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BobbyDigital 04-05-2010 02:37 PM

The Evolutionary Effects of Ultraviolet-B Radiation on the Psychoactive Potency and Cannabinoid Content of Cannabis sativa L.
The Evolutionary Effects of Ultraviolet-B Radiation on the Psychoactive Potency and Cannabinoid Content of Cannabis sativa L.

Written by BobbyDigital for
March 25, 2004

After a review of some scientific literature relating to the psychoactive potency of Cannabis, it is the author's opinion that Ultraviolet-B type radiation is the single most important environmental factor for developing varieties with highly narcotic properties. Ultraviolet-B radiation (UV-B) is defined as that part of the electromagnetic spectrum between 280 and 315 nanometers.

Cannabis sativa has two main chemotypes, one almost devoid of psychoactive principals ("fiber-type") and the other with an abundance of said principals. This is actually where the taxonomical split between C. indica and C. sativa originated, when in 1793 Lamarck named Cannabis indica as a distinct species from Cannabis sativa because of slight morphological differences, but mainly because of the intense mind-altering effects after ingestion of C. indica, as opposed to the fiber-type C. sativa (Schultes and Hofmann, 1980(?)). Almost every "fiber-type" variety has been grown outside the range of intense levels of UV-B radiation, whereas the opposite is true for "drug-type" varieties. This can be seen in a chart made by David Pate for his Ph.D. dissertation for the University of Missouri, where he used the data of Small and Beckstead (1973), taking careful steps to disqualify any varieties whose origins could have been in question, and plotted their THC content in relation to their UV-B radiation intensity (Image 1), and also their THC to CBD ratio in relation to UV-B radiation intensity (Image 2). About the data he says,

The remaining data (Table 1) are assumed to be plants native to their respective areas or introduced long enough ago to be well adapted. (Pate, 1979)

Higher levels of delta-9-THC are evident in plants from origins of intense UV-B (Fig. 26). Even with the rather non-specific data base used, the results are highly significant (prob. = .0001) and ambient UV-B levels of seed origin account for over 40% (r^2 = .409537) of the observed variation in % delta-9-THC content. As could be expected, there is also a negative correlation between % CBD and UV-B intensity. (Pate, 1979)
This is a rather interesting observation, and one that has been noted by Bouquet,

In Egypt, when the Viceroy Mehemet Ali wished to create a navy, he got Cannabis seeds from Europe in order to obtain suitable fiber for cordage. New seed had to be brought periodically, because the hemp plants obtained soon became incapable of producing good textile fibers. On the other hand, they began to secrete abundant quantities of the inebriating resin. (Bouquet, 1950)

Hemp cultivated in the plains gradually loses the property of supplying active resin. (Bouquet, 1950)
Bergel reported similar findings when he wrote,

When we were still working in this field we were told that the production of active resin, in any kind of Cannabis plant, depends entirely on the altitude of the plantation; for example, you get rich charas or bhang in Northern India only at a certain height above sea level. It was also reported that in order to obtain active resin one had to plant Cannabis in Germany or near Rosenheim not far from Munich, which again is above a certain altitude. (Bergel, 1965)
David Pate discusses Bouquet when he says,

The work of Small and Beckstead (1973) has indicated a substantial biosynthesis of (delta-9-THC) in plants originating between 30 degrees North and South latitudes. This is complimented by their observations of high-latitude CBD-predominant strains and an intermediate chemotype from border areas. Is it only coincidence that this pattern follows latitudal increases of UV-B, with the 30 degrees North to 30 degrees South belt exposed to the greatest intensities? Certain regions somewhat outside this belt that are known for their Cannabis products (including Morocco, Afghanistan, Lebanon, and the Yarkand district of China) raise their crops at UV-B enriched altitudes. (Pate, 1979)
He goes on to say,

