Cannabigerol (CBG) dominant plants are becoming the rage for next season among smokeable/raw hemp flower growers (almost entirely due to the USDA interim rule making most CBD varieties susceptible to testing hot).
So I want to discuss and compile some information about breeding for CBG varieties that will pass for compliance.
Firstly some background:
Identification of a New Chemotype in Cannabis sativa : Cannabigerol - Dominant Plants, Biogenetic and Agronomic Prospects
-CBG dominant plant first ID'd by Fournier at al, 1987.
The draft genome and transcriptome of Cannabis sativa
Gene duplication and divergence affecting drug content in Cannabis sativa
-showed there were multiple THCAS/CBDAS sequence homologs in individual plants
Sequence heterogeneity of cannabidiolic- and tetrahydrocannabinolic acid-synthase in Cannabis sativa L. and its relationship with chemical phenotype.
-different synthases have different efficiencies
A physical and genetic map of Cannabis sativa identifies extensive rearrangements at the THC/CBD acid synthase loci.
This paper shows (at least for one variety of fiber hemp (Finola) and one marijauna (Purple Kush)) that the fiber-derived linked cannabinoid synthases (CBDAS, THCAS) are very different in their arrangement. This suggests:
- A lot of derivation once the two gene pools separated.
- Residual THC production in hot hemp varieties is probably produced by the CBCAS, which are unlinked from THCAS/CBDAS
- -the putative THCAS identified by Kojoma et al, 2006 in hemp are actually CBCAS. Both Purple Kush and Finola had CBCAS.
The Inheritance of Chemical Phenotype in Cannabis sativa L
This paper talks about chemotype inheritance and crosses a fiber-dervied CBG variety to a high THC drug variety. in the F2 the CBG segregates, and again produces no detectable THC:
The inheritance of chemical phenotype in Cannabis sativa L. (IV): cannabinoid-free plants.
This 2009 deMiejer Paper talks about the inheritance of cannabinoid free plants and an alternative CBG producing genotype derived from the USO-31 hemp variety. This variety apparently has two gene knockouts; one that prevents cannabinoid production when homozygous and severly suppresses it in heterozygotes, and another that blocks CBD production causing CBG to accumulate. The USO-31 derived region responsible for CBG accumulation produces extremely pure CBG (99.75% of cannabinoids) with residual CBD (0.25%).
DeMiejer also has a 2014 book chapter in the "Handbook of Cannabis" that discusses a similar cross using fiber-derived versus a marijuana-derived (high-THC variety that had a CBG variant) CBG gene region. The fiber-derived linked synthase region produce residual amounts of CBD and almost no THC. Whereas the marijuana derived CBG region variant produces residual THC.
Recently Oregon CBD made their CBG variety announcements on instagram. In their post, they explained how they crossed a marijuana derived CBG variety (that produces THC at about 1:27 ratio CBG:THC) with a (probably) hemp derived CBG variety that has a ratio of 1:100-200. (you can see their tests here
By doing this they have rather cleverly prevented people from producing F2s that will all be compliant (though on a field level the average still would be). Oregon CBD also loves to pretend that you cant use F1 material as breeding material, when in fact F1 material is often the starting point to develop variation in the creation of new lines. I suspect that, because the one of their CBG variants is almost certainly fiber-derived, compliant 1:100-200 ratio plants will emerge easily among the F2 progeny, which would be truebreeding for CBG if these are inbred to F3+. Of course the MTA they have you sign means you aren't even permitted to save seed for on farm use, let alone breed with any of their germplasm, anyway.
Oregon CBD also made an argument that 8 gene/pseudogene regions may be responsible for residual THC production. Medicinal Genomics also has made this claim (these companies work together, so MG is probably the source of this info). But active THCAS and CBDAS are tightly linked, with residual THC from the CBCAS as well. I am not sure how many active copies of each synthase exist among various varieties.
Ultimately, I suspect for those looking to breed for CBG, if you use a fiber-derived CBG gene region, you will be able to easily produce a true-breeding, CBG-dominant, THC-compliant hemp variety, with crosses mostly behaving as a simply inherited single locus with some residual THC from CBCAS. The negative of this is that you will be starting from a low point for total cannabinoid synthesis. But backcrossing the CBG gene region into high-cannabinoid drug plants or populations should overcome this.
CBG seed sources:
CanapaRoma- 8%CBG under 0.1%THC. No MTA. putatively truebreeding for complaint (at about a 1:65 THC:CBG ratio), fiber derived CBG variant.
Sovereign Fields-$2/seed, unknown specs. MTA required
HGH seed- 15+% CBG, Matterhorn CBG, $1+/seed. not sure about MTA
Oregon CBD- 15+% CBG, $1/seed, MTA required
European fiber varieties (I am not certain, but these are probably protected by plant variety protection (PVP), meaning you can save seed for on-farm use and breed with them):
Santhica-27: monecious 1-3% CBG, CBD residual
Carma - monecious ~3% CBG
USO-31- monecious. low cannabinoid, some cannabinoid free plants, some CBG dominant plants with very little residual CBD production.
Please share any relevant information on CBG breeding and seed sources. Thanks!