Understanding the Genetic Basis of Resistance to Goss's Bacterial Wilt and Leaf Blight in North American Maize.

Goss’s wilt and leaf blight is a bacterial disease of maize (Zea mays L.) caused by gram positive bacterium Clavibacter michiganensis subsp. nebraskensis (Cmn). Goss’s wilt has re-emerged as an important disease in the Midwestern United States and is spreading to other areas of North America. While the reasons for rapid re-emergence of Goss’s wilt are not completely known, one possibility is an increase in susceptibility within the germplasm base used for breeding commercial maize hybrids, making an understanding of the genetic basis of resistance important.  Only a few studies in the 1990s have addressed inheritance of resistance to Goss’s wilt. The objectives of this study were to (1) map quantitative trait loci (QTL) underlying the resistance to Goss’s wilt, (2) study possible interactions between Cmn isolates and maize inbred lines differing in resistance to Goss’s wilt. To map the QTL for Goss’s wilt resistance, joint linkage as well as linkage mapping approaches were used. The three bi-parental linkage mapping families B73 x Oh43, B73 x HP301, and B73 x P39 were phenotyped for Goss’s wilt in 2012, 2013, and 2014 in Nebraska. The bi-parental families were previously genotyped with 1106 single nucleotide polymorphism (SNP) markers. Eleven QTL were detected on chromosomes 1, 2, 3, 4, 5, and 10 through joint linkage mapping. The detected QTL together explained 45% of the phenotypic variation for Goss’s wilt. Linkage mapping in three families separately, identified nine, six, and four QTL in families B73 x Oh43, B73 x HP301, and B73 x P39 respectively. The QTL on chromosome one and four have potential candidate genes and co-localized QTL for other maize diseases identified in earlier studies. Host genotype-by-isolate interaction study revealed that Cmn isolates vary significantly in their virulence among the maize inbred lines and the maize lines have significant differences in the level of resistance to Cmn. Overall, the results from this study will help to better understand the genetic basis of resistance to Goss’s wilt and may facilitate the maize breeding programs for incorporating resistance to Goss’s wilt into elite hybrids.