Combined inoculation of wheat pathogens Zymoseptoria tritici and Fusarium culmorum as a tool for increasing selection intensity in resistance breeding

Resistances to Septoria tritici blotch (STB) and Fusarium head blight (FHB) are important goals in European wheat breeding. We tested 25 winter wheat cultivars differing in their resistance to both diseases by inoculating Zymoseptoria tritici or Fusarium culmorum either separately on different plots or combined on the same plot. Experiments were carried out across three location × year combinations in four variants: non-inoculated, STB inoculated, FHB inoculated and STB+FHB inoculated at the respective optimal plant stages. On the individually inoculated plots, mean STB severities ranged from 12% to 70% and mean FHB severities from 0.3% to 67% across wheat cultivars. The resistances to STB and FHB were not correlated. Mean disease severities of the respective inoculation variants, STB vs. STB+FHB and FHB vs. STB+FHB, were not significantly different (P > 0.1), and correlations between both inoculation variants were extremely high (r = 0.98) for STB. In conclusion, breeding populations have to be selected for both resistances separately, but phenotyping can be performed on the same plot without ranking differences of the respective resistance.