scholarly journals First Report of White Rust of Arugula Caused by Albugo candida in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (2) ◽  
pp. 207-207 ◽  
Author(s):  
R. Zapata ◽  
A. M. Romero ◽  
P. H. Maseda
Keyword(s):  
Buenos Aires ◽  
Pathogenic Fungi ◽  
Buenos Aires Province ◽  
Eruca Sativa ◽  
Abaxial Epidermis ◽  
Albugo Candida ◽  
White Rust ◽  
Plastic Bags ◽  
Pathogenicity Tests ◽  
Zoospore Formation

Production of arugula (Eruca sativa) has increased greatly in Argentina. Since 2002, particularly during the fall, a foliar disease has affected commercial crops in Capilla del Señor (northeast of Buenos Aires Province, Argentina). The disease appeared in foci, spreading throughout the whole production field or greenhouse. Severely affected crops were plowed under. Diseased leaves were chlorotic and had white sori that emerged through the abaxial epidermis. Sori corresponded to the white rust agent, Albugo candida (Pers.) Kunze (1). Sporangiophores were hyaline and clavate, and sporangia were globose and hyaline with a mean diameter of 16.2 μm (14.2 to 19.2 μm). Pathogenicity tests were performed by spraying a suspension of 106 zoospores/ml or 5 × 104 sporangia/ml on four healthy 30-day-old arugula plants. Inoculum was prepared by scrapping sporangia from infected leaves. Sporangia were used directly or incubated in sterile distilled water (SDW) for 14 h at 5°C to induce zoospore formation (2). Four additional healthy plants were sprayed with SDW to serve as controls. Plants were kept in plastic bags for 48 h and maintained in the greenhouse thereafter. White rust symptoms, similar to those observed on the original plants from the field, were observed on inoculated plants 10 days after inoculation. To our knowledge, this is the fist report of A. candida on arugula in Argentina. References: (1) K. Mukerji. No. 458 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1975. (2) H. Scheck and S. Koike. Plant Dis. 83:877, 1999.

scholarly journals First Occurrence of White Rust of Arugula, Caused by Albugo candida

Plant Disease ◽  
1999 ◽  
Vol 83 (9) ◽  
pp. 877-877 ◽  
Author(s):  
H. J. Scheck ◽  
S. T. Koike
Keyword(s):  
Brassica Campestris ◽  
Secondary Infection ◽  
Eruca Sativa ◽  
Santa Barbara ◽  
Albugo Candida ◽  
White Rust ◽  
First Occurrence ◽  
Pathogenicity Tests ◽  
Zoospore Formation ◽  
Plant Pathol

In California, arugula (Eruca sativa) is grown commercially as a component of specialty mixed green salads. In 1999, white rust was observed on arugula in the central coast county of Santa Barbara. Symptoms consisted of white, blisterlike sori beneath the raised host epidermis on the underside of leaves from the seedling stage onward. Secondary infection of flower heads led to staghead development. Affected plantings were severely diseased and were not harvested. The pathogen was confirmed to be Albugo candida (Pers.) Kunze (2). Sporangia diameters ranged from 19.5 to 22.2 μm. Inoculum for pathogenicity tests was prepared by scraping sporangia from infected leaves and incubating them in sterile, distilled water for 12 h at 5°C to induce zoospore formation (1). The following plants were then spray inoculated: arugula, cauliflower (Brassica oleracea subsp. botrytis), Chinese cabbage (Brassica campestris subsp. pekinensis), Japanese mustard (Brassica campestris subsp. nipposinica), red mustard (Brassica juncea subsp. rugosa), and tah tsai (Brassica campestris subsp. narinosa). Twelve plants of each species were inoculated with 1.5 × 104 spores per ml at the six- to eight-leaf stage. Plants were incubated in a dew chamber for 48 h at 18°C and then maintained in a greenhouse at 20 to 24°C. After 10 to 12 days, white rust pustules similar to the original symptoms observed in the field developed only on arugula. The experiment was conducted three times and the results were the same. Distinct biological races of A. candida have been described for some Brassicaceae hosts of white rust (1). This is the first report of white rust of arugula in California caused by A. candida. References: (1) R. S. Pidskalny and S. R. Rimmer. Can. J. Plant Pathol. 7:283, 1985. (2) G. S. Pound and P. H. Williams. Phytopathology 53:1146, 1963.