One of the samples that Small et al. (1975) investigated originated from seed of a Mexican strain raised in Mississippi by Turner et al. for NIMH distribution as 'standardized marijuana.' This strain produced only 1.5 % (delta-9-THC) in Canada, about 50% of its content when grown in the more southerly location. ... one might plausibly suspect the ~150% UV-B exposure difference between the two locations (for the increase in delta-9-THC). (Pate, 1979)
Other data he found supporting his idea was from Davis et al., who in 1963 analyzed and plotted Cannabis from Morocco, Greece, Brazil, Canada, Switzerland, Germany, and a seizure sample thought to be from Mexico (Davis et al., 1963). In it, Davis found while comparing high latitudes and tropical climates that,

Samples with the highest ratios (of delta-9-THC to CBN/CBD) came from regions whose sunshine was least attenuated by cloud cover, a variable affecting levels of UV-B irradiances. (Pate, 1979)
Not long after that, at the first symposium organized by the Institute for Drug Dependence, whose topic was Cannabis, the topic of UV-B radiation was slightly covered. In the discussion on biosynthesis, when Agurell was discussing the cannabinoid content from an experiment, this discussion took place,

Haney: Were the plants you were working with grown outdoors, or under glass?
Miras: Outdoors.
Agurell: In a greenhouse, with U.V. tubing.
Haney: Ultra-violet light is a very important factor. (Joyce and Curry, 1970)
The chart that David Pate made showing the ratio of THC/CBD in relation to origin can also be seen slightly changed (names of origins added) in Robert C. Clarke's book Marijuana Botany on page 159 (Image 3). From this, Clarke concludes,

Possibly environmental factors are of more importance than cultural selection in establishing Cannabis phenotypes. (Clarke, 1981)
He does hint at the reason why when he says,

His (Small's) conclusion that there is a strong correlation existing between high-THC cannabinoid phenotypes and cultural selection for potent strains does not take into consideration that his data also reflects that individuals of phenotype I, considered drug Cannabis, are usually grown south of 35 degrees latitude. (Clarke, 1981)
Although Clarke would like to contribute this to longer days, he failed to realize that intense UV-B radiation is another important factor missing from climates outside 35 degrees North and South latitude.

In John Lydon's Ph.D. dissertation, he showed experimentally that Cannabis plants irradiated with intense UV-B had a higher content of delta-9-THC and a lower content of CBD than those without UV-B. Although his experiment did not use clones, he reported a significant 38% difference in the content of delta-9-THC. (Lydon, 1985). Another issue he reported about was that Cannabis was morphologically and physiologically insensitive to UV-B radiation. That means that the plant did not encounter any growth changes or health problems in an area of UV-B exposure equal to that of 3000 Meters above sea level at 0 degrees latitude. Also in his dissertation are two graphs that show the strikingly different cannabinoid contents between "fiber" and "drug" Cannabis with the "fiber-type" coming from high latitude origins and the "drug-type" coming from low latitudes originally (Images 4 and 5). He quotes a different article from David Pate (Pate, 1983) when he says that Pate,

Proposed that the two distinct C. sativa chemotypes (delta-9-THC producing, drug type and CBD producing, fiber type) evolved as a result of selective pressures brought about by UV-B radiations. (Lydon, 1985)
In Pate's closing paragraph he says,

The results of the experiment clearly indicate that individuals of Cannabis have been selected to produce large quantities of (delta-9-THC) in situations of high UV-B exposure. This seems to be the consequence of an advantage conferred by the organism by the UV-B screening properties of this compound. (Pate, 1979)
Pate does not get into finding out why this phenomenon occurs in his dissertation, but he does discuss it some time later in 1994 when he published the "Chemical Ecology of Cannabis." The papers subject was the environmental factors that affect the potency of Cannabis, and UV-B radiation is covered in detail. He says,

... the more intense ambient UV-B radiation of the tropics, in combination with the UV-B lability of cannabidiol, may have influenced the evolution of an alternate biogenetic route from cannabigerol to tetrahydrocannabinol in some varieties. (Pate, 1994)
He explains later, saying,

