also played an important role in gaining insights into the structure of the sex
chromosomes.
However, from the point of view of genetics and breeding, the real challenge is
identifying markers linked to the monoecious trait, particularly in view of the
current widespread use of monoecious hemp and its better compatibility with
modern agriculture strategies. The karyological identity of monoecious plants to
female ones (Faux et al. 2014 ; Razumova et al. 2015 ) makes the identification of
tightly-linked markers difficult, and the phenotypyzation itself a challenging task.
Therefore, new approaches had to be applied to this trait.
One step toward the marker-based study of monoecy has been provided by the
recognition of the quantitative nature of the variation in sex expression in
monoeciousC. sativa, and in successfully describing it as a logistic function of the
node position (Faux and Bertin 2014 ); consequently, the investigation of the trait by
the QTL approach and interval mapping has been performed, starting from the
identification of AFLP markers of the same classes as described by Peil et al. ( 2003 )
in an F1 progeny between monoecious plants.
QTL analysis of a monoecious population, compared with two dioecious F1 s,
led to the identification offive QTLs associated with sex expression in the
monoecious progeny (Faux et al. 2016 ). The authors underlined that two of these
QTLs mapped in a region homologous to a sex-locus region (as defined on the basis
of dioecious mapping), suggesting the existence of monoecious-determining traits
on the X sexual chromosome. Each of the variables used to describe the monoecy
trait, showed from zero to three QTLs. Therefore, it seems that this approach based
on quantitative phenotypization of monoecy and QTL mapping, is suitable to frame
markers linked to chromosomal regions involved in the determination of the trait.
The identification of the number of such regions was an initial result, though for
higher resolution and development of markers tightly linked to the trait,
higher-density maps are likely to be necessary. Finally, it has been suggested that
the identified QTLs could be linked to the genetic factors determining hormone
balance, which calls for more in-depth knowledge of the physiological bases of the
monoecy trait and for efficient phenotypyzation of this in the plant.
15.4 Genomics and Marker-Assisted Selection
for Chemotype
Forensic applications of markers call for molecular tools with a high degree of
reproducibility and reliability in identifying illicit plants, but also for a deeper
understanding of the chemotype expression. Without any doubt, markers directly
linked to the genes, which code the enzymes relevant to chemotype determination
can be considered highly reliable. Among these genes, the ones that code for
THCAS, responsible for production of theCannabispsychoactive agent THC, is of
course the most interesting and the most widely studied.
330 C. Onofri and G. Mandolino