Poster # 405

Mara J. Krone ¹ and Santiago X. Mideros ¹
1. University of Illinois Urbana-Champaign, Department of Crop Sciences, Urbana, IL
Corresponding Author: Santiago Mideros. smideros@illinois.edu

Mideros, Santiago

smideros@illinois.edu

Quantitative host resistance is the best method to control Fusarium head blight (FHB). However, the impact of wheat resistance on the pathogen population remains poorly understood. This study aimed to determine if the presence or absence of wheat resistance influenced the fitness components and genomic regions of F. graminearum. We collected isolates across five locations in Illinois from two naturally infected wheat varieties: IL11-28222 (moderately resistant) and 25R47 (highly susceptible). We obtained 31 isolates from the highly susceptible and 25 isolates from the moderately resistant variety. We evaluated the isolates aggressiveness in the greenhouse on ‘Norm’ spring wheat. The experiment was established in a randomized complete block with three replications. Wheat plants were inoculated at anthesis with. FHB severity was evaluated at one, two, and three weeks post inoculation. Isolate aggressiveness was quantified using the area under the disease progress curve (AUDPC), Fusarium damaged kernels (FDK), and deoxynivalenol (DON) contamination. We also measured in vitro growth rate and spore production for each isolate. DNA was extracted from all the isolates for whole-genome resequencing using Illumina short-read technology. Variant calling was completed using GATK and a dataset of 333,297 SNPs was used to complete two whole-genome scans for selection: one across the entire sample, and another comparing isolates from moderately resistant and highly susceptible wheat. Isolates from highly susceptible wheat were significantly more aggressive than the isolates from moderately resistant wheat. Conversely, isolates from moderately resistant wheat exhibited significantly higher in vitro growth rates. These results suggest that isolates with greater saprophytic ability may be less aggressive in planta. AUDPC, FDK, and DON were all significantly correlated. We identified several regions of the F. graminearum genome with signatures of selection. A total of 936 nonsynonymous SNPs were found in these regions, which included the trichothecene gene cluster, the TRI101 locus, and other loci previously associated with DON production or pathogen aggressiveness. Three genomic windows showed evidence of divergent selection between isolates from the two wheat varieties. Our findings suggest that the moderately resistant wheat varieties do not select for more aggressive isolates, supporting the durability of genetic resistance as a strategy for FHB control.

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