Sexual Development of Botrytis Species PhD Thesis Razak bin Terhem The fruiting bodies of species in the genus Botrytis are called apothecia. Apothecia are ascomas with an open cup shape on top of a stipe. Currently there is little information on processes occurring during apothecium development in Botrytis species. The aims of the research described in this thesis were to study the mechanisms involved in apothecium development of Botrytis cinerea, and to describe the morphology of Botrytis species and their fruiting bodies. Chapter 2 describes a genome-wide transcriptome analysis of different stages of apothecium development and a study on the function of MAT genes in apothecium development of B. cinerea. Functional analyses by targeted knockout mutagenesis revealed that the MAT1-1-1 gene and the MAT1-2-1 gene are both required for the initiation of sexual development. By contrast, mutants in the MAT1-1-5 gene and the MAT1-2-4 resulted in normal development of stipes which, however, were defective in the formation of an apothecial disk, asci and ascospores. Chapter 3 describes the functional analysis of three hydrophobin genes in sclerotium and apothecium development of B. cinerea. All three genes contribute to sclerotium and apothecium development. Chapter 4 describes the structure of the MAT1-1 and MAT1-2 locus in Botrytis elliptica and the morphology of apothecia of B. elliptica. Chapter 5 provides a morphological and phylogenetic description of Botrytis deweyae, the only species within the genus that behaves as an endophyte and in certain conditions is able to cause disease on Hemerocallis plants. Chapter 6 discusses the results presented in this thesis and puts them in a broader perspective. A model of processes and mechanisms involved in apothecium development is proposed.