Aggressiveness of Certain Fusarium graminearum Isolates on Wheat Seedlings and Relation with their Trichothecene Production

Fusarium fungi, including F. graminearum, cause seedling blight, foot rot and head blight diseases in wheat resulting in yield loss. Trichothecene mycotoxins are a group of toxic fungal secondary metabolites. This group of toxins is found associated with Fusarium diseases in wheat in numerous countries worldwide. Five isolates of F. graminearum were examined for their degree of disease severity (virulence) and trichothecene production on Sakha 69 wheat cultivar. In greenhouse experiments, following soil infestation all isolates caused pre and post-emergence death of wheat seedlings. Dry weight of infected seedlings was reduced as compared with uninoculated control seedlings. The F. graminearum isolates resulted in varying degree of disease severities in seedlings. All tested isolates caused seedling blight symptoms. However, they differed in their degree of pathogenicity. The reaction of wheat cultivars against seedling blight varied. While cv. Sakha 69 was the most susceptible (35.22%), cv. Giza 164 exhibited the highest level of resistance (14.61%) and cv. Giza 168 showed a moderate degree of resistance (23.17%). The F. graminearum isolates were examined with regard to possible relation between seedling blight severity and trichothecene production. The trichothecenes contents were detected by using gas chromatography equipped with an Electron Capture Detector (GC-ECD). The amount of trichothecenes produced by the various isolates on autoclaved oat grains ranged from 1393-57081 μg kg-1 ground grain. All isolates produced trichothecene in vitro but differed significantly in their level of production. The highest amounts of total trichothecene were detected in grains inoculated with isolate Fg 4.3 (57081 μg kg-1 ground grain) while grains inoculated with isolate Fg 33 and 18.7 had the lowest amounts of total trichothecenes. There was a close relationship between the degree of disease severity and trichothecene concentration.