Aggressiveness variation of Fusarium graminearum isolates from Argentina following point inoculation of field grown wheat spikes

Aggressiveness variation among isolates of Fusarium graminearum from Argentina was analyzed by following disease development on point inoculated spikes of field grown wheat. Two aspects of the capacity of the isolates to induce disease were observed: (i) the infection efficiency reflected by the ability to produce symptoms and evaluated as the number of symptomatic spikes over the inoculated ones; and (ii) the size of the lesion provoked, which is reflected by the number of symptomatic spikelets over its total number. One hundred and twelve isolates were found to induce significantly different levels of disease severity, reflecting variation in aggressiveness. Differences were also found between the isolates for the thousand kernel weight (TKW) and the area under the disease progress curve (AUDPC) and the correlations between disease severity, AUDPC, and TKW were highly significant. Based on disease severity, isolates were clustered as low, medium and highly aggressive and both lesion size and infection efficiency were significantly different between these groups. The movement of the pathogen in the spike occurred primarily downwards the point of inoculation. Movement toward the upper portion was related with the aggressiveness of the isolates and the premature ripening of the spike appeared to be a function of isolate aggressiveness. In this work point inoculation allowed us to study not only the aggressiveness of a large collection of F. graminearum isolates but also to analyze the development of Fusarium head blight symptoms in large numbers of spikes under conditions similar to those in which this disease naturally occurs. ► Point inoculation allowed to study aggressiveness and development of symptoms. ► Severity was divided into infection efficiency and size of the lesion. ► Isolates were clustered as low, medium and highly aggressive. ► Groups differed in infection efficiency and size of the lesion induced. ► Premature ripening of the spike appeared to be a function of isolate aggressiveness.