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Help! to ID symptom: grainy bumps only on undersides of leaves

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plaisir8

Hey guys, I'm new to indoor growing since last fall when I brought my plants in from the balcony of my old apt to my new place--managed to deal with multiple mite outbreaks, exterminate a fungus gnat infestation, but I'm stumped with this one. Hope someone can help me identify and if necessary, fix this problem.
 
Symptom: Miniscule granular bumps forming on the underside of leaves. Larger and more numerous than the normal patterns or anomalies seen on leaves (see exhibition a)
 
Progression: Starting with my 3-4 week old Thai minis in Feb. Spreads to nearby foliage, starting with young leaves progressing to mature leaves. Also jumped first to adjacent plants that had leaves brushing. However, limited only to Thai minis for 3 months. Had isolated 5 plants on balcony during April, left 1 untouched plant (A), 1 other that had grown big but had to shaved down to the stem (B) and 3 that had shown only minor damage after some pruning and showering. (A) and (B) are totally fine, 2 of the other 3 have had a few leaves with the bumps but are fine after removing/showering. On the other hand symptom has appeared for first time on Korean chili plant last weak, but diffusion to other leaves is much slower. Chopped off the end of the branch but symptoms are beginning to appear on the next node after about a week (exhibition b).
 
Environment: Indoor growing, however I open the windows often to aerate the apt after I cook in the evenings. Was ultry dry and warm during Nov-Mar (under 20% humidity and temps 25-30C/hi 70s to hi 80s). Started managing humidity levels in April (50-60% day and evening, dropped during night to 20-30% by morning). Heating is off now, so constant 22-24C/mid to low 70s F, and 40% humidity).
 
Not oedema, no sugary formations. Doesn't make sense with ultra arid environment Feb-Mar. Also induced oedema in one Thai mini to compare. Is different (exhibition c)
Not mites, no chlorosis, no webs, no curling.
Not thrips, no chlorosis, no damage to buds, no deformation of leaves.
Not pysiological trait of thai minis, as symptom has spread to the other c. annuum.
Haven't heard of any symptoms like this of viral or fungal diseases that afflict peppers or other nightshades.
 
On the other hand, I have discovered two specimens that look like thrips larvae today in the grow room, but I would have expected to have a swarm of thrips by now if they were the cause. I believe they most prob. came in through the window yesterday.
Interesting thing is, there has been absolutely no damage on the sweet potatos, alpine strawberry, mini rose that grow together with the peppers in a crowded space. New plants germinated early May (basil, florence fennel, anise, soybean, tomato) have not been scathed either.
 
exhibiton a) damage on Thai mini https://files.ucloud.com/pf/D630936_6305288_170536
exhibition b) damage on Korean chili (new damage developing) https://files.ucloud.com/pf/D630936_6305288_170534
exhibition c) oedema on Thai mini https://files.ucloud.com/pf/D630936_6305288_170538
exhibition d) looks like thrips (1mm=1/25th" long, white, crawl around then rest a bit * repeat) https://files.ucloud.com/pf/D630936_6305288_170530
exhibition e) different bumps from leaf with thrips https://files.ucloud.com/pf/D630936_6305288_170532
 
Can't say if the damage has stunted growth or not, my freaking out and stripping the leaves multiple times set back the plants too much. However, despite the "damage" the plants seem to be developing relatively normally. They're also putting out flowers (root bound, didn't pot up).
 
Thanks for going through the long read, trying to provide as much relevant info as possible. Please shed some light on this! Without resolution of this issue, to be on the safe side, I'm considering burning all of the peppers, the healthy ones too.
 
Thank you Nightshade! That's a big relief.
 
Just one question: how come it looks different from the oedema I induced by intentionally over watering, pics on the net, or oedema that I've seen on other plants?
I had ruled out oedema because the bumps were distributed evenly all over the leaf instead of being concentrated near the veins, while the symptoms first occured and had been the most rampant when the env was hot and dry.
 
Just an update, I've continued my observation of the two plants that were hit the hardest.
I have doubts as to the condition being oedema caused by overwatering persay.
 
At the point of my last post, they hadn't been watered for 5 days. They're in small see through pots, so I could tell the soil was dry by then. And they've gone without a drop of water for 6 more days now. I marked the leaves that were affected with red dots, left one alone by the window with the 3 thrips larva I found on it, sprayed the other with pyrethrin and left it at another window.
 
The results: There are still a few new leaves that are developing bumpiness (not much primarily because they're drying up and haven't put up much new growth/only a few of the existing leaves are clean). But exactly the same on both plants.
 
Conclusion: Based on the lack of a differential between the two, I'm ruling out insects.
Based on the fact that there was no watering, I'm also ruling out overwatering.
As of now the plants aren't dying, so I'm content to believe that the Thai mini seeds I got are either a) naturally susceptible to oedema (even in relatively dry conditions) or b) just have a genetic tendency to develop bumpy leaves. As for the Korean chili, no more trouble found, now that must have been my overwatering--chance coincidence that caught my attention. Case closed!
 
Plaisir did you end up figuring out what it was? My Thai Dragon is doing the same. Curious as to what you came out with.
 
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