Canola (Brassica napus) is a developing oleaginous crop grown commercially in Argentina, primarily in the southeastern region of Buenos Aires Province. Since 2002, plants exhibiting symptoms of wilt and xylem discoloration were observed in canola plants in experimental field plots located at the University of Buenos Aires, Buenos Aires, Argentina. Average disease incidence in 5- to 6-month-old canola cultivars developed in different countries was 18% (range = 9 to 27%). Disease symptoms that included yellowing, wilting, stunting, and necrosis of leaf tissue and suppressed root development appeared in irregular-shaped patches following the rows of plants. The first symptom observed was leaf yellowing followed by an irregular, brown necrosis of the leaf margins. Lesions coalesced to form large necrotic areas that led to severe defoliation beginning with the lower leaves. As the disease developed, a pale brown discoloration girdled the stems that progressed from the basal tissues to the apex. Affected plants were stunted and had small pods with no seeds. Diseased plants eventually collapsed and died. From June to July 2003, six samples consisting of five affected plants per sample were randomly collected from experimental field plots. Pieces (1 cm long) of disease basal stem tissue were thoroughly washed, surface sterilized in 1% sodium hypochlorite for 1 min, rinsed in sterile distilled water, blotted dry on sterile Whatman's filter paper, and incubated on potato dextrose agar in the dark at 26°C for 10 days. Ten resulting colonies were examined microscopically and identified as Fusarium oxysporum Schlechtend.:Fr. f. sp. conglutinans (Wollenweb.) W.C. Snyder & H.N.Hans. (3). Pathogenicity tests for three single-spore isolates of the fungus were performed on 6-week-old canola plants of cvs. Impulse, Master, Mistral, Monty, Rivette, and Trooper. Koch's postulates were completed for each isolate by dipping the roots of seedlings in a conidial suspension (2 times; 105 conidia per ml) for 15 min. Plants were repotted in a sterilized soil mix (soil/sand, 2:1). The experiment, which included five inoculated plants and three noninoculated (roots dipped in sterile distilled water) control plants for each cultivar, was conducted in a greenhouse at 23 to 25°C and 75% relative humidity with no supplemental light. Characteristic symptoms, identical to the original observations, developed within 14 days after inoculation on 100% of the inoculated plants for all three isolates. The pathogen was successfully reisolated from internal diseased stem tissue in all instances. Symptoms included stunted seedlings, leaf necrosis, and external stem discoloration. None of the control plants developed disease. The experiment was repeated once with similar results. F. oxysporum f. sp. conglutinans, which has been reported to cause disease in canola in Canada (1) and the United States (2), represents a serious threat to the main canola cultivars grown in Argentina. To our knowledge, this is the first report of canola wilt incited by F. oxysporum f. sp. conglutinans in Argentina. References: (1) D. Bernard et al. Can. Plant Dis. Surv. 81:102, 2001. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN, 1989. (3) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press. University Park, PA, 1983.

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.

