Drug strains bred to hemp strains

Cannabinoid Composition of F1 Hybrids between "Drug" and "Non-drug" Strains of Cannabis

E. Small and H. D. Beckwith. 1979. In E. Small, The Species Problem in Cannabis. Corpus. Toronto. p 121-127

Abstract Twenty-five sets of F1 hybrids [an F1 hybrid means the plants grown from the seed of a cross pollination between types] , mainly between "drug strains" of Cannabis (those in which the resin is chiefly of tetrahydrocannabinol[THC]) and "non-drug strains" (those in which the resin is composed chiefly of cannabidiol [CBD]) were examined. The majority of these were chemically intermediate between their respective parents, showing no dominance toward either parent.
[So, in the plants grown from the resulting seed (the "F1" generation), THC went down with respect to the "marijuana" parent and up with respect to the "hemp" parent. The converse was true of CBD.]

Discussion:
...It appears that generally crosses between drug strains and non-drug strains produce plants of intermediate potency.

...[In studies of drug strains...] The importance of protecting the [genetic] stock against contamination from pollen by non-drug strains is stressed by the fact that the amount of THC may be halved in hybrid plants.

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What these authors don't go on to discuss is what would happen next, in practical terms.

We know, then, that the first generation has been degraded by half. If that "mixed-blood" seed is grown hidden again among hemp plants that will again provide the pollen, then the next generation will again lose by half, gradually by this means (it's called a "backcross" by plant breeders) converging toward the hemp type. But it is unlikely it would get that far as the material would be undesirable after the first contamination.

This is why marijuana growers want to stay away from hemp.

Quote from David Watson AKA Skunkman
QUOTE “ it looks like dope but its really hope”, explains the proprietor, American entrepreneur David Watson. What he meant was that these plants have been specifically bred not to produce an intoxicating resin or hashish. Hortapharm hopes to thwart the aims of the average recreational user. They are already close to finding the Holy Grail, seeds that will produce a one-of female seedless crop of plants with no psychotropic effects (THC high) for the consumer. Why? The answer is that Watson and his Amsterdam based scientists are working to create a stable plant based medical product. They want to isolate the beneficial effects of cannabis’ various properties and then replicate ad infinitum from specialized parent plants. Hortapharm is only interested in developing female plants that are all sterile, not to just protect their genetic copyright, “ if plant is not kept busy producing seeds all its energy goes into resin production”. GMO seeds, terminator technology, sterile crops. Just imagine if this pollen is dusted on crops around the globe. Hortapharm would have a global monopoly.

UN 2006 World Drug Report
There have also been a number of technological innovations that have lost currency. The use of carbon dioxide enriched environments to boost yields has largely been abandoned, due to the greater importance of good air circulation in the hot and humid environment of an indoor grow. The use of ‘feminised’ seeds, produced from hermaphroditic mothers, has also lost popularity, as the risk of further hermaphrodites (and thus pollen contamination) is a threat, and it is much easier to work with female clones.