Their experiments (Lydon, 1987) demonstrate that under conditions of high UV-B exposure, drug-type Cannabis produce significantly greater quantities of THC. They have also demonstrated the chemical lability of CBD upon exposure to UV-B (Lydon and Teramura, 1987), in contrast to the stability of THC and CBC. However, studies by Brenneisen (1984) have shown only a minor difference in UV-B absorption between THC and CBD, and the absorptive properties of CBC proved considerably greater than either. (Pate, 1994)
He then gives two explanations for the phenomenon. First, THC would be more energetically efficient to produce because it would last longer as a UV-B blocker than CBD. The other explanation is,

The greater UV-B absorbency of CBC compared to THC and the relative stability of CBC compared to CBD might nominate this compound as the protective screening substance. The presence of large amounts of THC would then have to be explained as merely an accumulated storage compound at the end of the enzyme-mediated cannabinoid pathway. (Pate, 1994)
He goes on to say,

This CBC pigmentation hypothesis would imply the development of an alternative to the accepted biochemical pathway from CBG to THC via CBD. Indeed it has been noted (De Faubert Maunder, 1970) and corroborated by GC/MS (Turner and Hadley, 1973) that some tropical drug strains of Cannabis do not contain any CBD at all, yet have an abundance of THC. This phenomenon has not been observed for northern temperate varieties of Cannabis. Absence of CBD has led some authors (De Faubert Maunder 1970, Turner and Hadley 1973) to speculate that another biogenetic route to THC is involved. (Pate, 1994)
It is Pate's understanding that the biosynthesis of THC can happen along different routes using different precursor cannabinoids, depending on environmental factors. CBD and THC have the same UV-B absorptive properties, except CBD readily breaks down upon exposure to UV-B, while THC does not. The cannabinoid CBC has significantly higher UV-B absorptive properties than both CBD and THC. CBD would then be viewed as energetically inefficient in areas where additional UV-B screening is needed. The plant would then take an alternate biosynthetic route, creating CBC from CBG to get to THC. This route would provide the plant with the UV-B protection it needed, whereas the route involving CBD would be less functional for that purpose.

Although further investigation is needed along this line of inquiry, the theory is somewhat supported by Robert Nelson when he writes,

The phenotypes rich in THC always possess Cannabichromene (CBC), sometimes in large amounts. (Nelson, 2000)
And also by Bassman when speaking in general of UV-B radiation's effects on plants,

In addition, some secondary metabolites may increase with enhanced UV-B radiation, whereas concentrations of others may decrease. (Bassman, 2004)
In our case, CBC would be increased because of its UV-B absorptive properties, and CBD would decrease because it readily degrades upon UV-B exposure. Bassman then goes on to say,

Such changes may be due, at least in part, to competition for substrate by different enzymes along different branches of major biosynthetic pathways. (Bassman, 2004)
In our case, this would be relevant in the biosynthesis from CBG to THC through either CBD or CBC, with the CBC route given evolutionary favor in areas of intense UV-B.

Lydon wrote a good summary of the issue about UV-B radiation and Cannabis potency when he stated,

Thus, populations of C. sativa which produce more UV-B absorbing compounds when exposed to high levels of UV-B radiation (as demonstrated with the drug-type clone) may experience more reproductive success in high UV-B radiation environments. This would account for the present distribution of drug and fiber type C. sativa in temperate and tropical environments. (Lydon, 1985)
There has been a large group of individuals in modern times, who for various reasons attempt to grow Cannabis indoors under artificial lighting for its narcotic properties. These individuals try to mimic the output of the sun as closely as possible in order to grow their plant to their highest potential, although intense UV-b radiation is never represented in their indoor environments, mainly due to lack of information on UV-B's effects on Cannabis potency. There have been a few select individuals who have gone through the pains to supplement their HID (High-Intensity Discharge, the most common type of lamp used for this purpose) lighting with UV-B producing lamps and reported their findings, with almost all of them reporting positive results. This was observed on the Internet Cannabis growing community On that website, there have been five people who've supplemented UV-B through the whole life cycle of a Cannabis plant, aallonharja, Alchemy Grower, middle_aged_crazy, maxgrow_de, and Sam_Skunkman.

