distributed across theCannabisgenome (Mandolino and Ranalli 2002 ); so far, no
molecular marker or SNP has been described as beeing associated to the monoe-
cious trait, suggesting the need for a strategy change in the phenotypization of the
trait itself (see Sect.15.2).
Mapping in F1 has also been a strategy to locate markers on sex chromosomes,
like the AFLP/RAPD-based map developed on a specific hemp accession that led to
the identification by Bulk Segregant Analysis (Michelmore et al. 1991 ) of 2 (for
RAPDs) and 8 (for AFLPs) specific primer combinations, yielding 17 and 16 male
specific fragments. All the identified polymorphic bands mapped into a genetic map
of 5 linkage groups including 45 markers in addition to the sex-specific markers
(Peil et al. 2000 ). A subsequent implementation of this genetic map reached 122
molecular markers subdivided in 10 linkage groups (Peil et al. 2001 ).
A new linkage map has recently been constructed using an F2 population
derived from selfing (upon partial sex-reversion) an F1 individual obtained from a
cross between inbred lines (S5) hemp x marijuana (Weiblen et al. 2015 ). This map
included 103 AFLPs markers, 16 microsatellites, besides cannabidiolic acid
(CBDA)-synthase and tetrahydrocannabinolic acid (THCA)-synthase sequences.
The map is composed of 9 linkage groups and covers a genetic distance of
335.7 cM with an average between-marker distance of 6.10 cM. Analysis of the
cannabinoid profiles (THCA/CBDA) of the individuals which form the mapping
population allowed the identification of a putative Quantitative Trait Locus
(QTL) in linkage group 6, significantly associated with plant cannabinoid com-
position (expressed as THCA/CBDA). The implications of thesefindings, also from
the functional point of view, will be discussed in the section dedicated to
chemotype-associated markers (15.3).
15.3 The Search for Markers Linked to Sex in Dioecious
Hemp and to Monoecy inC. sativa
C. sativais a dioecious species, with male and femaleflowers separated on different
plants (Fig.15.1a, b), and with strong sexual dimorphism: male plants are usually
taller and more slender than female plants. The sex of the plants also influences
economically relevant traits, like the quality of thefibers produced: male plants
have a higherfiber content and betterfiber quality, but mature earlier than female
plants, and therefore picking and scoring of male plants forfiber quality prior to
anthesis used to be an essential operation during selection for fiber quality
(Bredemann 1938 ), in order to allow only the best scoring male plants to pollinate.
Modern monoecious varieties, bearing male and femaleflowers on the same
plant (Fig.15.1c), have been obtained by selection processes of naturally occurring
variants (von Sengbusch 1952 ; Bocsa 1958 ) and offer several agronomic advan-
tages when compared to dioecious cultivars: higher homogeneity, higher seed yield,
etc. However, monoecy is also associated to some drawbacks, mainly due to their
326 C. Onofri and G. Mandolino