Seed Size Versus Seed Quantity
Although some cultivars ofC. sativahave quite large seeds, until recently oilseed
forms appear to have been selected mainly for a heavy yield of seeds. In Europe,
most cultivars have been bred forfiber yield, and these biotypes do not differ much
in oilseed potential (Mölleken and Theimer 1997 ). By contrast, some drug strains
(which have been selected for prodigious production offlowers), when left to go to
seed, can yield a kilogram of seeds on a single plant (Clarke and Merlin 2013 ).
Piluzza et al. ( 2013 ) reported that the seeds offiber cultivars are larger than those of
drug strains, which is consistent withfiber plants having a more extensive historical
food usage for seeds than drug forms.
Fatty Acid Quality
Percentage and quality of oil in the seeds do not appear to have been important in
the past, in part because techniques for analysing the nutritional chemicals were
simply not available until fairly recently. Theimer and Mölleken ( 1995 ) concluded
that breeding to obtain hemp varieties producing oils with specifically desired fatty
acids had not taken place, although selection for oil quality is now being conducted.
Today, content of the relatively unsaturated fatty acids is an important breeding
objective.
Hull Thickness
Thinness of pericarp (hull) is an important criterion for modern hemp oil seed
breeders since the pericarp is a waste product. Small and Marcus ( 2000 ) surveyed
62 accessions and found the hull varied from about 30 to 42% of the weight of the
seed. However, oilseed hemp breeding is too recent to have changed pericarp
thickness appreciably, and the pericarp needs to be thick enough to exclude oxygen
and water which would rapidly deteriorate the seeds.
1.6.3.3 Physiology
Cultivars dedicated to oilseed production are quite recent and do not differ dra-
matically fromfiber cultivars. Of course, unlikefiber hemp, oilseed hemp benefits
from mineral nutrition specifically forflowering and seed production. Hemp seed
development for a given variety requires a warmer climate and a longer season
(5–6 weeks) than the correspondingfiber crop, to allow time for seed maturation
(Bócsa and Karus 1998 ).
1 Classification ofCannabis sativaL. in Relation... 21