Abstract
Flowering time and sex determination in hemp (Cannabis sativa L.) strongly influence fiber quality and seed production of this crop. The control of these traits is paramount for the breeding of new cultivars. Yet, little is known about the genetics underlying such complex traits and a better understanding requires in depth knowledge of the molecular mechanisms responsible for these traits. In this report, the genetic architecture of flowering time and sex determination in hemp was studied using a Genome-Wide Association Studies (GWAS) approach. Association studies were performed on a panel of 123 hemp accessions, tested in three contrasting environments, using a set of 600 K SNP markers. Altogether, eight QTLs were identified across environments; six for flowering time traits and two for sex determination. These QTLs covered genomic regions with 33 transcripts predicted to be involved in flowering and sex determination as well as a microRNA, miR156. Genes related to perception and transduction of light and transcription factors well-known to regulate flowering were identified in QTLs for flowering time traits. Transcription factors and genes involved in regulating the balance of phytohormones, specially auxins and gibberellic acid, were identified in QTLs for sex determination. Sex determination QTLs were associated with the development of male flowers in female plants and thus with the stability of sex determination in monecious plants. The present study elucidates relevant knowledge on the genetic mechanisms of flowering and sex determination traits in hemp, and provides new tools for hemp breeding.
Highlights
Hemp (Cannabis sativa L.) is naturally a diecious species with distinct male- and female plants
The present study describes a Genome-Wide Association Studies (GWAS) approach to characterize the genetic architecture underpinning the length of the vegetative period, flowering time, and sex determination in hemp
The extensive phenotypic variation and the large heritable behavior of beginning of flowering, full flowering, length of the vegetative growth period (VEG) and sex determination enabled the study of the genetics underlying flowering and sex in hemp, through a GWAS approach (Supplementary Tables 2, 3; Petit et al, 2020b)
Summary
Hemp (Cannabis sativa L.) is naturally a diecious species with distinct male- and female plants. The sexual phenotype of Cannabis frequently shows some flexibility leading to differentiation of hermaphrodite plants, known as monecious phenotypes (Moliterni et al, 2004). The species is a short-day plant characterized by sexual dimorphism. True males can be recognized by their typical morphology characterized by slender stature, few leaves and hanging inflorescences carrying male. Female plants produce female pistillate flowers in dense panicles heads interspaced with leafy bracts. Monecious plants morphology resembles that of female plants (Faux et al, 2016). Male plants mostly flower earlier than female plants (Bócsa and Karus, 1998; Struik et al, 2000) and die shortly after flowering, while female plants remain alive until seed maturation
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