Impact of moisture, host genetics and Fusarium graminearum isolates on Fusarium head blight development and trichothecene accumulation in spring wheat.

The impact of moisture on the development of Fusarium head blight (FHB) and accumulation of deoxynivalenol (DON) in Fusarium-infected wheat was examined. The field experiments were designed as split-split-plot with five replicates. Main plots were durations of mist-irrigation [14, 21, 28 and 35 days after inoculation (DAI)]; sub-plots were wheat cultivar; and sub-sub-plots were F. graminearum isolates differing in aggressiveness and DON production capacity. The wheat cultivars 'Alsen' (moderately resistant), '2375' (moderately susceptible) and 'Wheaton' (susceptible) were inoculated at anthesis. Severity of FHB was assessed 21 days after inoculation. Visually scabby kernels (VSK) and mycotxin content (DON, 15-AcDON, 3-AcDON and nivalenol) were determined on harvested grain. The damage to grain, as measured by VSK, was significantly lower in the treatments receiving the least amount of mist-irrigation (14 DAI) suggesting that extended moisture promotes disease development. DON was, however, significantly lower in the 35-DAI misting treatment than in treatments receiving less post-inoculation moisture. The reduction of DON observed in treatments receiving extended mist-irrigation was greatest in 'Wheaton' which recorded the highest FHB severity, VSK and DON of the cultivars examined. Our results suggest that DON and other trichothecenes may be reduced by late-season moisture despite increased grain colonization. We suggest that leaching may explain much of the reduction of mycotoxins, and that differences in tissue morphology and metabolism may determine the rate of leaching from specific tissues.