Quantitative Approach of Sex Determinism in Hemp (Cannabis sativa L.).

Ask me if I am male or female and I would answer that not only can I be both but also can I change depending on my environment… Hemp (Cannabis sativa L.) belongs to this category of plants presenting a complex mechanism of sex determination. The species is naturally dioecious with male and female individuals characterized by sexual dimorphism, in size and precocity in particular. Monoecious varieties have been developed in order to reduce the crop heterogeneity. However, their multiplication remains an eternal renewal because of their instability: firstly, dioecious male plants occur sporadically during the selection process and, secondly, the monoecious state presents a continuous distribution between the male and female extreme phenotypes. Furthermore, sex in hemp is influenced by environmental factors, such as hormones, photoperiod or nitrogen status, and total or partial sex reversal has been observed in some genotypes. If the sexual determinism in dioecious hemp varieties is thought to be controlled by a X:autosomes equilibrium, the genetic determinism of other sexual forms is yet unknown. The entire genome assembly of the plant and the gene and chromosome interactions are supposed to play a role in sex determinism. In this context, the present research aims to contribute to the comprehension of the sex determinism of intersexual forms of hemp by identifying quantitative trait loci (QTL) associated to the monoecious trait.

A segregant population of 174 individuals was created from a cross between two monoecious cultivars selected for their opposite average sexual phenotypes. The plants were phenotyped at the nodal level by attributing a figure comprised between 1 and 5 according to the sex ratio. Genomic DNA is currently being screened with AFLP markers. The AFLP technique was chosen for its reliability and for the potentially high number of amplified fragments, making it an enabling technology for the construction of genetic maps. Finally, phenotypic observations and molecular data will be integrated in order to identify QTL involved in the sex determinism of monoecious hemp.