scholarly journals First Report of Botrytis cinerea on Pansy Flowers in Buenos Aires

Plant Disease ◽  
2004 ◽  
Vol 88 (10) ◽  
pp. 1164-1164
Author(s):  
M. C. Rivera ◽  
S. E. Lopez
Keyword(s):  
Botrytis Cinerea ◽  
Buenos Aires ◽  
Rapid Development ◽  
Pathogenic Fungi ◽  
Gray Mold ◽  
Conidial Suspension ◽  
New Host ◽  
Disease Symptoms ◽  
Plastic Bags ◽  
Pathogenicity Tests

Pansy (Viola × wittrockiana) is an ornamental annual plant produced as a potted plant in greenhouses around Buenos Aires, Argentina. Flower rot with signs of gray mold was observed on pansy cv. Crown during the autumn of 2003. Diseased tissues were surface sterilized by immersion in 2% NaOCl for 1 min, placed on 2% potato dextrose agar (PDA), and incubated at 22°C. Fungal mycelia were initially white and became gray after 72 h. After 4 days, colonies were 4 cm in diameter and sporulated profusely. Black sclerotia developed after 7 days. Mycelia were septate with dark branched conidiophores bearing unicellular, ellipsoid, hyaline conidia that measured 8 to 12 × 6 to 8 μm in botryose heads. These characteristics agree with Botrytis cinerea Pers.:Fr. (1). Pathogenicity tests were performed by spraying 10 healthy pansy plants during bloom with 3 ml of a conidial suspension (106 conidia per ml) per plant. Controls were treated with sterilized distilled water only. Plants were covered with plastic bags for 2 days and incubated at 18 to 22°C. The flowers developed water-soaked lesions between 4 and 6 days after inoculation. Fifty percent of the flowers were pendulous because flower blight reached the peduncle. The pathogen was reisolated from diseased flowers after superficial sterilization with 2% NaOCl and isolated on PDA. Gray mold has a rapid development during bloom, and the pathogen was able to enter undamaged flower tissues. No disease symptoms were observed on leaves. This report adds pansy as a new host of B. cinerea to a previous list of ornamentals grown in Argentina where gray mold was observed. Reference: (1) M. V. Ellis and J. M. Waller. Sclerotinia fuckeliana (condial state: Botrytis cinerea). No. 431 in: Descriptions of Pathogenic Fungi and Bacteria, CMI, Kew, Surrey, UK, 1974.

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 Severe Outbreaks of Soybean Frogeye Leaf Spot Caused by Cercospora sojina in the Pampean Region, Argentina

Plant Disease ◽  
2009 ◽  
Vol 93 (9) ◽  
pp. 966-966 ◽  
Author(s):  
M. A. Carmona ◽  
M. Scandiani ◽  
A. Luque
Keyword(s):  
Leaf Spot ◽  
Buenos Aires ◽  
Buenos Aires Province ◽  
Santa Fe ◽  
Cercospora Sojina ◽  
Northwest Argentina ◽  
Pampean Region ◽  
Frogeye Leaf Spot ◽  
Plastic Bags ◽  
Severity Levels

