36th International Carrot Conference Abstract

Pathogenicity, chemical sensitivity and management of Fusarium spp. infecting carrots

M.M. MACDONALD, R.D. PETERS, L. HALE, J. KEMP, T. BARASUBIYE, J. DRISCOLL, G. DYKERMAN, S. ADAMS, A. RYAN, C. BANKS, A. MACPHAIL, D. GREGORY and K.A. DRAKE.

University of Prince Edward Island, 550 University Ave., Charlottetown, PE C1A 4P3, Canada; (R.D.P, A.M, D.G, K.A.D.) Agriculture and Agri-Food Canada, Crops and Livestock Research Centre, 440 University Ave., Charlottetown, PE C1A 4N6, Canada; (T.B.) Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Research Centre, 960 Carling Ave., Ottawa, ON K1A 0C6, Canada; (J.D., S.A., A.R.) Prince Edward Island Horticultural Association, P.O. Box 2232, Charlottetown, PE C1A 8B9, Canada; (G.D.) Brookfield Gardens, 1067 Millboro Rd., RR#4 North Wiltshire, PE C0A 1Y0, Canada; and (C.B.) Prince Edward Island Department of Agriculture and Forestry, P.O. Box 2000, Charlottetown, PE C1A 7N8, Canada.

Fusarium crown rot, formerly a storage disease of carrots, was present in Prince Edward Island (PEI) fields in 2011 and 2012. Crown lesions on carrots resulted in rejection rates as high as 60-70% during grading for storage in 2011. Infecting organisms were identified as Fusarium avenaceum and F. oxysporum in samples obtained from field and storage. Research was conducted to assess the pathogenicity and chemical sensitivity of isolates of each species. In a replicated trial conducted according to Koch’s postulates, all isolates (10) of F. avenaceum were highly pathogenic to carrot tissue and all isolates (4) of F. oxysporum were weakly pathogenic in comparison to F. avenaceum and treatment controls (uninoculated). Isolates were tested for fungicide sensitivity in an amended agar assay, using six concentrations of five commercial fungicides as well as technical grade difenoconazole, fludioxonil, and thiabendazole. EC₅₀ values (the fungicide concentration at which fungal growth is inhibited by 50% compared to the control) were determined for each isolate. Analysis of isolates indicated growth suppression occurred when F. oxysporum was exposed to Quadris Top (azoxystrobin/difenoconazole; EC₅₀ = 1-2 mg/L), difenoconazole (EC₅₀ = 5-7 mg/L), or thiabendazole (EC₅₀ = 0.5-1 mg/L) and when F. avenaceum, the organism of greater pathogenicity, was exposed to thiabendazole (EC₅₀ = 1-10 mg/L) or fludioxonil (EC₅₀ = 1-10 mg/L). Five commercial fungicides including Bravo (chlorothalonil), Manzate (mancozeb), Polyram (metiram), Pristine (pyraclostrobin/boscalid) and Quadris Top (azoxystrobin/difenoconazole), were applied in a replicated field trial containing nine treatment schedules (eight with fungicide plus one control). Field ratings indicated that all treatments significantly decreased the incidence of Sclerotinia rot and Alternaria leaf blight. Data collected post-harvest indicated that none of the treatments significantly decreased Fusarium crown rot. Further studies are underway to develop management options to combat this destructive disease, including field application of chemistries found to be inhibitive to fungal growth in in vitro assays.

Last updated Thursday, 25-Jul-2013 11:52:37 CDT