The main goal of this project is the thorough genetic and functional characterization of host resistance to narrow brown leaf spot (NBLS) of rice. NBLS is an emerging and economically import disease, capable of causing yield losses of 10-40%. Preliminary data has mapped a major NBLS resistance gene to rice chromosome two. Objective 1 aims to fine map and physically delimit this resistance locus for candidate gene identification. The screening of a mutant population, along with genomic and gene expression analysis of the wild-type line and resistance-compromised mutants will lead to the identification of candidate genes. Objective two focuses on the functional validation of the candidate genes through the generation of CRISPR/Cas9-mediated gene disrupted transformants and the overexpression of candidate genes in a susceptible genetic background. Following gene validation, an efficient and breeder-friendly marker will be designed and validated. Objective 3 aims to identify quantitative resistance through the phenotyping of recombinant inbred line (RIL) and multi-parent advanced generation intercross (MAGIC) populations.