The first, aallonharja, though only using a 15 Watt tanning fluorescent bulb, but failing to report his strain or growing conditions stated a

5-10% (increase in resin production)
although he felt it wasn't worth the trouble. middle_aged_crazy has added supplemental UV-B lamps to his indoor environment, with plant harvests intended for medical users, and reports such a large difference that he won't go back to an environment without UV-B represented. He said that the patients he supplies reported that they needed 25% less plant product to fulfill their medical needs. The same situation was reported by Alchemy Grower, another medical grower, who feels that it makes such an impact that he will keep the UV-B producing lamp in his growing area. maxgrow_de reported positive results, also, when he said,

You can determine clear differences in between the UV powered plant and the other two ladies.
The only person to report unvaried results was Sam_Skunkman. He supposedly had his close associate David Pate set up a UV-B experiment in his greenhouse and found no difference between the controls and the UV-B supplemented product, although it was not explained how he tested them. He failed to give the strain used, any procedure, or growing conditions of the experiment; therefore his test is hard to draw conclusions from. (All taken from )

Out of the five people to have added supplemental UV-B to their indoor growing environments and reported about it, four report an increase in the narcotic properties of their final product. Three felt that there was such a difference that they will not go back to using no UV-B supplementation. Sam_Skunkman reported no difference, although the strain he used and procedure were never reported. aallonharja, despite reporting a positive increase in resin production, felt it wasn't important enough to do again, but that could be due to the fact that he is an extremely experienced cultivator and there was not that much psychoactive difference between his products with UV-B and those without. Now that a direct correlation has been shown between UV-B radiation and the potency of Cannabis, one would suspect more people attempting UV-B supplementation in their indoor environment, with positive results reported.
In support of the fact that Ultraviolet-B radiation positively influences the narcotic properties of Cannabis, one could look at the writings of Ed Rosenthal, an author who specializes in indoor Cannabis growing. He seems to believe that UV-B is important in growing a narcotically potent Cannabis plant. His advice has been taken by more people on indoor Cannabis growing than any other author, mostly from his "Ask Ed" column which appears in Cannabis Culture magazine, or his best selling books on Cannabis growing. There have been at least two "Ask Ed" articles that speak of UV-B radiation, both in a positive light.

The first is from the November 2002 issue of Cannabis Culture in an article entitled "Light Disagreement", where an individual claims that Metal Halide HID lamps are better for the flowering cycle because of the UV radiation emitted by them. The person claims,

MH lamps produce more (Ultraviolet light) than HPS lamps and the more UV, the higher the potency climbs in normally high potency plants. (Rosenthal, 2002)
In response, while probably speaking of Lydon's dissertation, Rosenthal says,

A researcher conducted a controlled experiment in a greenhouse. ... He found that the percentage of THC increased in a direct ratio with the increase in UVB light. This research confirms the adage that high altitude plants are more potent than those grown at low altitudes. If you look at old-world land races of Cannabis plants that have become adapted to the climate and latitude, the ratio of THC to CBD starts at 100:1 at the equator. At the 30th parallel (the Hindu Kush Valley) the plants have a ratio of 50:50. At the 45th parallel the ratio is near 1:100. This corresponds roughly with the amount of UVB light received at these latitudes. There is much more UVB at the equator than the 45th parallel. (Rosenthal, 2002)
The second instance of Mr. Rosenthal speaking on UV-B radiation is from the February 2003 issue of Cannabis Culture. In the article entitled "Metal Halide for Flowering?" Rosenthal says,

Third, the lamps emit more UVB than HPS lamps, although still in very small amounts. The amount of UVB light plants receive is directly related to the quality of buds. The more UVB, the higher the quality. (Rosenthal, 2003)
Mr. Rosenthal's advice should not be taken lightly due to his reputation and widespread audience in the Cannabis growing community.

