A Genetic Analysis of Tolerance to Goss\u27s Bacterial Wilt and Leaf Blight in North American Maize

Goss’s bacterial wilt and leaf blight, caused by Clavibacter michiganensis subsp. nebraskensis (Cmn), has reemerged as an economically important disease across much of the U.S. Corn Belt. The devastating effect on corn yields and widespread incidence of disease have raised questions about the genetic architecture underlying tolerance to Goss’s wilt. We initiated studies in 2012 to: (i) identified quantitative trail loci (QTL) associated with Goss’s wilt tolerance, and (ii) to determine if isolates of Cmn vary in virulence to corn inbred lines with different degrees of tolerance to Goss’s wilt. We evaluated a mapping population consisting of recombinant inbred lines derived from a cross between B73 and OH43 and performed composite interval mapping (CIM) to identify QTL for tolerance to Goss’s wilt. Individual plots at two Nebraska locations were inoculated with Cmn isolates and rated using a 1-9 visual scale. Phenotypic data from both locations were combined into one dataset because of insignificant genotype by environment interactions. The CIM analysis of the combined dataset revealed three QTL explaining 38% of the phenotypic variation (R2). Interestingly, the resistant parent B73 contributed to susceptibility for the QTL identified on chromosome one; however, B73 contributed to tolerance for the other detected QTL. Greenhouse studies were performed to elucidate possible interactions between corn genotypes and bacterial isolates collected across Midwestern U.S. Assessing the isolate-line interaction can reveal if geographically diverse isolates vary in virulence due to genetic diversity contributing to higher levels of population structure. Pathogenicity tests were conducted with four geographically dispersed isolates and four corn genotypes with resistance ratings ranging from susceptible to resistant. Results revealed a significant interaction indicating the amount of disease caused by each isolates varied according to the tolerance of the inbred lines. Limited differences existed between isolates on susceptible genotypes; however, substantial variation was found between isolates inoculated on tolerant genotypes. The results from this study showed that selection of isolates for artificial inoculation is important when breeding durable tolerance to Goss’s wilt. Advisor: Aaron J. Loren