotia (average size 5.5 × 2.8 mm) inside necrotic stem tissue were the typical signs of the pathogen. From September to October 2003, four samples consisting of six affected plants per sample were arbitrarily collected from two commercial fields located at Bragado. Sclerotia were taken from diseased stems, dipped in 70% ethanol, surface sterilized with 1% sodium hypochlorite for 1 min, and rinsed in sterile water. Each sclerotium was blotted dry on sterile Whatman's filter paper and placed on potato dextrose agar. Plates were incubated in the dark at 25°C for 2 to 3 days, followed by incubation under 12-h NUV light/12-h dark for 6 to 8 days. Six resulting colonies were identified as Sclerotinia sclerotiorum (Lib.) de Bary on the basis of taxonomic characteristics of the plant pathogenic species of Sclerotinia (3). Koch's postulates for three fungal isolates from infected plants were carried out on 6-week-old canola plants (cvs. Eclipse, Impulse, Master, and Mistral) by placing a colonized agar disk into wounds made in the basal stem region with a sterile scalpel. Pathogenicity tests, which included five inoculated and three control plants potted in a sterilized soil mix (soil/sand, 3:1), were conducted in a greenhouse at 23 to 26°C and 75% relative humidity with no supplemental light. Characteristic symptoms identical to the original observations developed within 12 days after inoculation on 100% of the inoculated plants for three isolates. Symptoms included wilted foliage, collapsed plants, and plant death. White mycelium and sclerotia developed on infected tissues, and the pathogen was successfully reisolated from symptomatic plants in all instances. Control plants, which were treated similarly except that the agar disk did not contain fungal growth, remained healthy. The experiment was repeated, and the results were identical to the first inoculations. Canola stem rot disease incited by S. sclerotiorum was first reported in Argentina during 1995 at experimental field plots in Buenos Aires. S. sclerotiorum, which has been reported to cause disease in canola in Canada (2) and the United States (1,4), currently represents a serious problem to the main canola cultivars grown in Argentina. To our knowledge, this is the first report of the occurrence of S. sclerotiorum causing a high incidence of stem rot in commercial crops of canola in Argentina. 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) L. B. Jamaux et al. Plant Pathol. 44:22, 1995. (3) L. M. Kohn. Phytopathology 69:881, 1979. (4) D. V. Phillips et al. Phytopathology 92:785, 2002.

scholarly journals First Report of Cochliobolus sativus Causing Leaf Spot on Paper Mulberry in China

Plant Disease ◽  
2011 ◽  
Vol 95 (12) ◽  
pp. 1586-1586 ◽  
Author(s):  
P. S. Wu ◽  
K. Chen ◽  
H. Z. Du ◽  
J. Yan ◽  
Q. E. Zhang
Keyword(s):  
Leaf Spot ◽  
Leaf Tissue ◽  
Pathogenic Fungi ◽  
Bipolaris Sorokiniana ◽  
Causal Agent ◽  
Cochliobolus Sativus ◽  
Conidial Suspension ◽  
Sterile Water ◽  
First Report ◽  
Forest Park

