Disease Note.

First Report of Septoria steviae on Stevia (Stevia rebaudiana) in North America. N. M. Lovering, Royal Sweet Intl. Technol. Ltd., P.O. Box 186, Delhi, Ontario, Canada, N4B 2W9 . R. D. Reeleder, Pest Management Research Centre, Agriculture and Agri-Food Canada, P.O. Box 186, Delhi, Ontario, Canada, N4B 2W9. Plant Dis. 80:959. Accepted for publication 28 May 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0959D.

Stevia (Stevia rebaudiana Bertoni, family Asteraceae) is the source of highly sweet glycosides that arc popular low-caloric sweeteners in southeast Asia. In 1995, diseased stevia plants were observed in British Columbia and Ontario, Canada. Symptoms included depressed, angular, shiny olive-gray foliar lesions that rapidly coalesced and were often surrounded by a chlorotic halo. Leaves quickly became necrotic and often dropped off the plant. Septoria was consistently isolated from diseased leaves on acidified potato dextrose agar, and on water agar amended with streptomycin sulfate and chlortetracycline. Single-spore isolates were made on V8 agar. Pycnidia from these cultures were black, spherical, partially immersed, and measured 60.0 to 300.0 µm in diameter. Conidia were hyaline, filiform, and measured 1.3 to 2.5 x 33.6 to 126.0 µm. This description is consistent with that given for Septoria steviae Ishiba, Yokoyama, & Tani (1). Isolates from British Columbia and\Ontario were morphologically indistinguishable. To confirm pathogenicity, a mixed conidial suspension was prepared from four isolates (two from each province). Six- and 9-week-old stevia plants were inoculated with a conidial suspension (one million spores per ml), placed in a dew chamber for 72 h, and then in a growth chamber for 10 days (240C during the day and 200C at night). The inoculated plants developed angular shiny, olive-gray lesions, often bounded by a vein, and surrounded by a chlorotic halo. S. steviae was re-isolated from diseased tissue. This is the first report of Septoria steviae on Stevia rebaudiana in North America.