EVIDENCE FOR INCREASED AGGRESSIVENESS IN FUSARIUM SPECIES CAUSING HEAD BLIGHT DETECTED USING SERIAL PASSAGE ASSAYS THROUGH BARLEY CULTIVARS OF CONTRASTED QUANTITATIVE RESISTANCE LEVELS IN VITRO

Abstract

Fusarium head blight (FHB) leads to significant quality and yield losses makes the FHB disease an important threat in all barley-growing areas of the world. Till now, available empirical data are limited on the efficiency of quantitative barley resistance expected to reduce in several generations because of the selection of FHB isolates with a high level of quantitative component of pathogenicity, i.e., aggressiveness, because of the difficulty of conducting such studies in the field. To achieve this goal, the evolutionary aggressiveness response were analyzed in four FHB pathogens faced with selective pressure using in vitro serial passage assays on susceptible “S” and moderately resistant “MR” barley. Differences due to the selective effect of a cultivar among non-selected and selected FHB isolates were quantified for traits participating to parasitic (area under disease progress curve (AUDPC) and latent period (LP)) fitness. The pathogen populations adapted quickly to the “MR” cultivar than the “S” cultivar. The selective barley impact on the analyzed FHB pathogens seemed to be species-specific. The results showed that selected isolates on the “MR” cultivar presenting a high level of aggressiveness than selected isolates from “S” cultivar, as they had a shorter LP (21.8%) and a higher level of AUDPC (22.1%). These findings provide the first direct evidence that FHB pathogens evolve rapidly to adapt by increasing aggressiveness to barley, indicating a risk of directional selection (i.e., deployment of a resistance gene) and possible erosion, evolution of aggressiveness due to resistance selection pressure over generations can lead to quantitative resistance erosion, of barely resistance, a vital component for the progress of durable control policies for resistant barley cultivars to FHB infection.