As breeders, our success depends on understanding what kind of trait, or we’re working with. Some traits are like light switches - they’re either on or off. Others are more like dimmer switches, with a continuous range of possibilities. Let’s see why this matters for your breeding program.

Qualitative Traits: The Easy Ones (Sort Of)

Qualitative traits are controlled by one or a few genes and show clear, distinct categories. In cannabis, these include:

• CBD:THC chemotype (Type 1, 2, or 3)
• Sex determination (male vs female)
• Photoperiod sensitivity vs autoflowering
• Purple stem color vs green

These traits typically follow Mendelian inheritance patterns, making them relatively straightforward to work with. When you cross two plants, you can often predict the ratios you’ll see in the offspring.

For example, if you cross two heterozygous plants carrying the autoflowering trait (which is recessive), you’ll typically see a 3:1 ratio of photoperiod:autoflowering plants in the offspring.

Quantitative Traits: The Complex Reality

However, most traits that breeders care about are quantitative. These include:

• Yield
• Cannabinoid content (the actual percentage, not just the ratio)
• Terpene levels
• Flowering time
• Plant height
• Branching pattern
• Drought tolerance

These traits:

• Are controlled by many genes
• Show continuous variation
• Are heavily influenced by environment
• Take longer to stabilize in breeding programs
• Require larger populations for effective selection

Real World Example: Trichome Production

Take trichome production as an example. While it might seem simple - more is better, right? - it’s actually a complex trait influenced by:

• Trichome density
• Trichome size
• Trichome maturation rate
• Environmental factors
• Plant vigor
• And more

This is why you can’t just cross your frostiest plants and expect all offspring to be equally frosty. You need to:

1. Work with large populations
2. Select over multiple generations
3. Test under consistent conditions
4. Use appropriate selection methods

Selection Strategy Changes Based on Trait Type

For qualitative traits:

• You can often select in early generations
• Smaller populations can work
• Test crosses can reveal genetic makeup
• Goals can be achieved in fewer generations

For quantitative traits:

• Selection should be delayed until later generations
• Larger populations are essential
• Progress is measured in population averages
• Multiple generations of selection are needed
• Environmental control is crucial

Practical Application

When planning your breeding program:

1. Identify whether each target trait is qualitative or quantitative
2. Set realistic timelines based on trait type
3. Plan population sizes accordingly
4. Choose appropriate selection methods
5. Tightly control the environment when evaluating quantitative traits

Common Mistake to Avoid

One of the biggest mistakes newer breeders make is treating quantitative traits like they’re qualitative. You can’t just select two high-THC plants, cross them, and expect all high-THC offspring. Understanding this fundamental difference will save you time and help you design better breeding strategies.

Looking Forward

In the next post, we’ll explore the cannabis genome and how understanding its structure can inform breeding decisions. For now, consider:

• What traits are you currently selecting for?
• Are they qualitative or quantitative?
• Is your population size appropriate for the traits you’re targeting?
• Are you controlling environmental variables sufficiently to make good selections?

References

1. Clarke, R.C., & Merlin, M.D. (2016). Cannabis domestication, breeding history, present-day genetic diversity, and future prospects. Critical Reviews in Plant Sciences, 35(5-6), 293-327. https://doi.org/10.1080/07352689.2016.1267498
2. Lynch, R.C., et al. (2016). Genomic and chemical diversity in Cannabis. Critical Reviews in Plant Sciences, 35(5-6), 349-363. https://doi.org/10.1080/07352689.2016.1265363
3. Onofri, C., & Mandolino, G. (2017). Genomics and molecular markers in Cannabis sativa L. In Cannabis sativa L.-Botany and Biotechnology (pp. 319-342). Springer. https://doi.org/10.1007/978-3-319-54564-6_15
4. Small, E. (2018). Dwarf germplasm: the key to giant Cannabis hempseed and cannabinoid crops. Genetic Resources and Crop Evolution, 65(4), 1071-1107. https://doi.org/10.1007/s10722-017-0597-y

Remember: Professional breeding programs succeed because they match their methods to the traits they’re working with. Understanding the difference between qualitative and quantitative traits is your first step toward more professional-level breeding.

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[This content assumes legal hemp/cannabis breeding in compliance with all applicable laws and regulations.]