Paper mulberry, Broussonetia papyrifera (L.) Vent., is a highly adaptable, fast-growing tree that is native to eastern Asia. Its ability to absorb pollutants makes it ideal for ornamental landscapes, especially in industrial and mining areas. During the summer of 2010, brown lesions were observed on leaves of paper mulberry in Baiwangshan Forest Park, Beijing, China. These lesions were ovoid to fusiform and 4 to 9 × 2 to 4 mm with dark brown centers and light brown irregular edges. Spots on severely infected leaves sometimes coalesced to form long stripes with gray centers. To isolate the causal agent of the lesions, 4-mm2 pieces of diseased leaf tissue from 12 leaves were collected at the lesion margins and surface disinfected in 0.5% NaOCl for 3 min, rinsed three times with sterile water, plated on water agar, and incubated at 25°C with a 12-h photoperiod. After 5 days, the cultures, which became dark brown to black, were observed. Conidiophores (120 to 220 × 4 to 7 μm) were solitary or in groups of two to five, straight or flexuous with swollen bases, and light or dark brown. Conidia were dark olive brown, spindle- or oval-shaped with truncated ends (60 to 120 × 15 to 30 μm), slightly curved, and containing 3 to 12 distoseptate (mostly 6 to 10). Pseudothecia, produced after 14 days in culture, were dark brown to black and flask shaped (420 to 530 μm in diameter with 85 to 100 × 75 to 90 μm ostiolar beaks). Asci were cylindrical (100 to 220 × 30 to 40 μm) and contained eight ascospores. Ascospores were filiform, (150 to 360 × 6 to 9 μm), hyaline, with 6 to 11 septations. Isolates were identified as Cochliobolus sativus (Ito & Kurib.) Drechsler & Dastur (anamorph Bipolaris sorokiniana (Sacc. & Sorok.) Shoem.) on the basis of culture color and dimensions and colors of pseudothecia, asci, ascospores, conidiophores, and conidia (2,3). The identity of one isolate was confirmed by ITS1-5.8S-ITS2 rDNA sequence (GenBank Accession No. HQ 654781) analysis that showed 100% homology to C. sativus listed in Berbee et al. (1). Koch's postulates were performed with six potted 3-month-old paper mulberry plants. An isolate was grown on potato dextrose agar for 14 days to obtain conidia for a conidial suspension (3 × 104 conidia/ml). Three of the potted plants were sprayed with the conidial suspension and three were sprayed with sterile water as controls. Each plant was covered with a plastic bag for 24 h to maintain high humidity and incubated at 25°C with a 12-h photoperiod. After 7 days, the inoculated plants showed leaf symptoms identical to those previously observed on paper mulberry trees in the Baiwangshan Forest Park, while control trees remained symptom free. Reisolation of the fungus from the inoculated plants confirmed that the causal agent was C. sativus. C. sativus is widely distributed worldwide causing a variety of cereal diseases. Wheat and barley are the most economically important hosts. To our knowledge, this is the first report of C. sativus as a pathogen causing leaf spot of paper mulberry in China. References: (1) M. L. Berbee et al. Mycologia 91:964, 1999. (2) M. B. Ellis. Dematiaceous Hyphomycetes. CABI, Oxon, UK, 1971. (3) A. Sivanesan et al. No.701 in: Descriptions of Pathogenic Fungi and Bacteria. CAB, Kew, Surrey, U.K., 1981.

scholarly journals First Outbreak of Bacterial Leaf Spot Caused by Xanthomonas campestris on Canola in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (6) ◽  
pp. 683-683 ◽  
Author(s):  
S. Gaetán ◽  
N. López
Keyword(s):  
Host Range ◽  
Leaf Spot ◽  
Xanthomonas Campestris ◽  
Pathogenic Bacteria ◽  
Buenos Aires ◽  
Disease Incidence ◽  
Bacterial Suspension ◽  
Leaf Margin ◽  
Buenos Aires Province ◽  
Bacterial Leaf Spot

Canola (Brassica napus) is an alternative crop to wheat in Argentina and ~16,000 ha are grown commercially in southern Buenos Aires Province. During 2003, experimental field plots of canola plants located at Agronomy Faculty, University of Buenos Aires, in Buenos Aires were severely damaged by a bacterial leaf spot. Average disease incidence across 25 2- to 5-month-old canola cultivars was 58% (range = 27 to 89%). During 2004, identical infection associated with blackened veins (8 to 12% of plants) were found in two commercial fields and experimental crops (rosette and flowering stages) in Tres Arroyos in southern Buenos Aires Province. Symptoms observed on adaxial surfaces consisted of v-shaped necrotic lesions on leaf margin surrounded by yellow halos. Yellow bacterial ooze was found on young lesions. The advanced phases of the disease included lesion enlargement, foliar chlorosis, and death of leaves. The disease developed from the lower leaves to the apex, resulting in complete leaf necrosis and defoliation. Ten samples (five plants per sample) with lesions were arbitrarily collected from 2003 to 2004 from commercial and experimental canola crops. Diseased leaf tissue was surface sterilized in 0.50% sodium hypochlorite for 30 s and rinsed in sterile distilled water (SDW). Leaf sections were macerated in SDW, and the extract was streaked onto nutrient agar. Plates were incubated at 28°C for 3 days. Resultant colonies were yellow, mucoid, and convex. Gram-negative, aerobic, and rod-shaped bacteria were obtained. Eight strains were biochemically characterized using API 20NE (BioMerieux, Marcy l'Etoile, France) and identified as Xanthomonas campestris (1). Strains hydrolyzed starch, gelatine, and aesculin and were positive for catalase and negative for oxidase, nitrate reduction, ureasa, and triptophanase. Strains were capable of utilizing D-glucose, D-mannose, D-maltose, malic acid, and N-acetyl-glucosamine. X. campestris. pv. campestris 8004 was used as a reference strain (2). Pathogenicity and host range for three isolates were completed by injecting a bacterial suspension (107 CFU/ml) into leaves of 2-week-old canola plants (cvs. Eclipse, Impulse, Master, and Mistral), cabbage (B. oleracea var. capitata), and cauliflower (B. oleracea var. botrytis) seedlings (two-leaf stage). The experiment (four inoculated and two control plants for each cultivar and each strain) was conducted in a greenhouse at 24°C and 75% relative humidity. Inoculated and control plants were enclosed in a plastic bag for 48 h after inoculation. Chlorotic patches on the leaves followed by a dry, brown necrosis spread beyond the initial injected area were observed in inoculated plants 8 days after inoculation. Enlarged spots caused death of leaves. The pathogen was successfully reisolated. Control plants, inoculated only with SDW, remained symptomless. The results suggest that the bacterium represents a potential threat to canola production in Argentina and indicate the need for further study to identify the pathovar involved in canola leaf spots. To our knowledge, this is the first report of an outbreak of X. campestris causing leaf spot of canola and in which the bacteria affecting canola commercial crops was biochemically characterized and host range was carried out in Argentina. References: (1) N. W. Schaad et al. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul. MN, 2001. (2) P. Turner et al. Mol. Gen. Genet. 195:101, 1984.

