Review of Flowering Control in Industrial Hemp

Hemp ( Cannabis sativa L.) is a dioecious annual that commences its reproductive cycle when photoperiods are shorter than a critical length. Photoperiod-sensitive varieties grown in low latitudes with short-day lengths tend to produce early flowering, short plants affecting the yield and quality of the fiber. The photoperiodic sensitivity of the crop could be controlled by the activation or deactivation of genes triggered by the change in light duration perceived by photoreceptive pigments. The sexual dimorphism of Cannabisis genetically determined by the XY chromosomal mechanismal though sexual morphology is primarily a result of endogenous plant growth regulator levels that fluctuate in response to environmental variables. Occurrence of occasional hermaphroditic flowers and monoecious plants are probably the result of these fluctuations. Understanding the mechanisms of photoperiodicity and sexual inheritance contributes to advances in breeding and crop management that may underpin the expansion of the commercial cultivation of the crop in nontraditional agroecological domains

Identification of QTLs for sex expression in dioecious and monoecious hemp (Cannabis sativa L.)

Hemp (Cannabis sativa L.) is a diploid species including both dioecious and monoecious cultivars with hetero- and homomorphic sex chromosomes, respectively. It displays a high plasticity of sex expression, i.e., the ratio of female and male flowers. In this study, we investigated the role of sex chromosomes in the genetic determinism of sex expression in dioecious and monoecious hemp. The experimental materials were three F1 segregating populations, two dioecious (C1 and C2: ‘Carmagnola’ ♀ × ‘Carmagnola’ ♂), and one monoecious (UF: ‘Uso 31’ × ‘Fedora 17’). A ‘sex’ phenotypic marker was mapped in C1 and C2. In total, 23, 42, and 26 AFLP markers (71 markers in total) were mapped to three, nine, and three co-segregation groups putatively located on sex chromosomes in C1, C2, and UF, respectively. Recombination rates with sex ranged from 0 to 0.5. Five sex-linked markers were detected in UF, revealing homologies between the X chromosomes of monoecious hemp and the X and Y chromosomes of dioecious hemp. Five QTLs associated with quantitative variations in sex expression were identified in each map. Four markers associated with variations in sex expression in UF segregated with sex or accounted for a putative QTL in C1 or C2. Two QTLs and three of these markers were mapped in UF in a region homologous to the sex-locus region of the dioecious maps. Given these results, conducting further research on the genetic determinism of sex expression in hemp using a quantitative approach appears relevant