Plant stress and pepper heat -- recent research

[TheTRPV1Agonist]

It's well known that stressing pepper plants by reducing watering can result in hotter peppers, and that this comes at the cost of decreased yields. But what level of stress is optimal? And which varieties respond best?   
 
A fairly recent article in Food Science, looked into the influence of water stress in four varieties of C. chinense, by comparing the differences in yields and capascinoid concentrations in peppers watered daily or every 2, 3, or 4 days, to determine how to get the most capscacinoids out of a pepper plant. 
 
The varieties included Bhut Jolokia, Orange Habanero, BGH1719 (a smallish plant, with many small pods), and Akanee Pirote (the largest plant, with large pods around 350k)
 

 

 
It was concluded that varieties that are hotter and have larger fruit are more sensitive to drought stresses and that mild stresses may have the potential to significantly increase capscacin in some varieties, but not others. The Akanee produced significantly more capascin in the milder 2-day stress group (from around 350k to 450k), whereas the Bhut Jolokia and Orange Habanero produced significantly more only in the 3-day stress group. Moreover, it appeared there were diminishing returns, with the 4-day group, capsacin levels were no higher (or even lower) than in the 3-day group, and plant yields continued to decline.
 
Looking at the specific capsacinoids, it appears that dihydrocapsacin (which is typically found in larger proportion in C. pubescens) might increase to a greater extent than capascin. So your stressed peppers might not only have a hotter burn, but a different burn.
 
So how might we use this information to inform our own growing practices?
 
Perhaps by aiming to achieve the same reduction in plant height and pod numbers, you can determine how much water stress is optimal for your climate. The data is there for Bhut Jolokias and Orange Habs, but it could potentially be generalised to other varieties. For example, the unstressed Bhut was around 1m (3ft) and yielded 32 pods, where the hotter one was ~65cm/2ft tall, with 20 pods (that's about a 1/3 reduction). A potential experiment to determine the water stress you need to apply might be to have two plants (at least), and apply stress to one, aiming for a 1/3 reduction in growth compared to the other. Then adjust in future seasons depending on how far off you were from that goal.
 
TL;DR: Stress your larger superhots for hotter peppers, but maybe don't bother with your small milder peppers, it might only just decrease your yields. Also, drought stress has diminishing returns, so don't torture your peppers too much!
 
References: Jeeatid N, Techawongstien S, Suriharn B, Chanthai. S, Bosland P. Influence of water stresses on capsaicinoid production in hot pepper (Capsicum chinense Jacq.) cultivars with different pungency levels. Food Chemistry [serial online]. April 1, 2018;245:792-797. Available from: FSTA - Food Science and Technology Abstracts, Ipswich, MA. Accessed July 18, 2018.
 
 
 



 

 

[karoo]

Thank you ,
good science , always welcome!

 

[ShowMeDaSauce]

I got my first freak jalapeno yesterday. Its was a total scorcher for a jala!! Ive got a chichimeca jalapeno in a very fast draining mix. In the heat it will droop a little almost everyday if im not careful about watering. Oddly it cranks out the pods too.

 

[solid7]

This has been discussed alot - and even hotly debated on this forum.  I tend to disregard this study for a few reasons. First and foremost, how many plants were utilized in each sample?  It appears to be one per variety.  If that's true, it wouldn't even get us out of the territory of statistical error.  There needs to be a much wider sampling, for this to be taken seriously.  Or, if it is a larger sampling, that should be quantified.
.
Second point...  and of the most importance - there are OTHER studies which suggest that the greatest deviation in capsaicin levels, occurs in those varieties with a much lower capsaicin content. (or lower Scoville rating, to keep it simple)  A study at the University of New Mexico found that drought stress was most effective in lower heat level varieties - like any NuMex anuum, jalapeno, serrano, etc.  That contradicts this study.  And I know that the NM study was quite a bit more comprehensive, because it involved money being invested for the direct benefit of commercial growers. (who wouldn't want to make a hotter pepper, and use less water - reduce costs, maintain desirability of product, right?)
 

 

[Ghaleon]

Seems unnecessary for superhots anyway. Did any of you eat the chocolate bhutlah and think it wasn't hot enough?

It would be interesting to bring up the heat of peppers that are under 700k SHU, though.

 

[TheTRPV1Agonist]

I don't have time just yet to write a full reply. But obviously this is a complex area, and I've simplified the presentation for a general audience, so perhaps omitted some of the more nuanced results/discussion from the paper. 
 

