Effects of Wheat Genotypes and Inoculation Timings on Fusarium Head Blight (fhb) Severity and Deoxynevalenol (don) Production in the Field

Fusarium head blight (scab), caused primarily by Fusarium graminearum (teleomorph: Gibberella zeae), is an important disease of wheat and other cereals worldwide. The disease affects both yield and quality due to contamination of grains with various mycotoxins. Since 1993, the disease has caused billions of dollars loss to the wheat industry in the USA. Due to lack of effective resistant cultivars, FHB is managed through fungicide applications and cultural practices. New fungicides such as ‘Proline’ are effective in FHB management and DON reduction. It has been hypothesized that all wheat cultivars do not respond to fungicide applications in similar manner for DON production and yield increase. Research is in progress to make the FHB forecasting system more accurate. Information on wheat cultivars with various levels of resistance to FHB and their responses to the disease development are important parameters of accurate disease forecasting system. The main objectives of this study were to determine the effects of three hard red spring wheat cultivars, Glenn (FHB resistant), Steel-ND (moderately susceptible) and Trooper (susceptible), and two inoculation timings on FHB development, and to examine the correlation between FHB severity and DON production under field conditions. Wheat cultivars were planted on May 4 and May 14, 2007 at North Dakota State University Experimental Station, Fargo. The experiment was planted as a split-split plot design with 3 replications. Planting date (early and late), wheat cultivars (Glenn, Steel-ND, and Trooper), and inoculation timing (no inoculation, inoculation at early flowering, and inoculation at mid flowering) were assigned in main plot, sub-plot, and sub-sub plot, respectively. Plants were spray-inoculated with F. graminearum (~100,000 spores/ml). Two hundred-twenty-five heads from each sub-plot were examined for FHB incidence and severity, and 20-40 heads with disease severity of 0%, 7-21%, 22-50%, 51-79%, and 80-100% in each sub-plot were tagged at dough stage (Feekes GS 11.2). Wheat ear heads with each disease severity category were collected separately to estimate DON, and correlation between FHB severity and DON production. The cultivars differed significantly in FHB severity, but not in disease incidence and DON production. The resistant wheat cultivar Glenn has the lowest severity (20.6%) while the susceptible cultivar Trooper has the highest disease severity (28.12%). Inoculation timings also had significant effect on FHB incidence, severity, and DON production. All three disease components incidence (12.75%), severity (41%), and DON (2.45 ppm) were higher when the cultivars were inoculated at mid flowering stage (GS 10.52). A positive correlation (r = 0.98) was observed between FHB severity and DON concentration in all three cultivars. As expected, the susceptible cultivar Trooper had higher DON concentration in all five disease severity categories (ranged from 1.06 to 75.68 ppm) as compared to Steel-ND (1.39 to 56.86 ppm) and Glenn (0.91 to 64.63 ppm). The samples with high DON concentration also had with high amount of 3-ADON. Our results indicate that infection at mid flowering growth stage is crucial in FHB incidence, severity, and DON production.