Agriculture Reference
In-Depth Information
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elimination of undesirable monoecious
not exist alone in a dioecious stand and it is
therefore necessary to 'rogue' (cull) the male
plants (amounting to some 50% of the stand).
This work is onerous and labour-intensive; it
can therefore only be realized on a small scale.
If done well, the result of this cross is a genera-
tion of predominantly (>95%) female plants.
In the following generation, this F1 is
crossed with a monoecious variety that pro-
vides the pollen necessary for fertilization. The
next generation, corresponding to the com-
mercial seeds, is produced by open pollination,
as described in the previous chapter.
The quality and control restriction are as
described in the previous description and will cause
similar delays to the marketing of these varieties.
masculinized plants during the flowering
stage, leading to foundation increases.
This further reduces the presence of unde-
sirable monoecious masculinized plants in
the final commercial seed.
Between each cycle it is essential that strict
tests be conducted to identify and select the
right groups of plants for multiplication:
Varietal conformity must be checked.
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Generally speaking, this is a formality, but
must be conducted in order to ensure the
absence of undesirable outcrossing and/or
mixing after harvesting.
The THC content of batches must also be
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checked. Here again this is a formality, as
the THC content remains stable between
generations. These checks do, however,
provide an additional check against unde-
sirable pollination.
Male purity must also be checked. It is, in
Multiplication of monoecious varieties
On today's market, there are no seeds of dioe-
cious varieties in widespread use. For these
varieties, the constraints are very different:
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effect, impossible to eliminate male plants
completely before the flowers open. There
is, therefore, always a small amount of
pollination by dioecious plant pollen. This
must be controlled and may require a rese-
lecting of plants at the next cycle. The effi-
ciency of this selection process is only to
be relied upon if the proportion of male
plants to be eliminated is small.
1. No a posteriori controls on male purity are
required in these batches. Controls are less
onerous and varieties easier to get to market.
2. There is no need to eliminate male plants
and production is less labour-intensive, and
therefore cheaper. The elimination of plants
that do not meet requirements is still neces-
sary, but this problem is true for all species.
3. The seed yields are a lot lower (approxi-
mately 35% lower), which places the benefits
detailed in 1 and 2 above into perspective. In
addition, seed increase is not faster or cheaper.
These checks necessitate 2-3 years of controls
between each generation. One check in particu-
lar is that of the male purity of batches (while
ideally the batch would be free of male plants, the
fact is that some always remain - seed producers
must have an idea of the level of remaining plants
in order to ascertain if the batch is commercially
viable). This increases greatly the time taken to
place a new variety on the market.
Finally, it should be noted that the biggest dif-
ficulty with monoecious varieties lies in the
absence of a mechanical harvesting system
that is appropriate for crops of this type. In
effect, by the time the seeds are mature and
ready for harvest, the male plants will have
been dead for about a month and will be com-
pletely retted. Classical harvesting systems,
needed for the cutting of fruit-bearing female
plants, are unable or inefficient at harvesting
male plants. The latter will be dry at the time of
harvest and will often roll around the machine
axle, thus jamming the operation.
In France, this problem has been solved
experimentally (and on a small scale) by elimi-
nating 90% of the male plants manually,
as early as the end of the fertilization period.
Multiplication of monoecious-dioecious
hybrid varieties
We have already seen how the complexities inher-
ent in the formation of
monoecious-dioecious
hybrids
alter the seed production scheme.
In the first step, monoecious plants are
used as male (pollinators) and female plants of
a dioecious variety as female (seed bearers)
(Fig. 4.17). Unfortunately, female plants do
