Genetics and Selection of Hemp - Hemp: Industrial Production and Uses - page 54

Spontaneous mutations frequently occur
in the somatic tissues of hemp and are situated
in identifiable parts of the plant (chimeras;
Fig. 4.6). 6 These mutations do not, however,
transmit themselves to the next generation.
Where selection is concerned, only the
spontaneous mutations arising in the germ
cells are used. For example, monoecious hemp
is considered to have arisen as a result of a
spontaneous mutation in dioecious hemp. 7
Another example is that of the phenomenon
described as 'yellow stems' recognized and
used by hemp breeders.

TRANSGENIC HEMP . Recent developments in the
science of molecular genetics have resulted in
increasing sophistication in the techniques pro-
posed for plant selection. Recombinant DNA
technology allows a specific gene from an
organism's DNA, coding for a desirable char-
acteristic, to be isolated, cloned and inserted
into the genetic material of a plant. Feeney and
Punja (2003) claim to have inserted the gene
coding for isomerase phosphanamose suc-
cessfully into hemp using the bacterium
Agrobacterium tumefaciens as a vector. This
transgenic hemp was of no commercial value,
but its creation demonstrated that hemp might
be added to the list of plants that could be mod-
ified genetically where necessary.

Fig. 4.6. Yellow chimera of hemp leaves, arising
from a spontaneous mutation in the somatic cells
of the leaf.

itself better to the production of fibres, while
monoecious hemp is better suited to the 'dual
need' of both seed and fibre. Watson and
Clarke (1997) provided an excellent overview
of the objectives of hemp breeders, reproduced
below.

HURD YIELD . Late-flowering cultivars pro-
duce higher stem and fibre yields than early-
flowering cultivars, due to a longer growing
season (van der Werf et al ., 1994). Date
of flowering was highly heritable and had a
significant relationship with stem yield
(Hennink, 1994).
Hybrid cultivars expressing heterosis con-
tributed significantly to the increase of genetic
yield potential for stem yield.

Objectives and results of hemp selection

Hemp is a multi-purpose crop of increasing
importance for Europe and other parts of the
world (Berenji, 1996, 2004). When hemp is
used as a fibre crop, the main objectives of
selection are: hurd yield, fibre content and fibre
quality. Research has also been conducted to
increase oil production with the development
of a hemp variety with this characteristic. More
recently, hemp selection to meet these dual
needs has been prioritized. Specific selection
programmes for 'drug varieties of hemp' in
order to produce marijuana or hashish as well
as medicinal substances have also been under-
taken. The production of ornamental hemp is
yet another example.
The objectives detailed below concern
both monoecious and dioecious hemp. It would
appear, however, that dioecious hemp lends

FIBRE YIELD . Since the beginning of fibre hemp
breeding, bast fibre has more than doubled
from about 12-15% to 25-35% (Heimann,
1990, cited in Hennink, 1994). As a result of
selection for fibre content, contemporary dioe-
cious hemp cultivars have a genetic potential
of 38-40% fibre content in the stem, resulting
in 28-30% fibre content in large-scale produc-
tion (Bócsa and Karus, 1998; Berenji and
Sikora, 2000).
Simultaneous selection for bast fibre con-
tent and stem yield is the best breeding
strategy for improvement of bast fibre yield
(Hennik, 1994).