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Creating True Marijuana Cannabis Breeding Strains
written by anonymous
Return Back To OnlinePot's Grow Guides
Main
Grow Page#1 Or Main
Grow Page#2
I've been hearing a fair bit of confusion from many on how to create a true
breeding strain and so I'm writing this page to try and help shed some light
on the subject. There are a few situations where a plant breeder would want to
create a true breeding strain (IBL) and a few ways of accomplishing the task.
But understanding the subtle differences of the various techniques is not so
easy.
This paper will attempt to give a basic understanding of what is
actually happening with each technique and then apply what is learned to
actual projetcs. As a friend worked overtime making sure I didn't forget,
breeding is not a black and white subject and as a whole, it would be too
complex to put on paper in an easily understood form. Therefore, I will create
small fictional examples to reinforce various concepts and then we will take
those examples and concepts and apply some reality to them. Try not to get
hung up on the erroneous assuptions used here such as flavour being monogenic,
the assumption is simply used to make it easier to learn a certain concept.
Just What Is It That We Are Doing?
Before we dive in, maybe we should take the time to understand what we are
trying to accomplish when we set out to create a true breeding strain. There are
hundreds of possible phenotypic traits that we could observe within a cannabis
population. Are we trying to make all of them the same and remove ALL variation?
Not likely, the genetic code is just too complex to try. Plus, since phenotype
(what we see) is 1/2 genotype + 1/2 environment, everytime the population was
grown under new conditions, new heterozygous traits would be observed.
Basically, all we are trying to create is an overall uniformity while not
worrying about the minor individual varioations. No different than a dog breed.
You can look at a german shepard and recognise it as belonging to a discrete
breed. But if you look closer at several german shepards all at the same time,
you will find variations with each and every one of them. Some will be a little
taller, some a little wider, some more agressive, some a little fatter, some
darker, etc. But they would all fall within an acceptable range for the various
traits. Generally speaking, this is what a plant breeder is trying to
accomplish when creating a true breeding strain, or IBL.
However this isn't always the case. Sometimes a breeder will just concentrate
on a specific trait, like say outdoor harvest date, or mite resistance. You
could still have a population where some are 2' bushes and some 10' trees.
In this case, you would say that the strain was true
breeding for the particular trait, but you wouldn't consider it a
true breeding strain per se. In genetics, wording plays a big part in meaning
and understanding. As does reference point as my F1 vs F2 comparison page
illustrates.
Ok, so we want to make a cannabis population fairly uniform over a few
phenotypically important traits, like say flavour for instance. For simplicity
sake, we'll just deal with the single trait flavour, it's complex enough. And
although flavour is controlled by several gene pairs (polygenic),
we'll make the simplistic assumption that it's controlled by a single gene
pair (monogenic) for many of the models and
examples in this paper. There are many flavours such as chocolate, vanilla,
musky, skunky, blueberry, etc, but in this paper we'll just deal with two
flavours, pine and pineapple. Either gene in the gene pair can code for either
of the flavours. If both genes code for pineapple or both genes code for pine
flavour, we say that the gene pair (and individual plant) is homozygous
for flavour. If the one gene codes for pine and the other codes for pineapple,
we say that the gene pair (and individual plant) is heterozyous
with respect to flavour. The heterozygous individual can create gametes
(pollen or ovules) that can code for either pine flavour or pineapple
flavour, the homozygous individuals can only create gametes that code for one OR
the other. A homozygous individual is considered true
breeding and a heterozygous individual is not.
However, as the words imply, when we are creating a true breeding strain, we
are looking at a population, not individuals. We are trying to make all the
individuals in the population homozygous for a particular trait or group of
traits. Lets say we have a population of 50 individual plants, and each plant
has has a gene pair coding for flavour. That means that 100 flavour genes make
up the flavour genepool (reality is much more complex). When trying to create a
true breeding strain, we are in fact trying to make all 100 of those genes code
for the same trait ( pineapple flavour in our case). The closer our
population comes getting all 100 genes the same, the more homozygous or true
breeding it becomes. We use the terminology gene
frequency to measure and describe this concept, where gene frequency
is simply the ratio or percentage of the population that actually contains a
specific gene. The higher the gene frequency, the more true breeding the
population is. A fixed trait is where the gene frequency of the trait reaches
100%.
And folks, this is the basic backbone of what breeding
is all about, manipulating gene frequencies. It doesn't matter if your making
IBL, F1s, F2s, selecting for this or selecting for that, all you are really
doing is manipulating gene frequencies. Therefore, to ever really understand
what is happening in any breeding project, the breeder must pay attention to
gene frequencies and assess how his selective pressures and models are
influencing them. They are his measure of success.
An overview of Inbreeding Strategies
What are we trying to create a true breeding strain from?
This a good question. Sometimes a gardener will notice a sport or unique
individual in an IBL or F2 population, like say it has pineapple flavour when
the rest have pine flavor. For one reason or another he decides he wants
to preserve this new trait or combination of traits from that single individual.
For the sake of ease of comprehension, we tend to call this special unique
individual the P1 mom. He could start by selfing
the individual OR breeding that individual with another and create what can be
described as F1 offspring. If the F1 route was chosen, then breeders can diverge
down two new paths. Some breeders will take the progeny of the F1 crossing and
breed it back to the P1 mom, and then repeat for a couple more generations. This
is referred to as backcrossing or cubing
by cannabis breeders. Another common strategy is to make F2 progeny
from the F1 population and then look for individuals that match the P1 mom. They
would repeat the process for a few generations. We can call this filial or
generational inbreeding since the parents from each cross belong
to the same generation.
In another situation, sometimes a farmer will notice a few individuals in his
fields that stand out from the crowd in a possitive manner. Like say the are
resistant to a problem pest. In this case, he will collect the best of the
individuals and his starting population will contain several similar individuals
and not a unique single individual as in the previous example. He would skip the
hybridizing step (making the F1s) and go straight to the generational inbreeding
step. Links to pages going into detail of each of these scenarios and
techniques are at:
Future topics to flesh out:
As we pointed out in the previous sections, selection plays an important role
in successfully maximizing a gene's frequency. There are many factors effecting
our ability to select the right parents.
One of the tricks for identifying the right parents is progeny testing
Applying the theory to practical situations. And finally, variations on
various strategies, like RRS, acclimization, pest tolerance, etc.
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