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Variation among putative necrotrophic effector genes in host-specialized populations of Corynespora cassiicola

Leilani Sumabat: University of Georgia

<div>Numerous plant-pathogenic fungi secrete necrotrophic effectors (host-selective toxins) that are important determinants of pathogenicity and virulence in species that have a necrotrophic lifestyle. <em>Corynespora cassiicola</em> is a destructive fungal pathogen causing emerging target spot epidemics in the southeastern U.S. Previous findings revealed <em>C. cassiicola</em> populations from cotton, soybean, and tomato showed host specialization. In addition, other studies have identified the necrotrophic effector cassiicolin from <em>C. cassiicola</em> isolates, as a critical toxin for virulence on rubber. It is encoded by 6<em> Cas</em> gene variants. Our goal is to conduct comparative genomic analyses to identify variation among putative necrotrophic effector genes in <em>C. cassiicola</em> causing outbreaks in the southeastern U.S. A total of 12 <em>C. cassiicola</em> genomes, representative of different hosts of origin and geographic regions, were sequenced on an Illumina NextSeq platform. Reads for each genome were assembled <em>de novo</em> and searched for known <em>Cas</em>, <em>Tox</em>, and other homologs for effector-encoding genes. Preliminary results revealed all 6 <em>Cas</em> variants encoding for cassiicolin in the different genomes. Moreover, more than one <em>Cas</em> variant was detected in one genome. Knowledge on the diversity of necrotrophic effector genes is critical in understanding the genetic basis of host specialization and disease emergence of target spot of cotton, soybean, and tomato in the southeastern U.S.</div>