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.

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.

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.

Canola (Brassica napus) is a minor rotation crop grown since the 1990s in Buenos Aires Province, Argentina because of its potential as a source of biodiesel. During the spring of 2006, typical signs and symptoms of Sclerotinia stem rot were observed on canola plants (cv. Master) in one production field at 9 de Julio locality in Buenos Airs Province. Affected plants were distributed in patches throughout the rows at flowering and podfilling stages resulting in approximately 7 to 11% plant loss. Initial symptoms consisted of yellowing of mature leaves, decaying, and necrosis of lower stems. Ultimately, crowns and lower stems rotted, stems bleached, pods remained unfilled, and entire plants collapsed. White mycelium and numerous small sclerotia appeared on crown tissues. Samples of 20 infected plants were randomly collected in one production field, and 5- to 10-mm pieces of symptomatic tissues were cultured on potato dextrose agar (PDA) for 7 to 8 days after disinfestation with 2% sodium hypochlorite. Four colonies isolated from symptomatic tissues were identified as Sclerotinia minor Jagger (3) on the basis of white, fluffy mycelium containing black, irregularly shaped sclerotia (≤2 mm in diameter) abundantly scattered over the cultured surface. Crown inoculations were performed for two isolates by placing a plug taken from an actively growing culture of S. minor into wounds made on 6-week-old canola plants (cvs. Eclipse, Master, and Mistral). Control plants received plugs of sterile PDA. Inoculated and control plants were enclosed in plastic bags for 72 h. Symptoms similar to those in the affected fields were evident within 2 weeks of postinoculation on inoculated plants, whereas control plants remained healthy. The pathogen was successfully recovered from infected tissues fulfilling Koch's postulates. The experiment was repeated with similar results. Sclerotinia stem rot caused by S. sclerotiorum (Lib.) de Bary was previously reported on canola in Argentina in 2005 (2), and S. minor is a pathogen of B. napus in the United States (1). To our knowledge, this is the first report of Sclerotinia stem rot of canola incited by S. minor 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) S. Gaetán and M. Madia. Plant Dis. 89:530, 2005. (3) C. L. Patterson and R. Grogan. Plant Dis. 72:1046, 1988.