Assistant Professor University of Minnesota Saint Paul, MN, USA
Clavibacter nebraskensis, the Gram-positive bacterium causing Goss’s wilt and leaf blight in maize, exhibits dynamic virulence evolution and genomic complexity. Integrated analyses of historical and modern strains reveal post-2010 isolates are more virulent and genetically divergent than earlier counterparts. Multi-strain competition assays showed weakly virulent strains (e.g., CIC354/370) outperformed highly virulent strains in planta, regardless of host resistance. Genomic comparisons identified candidate virulence factors: a secreted cellulase linked to strain success variation, and an expansin-like cellulose-binding domain plus pectate lyase exclusive to pathogenic strains (absent in a 2012 epiphytic maize isolate). Five novel plasmids were detected in pathogenic strains, expanding known genetic diversity despite unclear pathogenicity roles. While gene presence/absence and copy number variations did not correlate with virulence, haplotype analysis of eight concatenated genes separated strains by virulence phenotype. These findings highlight evolving ecological strategies, with strain success decoupled from single-strain pathogenicity, and implicate cellulolytic/pectolytic enzymes as key genomic targets. This work bridges phenotypic virulence trends with structural and plasmid-mediated genomic diversity, guiding future functional studies to combat this economically critical disease.
