Genetic Diversity and Population Structure of Cannabis

Cannabis is one of the oldest cultivated plants. Its use for medicinal purposes was documented in China over 10,000 years ago. Today, after many years of prohibition, the plant is once again attracting interest and gaining popularity due to its potential therapeutic effects.

There are many standards for classifying cannabis. From a practical standpoint, cannabis is divided into four types: wild-growing, fiber-producing, oilseed, and psychoactive. Based on the degree of domestication, cannabis is categorized as wild, domesticated, or intermediate.

Previous studies have shown significant genetic and morphological differences between wild and cultivated cannabis species. Tools for analyzing genomic sequences and molecular markers have only emerged in the past few decades, so scientific research in this area is just beginning to accelerate.

Methods for Assessing Genetic Diversity

Genetic diversity is usually assessed using DNA sequences (polymorphisms between species), as well as cytological and morphological markers. However, morphological characteristics are often influenced by the environment. Therefore, molecular markers are relatively more stable and popular than morphological markers.

Various types of molecular markers are used to assess the genetic diversity of cannabis, such as ribosomal DNA, inter-simple sequence repeats (ISSR), amplified fragment length polymorphism (AFLP), random amplified polymorphic DNA (RAPD), and sequence-characterized amplified regions.

SSR markers, which are based on microsatellites, are considered the most effective and widely used molecular markers with a high genome coverage rate. They are highly reproducible and can be used to study codominant inheritance. Moreover, SSR polymorphisms are used to identify and characterize germplasm resources, and the development and characterization of genomic SSRs are important for genetic research and marker-assisted breeding. Since SSR markers have more polymorphisms than other molecular markers, they are popular and ideal for analyzing population structure and genetic diversity, as well as for identifying fiber crop varieties.

Among 80 pairs of genomic SSRs, 59 have confirmed polymorphism. This information is valuable for developing cannabis “fingerprints” to help identify varieties.

Research Findings on Cannabis Populations

Understanding the genetic diversity and population structure of crop germplasm resources can accelerate genetic research and the development of new plant varieties. Therefore, the results obtained here can also help in the conservation and use of specific high-quality germplasm resources.

Researchers analyzed 81 samples of psychoactive and 43 samples of non-psychoactive cannabis and divided them into three groups based on genetic relatedness:

• The first group included samples from Europe, America, Asia, and the southwestern, central, northeastern, and northwestern regions of China.
• The second group consisted of plants from northern China.
• The third group included cannabis from the east-central region of China.

The samples demonstrated a stable genetic structure and moderate genetic diversity. Populations from different geographic regions did not differ significantly from each other. It was confirmed that the similarity between populations analyzed for genetic diversity is the result of a genetic “bottleneck” effect.

Researchers found a significant genetic difference between psychoactive and non-psychoactive cannabis, but no genetic difference was found between wild and cultivated cannabis.