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The fungal pathogen Bipolaris sorokiniana causes a wide spectrum of diseases including spot blotch disease. To achieve a better understanding of the biology of the fungus, the interaction of B. sorokiniana with the host barley (Hordeum vulgare L) and the resulting disease spot blotch was investigated.In this PhD work it could be shown that light dependent disease symptoms were associated with less fungal colonization, while suppressing the rate of photosynthesis by keeping plants in darkness made them super-susceptible to B. sorokiniana colonization. Likewise, partial suppression of photosynthesis with DCMU (3-(3,4-Dichlorophenyl)-1,1-dimethylurea) reduced the formation of necrosis after infection and led to increased susceptibility, strongly implying that active photosynthesis is involved in disease symptom formation and that these symptoms negatively affect fungal colonization.In contrast to what is commonly referred in the literature, barley plants carrying a mlo mutation were not per se more susceptible to B. sorokiniana infection, but instead there might be a correlation between leaf senescence and increased susceptibility and the mlo mutation may promote leaf senescence. Crude toxin infiltration without fungus led to light dependent symptoms similar to disease, implying that fungal toxic metabolites are responsible for the light dependent symptom occurrence. By using histological analysis the importance of the steps involved in basal host resistance were further studied. Conclusively, this study highlights the importance of finding new traits of durable resistance against B. sorokiniana and spot blotch disease