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misc Scientific Observations of Environmental Stress on Pepper Varieties

In response to solid7, "You're the overzealous master of link posting, about things, and for the sake of. Feel free to find it, and repost it, yourself. If you can find an animated gif of Obama sitting on a crate yawning, you should have no problem finding a study that I linked to.", my response is - others with much more resources than any gardener has in his backyard and a single link posted I don't know when or where it came from, I'll take the links to well funded research by organizations that are internationally respected. Unlike those whose single mindedness is of their own observations with closed acceptance to widely accepted research I did due diligence and looked for and found it is a complex combination of many things but genetics, amount of stress, type of stress, and when applied can and caused slight decrease - no change - to substantial increase....


Aerican Society for Horticultural Science/Impact of Drought Stress on the Accumulation of Capsaicinoids in Capsicum Cultivars with Different Initial Capsaicinoid Levels

"In conclusion, capsaicinoid levels increased for all cultivars studied when subjected to drought stress, except for the cultivars in the high pungency group. A yield response under drought stress for the medium pungency group varied and was not found to be associated with drought stress."

American Society for Horticultural Science/Water Deficit Affects the Accumulation of Capsaicinoids in Fruits of Capsicum chinense Jacq.

"Habanero pepper plants under water stress had a lower height, root dry weight, and root/shoot relation than control plants, which were irrigated daily. However, fruit growth and production were unaffected by water stress. Capsaicin and dihydrocapsaicin concentrations increased in fruits of stressed plants compared with control plants, and this effect was correlated with fruit age. "


MDPI/Characterization of Different Capsicum Varieties by Evaluation of Their Capsaicinoids Content by High Performance Liquid Chromatography, Determination of Pungency and Effect of High Temperature

"High temperatures can be a negative factor in the accumulation of capsaicinoids in certain varieties
of chili peppers, this study showed that the varieties most affected were Jalapeño and De árbol peppers
as they lose 61.5% and 32.5% of total capsaicinoids, respectively. Moreover, the temperature rise in
greenhouse favored the accumulation of total capsaicinoids in varieties Guajillo and Serrano and
corresponding to an increase 3-fold. Furthermore, the Puya variety showed a slight increase of 21% in
the amount of total capsaicinoids; while having a slightly positive effect on Ancho with an increase of
8.6%. These data demonstrate that the responses of the peppers did not show a homogeneous behavior.
In literature it has been reported that levels of capsaicinoids increase in spicy peppers varieties more
than in sweet peppers when the temperature rises in the place where cultivated, however, our results
show a decrease in the amount of capsaicinoids in Jalapeño and De árbol varieties.
"

Some like it hotter: UC Cooperative Extension tries to grow a spicier jalapeño

"Research studies in Mexico, Taiwan, Thailand and Spain have shown that water stress results in hotter peppers so Sanders and Baameur tried irrigating with less water. For us, it did not show that, Baameur said. We sampled fruit and we analyzed it for capsaicin content, which makes a pepper hot. It was fairly low, actually it was almost half of what the normal treatment, or control, would be.

The relatively cooler climate of the Santa Clara County area may be the reason the pepper plants produce different results. I think it's more a relation to heat, ambient temperature, much more than just water, Baameur said. Cool years and hot years will result in different heat units for the same jalapeño variety.[/size]

My conclusion is different influences have different results at different times but generally environmental stress has an influence on the pungency of peppers, YMMV.

NECM

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Malarky said:
I'll keep my plants happy
HappyPlant.jpg
 
juanitos said:
thanks
 
now when people talk about stressing everyone can link them here to see there is no consensus either way.
 
Exactly! I spent hours researching this and I have more non-accredited observations both ways - no increase or positive increase.... But it was the negative increase ones that raised my eyebrows!
 
juanitos said:
it's fine to give opinions / experience / empirical evidence though... it is a forum.
Emphatically agree! Your experiences can be different from mine, doesn't mean either is better, it's what worked for you and myself at that time... But scientific observations should hold a certain weight above individual grow results, no?
 
This needed a 
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UC Cooperative Extension tries to grow a spicier jalapeño...

Baameur is trying to grow a hotter jalapeño by studying the variables that raise the Scoville units, which measure a pepper's heat. For the past four years, he has been documenting the effects of different rates of water, potassium, sea salt and nitrogen applied to the jalapeño crop at George Chiala Farms in Morgan Hill.

