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Resistance to host damage is distinct from resistance to pathogen reproduction in the major wheat pathogen Zymoseptoria tritici

Alexey Mikaberidze: Epidemiology of Plant Diseases, ETH Zurich

<div><span lang="en-GB">Septoria tritici blotch (STB) caused by the fungus </span><span lang="en-GB"><i>Zymoseptoria tritici </i></span><span lang="en-GB">is a major disease of wheat worldwide. The pathogen adapts rapidly to deployment of fungicides and qualitative host resistances. Quantitative resistance is likely to be more durable, but phenotyping based on conventional visual scoring does not readily detect quantitative differences between cultivars, which hinders breeding for quantitative resistance. We used automated analysis of digital images of 21420 leaves from 335 elite winter wheat cultivars naturally infected by a diverse population of </span><span lang="en-GB"><i>Z. tritici</i></span><span lang="en-GB"> to evaluate quantitative STB resistance. This novel, high-throughput phenotyping method not only quantifies leaf necrosis, but also counts asexual fruiting bodies of the pathogen. This allowed us to obtain precise and reproducible quantitative measures of STB intensity and separate resistance affecting host damage from resistance affecting pathogen reproduction. Cultivar rankings with respect to the two measures exhibited only a weak correlation (</span><span lang="en-GB"><i>r</i></span><sub><span lang="en-GB">s</span></sub><span lang="en-GB">=0.17), indicating that the two measures are largely independent. Moreover, a genome-wide association study revealed that the two forms of resistance are under separate genetic control. Our findings suggest that resistance to host damage and resistance to pathogen reproduction can be considered separately in breeding programs, but can also be combined to form new cultivars highly resistant to STB.</span></div>