Frogeye leaf spot of soybean (Glycine max (L.) Merr.) caused by Cercospora sojina Hara was reported to be severe from 1998 to 1999 in northwest Argentina (2). Although the disease was detected at low prevalence (5 to 25%), incidence, and severity in the Pampean Region from 2005 to 2008, no severe outbreaks have been recorded in the provinces of Córdoba, Santa Fe, and Buenos Aires. During the 2008–2009 growing season, disease spread rapidly throughout most soybean-growing areas of the Pampean Region. Disease was observed on almost all varieties of maturity group (MG) III, IV, and V. Symptoms on leaves were circular, reddish brown-to-gray spots (1 to 6 mm) and bordered by typical, narrow, reddish purple margins. Morphology of the fungi was examined on infected tissues. Conidiophores were light-to-dark brown, fasciculate, geniculate, and measured 110 to 203 μm long. Conidia were 1 to 9 septate, hyaline, elongate to fusiform, and measured 26 to 111 (47.3 ± 14.7) × 5.2 to 7.4 μm (6.1 ± 0.7). Pathogenicity tests were conducted on seedlings of a susceptible cultivar by spraying leaves of each of 80 plants at the V3 growth stage with 18 ml of a conidial suspension (3 × 104 conidia/ml) with a hand-held atomizer. Plants were covered with plastic bags and placed in a greenhouse at 28 to 30°C for 48 h. The plastic bags were removed and plants were maintained in high humidity at the same temperature. The same number of noninoculated plants was used as controls. After 10 to 12 days, all inoculated plants showed typical symptoms. Koch's postulates were fulfilled by isolating C. sojina from inoculated plants. Control plants remained healthy. Foliar lesions and morphological characteristics of the pathogen were consistent with C. sojina (1). Disease assessments were made for the middle and upper canopy from 15 arbitrarily collected plants. Soybean plants were in growth stages between R3 and R5 during the survey. Incidence (percentage of plants affected) and severity (percentage of leaf area affected with lesions) were visually estimated from each of the 30 soybean-production fields located in Monte Cristo, Alta Gracia, Jesús María, W. Escalante, Monte Buey, (10 fields, Córdoba Province), Venado Tuerto, Villa Cañás, Cristophersen, María Teresa, (12 fields, Santa Fe Province), Pergamino, Rojas, and Salto (8 fields, Buenos Aires Province). Incidence was 100% in all fields from Córdoba and Santa Fe. Incidence in Buenos Aires was 0 to 100%. Highest severity levels were quantified from fields in Córdoba (severity of 30 to 60%). Lesions also developed on stems and pods. In samples from Buenos Aires, severity levels were ≤10% in the eight soybean fields. Number of lesions per leaflet was recorded from central leaflets in samples from Monte Cristo, Alta Gracia, Venado Tuerto, and María Teresa with 20 to 55 typical lesions per leaflet. Since the disease was always more important in northwest Argentina, genetic resistance is more commonly available in varieties of MG VII to VIII, so most of the varieties of MG III, IV, and V frequently planted in Pampean Region are susceptible. This fact in combination with rainfall, warm temperatures, and high relative humidity in no-till fields during this summer have encouraged the severe outbreak of frogeye leaf spot, especially in the province of Córdoba and in some regions of Santa Fe. References: (1) D. V. Phillips. Page 20 in: Compendium of Soybean Diseases. 4th ed. The American Phytopathological Society. St. Paul, MN, 1999. (2) D. L. Ploper et al. Plant Dis. 85:801, 2001.

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 First Report of White Rust Caused by Albugo tragopogonis on Sunflower in Belgium

Plant Disease ◽  
2006 ◽  
Vol 90 (3) ◽  
pp. 379-379 ◽  
Author(s):  
C. Crepel ◽  
S. Inghelbrecht ◽  
S. G. Bobev
Keyword(s):  
Morphological Characteristics ◽  
Pathogenic Fungi ◽  
First Record ◽  
Cut Flowers ◽  
Abaxial Surface ◽  
Adaxial Surface ◽  
White Rust ◽  
Initial Symptoms ◽  
Pathogenicity Tests ◽  
Stem Lesions

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.

scholarly journals First Report of Didymella bryoniae Causing Gummy Stem Blight of Chayote in Taiwan

Plant Disease ◽  
2012 ◽  
Vol 96 (10) ◽  
pp. 1578-1578 ◽  
Author(s):  
Y. C. Tsai ◽  
J. F. Chen
Keyword(s):  
Morphological Characteristics ◽  
Pathogenic Fungi ◽  
Molecular Data ◽  
Pathogenicity Test ◽  
Didymella Bryoniae ◽  
Stem Blight ◽  
Gummy Stem Blight ◽  
Plastic Bags ◽  
Pathogenicity Tests ◽  
Stems And Leaves

