On the genetic basis of flowering time control in hemp (Cannabis sativa L.)

Despite being one of our most ancient crops, hemp (Cannabis sativa) has been largely ignored by the scientific community for the last half-century. Thus our knowledge of how fundamental traits are genetically determined in this fascinating species is lacking. Prior to this thesis, a substantial gap in the scientific literature existed regarding how flowering is genetically determined in hemp. Here, I demonstrate that bulked segregant analysis gene mapping techniques can be effectively applied to quantitative traits in hemp. One locus, Autoflower2, is associated with photoperiod-insensitive flowering in hemp. Located within Autoflower2 is the ortholog of a florigen gene previously described in Arabidopsis thaliana, FLOWERING LOCUS T (FT). Termed Cannabis sativa FT1 (CsFT1), the gene's expression, structure and sequence differs between photoperiod sensitive and insensitive accessions. Molecular markers testing for Autoflower2 in diverse accessions revealed that photoperiod-insensitivity has two independent origins in hemp. Subsequently, a comparative genomic analysis of the FT gene family in hemp and the related species hops was conducted, revealing the retention of expanded florigen and anti-florigen clades in the Cannabaceae indicating an important contribution to phenotypic variation. FT gene family members have signatures of both conservation and neofunctionalisation, with putative connections to flowering phenotypes such as photoperiod insensitivity and sexually dimorphic flowering. The genetic insights and resources generated in this thesis will be useful for future breeding efforts in hemp.