scholarly journals Leaf Spot and Stem Blight Caused by Botrytis cinerea on Poinsettia in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (12) ◽  
pp. 1359-1359
Author(s):  
H. E. Palmucci ◽  
P. E. Grijalba
Keyword(s):  
Botrytis Cinerea ◽  
Leaf Spot ◽  
Buenos Aires ◽  
Pathogenic Fungi ◽  
Pathogenicity Test ◽  
Euphorbia Pulcherrima ◽  
Conidial Suspension ◽  
Stem Blight ◽  
Potted Plants ◽  
Leaf Spots

Poinsettia (Euphorbia pulcherrima Will. ex. Klotzsch) is a worldwide potted or landscape ornamental plant that belongs to the Euphorbiaceae family. During 2003 and 2004, several symptoms were observed on poinsettia potted plants in nurseries and crops near Buenos Aires. Symptoms included irregular, brown, water-soaked spots on adult plants and leaf spots that extended causing stem blight in seedlings. Small pieces of diseased tissues were surface disinfected for 2 min in 2% sodium hypochlorite, plated on 2% potato dextrose agar (PDA), and incubated at 22°C for 48 h. Dense, whitish mycelia developed on PDA and then turned gray when asexual structures were formed. The fungus conidia were ellipsoid, hyaline, nonseptate, and were formed on botryose heads. The pathogenicity test was carried out on 10 plants using a conidial suspension (2 × 106 spores per ml) that was sprayed on leaves with and without injuries. All plants were incubated in a moist chamber at 22 ± 2°C for 48 h and then maintained in a greenhouse. After 3 days, symptoms similar to the original were observed on the inoculated plants. Control plants sprayed with distilled water remained symptomless. Koch's postulates were confirmed by reisolating the same fungus from diseased plants. In accordance with conidial and cultural characteristics, the pathogen was identified as Botrytis cinerea Pers: Fr. (1). To our knowledge, this is the first report of B. cinerea causing leaf spot and stem rot on poinsettia in Buenos Aires, Argentina. Reference: (1) M. V. Ellis and J. M. Waller. No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1974.

scholarly journals First Report of Blueberry Botrytis Blight in Buenos Aires, Entre Ríos, and Córdoba, Argentina

Plant Disease ◽  
2007 ◽  
Vol 91 (5) ◽  
pp. 639-639 ◽  
Author(s):  
P. Vasquez ◽  
J. A. Baldomá ◽  
E. R. Wright ◽  
A. Pérez ◽  
M. Divo de Sesar ◽  
...  
Keyword(s):  
Botrytis Cinerea ◽  
Buenos Aires ◽  
Morphological Characteristics ◽  
Leaf Tissue ◽  
Pathogenic Fungi ◽  
Vaccinium Corymbosum ◽  
Distilled Water ◽  
First Report ◽  
Conidial State ◽  
Entre Rios

