First Report of Target Spot of Tobacco Caused by Rhizoctonia solani (AG-3) in Canada. R. D. Reeleder, Agriculture and Agri-Food Canada, Delhi ON, Canada N4B 2W9 . S. Monette, Agriculture and Agri-Food Canada, Delhi ON, Canada N4B 2W9; and D. VanHooren and N. Sheidow, Ontario Ministry of Agriculture, Food and Rural Affairs, Delhi
ON, Canada N4B 2W9. Plant Dis. 80:712. Accepted for publication 19 April 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/PD-80-0712C.
In southwestern Ontario, tobacco (Nicotiana tabacum L.) seedlings are produced on beds of steamed muck in greenhouses prior to transplanting. Damping-off caused by R. solani Kuhn is commonly reported and is usually controlled in greenhouses with applications of benomyl. In May 1993, seedlings with symptoms of damping-off and target spot (2) were collected from greenhouses located on a farm in Norfolk County, Ontario. Basidia and basidiospores of Thanatephorus cucumeris (A B. Frank) Donk (anamorph R. solani) were observed in target spot leaf lesions. Isolates from lesions were paired with AG tester strains and were found to anastomose with AG-3 (ATCC 76167). Isolates causing damping-off, but not target spot, in greenhouses on other farms were assigned to AG-l-IC or AG-2-2. In 1994, target spot was observed in several tobacco fields in Norfolk County and, in 1995, was reported as well from adjacent counties covering much of the tobacco production area in Ontario. Basidia and basidiospores were not observed on affected plants in the field but isolates of R, solani from these plants anastomosed with AG-3 testers. Both basidiospore suspensions (1 × 105 basidiospores per ml) and blended mycelial suspensions (1 × 105 CFU per ml) of field isolates reproduced target spot symptoms on 4-week-old seedling leaves (cv. Del-gold) when inoculated under growth chamber conditions. This disease has previously been reported from South America, South Africa, and the southern United States (1).References: (1) J. S. Johnk et al. Phytopathology 83:854, 1993. (2) J. C Meyer et al. Plant Pathol. 39:206, 1990.