Research studies in Mexico, Taiwan, Thailand and Spain have shown that water stress results in hotter peppers so Sanders and Baameur tried irrigating with less water. “For us, it did not show that,” Baameur said. “We sampled fruit and we analyzed it for capsaicin content, which makes a pepper hot. It was fairly low, actually it was almost half of what the normal treatment, or control, would be.”
The relatively cooler climate of the Santa Clara County area may be the reason the pepper plants produce different results. “I think it's more a relation to heat, ambient temperature, much more than just water,” Baameur said. “Cool years and hot years will result in different heat units for the same jalapeño variety.”

The amount of potassium hasn't made a difference, but adjusting nitrogen fertilizer seems promising.

“High nitrogen is promising because it produces a hotter pepper and also allows for high crop yields,” Baameur said. “Low nitrogen also resulted in higher pungency, it brings a lot of heat in the peppers,” he said. “However it is correlated with lower yields.”

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This thread needed an update.....
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Water Deficit Affects the Accumulation of Capsaicinoids in Fruits of Capsicum chinense Jacq. 
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Both water stress treatments led to a significant increase in the concentration of capsaicin [an increase of 16 mg·g−1 dry weight (DW) with respect to control] and dihydrocapsaicin (19 mg·g−1 DW increase with respect to control) in the placenta of 45 DAA fruits but did not significantly modify the capsaicinoid concentration in 25 DAA fruits (Fig. 3C). 
 
So the difference between 25 & 45 DAA is Days After Anthesis (the flowering period of a plant, from the opening of the flower bud.)= don't bother stressing early on and let your plants grow & increase fruit production, as others recommend because stressing will inhibit this, then stress to your hearts content to increase heat!
 
 
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Jal_Un-Stressed_50_percent1b_zps5h0rdp3t.jpg

 
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Jal_Stressed_50_percent1a_zpsrtko6py9.jpg
 
My two favorite papers about environmental factors are:
 
Harvell, K., and Bosland, P.W. 1997. The environment produces a significant effect on pungency of chilis. HortScience, 32: 1292.
very short paper, and probably obvious to most of us, but its the thing you need to reference when describing why the Guinness test is BS.
 
Zewdie, Y., and Bosland, P.W. 2000. Evaluation of genotype, environment, and genotype-by-environment interaction for capsaicinoids in Capsicum annuum L. Euphytica, 111: 185–190.
This paper does a better job of modeling the effect of environment, and has the interesting result that some lines are not effected by the enviroment at all when it comes to pungency
 
I swear there's a paper about heat stress but I can't find it
 
The_NorthEast_ChileMan said:
Aerican Society for Horticultural Science/Impact of Drought Stress on the Accumulation of Capsaicinoids in Capsicum Cultivars with Different Initial Capsaicinoid Levels
 
"In conclusion, capsaicinoid levels increased for all cultivars studied when subjected to drought stress, except for the cultivars in the high pungency group. A yield response under drought stress for the medium pungency group varied and was not found to be associated with drought stress."
 
Phimchan, P., Techawongstien, S., Chanthai, S., & Bosland, P. W. (2012). Impact of drought stress on the accumulation of capsaicinoids in Capsicum cultivars with different initial capsaicinoid levels. HortScience47(9), 1204-1209.
This paper is good too, Bosland is on it as well. I'm kind of a fanboy. Does Paul read these forums?
 
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Dave DeWitt, another respected hot pepper chillihead, and the aforementioned Paul W. Bosland coauthored The Complete Chile Pepper Book: A Gardener's Guide to Choosing, Growing, Preserving, and Cooking, and in it they wrote:
 
PUNGENCY.

About 50 percent of pungency is genetic and about 50 percent is environmental. Generally speaking, stressing pepper plants increases their pungency. Both restricting water and overwatering (a dangerous practice) will increase the amount of capsaicin in the pods. Restrict the water until the plants just start to wilt, then water them slightly to perk them back up. Do this several times throughout the growing season and the pods should be hotter. The pungency is also increased when the fruit ripens at higher temperatures. In fact, the pods of New Mexican varieties ripening at temperatures between 86 and 95°F have twice as much capsaicin as those ripening at 59 to 72°F. Applying nitrogen after fruit set can lower the capsaicin levels.

Interesting statement about nitrogen application.
 
