Here's an excerpt from an academic book on plant physiology which is shedding some light on the flowering process of Cannabis Indica. Unfortunately, it's in my mother language german, but I can translate the relevant parts and point out some keywords, so that you can understand the relevant graphics:
(Dieter Hess: Allgemeine Botanik)
KTP = short daylength plant
LTP = long daylength plant
kritische Dunkelperiode - critical dark phase (night time)
blüht = flowers
Stunden = hours
Störlicht = irritating light
HR = light/bright red (art.) light
DR = dark red (art.) light
"
Daylength and photoperiodic induction. Numerous plants require a specific day- or nighttimelength to induce flowering. We differentiate between shortdayplants (KTP) and longdayplants (LTP). (on p.269 Cannabis sativa is identified as shortdayplant - but I suspect only indica-related plants because sativas follow different rules, at least, that's my experience). The critical daytimelength lies between 10 and 14 hours, depending on species. Shortdayplants induce flowering when their daytimelength falls below the critical threshold. Longdayplants when it falls above that threshold. [...]
The processes during the the dark periode are the ones relevant for flower-induction. When one gives irritating light during the dark period, shortdayplants will not induce flowering (this is why the Gas LanternRoutine works in Cannabis) [...]
Place of perception are the leaves. The light absorption for this is mostly done in blue/UVA-receptors (--> p.277) and phytochrome, like has been identified in various studies involving lighting experiences. Because one can make the same pendulumplay involving lightred/darkred, like we've seen in the sprouting of lettuce (--> p. 131). Just that the active form of phytochrome(brightred) doesn't support the flowering induction but instead, hinder it (graphic 4.3.7). From the various phytochromes the most important is phytochrome B."
In this graphic the relevant flowering-inducing genes and their pathway expression is show:
what I find remarkable is that the photoperiodic daytimelength is clearly shown as being determined by bluelight or UVA (Photoperiode: Blau oder UV-A)
@Dr. Who this is some evidence which confirms my theory and it would also explain why my photoperiodic plants did flower under 18/6 of constant light: only 12h of these 18h were filled with blue/UV - the rest was 6h HPS light + 6h dark.
Now if this theory is true, then maybe I can even bring Cannabis to flower under 24h over consecutive hard HID light:
24h HPS + 12h MH:
12h day: HPS + MH (was 50k lux at canopy in my setup)
12h night: HPS (was 30k lux at my canopy...)
--> increase of 3/5th in possibly PAR; ie. lowering the ppfd-requirements by 3/5th if one hits the Daily Light Integral with the combination of day+night light.
Especially on LED boards that operate blue diodes & red diodes on separate channels, this could decrease the amount of necessary diodes by MUCH; or: increase the area to light out by the same percentage (ie: board could be placed higher).
I find this especially important because we're talking here about photoperiodic plants, where we traditionally reduce the amount of light that can be
given from 18/6 to 12/12 - a decrease of 50%. To compensate, we increase luminosity. This means:
- hardware potential in veg is not fully utilized
- locale leaf temperature rises through increased lux
- unnatural state: luminosity goes up at the beginning of flower when in nature it actually gradually sinks. shortdayplants usually get the highest lux in mid-to-late veg phase.
- late in flower lots of plants loose fanleaves which reduces the surface area with which to do photosynthesis. Plants do have less potential then to fabricate & store carbohydrates.
- We cannot increase lux endlessly to compensate the lack of photo-potential because of the dangers of
photo-destruction after crossing the
light saturation point.
24h of light could mean lesser evolved rootsystem. However, in generative mode plants gradually form less and less roots - as they put all thier power into the buildup of flowers. So this disadvantage is mitigated a bit.
The book then ventures on to explain the underlying genes which are responsible for flowering expression (as seen in the illustration above) - the gene CO (CONSTANS) seems to be critical for this. This knowledge is drawn from the plant
thale cress (
Arabidopsis thaliana) - which is a rolemodel-plant in genetics and which is very close to Cannabis - as both are
rosids (read more about this in the wiki link given).
According to the text it is the gene CONSTANS that induces flowering and which is expressed over a pathway initiated by "Cryptochrom 2 [CRY2]" stimulated by blue/UVA light. The book tells this in somewhat vague terms, so I went to wikipedia:
https://en.wikipedia.org/wiki/Cryptochrome
this sentence is particularily interesting:
"
A double loss-of-function mutation in Arabidopsis thaliana Early Flowering 3 (elf3) and Cry2 genes delays flowering under continuous light and was shown to accelerate it during long and short days, which suggests that Arabidopsis CRY2 may play a role in accelerating flowering time during continuous light.[15]" [
bolding by me]
and:
"Despite much research on the topic, cryptochrome
photoreception and
phototransduction in
Drosophila and
Arabidopsis thaliana is still poorly understood."
--> this could explain why the industry doesn't make use of this Doc - maybe we're in unchartered territory here :O
but: (from the reference [15] study
https://academic.oup.com/jxb/article/62/8/2731/476001
"
Abstract: [...]
The results suggest that CRY2 may play more essential roles in the acceleration of flowering under LL than LDs or SDs." [!]
LL = continous light (24/0),
LD = longday (18/6),
SD = shortday (10/14)
I find this sentence absolutely remarkably! If this is true then perhaps an LED board could simply induce flowering by giving light off which stimulates the responsible cryptochromes, and not with a changed/increased dark phase.
If it is further true that this way flowering is not also induced - but also ACCELERATED - then, the combination of both advantages ("more potential light" + accelerated flowering] could mean a drastic paradigm change in the way indoor crops are lighted out.
RangiSTaxi already pointed out a significant decrease in flowering time, from commonly 60-80 days down to ~35. I'm estimating an increase in area lighting out by up to 50%. Combine both, harvest could be increased considerably (with more energy + more area used)
So if this all is true, an LED manufacturer who incorporates this knowledge would be able to beat even the best-quality reference boards in a direct comparison by perhaps a minimum of 150% more dry harvest [@Grow Lights Australia,
@ANC]
Disclaimer: The book I draw these info's from is not the newest, so to speak. However, the infos available has all been gathered by empirical methods - they are valid.
Have a nice sunday my friends
@Kassiopeija you have the passion and drive to be a leader in this industry [...] Kassiopeija, work it out and you will make a mint.
LMAO actually I'm a just a poor homegrower... I fought a severe depression for almost a decade - in this time, only reading was possible. My preferred topics: Natural sciences: biology, physics, chemistry (in that order). So my purse is empty - but my head full XD and maybe if I would live in a country like the US where the state offers alot of potential to live "the American dream" I could maybe fill that purse, but here in rusty Germany? don't think so... :/
