Improvement of Resistance Against Septoria Leaf Blotch Caused By Zymoseptoria tritici in Danish Winter Wheat Cultivars

Septoria tritici blotch (STB) caused by the ascomycete fungus Zymoseptoria tritici (formerly Mycosphaerella graminicola), is a devastating disease causing major yield losses in winter wheat. It is therefore important to develop varieties with a broad range of resistance towards the disease. The purpose of this study is to identify new and effective resistance genes and implement them in the wheat breeding program at Nordic Seed. Earlier analyses have identified 18 resistance genes, Stb1-Stb18. In addition, several QTL against STB have been mapped. In this study, 170 lines from Northern Europe were evaluated for STB resistance in field trials in Denmark. All 170 wheat lines were genotyped with iSelect 15k SNP wheat array. We identified four QTL associated with resistance towards STB, located on chromosome 1B, 2A, 5D and 7A. Already identified resistance genes towards STB, Stb2 and Stb11, have been mapped to chromosome 1B and Stb3 to chromosome 7A (Liu et al. 2012; Chartrain et al. 2005; Tika and Stephen 2004). Furthermore, an additional QTL providing resistance to STB has been identified on chromosome 7A (Risser, PhD 2010). The same markers were used for the subsequent analysis of population structure of the 170 lines. The optimal number of groups (K) was calculated using STRUCTURE 2.3.4 and estimated to 3. Additionally, markers on chromosome 4A were found to contribute the most to the grouping. While several QTL with moderate effects were identified, no major QTL for resistance towards STB were identified in this study. The preliminary results indicate that STB resistance is more quantitative than qualitative.