The scientific data has shown that intense levels of Ultraviolet-B radiation have been the single most important environmental factor in developing Cannabis varieties with highly narcotic properties. The environmental stress of UV-B radiation coupled with the obvious artificial or cultural selection carried out by the human race, has resulted in varieties of Cannabis with large quantities of the psychoactive principal delta-9-THC. It would seem that today, Cannabis breeders are focused mainly on artificial selection, with little or no emphasis on the environmental factors that would affect the cannabinoid biosynthetic pathway, content, and ratio.
The author has no knowledge of modern breeders trying to give their plants an intense level of UV-B radiation, although it would seem that this was the case for cultivators in the distant past. With the amount of high quality, highly narcotic Cannabis strains available today, it would seem that the last step would be to give the plant a supplemental dose of Ultraviolet-B type radiation equal to that of low-latitude or high-altitude environments in order to fully develop the biosynthetic pathway to THC with little or no CBD involved. The lack of UV-B radiation in a Cannabis growing environment would effect the potency of the mind-altering attributes, as in the plant would not be as narcotic as if there was a quantifiable level of UV-B radiation in the light. Highly potent Cannabis can be grown without UV-B radiation being represented due to intense cultural selection, although it would seem that almost all the strains grown today are originally from areas of intense UV-B radiation.

Ultraviolet-B radiation is the single most effective environmental stress to increase the psychoactive potency of Cannabis. In fact, it's evolutionary, and over the years, along with a human hand, it has played the most important role in developing Cannabis with large quantities of its main psychoactive principal, delta-9-THC. The words of David Pate can best conclude this discourse when he wrote,

This study was done as a library thesis due to restrictions placed on even the scientific investigation of this genus. However, the approximate limits of inquiry possible with this technique have now been reached. Conclusive answers to many remaining questions demand carefully controlled experimentation. (Pate, 1979)

BobbyDigital 04-05-2010 02:38 PM

C.R.B. Joyce and S.H. Curry. 1970. The Botany and Chemistry of Cannabis. J. and A. Churchill: London.

R.C. Clarke. 1981. Marijuana Botany. And/Or Press: Berkeley.

E. Rosenthal. 2002. “Light Disagreement” Cannabis Culture (Nov.)

E. Rosenthal. 2003. “Metal Halide for Flowering?” Cannabis Culture (Feb.)

R.A. Nelson. 2000. Hemp Husbandry. Rex Research Archives: Jean (NV).

D.W. Pate. 1979. The Phytochemical Ecology of Cannabis. Dissertation for Ph.D. at University of Missouri-St.Louis.

J. Lydon. 1985. The Effects of Ultraviolet-B Radiation on the Growth, Physiology and Cannabinoid Production of Cannabis sativa L. Dissertation for Ph.D. at University of Maryland-College Park.

BobbyDigital 04-05-2010 02:42 PM

Just to let you all know that this was written in 2004, and I have learned a lot since then, and somewhat revised my ideas about this. I should edit it, but didn't have the time right now. Maybe sometime soon.

Also, unfortunately I have lost the images that used to go with the document. If anyone really wants to see them I think I still have the hardcopies around here somewhere and I can put them up.

raydiator 04-05-2010 07:43 PM

So bobbyD do you add UV to your grow rooms...or use MH to flower...has anyone here done any experiment with UVB...

lemarcel 04-06-2010 01:04 PM

Hello Bobby !

thank you very much for your article, that was very interesting :)

I am very happy to use UV(B) in my box :D

My best vibes to you !


LK-STINKMASTER 04-06-2010 02:51 PM

suppliment with mh lights
Very interesting. Does this mean that I should suppliment my two hps lights with a mh light. Would this be an increase in potency? Anybody trying to combine the two lighting systems. Lk-Stinkmaster

BobbyDigital 04-08-2010 04:05 PM

Sup guys,

I can't really say for certain what kind of effects UV-B would have on your plants. I just kept finding research about it as I looked into it. It would seem that UV-B was important to get cannabis to create a compound like cannabinoids, but I can't say if it is really that important now.

I wrote this in leMarcel's thread, so I'll just copy it over to this one:

Very interesting, I wasn't expecting that reasoning for adding the UV, although it makes sense.