Since 2003, a new field disease has been observed on several cultivars of highbush blueberry (Vaccinium corymbosum L.) in Buenos Aires (Baradero, Colonia Urquiza, Lima, Mercedes, and San Pedro), Entre Ríos (Concordia, Gualeguaychú, and Larroque), and Córdoba (Capilla del Monte and La Cumbre). Infected flowers turned brown to tan with a water-soaked appearance and shriveled up. Blighted flowers typically did not produce fruits; even an entire cluster of berries could be aborted. A chlorotic area, that later became necrotic and turned light brown, developed when leaves were in contact with blighted flowers. A watery rot developed on fruit occasionally before harvest but more generally after harvest. Infected tender green twigs also became blighted, with leaf tissue becoming brown to black. Older twigs and stems were also blighted. Abundant, gray mycelium with conidial masses developed on all affected tissues under moist conditions. Sections of infected leaves, twigs, stems, flowers, and fruits were surfaced sterilized with 0.2% NaOCl, plated on 2% potato dextrose agar (pH 7), and incubated at 22°C. Pure cultures formed a whitish dense mycelial mat and turned gray after 72 h. Conidia were ellipsoid, hyaline, nonseptate, and formed on botryose heads. They ranged from 5.8 to 9 × 8.1 to 13.7 μm (average 8.6 × 10.2 μm). Black, round, and irregular microsclerotia developed on 7-day-old cultures with an average size of 1.1 × 1.7 mm. Morphological characteristics agree with those described for Botrytis cinerea Pers.:Fr (1). Pathogenicity was tested on 10 12-month-old potted blueberry plants cv. O'Neal by spraying a suspension of 1 × 106 conidia per ml of sterile distilled water. Ten plants used as controls were sprayed with sterile distilled water. Each plant was covered with a transparent polyethylene bag for 48 h and incubated at 20 ± 2°C in humid chambers for 15 days. Lesions similar to those observed in the fields developed after 4 days and asexual fructifications developed after 5 days. The same pathogen was reisolated from the lesions, thus completing Koch's postulates. Water-treated plants remained symptomless. To our knowledge, this is the first report of a disease caused by B. cinerea on blueberry in Buenos Aires, Córdoba, and Entre Ríos provinces of Argentina. References: (1) M. V. Ellis and J. M. Waller. Sclerotinia fuckeliana (conidial state: Botrytis cinerea) No. 431 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1974.

scholarly journals First Report of Gray Leaf Spot on Pepper Caused by Stemphylium solani in Malaysia

Plant Disease ◽  
2012 ◽  
Vol 96 (8) ◽  
pp. 1227-1227 ◽  
Author(s):  
A. Nasehi ◽  
J. B. Kadir ◽  
M. A. Zainal Abidin ◽  
M. Y. Wong ◽  
F. Abed Ashtiani
Keyword(s):  
Leaf Spot ◽  
Disease Incidence ◽  
Leaf Tissue ◽  
Gray Leaf Spot ◽  
Universal Primers ◽  
Conidial Suspension ◽  
Internal Transcribed Spacer Region ◽  
First Report ◽  
Morphological Criteria ◽  
Pepper Leaves

Symptoms of gray leaf spot were first observed in June 2011 on pepper (Capsicum annuum) plants cultivated in the Cameron Highlands and Johor State, the two main regions of pepper production in Malaysia (about 1,000 ha). Disease incidence exceeded 70% in severely infected fields and greenhouses. Symptoms initially appeared as tiny (average 1.3 mm in diameter), round, orange-brown spots on the leaves, with the center of each spot turning gray to white as the disease developed, and the margin of each spot remaining dark brown. A fungus was isolated consistently from the lesions using sections of symptomatic leaf tissue surface-sterilized in 1% NaOCl for 2 min, rinsed in sterile water, dried, and plated onto PDA and V8 agar media (3). After 7 days, the fungal colonies were gray, dematiaceous conidia had formed at the end of long conidiophores (19.2 to 33.6 × 12.0 to 21.6 μm), and the conidia typically had two to six transverse and one to four longitudinal septa. Fifteen isolates were identified as Stemphylium solani on the basis of morphological criteria described by Kim et al. (3). The universal primers ITS5 and ITS4 were used to amplify the internal transcribed spacer region (ITS1, 5.8, and ITS2) of ribosomal DNA (rDNA) of a representative isolate (2). A 570 bp fragment was amplified, purified, sequenced, and identified as S. solani using a BLAST search with 100% identity to the published ITS sequence of an S. solani isolate in GenBank (1). The sequence was deposited in GenBank (Accession No. JQ736024). Pathogenicity of the fungal isolate was tested by inoculating healthy pepper leaves of cv. 152177-A. A 20-μl drop of conidial suspension (105 spores/ml) was used to inoculate each of four detached, 45-day-old pepper leaves placed on moist filter papers in petri dishes (4). Four control leaves were inoculated similarly with sterilized, distilled water. The leaves were incubated at 25°C at 95% relative humidity for 7 days. Gray leaf spot symptoms similar to those observed on the original pepper plants began to develop on leaves inoculated with the fungus after 3 days, and S. solani was consistently reisolated from the leaves. Control leaves did not develop symptoms and the fungus was not reisolated from these leaves. Pathogenicity testing was repeated with the same results. To our knowledge, this is the first report of S. solani causing gray leaf spot on pepper in Malaysia. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) M. P. S. Camara et al. Mycologia 94:660, 2002. (3) B. S. Kim et al. Plant Pathol. J. 15:348, 1999. (4) B. M. Pryor and T. J. Michailides. Phytopathology 92:406, 2002.

Sign in / Sign up

Export Citation Format

Share Document