de
en
Reading time: approx. 9–10 minutes
AI overview: Selection pressure in cannabis
- Selection pressure arises from every form of selection – conscious or unconscious.
- Not only targeted selection, but also handling, space, timing and repetition act selectively.
- Selection pressure shifts trait distributions, often without being immediately visible.
- It amplifies effects such as genetic drift and influences the effective population size.
What does selection pressure mean?
Selection pressure describes the influence that selection decisions have on the genetic composition of a population. What matters is not whether selection is intentional, but that it takes place.
Every decision about which plants are propagated further and which are not creates selection pressure. This pressure operates even when no formal criteria have been defined.
Conscious and unconscious selection
In practice, selection pressure is often reduced to obvious choices. Typical conscious criteria include:
- growth form and structure
- uniformity within a generation
- reproducibility of specific traits
Alongside this, however, there is a second level: unconscious selection. It arises from factors such as:
- which plants are selected first
- which are observed for longer periods
- which are grown under better conditions
- which are repeatedly used as parents
These forms of selection act continuously and are often more influential than explicit selection decisions.
Selection pressure without formal criteria
A common misconception is that no selection occurs if no criteria are defined. In reality, the genetic composition still shifts.
Examples include:
- repeated use of individual parent plants
- propagation from small sub-populations
- preference for “unproblematic” individuals
These effects are closely linked to genetic drift and intensify as the effective population size decreases.
Selection pressure and line narrowing
Selection pressure acts cumulatively. Over multiple generations it leads to:
- loss of rare traits
- increasing uniformity
- reduced genetic reserve
This process can be used deliberately, for example in combination with IBL and BX. Without control, however, it often results in gradual genetic narrowing.
Connection to drift, bottleneck and inbreeding
Selection pressure is not an isolated mechanism. It amplifies systemic effects:
- Genetic drift: random allele shifts gain influence
- Bottleneck effect: selection after constrictions fixes randomness
- inbreeding depression: repeated selection from few lines reduces vitality
These effects often receive attention only once a line is already strongly constrained.
Common misconceptions
- “I am not selecting, I just let it run”
- “Drift is random and cannot be influenced”
- “Large seed quantities mean high genetic diversity”
In reality, selection pressure is almost always present – it acts even without active intervention.
Context:
Selection pressure explains why genetic lines change even when no conscious selection was intended. It is the connecting mechanism between selection, drift, effective population size and long-term stability.
For the overarching framework, see Understanding stable cannabis lines, where these relationships are systematically placed in context.