This has been discussed alot - and even hotly debated on this forum.  I tend to disregard this study for a few reasons. 
 
Read it before you dismiss it?
 
 
First and foremost, how many plants were utilized in each sample?  It appears to be one per variety.
 
Three replicates per plant per treatment. So 42 plants total. 
 
If that's true, it wouldn't even get us out of the territory of statistical error.  There needs to be a much wider sampling, for this to be taken seriously.  Or, if it is a larger sampling, that should be quantified.
 
Yes, larger sample sizes are ideal as they allow for small effect sizes to be detected. But small samples can still detect statistically significant effects that are large. 
 
The argument can be made that the study might have been underpowered to detect smaller increases in capsaciacin at the 2-day mark, but with an alpha set to 0.05, the type 1 error rate is controlled. (i.e. false positives)  
 
Not only that, there is a clear dose-dependent effect here. 
 
.
Second point...  and of the most importance - there are OTHER studies which suggest that the greatest deviation in capsaicin levels, occurs in those varieties with a much lower capsaicin content. (or lower Scoville rating, to keep it simple)  A study at the University of New Mexico found that drought stress was most effective in lower heat level varieties - like any NuMex anuum, jalapeno, serrano, etc.  That contradicts this study.  
 
From the discussion section
 
The previous studies that worked with various types in fruit size and pungency of hot pepper revealed that the small-fruited cultivars are less affected by environment compared with the medium and large-fruited cultivars (Gurung et al., 2012, Gurung et al., 2011, Phimchan et al., 2012, Phimchan et al., 2014).
 
 
And from Primchan et al., 2012 
 
However, in our study, the significant increases in capsaicinoids were observed only for the low and medium pungent cultivars but not for the high pungent cultivars. These results might be explained by the fact that a genotype and genotype–environment interaction affected capsaicinoid content (Zewdie and Bosland, 2000), in which the genotype effect was larger than the environmental effect (Gurung et al., 2011b; Zewdie and Bosland, 2000). In addition, Gurung et al. (2012) found high stability of cultivars with high pungency, whereas the lower pungent cultivars were very sensitive to environment. From our results, it is notable that the fruits of the high pungent cultivars are smaller than the other cultivars used, and this might indicate that the capsaicinoids in the small fruit of the high pungent cultivars are less affected by drought stress than those of the big fruit with low and medium pungency.
 
 
I might also add the Bosland, head honcho at UNM, is a co-author on these papers. 
 
 
And I know that the NM study was quite a bit more comprehensive, because it involved money being invested for the direct benefit of commercial growers. (who wouldn't want to make a hotter pepper, and use less water - reduce costs, maintain desirability of product, right?)
 
This reasoning appeals to common sense but is a bit wishy washy. 
 
You could make a similar argument here, this study is for the benefit of the pharmaceutical industry, who want to extract the optimal amount of capscaicinoids out of their harvests are possible. 
 

 

 

[solid7]

I don't have time just yet to write a full reply. But obviously this is a complex area, and I've simplified the presentation for a general audience, so perhaps omitted some of the more nuanced results/discussion from the paper. 
 
 

 
 
Thanks for your replies.  Small sample sizes, but still better than what I thought was just one.  Good to know. 
 
As for the NM study - not wishy washy thinking.  My point was, they had no benefit in influencing the results, because it was strictly informational.  It was research used to better their own methods and processes.  We can argue all day long about how people use data to meet their ends, but sometimes a bias isn't advantageous.  If you just wanted to know how hot grow the best, hottest, and tastiest peppers, would you REALLY want to falsify info, to that end?  Methinks not...  
 
Unless we could prove that their was a financial benefit from some corporation producing fertilizer, for example, there is no reason to believe that the NM study was skewed.  There is literally NO reason why heat and drought disproportionately affecting pepper growth, would give anyone a competitive advantage.  In fact, it's just ag science, and since it's a local crop, it's utilized by all the local growers who bring that particular produce to market.

 

[Hafners]

I have noticed that my indoor peppers produce better, and are hotter than the ones in the garden. With my indoor plants i do occasionally drop the temp to stress them into ripening faster, but haven't determined what factor increases the heat level besides better certification since they are fed hydro nutes.

 

[solid7]

Your indoor plants are grown in a stable environment.  That makes a lot of difference.  It's not the nutrients.