Fusarium head blight and trichothecene production in wheat by Fusarium graminearum and F. meridionale applied alone or in mixture at post-flowering

Abstract

A greenhouse study was conducted to expand our knowledge of the disease and mycotoxin production by Fusarium graminearum (Fgra) and F. meridionale (Fmer) inoculated at post-flowering, either alone or in equal mixture, into three cultivars varying in their reaction to Fusarium head blight (FHB) in the field. In the first experiment, the entire spike was spray-inoculated and the proportion of diseased spikes (or incidence, INC) was monitored up to 15 days after inoculation (dai). In the second experiment, the inoculum was dispensed into the central-spikelet and the proportion of disease spikelets (or severity, SEV) was evaluated at 15 dai. The inoculum composition and the inoculum x cultivar interaction on both experiments were not significant. However, BRS 194, a standard for susceptibility, had significantly higher INC and SEV than BRS Parrudo and BRS 179, the latter a standard for moderate resistance. Fmer was less damaging to grain yield than Fgra and grain yield of BRS Parrudo was the least affected among the cultivars. Trichothecenes (DON + NIV) were detected in both experiments, irrespectively of the cultivar, at levels up to 2,000 and 15,000 μg/kg, in the spray-inoculation and central-spikelet inoculation experiment, respectively. Fgra alone produced only DON and Fgra+Fmer produced mainly DON and small amount of NIV. Fmer produced mainly NIV, but also trace amounts of DON. Our results suggest that post-flowering infections may contribute with trichothecenes in mature grain, especially DON. Nevertheless, NIV should be considered in analytical surveys due to its high toxicity.