Chayote (Sechium edule (Jacq.) Swartz, Cucurbitaceae), originally native to Mexico, is an important vegetable known as “dragon-whisker vegetable” and is cultivated for its shoots in Ji-an, Hualien County in eastern Taiwan. In June 2010, 70 to 80% of the chayote plants grown in Ji-an developed necrotic spots on stems, leaves, and fruits. The disease was severe during the warm and rainy season from June to August. The symptoms on stems, leaves, and fruits were water-soaked lesions that eventually dried up, cracked, and produced perithecia on necrotic tissues. A single ascospore was isolated from perithecia harvested from diseased stems and cultured on potato dextrose agar (PDA) at 25°C for 1 month. Colonies of three isolates (SE5, SE6, and SE7) were white to olivaceous green bearing unicellular conidia measuring 2 to 5 × 3 to 10 μm, which is consistent with the morphological characteristics of Didymella bryoniae (Auersw.) Rehm (anamorph Phoma cucurbitacearum (Fr.:Fr.) Sacc.) (1,2,3). DNA of SE5, SE6, and SE7 isolates were obtained using microwave-based method (4). The internal transcribed spacer (ITS) rDNA (GenBank accessions AB714984, AB714985, and AB714986), PCR-amplified using primers ITS1 and ITS4, had 98 to 99% nucleotide sequence identity with D. bryoniae (GenBank Accession Nos. GU045304 and GU592001). A pathogenicity test was conducted in a greenhouse with temperature ranging from 20 to 30°C. Three-day-old mycelial plugs (5 × 5 mm) of the three isolates were placed on the needle-pricked wounds of stems and leaves of 36 4-month-old potted chayote plants wrapped in plastic bags to maintain 100% relative humidity for 2 days. Six days after inoculation, water-soaked lesions formed on the stems and leaves. Controls inoculated with sterile water had no symptoms. The fungus reisolated from the lesions of diseased stems and leaves had morphological characteristics of D. bryoniae. Based on the results of morphology, molecular data, and pathogenicity tests, we reported for the first time to our knowledge that gummy stem blight of chayote is caused by D. bryoniae in Taiwan. References: (1) J. W. Huang and W. R. Hsieh. Plant Prot. Bull. 27:325, 1985. (2) A. P. Keinath et al. Phytopathology 85:364, 1995. (3) E. Punithalingam and P. Holliday. P. 332 in: Descriptions of Pathogenic Fungi and Bacteria. CMI, Kew, Surrey, UK, 1972. (4) S. R. Tendulkar et al. Biotechnol. Lett. 22:1941, 2003.

scholarly journals First Report of White Rust of Rocket (Eruca sativa) Caused by Albugo candida in Montenegro

Plant Disease ◽  
2019 ◽  
Vol 103 (1) ◽  
pp. 163-163
Author(s):  
J. Latinović ◽  
N. Latinović ◽  
J. Jakše ◽  
S. Radišek
Keyword(s):  
Eruca Sativa ◽  
First Report ◽  
Albugo Candida ◽  
White Rust

scholarly journals First Report of Downy Mildew of Arugula Caused by Peronospora parasitica in Argentina

Plant Disease ◽  
2005 ◽  
Vol 89 (6) ◽  
pp. 688-688 ◽  
Author(s):  
A. M. Romero ◽  
R. Zapata
Keyword(s):  
Downy Mildew ◽  
Gray Mold ◽  
Buenos Aires Province ◽  
Peronospora Parasitica ◽  
First Report ◽  
Linear Pattern ◽  
Plastic Bags ◽  
Mean Width ◽  
Pathogenicity Tests ◽  
Symptoms And Signs

Acreage of arugula (Eruca sativa), a crucifer used as a component of green salad mixes, has increased recently in Argentina. During 2004, a foliar disease affected commercial crops in Pilar (northeast of Buenos Aires Province). Arugula plants were affected from the seedling stage to harvest. Severely diseased plants were unmarketable and not harvested. Sunken, round, necrotic lesions (1 to 4 mm in diameter) were observed on the cotyledons. Diseased leaves had irregular, necrotic lesions (2 to 3 mm in diameter) that sometimes became confluent, forming a linear pattern. Necrotic tan patches developed on older leaves. Lesions on the abaxial surface appeared depressed and a gray mold, a typical sign of a downy mildew, was visible. Sporangiophores had dichotomous branches ending in slender curved tips. Sporangia were ovoid with a mean length of 20 μm (17.8 to 22.1 μm) and a mean width of 16 μm (14 to 18.2 μm). Pathogenicity tests were conducted by placing excised diseased leaves onto healthy 30-day-old arugula plants (1). Inoculated plants were placed in plastic bags, previously sprayed with water, for 48 h and maintained in the greenhouse thereafter. Downy mildew symptoms and signs that were similar to those observed in the fields developed 10 days after inoculation. The pathogen was identified as Peronospora parasitica (2). To our knowledge, this is the first report of P. parasitica on arugula in Argentina. References: (1) S. T. Koike. Plant Dis. 82:1063, 1998. (2) W. D. Yerkes and C. G. Shaw. Phytopathology 49:499, 1959.

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.

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