Abstract
Cercospora leaf spot (CLS), caused by the fungal pathogen Cercospora beticola, is the most economically important disease of sugarbeet. If left unmanaged, CLS can significantly reduce crop yields and sugar content. Recently, growers have adopted the use of commercial varieties utilizing the resistance gene BvCr4 (CR+) to help manage CLS. Unfortunately, populations of C. beticola that are capable of overcoming BvCr4 have been identified worldwide. Although a genome wide association study (GWAS) conducted on European populations of C. beticola identified a single gene (AvrCr4) associated with resistance mediated by BvCR4, there was no subsequent functional validation of this gene. Moreover, it is not clear if American C. beticola populations also utilize this gene to overcome the BvCr4 resistance mechanism. To gain an understanding of how American C. beticola strains have adapted to BvCr4, we conducted a population genomic analysis with populations collected from sugarbeet plants throughout American growing regions with and without BvCr4. Through this analysis, we identified 14 fungal genes putatively associated with the ability to overcome BvCr4. We have developed C. beticola mutants lacking these candidate genes to functionally validate them. Characterization of these mutants will be presented. This research aims to elucidate the interaction between C. beticola and the CLS-resistance gene, BvCR4, in order to broaden understanding of the BvCr4 resistance phenotype and predict durability of similar resistance genes. In addition, this knowledge will allow for the design of molecular-based assays to identify BvCr4-resistant strains.