Fire blight caused by the necrotrophic fungus Botrytis elliptica is the most destructive fungal disease on lily. Fungal secreted effector proteins play a key role in conferring pathogenicity, upon recognition by plant receptor proteins. In plant-necrotroph interactions, sensitivity to effector proteins often correlates with host susceptibility, whereas insensitivity to effectors renders the plant more resistant. Our previous studies have shown that programmed cell death-inducing activity of B. elliptica effector proteins is required for pathogenicity on lily. These effector proteins act as “host-selective toxins”, since they induce cell death exclusively in lily. However, both B. elliptica effector-proteins and the corresponding lily receptor-proteins remain to be identified. This project aims to identify and characterize the effector-protein(s) of B. elliptica, required for cell death-induction in lily. We will investigate virulence patterns in different fungal isolate-lily cultivar combinations, and identify effector genes by integrating proteomics, comparative genomics and gene expression data. Candidate effector-proteins will be expressed in yeast. Purified effector-proteins will be infiltrated into diverse lily cultivars to screen for differences in sensitivity. The prediction is that lily cultivars displaying insensitivity to effectors will show increased resistance to B. elliptica. The importance of effector-genes for virulence of B. elliptica will be tested by gene replacement. Finally, using a biochemical approach, we will attempt to identify lily receptor proteins, involved in effector recognition. This project will provide the biological tools to develop breeding programmes to eliminate effector sensitive host genes and to obtain lily cultivars with increased resistance to fire blight.