Understanding a plant genome in all it’s totality, the composition, structure and evolution is fundamental to the development of any crop. We dive into the complex genetic structure of both medicinal cannabis and industrial hemp, whilst understanding the evolutionary and domestication history of Cannabis as this remains poorly understood.
Simply put, Genomics is the study of an organism’s entire genome. In recent years, a genome has taken on a more complicated definition but most can agree that there are two major components. The first is the complete set of genes that guide an organism through its life and the second is the associated mechanisms to help regulate the genes (S.R.Zwenger 2014).
We recognise that Cannabis can be recognised in two sub-categories which are widely used to acknowledge it’s inherit abilities/uses. Drug types of Cannabis (medicinal cannabis), which contain medium to high levels of Δ9-tetrahydrocannabinol (THC) are used for medical, therapeutic and recreational uses whereas Hemp types are grown for the production of seed and fibre containing low amounts of THC. Two species or gene pools (Cannabis sativa and Cannabis Indica) are used to describe the pedigree or appearance of cultivated cannabis plants, it is important to take into consideration that medicinal cannabis and hemp are significantly differentiated at a genome level and this distinction between the two is not limited to genes underlying THC production (Jonathon E. Page 2015).
Image: Hemp phenotypes & chemotype research (MáGenetik – 2020)
A study conducted in 2014 by Oxford University using genotyping-by-sequencing set out to evaluate the genetic structure of commonly cultivated Cannabis, 81 medicinal/recreational and 43 hemp samples were tested. The medicinal/recreational samples represent a broad cross section of modern commercial strains and landraces, whilst the hemp samples included diverse European and Asian ancestral lineages within modern varieties.
Th results indicate that the genetic differences between the two are distributed across the genome and are not restricted to loci involved in overall cannabinoid production. In addition, we find that levels of heterozygosity (inherited different forms of a particular gene from each parent) are higher in hemp than in medicinal/recreational cannabis (Mann-Whitney 10-14, 2012), which suggests that hemp cultivars are derived from a broader genetic base than that of medicinal strains or that breeding among close relatives is more common in medicinal cannabis than in hemp.
Image: A close relative to Cannabis indica lineage, hemp varietal Ruby (Hemp Farms Australia – 2018)
We see and experience this throughout every hemp crop cycle, open pollinated dioecious hemp plants are more likely to cross-breed due to wind and surrounding crops of different strain backgrounds. This has attributed to the high levels of heterozygosity, whilst medicinal or recreational strains have been clonally propagated in order to retain their premium genetic identity with no risk of outside cross-contamination. The evolution of cannabis is still being mapped, with roughly 30% of the complete cannabis structure unknown and the evolutionary origins of cannabinoids somewhat a mystery.
Written by: Lauchlan Grout – Co Founder Hemp Farms Australia
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