Effect of harvesting time on incidence of seed-borne Fusarium spp. in spring wheat in eastern Ontario

The effect of five harvesting times on the incidence of seed-borne Fusarium spp. was examined using three spring wheat cultivars grown at two locations in eastern Ontario in 1999 and 2000. Twelve Fusarium spp. were isolated from 3831 of the 24 000 seeds, which were surface disinfected and plated onto modified potato dextrose agar. Fusarium sporotrichioides Sherb., F. graminearum Schwabe, F. poae (Peck) Wollenw., F. equiseti (Corda) Sacc., and F. avenaceum (Fr.) Sacc. were the most frequently isolated species and were isolated from 6.8, 3.7, 2.8, 1.8, and 0.6% of total seeds, respectively. The remaining species, F. acuminatum Ellis & Everh., F. crookwellense Burgess, Nelson & Toussoun, F. culmorum (W.G. Sm.) Sacc., F. oxysporum Schlecht., F. sambucinum Fuckel, F. solani (Mart.) Sacc., and F. tricinctum (Corda) Sacc., collectively infected only 0.3% of total seeds. The incidence of F. graminearum, F. sporotrichioides, and total Fusarium spp. increased about twofold, from 1.7, 3.9, and 9.5% in seed harvested very early to 5.5, 8.7 , and 19.8%, respectively, after delayed harvest. Also, F. poae had a significantly lower incidence at very early and early harvest times compared to normal or later harvest dates. Incidence of total other Fusarium spp., percentage of fusarium damaged kernels (FDK), and deoxynivalenol (DON) concentration were relatively low in the harvested grain and not affected by harvesting time. Of the three cultivars used, AC Barrie had the lowest incidence of Fusarium spp., FDK, and DON concentration in the grain; Quantum was intermediate; and Celtic had the highest. Variations in the incidence of Fusarium spp. for location and year were observed and likely related to levels of inoculum and weather conditions before and during harvesting times. Key words: Wheat, grain quality, farinograph, protein concentration, N management, cultivar selection and marketing