Effect of infection timing on severity of Fusarium head blight and deoxynivalenol accumulation in two wheat cultivars differing in resistance

Abstract

The effects of the timing of inoculation (before or after flowering) of ‘Shiranekomugi’ (moderately resistant) and ‘Yukichikara’ (relatively susceptible) cultivars of Triticum aestivum with Fusarium graminearum on the disease severity and subsequent accumulation of deoxynivalenol (DON) in the grain were examined in fields in Miyagi Prefecture, Japan, for three years. “Flowering” was defined as the time when 40-50% of the spikelets in a head were flowering. A conidial suspension of the fungus was periodically sprayed onto the heads of two cultivars from first heading (12-17 days before the flowering) to 30 days after the flowering. Consequently, both cultivars had the highest disease severity and DON levels in the grains when inoculated at various times from 3 days before to the day of flowering in both cultivars, indicating that this is the most susceptible period for each cultivar. At other times of inoculation, however, the levels of disease severity and DON were not always consistent. DON levels were significantly higher in grains of cv. Yukichikara after inoculation during the period. These results suggested that the levels of disease severity and toxin accumulation in relation to the timing of inoculation depends on the cultivar; thus, elucidating these relations for each wheat cultivar is important for developing effective control strategies. A high correlation coefficient between the ratio of flowering spikelets in a head and the ratio of heads with at least one flowering spikelet was observed for each cultivar in the field. This correlation suggests that evaluating the ratio of the flowering heads is useful for estimating the ratio of flowering spikelets in each head, which indicates the time of flowering. The ratio of flowering heads in a field could then be used as an indicator for timing the application of control measures.