 
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I can say for sure that the majority of my early season peppers were not as hot as late season. This did not hold true though for my lemon drops and citos. The heat level was pretty consistent all season but the season was shorter for ripe peppers too.
 
One year i had 2 Early jalapenos that looked like hell the entire time. Nothing i did would snap them out of it. Production was poor but the pods i did get were freakishly hot for jalapeno. Normally the first few jalapenos i get are on the milder side. By July they are all pretty much hot and the occasional freak. Our July temps are pretty much over 85F and often over 90F. Sofar we had temps over 95F but we also had a bit more rain during the end of June. I would say our temps this June were hotter than average.
 
My late season pods last year seemed hotter to me that than my early season pods. This year, I'm not really getting many early pods but we're experiencing heat waves and only sporadic rains so...

Maybe these things will will be extra hot?

Where I'm at right now, I'm still learning how to keep my plants happy and healthy. I'm not at a point yet where I want to be manipulating my harvest via stress... But I do find these factors to be fascinating...especially that ppl still have varying beliefs and experiences on the subject.
 
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Impact of Environments on the Accumulation of Capsaicinoids in Capsicum spp.

Pungency increases with environmental stress such as high temperature (Otha, 1960), water stress (drought or flooding) (Bosland and Votava, 2002; Sung et al., 2005), and soil fertility imbalances (Johnson and Decoteau, 1996; Medina -Lara et al., 2008; Montforte-Gonzalez et al., 2010). Medina-Lara et al. (2008) reported that nitrogen fertilizer significantly increased plant growth and fruit yield while maintaining high levels of capsaicin and that application of potassium has no effect on growth or productivity. Iwai et al. (1979) suggested that light exposure may be an important factor in the formation and accumulation of capsaicinoids.
 
The_NorthEast_ChileMan said:
`reported that nitrogen fertilizer significantly increased plant growth and fruit yield while maintaining high levels of capsaicin and that application of potassium has no effect on growth or productivity. Iwai et al. (1979) suggested that light exposure may be an important factor in the formation and accumulation of capsaicinoids.
 
Which is also why the idea of bloom boosters being bunk is so popular, these days...
 
NECM, It's too bad we got off to a rough start, because this is actually a really good thread, for a lot of different reasons.

At the end of all the discussion, the only thing that matters, should be helping others grow better, with no BS or gimmicky marketing in the middle.  Truth be told, every one of us can grow peppers, with the resources that we already have.  I find it troubling, whenever we see a newbie come to the forum, who has been made to believe that you have to be a botanist to grow peppers, or that some rocket-fueled nutrient, is the only thing that will make plants grow. 
 
Bicycle808 said:
Where I'm at right now, I'm still learning how to keep my plants happy and healthy. I'm not at a point yet where I want to be manipulating my harvest via stress... But I do find these factors to be fascinating...especially that ppl still have varying beliefs and experiences on the subject.
 
LOL...  I still say that when you need 'em hotter, you step up to a new variety.  Like when you just gotta pay more taxes, instead of adjusting your withholdings, why not just make more money? :D
 
In all seriousness, I don't spend much time anymore chasing this subject, because most of my peppers are too fucking hot the way it is.  Last time I sat down to a bowl of Carolina Reaper poppers, I...  Ok, nevermind.  I never really did that.
 
It probably does not have much scientific merit but I find that the stunted early pods seem to pack the most punch for their size. It's like all the anger of a large pod was concentrated into a smaller package. Or perhaps my tolerance dies down before the start of the season and they just seem like they're hotter because they're the first pods I've sampled in a while. 
 
Many of my first pods sofar have been plenty hot. First pod off the ghost seemed to be on the milder side but the last one was exactly what you would expect from a ghost. My chichimeca will droop within 2 days and all the pods now have been excellent. My Biker Billy in the ground havent drooped yet but pods are hot. A couple have been really hot for jalapeno.
 
Seems a bit odd that my Brazilian Starfish is on the milder side and it droops easily. The first 3 pods have all been super sweet and lower end jala heat levels. I actually hope it continues this way. The pods are delicious. Pretty much all the others have either been on point or hot for the variety. My MWCH MOA reds seem to be hotter than any bonnet ive tried yet. Might just be his seed stock but they are really damn hot for a bonnet.
 
Currently we are back to more normal temps in the mid 80s and slightly lower humidity. Plants are really digging it too.
 
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