The reason that I used to use them is because there is a lot of research out there that suggests UV-B in particular is important in growing potent plants. If nothing else, it was probably the major environmental factor that caused Cannabis to evolve to create a compound like THC in the first place. HID bulbs in general do not put out anything close to the suns amount of UV-B, except for the new CMH, but those weren't around back when I was growing indoors.

People always say, "then why are my indoor buds such chronic if there is not really any UV-B?" My answer is that Cannabis is known to evolve incredibly fast, and if plants are bred under indoor lights for potency, then it is completely normal for them to be potent without UV-B. That doesn't mean it won't help, though, but then again, it doesn't mean that it will help, because it would be somewhat dependent on how it was bred and the genetics latent in the seed and how they react.

I had actually wrote up a kind of 'research' paper about all the things I found while reading up about it. It's probably a little dated now, since I wrote it a couple years ago during Overgrow's time. I'll post it up somewhere on this site and point you to it in case you want to read it, I'm pretty sure I have a copy of it somewhere.

And honestly, I like outdoor buds more than indoor. I can't say for sure that it is the increased UV, but I'm sure it helps. Sam Skunkman helped me research it, and he admits that outdoor buds seem to smoke better than indoor, but he didn't want to say it was from the UV-B. Then again, I'm not quite sure I trust that guy now.

And I don't grow indoors anymore, unfortunately I don't really have a place to do it safely right now. I used to use Aquarium UV bulbs. There were reptile basking lamps and tanning lamps, too, but the reptile lamps are a little too small, and the tanning lamps were too long to get in the right position close enough to the plants.

BobbyDigital 04-14-2010 09:34 PM

I just went looking for the images that used to go with this document, and I found the dissertations, but the images that I used are missing from them.

I did find a copy of an article that I wasn't able to get my hands on when I wrote this article, but after I published it, Sam Skunkman actually had it and sent me a copy of it. It was by John Lydon, two years after his Ph.D. dissertation, and the article was called, "UV-B Radiation Effects on Photosynthesis, Growth, and Cannabinoid Production of Two Cannabis sativa Chemotypes". It was published in the journal Photochemistry and Phytobiology, which was very obscure and no longer around, so it makes sense that my librarians couldn't track it down!

These are the last two paragraphs of the abstract for the paper:

There were no significant physiological or morphological differences among UV-B treatments in either drug- or fiber-type plants. (It didn't cause any health concerns) The concentration of delta-9 THC, but not of other cannabinoids, in both leaf and floral tissues increased with UV-B dose in drug-type plants. None of the cannabinoids in fiber-type plants were affected by UV-B radiation.
The increased levels of delta-9 THC in leaves after irradiation may account for the physiological and morphological tolerance to UV-B radiation in the drug-type plants. However, fiber plants showed no comparable change in the level of cannabidiol (a cannabinoid with UV-B absorptive characteristics similar to delta-9 THC). Thus the contribution of cannabinoids as selective UV-B filters in C. sativa is equivocal.
Just some food for thought I guess.

BobbyDigital 04-14-2010 10:27 PM

Just as a strange side-note, while trying to find a copy of David Pate's dissertation, I just found out that he works for Hortapharm! That is Sam Skunkman's company, and when discussing this article, Sam had said that he did an experiment with Pate that was never published where they found no increase in THC from UV-B exposure (and the only scientific paper I've ever read that reported no change in drug-type varieties). I'm not sure what to make of this, yet, but I do find it a little interesting.

(edit)It also looks like he wrote a chapter for the book Advances in Hemp Research, published in 1999, titled "The Phytochemistry of Cananbis: It's Ecological and Evolutionary Implications". The title sounds a lot like mine, and I was able to read some of the pages from Google, but it is incomplete. He says in it explicitly, citing the Lydon '87 article I wrote an excerpt of the abstract above:

Their experiments demonstrate that under conditions of high UV-B exposure, drug-type Cannabis produces significantly greater quantities of THC.
I find it strange that David Pate wrote this, when Sam Skunkman says that they did an experiment together that showed no difference. Hell, Pate's Ph.D. dissertation was all about the effects of light on Cannabis. Something is not adding up.

~worm~ 04-30-2010 08:51 AM


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