Characterisation of major genes mediating resistance to Septoria tritici blotch disease in wheat.

The fungus Zymoseptoria tritici is one of the most destructive wheat (Triticum aestivum) pathogens in Europe and worldwide, causing crop losses of up to 50% in high risk climates (Goodwin, 2007). Traditionally this disease has been controlled with widely used resistance genes and fungicides, but the high selection pressures placed on the fungi result in a serious risk of these protections being overcome, particularly when heavily relied upon. Some major resistances have already been widely broken – for example, the Stb6 resistance gene present in most European wheat cultivars is now ineffective against many Septoria strains in the field. It is therefore important that new, more diverse sources of resistance be identified and utilised in elite wheat lines. These will allow us to prepare for the breaking of currently common resistances but may also extend their lifetimes – Chartrain et al. (2004) found that many wheat lines with highly durable Septoria resistance contain multiple resistance (Stb) genes, suggesting that gene pyramiding may be a viable method for enhancing the longevity of resistances in this pathosystem. The research described here will screen currently known Stb genes against an array of recent Septoria field isolates to identify resistances still effective in the field and potentially interesting combinations of resistances that in combination could provide protection against most or all isolates tested. Such resistances will then be fine mapped using KASP markers to enable breeders to more easily integrate them into elite lines. In light of the recent identification of the Stb6 gene as a wall-associated receptor-like kinase (WAK) (Saintenac et al., 2018), WAK genes in the regions identified will be further investigated using Virus-induced gene silencing to identify individual resistance genes where possible, aiding in further investigations that may establish the methods through which these resistances function.