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

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.