The effect of quantitative wheat resistance on the aggressiveness of Fusarium graminearum

Little is known about the selection pressures acting on plant pathogen populations, especially those applied by quantitative forms of resistance. Fusarium graminearum causes Fusarium Head Blight (FHB) in wheat, producing significant yield losses and mycotoxin contamination. Quantitative host resistance is the best method to control FHB. However, there needs to be more understanding of how disease resistance affects the evolution of plant pathogens. This study aimed to determine if the presence or absence of wheat resistance influenced the fitness components and genomic regions of F. graminearum. Thirty-one isolates from highly susceptible and 25 isolates from moderately resistant wheat lines were used. Isolate aggressiveness was measured by area under the disease progress curve (AUDPC), visually damaged kernels, and deoxynivalenol contamination. In vitro growth rate and spore production were also measured. Two whole-genome scans for selection were conducted with 333,297 SNPs. One scan looked for signatures of selection in the entire sample and the other scan was for divergent selection between the isolates from moderately resistant wheat and highly susceptible wheat. The population of isolates from highly susceptible wheat was primarily aggressive. Several regions of the F. graminearum genome with signatures for selection were identified. The moderately resistant wheat varieties used in this study did not select more aggressive isolates, suggesting that quantitative resistance is a durable method to control FHB.