Fusarium Development in Bread Wheat Heads Under Variable Humidity Conditions

Breeding for resistance to Fusarium head blight (FHB) pathogens often relies on irrigation before and shortly after anthesis to encourage disease development. However, some reports investigated the effects of post-anthesis weather on FHB growth in bread heads. To elucidate this, the impact of moisture on the development of FHB in three bread wheat of contrasting FHB susceptibility and infected with 16 fungal isolates of diverse aggressiveness of four different fungal species was examined. A pot experiment under natural climatic conditions was designed as split-split-plot with five replicates. Main plots were durations of spraying-irrigation of 0, 7, 14, 21, and 28 days; sub-plots were bread wheat cultivars; and sub-sub-plots were the FHB isolates. Incidence (DI) and severity (DS) of FHB were assessed 21 days after inoculation, and Fusarium-damaged kernel (FDK) percentages were determined on harvested grain. No significant differences were observed between treatments receiving the least amount of spraying-irrigation, suggesting that extended moisture promotes FHB development. As a result, 21 or 28 days of spraying had the same effect and were associated with an increase in mean DI, DS and FDK compared with 0 or 7 days of spraying, and 14 days of spraying was also associated with an increase in mean of these pathogenic criteria. This is the first investigation to show that extended post-flowering moisture can have a significant enhancing effect on DI, DS and FDK following infection with F. culmorum, F. solani, F. verticillioides, and F. equiseti, and is harmony with earlier reports conduced with bread wheat infected with F. graminearum.