Canola (Brassica napus) is a developing oleaginous crop grown commercially in the Buenos Aires and Santa Fe provinces of Argentina. During the autumn of 2003, typical signs of powdery mildew were observed on canola plants in experimental field plots in Buenos Aires. Average disease incidence was 42% on 3- to 6-month-old canola cultivars developed in the following countries: Argentina (Eclipse, Impulse Master, Mistral, and Nolza); Australia (Oscar and Rainbow); Canada (Sentry); France (Cadillac, Camberra, and Capitol); and Sweden (Maskot, Sponsor, and Wildcat). The range of incidence on these cultivars was 35 to 93%. Other cultivars exhibited an apparent high level of resistance or escaped disease. These included: Charlton (Argentina); 46CO3, Dunkeld, Insignia, Mystic, Monty, Outback, Rivette, and Surpass 400 (Australia), and Caviar (France). Climatic conditions in Buenos Aires, especially rainfall, from March to May 2003 were apparently favorable for powdery mildew development. On susceptible cultivars, fungal growth was observed on leaves, stems, and pods that resulted in premature senescence of the tissues. The mycelium, with multilobed hausthoria, was white to gray, dense or fine, and in patches or covering the entire adaxial leaf surfaces. Appressoria were lobed and conidiophores were straight. Foot cells were cylindrical, straight, measured 35 to 42 × 7 to 10 μm, and were followed by two cells. Conidia were produced singly, cylindrical to ovoid, and measured 36 to 40 × 18 to 20 μm. The conidial length-to-width ratio was 2.0. No fibrosin bodies were observed in the conidia and conidia germinated at the ends. Cleistothecia were not observed. On the basis of mycelial, conidial, and hausthoria characteristics observed on six leaves for each affected cultivar, the fungus was identified as Erysiphe polygoni DC (1). Pathogenicity was confirmed on 5-week-old canola plants of cvs. Eclipse, Impulse, Master, Mistral, and Maskot by gently pressing (1 min) one adaxial infected leaf with abundant sporulation onto one adaxial healthy leaf. The experiment, which included five inoculated plants and three noninoculated control plants for each cultivar, was conducted 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. Powdery mildew developed on all inoculated plants of all cultivars after 12 to14 days. The control plants did not develop disease. The experiment was repeated with similar results. E. polygoni has a worldwide distribution (2); however, the results suggest that this fungus may be a threat to the main cultivars being grown in Argentina (Eclipse, Impulse, Master, Mistral, and Nolza), since high levels of disease incidence, as much as 70%, were observed. Under propitious environments, this pathogen could cause severe yield losses in commercially grown canola in Argentina. To our knowledge, this is the first report of canola powdery mildew caused by E. polygoni in Argentina. References: (1) H. J. Boesewinkel. Rev. Mycol. Tome 41:493, 1977. (2) D. F. Farr et al. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St.Paul, MN, 1989.

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.

Since 2001, 15 to18% of commercial plantings of the medicinal plant St. John's-wort (Hypericum perforatum L.) in Buenos Aires Province, Argentina were affected by a new disease. Disease symptoms of crown and root rot, wilting, chlorosis, and necrosis of the leaves appeared in circular-to-irregular shaped sectors of 12- to 14-month-old plants. Symptoms began with foliage turning yellow followed by an irregular, brown necrosis of the leaf margins. Lesions coalesced to form large necrotic areas causing a severe defoliation of the basal and upper leaves. A soft rot affected the crown and roots causing a complete maceration of these tissues. Infected plants broke off easily because the crown region and the roots were destroyed. As the disease developed, a dark brown discoloration girdled the stems that progressed above the soil line to the apex. The infected stems became dry and breakable. Finally, the affected plants died. Segments (1 cm long) were taken from roots and rotted crowns of diseased plants, dipped in 70% ethanol, surface sterilized with NaOCl (1%) for 1 min, and rinsed in sterile water. Each segment was blotted dry and placed on potato dextrose agar. Plates were incubated in the dark at 26°C for 4 to 7 days. The predominate fungus isolated from the diseased tissue was identified as Fusarium solani (Mart.) Sacc. (1). Koch's postulates were completed by dipping the roots of seedlings in a 2 × 106 conidia per ml suspension of a single spore isolate for 45 min. Plants were repotted (20 inoculated and 10 controls) in a sterilized soil mix (soil/sand 2:1) and held in the greenhouse at 23 to 26°C. Characteristic symptoms identical to the original developed on 90% of inoculated plants within 2 weeks after inoculation. Symptoms included wilt and collapse, crown and root rot, and death of the plants. The fungus was recovered from symptomatic tissues. Control plants dipped into distilled water remained healthy. The experiment was repeated, and the results were identical to the first inoculations. To our knowledge, this is the first report of St. John's-wort as a susceptible host of F. solani. Reference: (1) P. E. Nelson et al. Fusarium species. An Illustrated Manual for Identification. Pennsylvania State University Press, University Park, 1983.