Breeding low heat chili peppers

[Ole Fosshaug]

I do not like very strong chili peppers, I prefer aroma and a subtle heat instead.
Anaheim and Gorria(Piment d'Espelette)
So my question is, how much will the heat differ when we start to crossbreed chili peppers?

Am I running a risk of getting some very strong ones or will they likely stay in the lower end of the Scoville scale as long as I only breed with the mild ones?

[Justin Jardinier]

Interesting question, I would love to know too! I really like Sweet Moruga (very low heat chinese with amazing floral flavours), and would love to cross it with a no-heat annuum. But I have the same worry.

I just harvested the first fruit of Aji Delight, a no-heat baccatum, pollinated by Habanada, a no-heat chinense. However, this fruit was hot! I guess it is a xenia effect. It's worrying though, now I wonder if the resulting interspecial cross might be hot.

I read in The Genes of Capsicum - Deyuan Wang - 2006:

Pungency
Pungency, or the sensation of heat when eating pepper fruit, comes from the presence of the capsaicinoid alkaloids in the fruit. Early genetic studies reported that a single dominant gene C controlled the expression of heat (Deshpande 1935, Greenleaf, 1952), which can be modified by other genetic and environmental factors. This gene was later redesignated Pun (Daskalov and Poulos, 1994), and probably functions as an acyltransferase to complete the capsaicinoid synthesis (Stewart et al., 2005). Loaiza–Figueroa and Tanksley (1988) reported a second nonpungency locus, pun2, in a wild, nonpungent pepper accession BG 3547; however, further studies cannot support the existence of this locus—most likely the nonpungent accession was expressing the lov gene (Votava and Bosland, 2002). Votava and Bosland (2002) described two novel nonpungent C. chinense accessions ÔNMCA 30036Õ and ÔPI 543190Õ, in which loss of the vesicles (lov) on the placental walls is responsible for nonpungency. The lov gene is epistatic to pun1 and results in pungent progenies. Blum and associates (2002) mapped the Pun locus to chromosome 2 in a hybridization between a pungent C. frutescens accession and a noheat C. annuum bell pepper, and developed a polymerase chain reaction-based cleaved amplified polymorphic sequence (CAPS) marker linked to Pun using the sequence of the Capsicum fibrillin gene located 0.4 cM from Pun. Recently, the Pun-1 gene was cloned and characterized based on the candidate gene approach (Stewart et al., 2005). The full-length genomic sequence of Pun-1 is 1897 bp, containing two exons of 738 bp and 585 bp respectively, and one intron of 348 bp. The pun-1 allele results from a large deletion at this locus.

I haven't gone deep into this but basically I am wondering, if there are forms of no-heat trait that require it to be homozygous, and if 2 peppers have different genes responsible, then maybe in the F1 they will be hot, but segregate in the F2?

[Justin Jardinier]

I just harvested the first fruit of Aji Delight, a no-heat baccatum, pollinated by Habanada, a no-heat chinense. However, this fruit was hot! I guess it is a xenia effect. It's worrying though, now I wonder if the resulting interspecial cross might be hot.

Update on this - I harvested some more fruits the same as the above. Almost no heat, just a trace. So it might have been a xenia effect or it might just have been a coincidence. But the next point is more significant:

I haven't gone deep into this but basically I am wondering, if there are forms of no-heat trait that require it to be homozygous, and if 2 peppers have different genes responsible, then maybe in the F1 they will be hot, but segregate in the F2?

It seems I have now proven my hypothesis. I just harvested a sweet annuum x sweet chilense pollinated with sweet baccatum. The fruit had excellent texture, a lovely crunch to it. But it's really hot! I don't eat hot peppers so I can't give much info on how hot, but I took only one bite and will not be taking any more! So, I am guessing that whatever made the chilense non-spicy is now heterozygous and .... actually I don't know exactly what's going on but would guess that if this were selfed, maybe in the F2 non-heat could be found? However, there is almost no pollen whatsoever and I was unable to get any fruit from the ... maybe 3 or so attempts I made for manually selfing. Not much of an issue for me since I'm using the F1 as a bridge to baccatum, but, this implies heat issue may likely be arising in both versions of this 3 species cross, and quite possibly in baccatum x chilense also, unless the parents happen to share the same genetic reason for lacking heat.

.... I just dared to try a bit more of this fruit. I tried avoiding the dangerous-looking yellow oil. The flesh was tolerable but the heat did still kick in after some moments. But before that I could taste the nice floral flavours of chilense. If selfing worked, this might be an appealing pepper for some folk.

Back to the theory - if all 3 species have different genetic reasons for no heat, then if all that's needed is one of the 3 options to be homozygous, then it might actually be fairly simple? The F1 in 2 species cross should be heterozygous for both, then presumably 75% of the F2 should be no-heat. Or crossing the F1 directly to the 3rd species, 25% of the next generation should be heterozygous for all 3 genes, still hot but high chance of getting at least 1 homozygous one generation further; or 50% chance of getting 2 genes heterozygous, if my maths is correct, and if 2 are heterozygous, then ... 75% chance of having at least 1 homozygous one generation further.

I don't know how many genes are actually involved in full no-heat (evidently there's more than 1 option and at least 2 of them require genes to be homozygous), or if there are some other complexities involved. But that's what I have to report so far. I'd be interested if anyone has more to say on this.

[Justin Jardinier]

New update - I have 2 no-heat chinese, Habanada, and Venezuelan Tiger. I just harvested the first F1 fruit of a cross I made of these 2 varieties. It is very hot! So, clearly, they have different genes responsible for their non-heat.

[AndrewB]

Hmm. This report is slightly worrying. I was thinking about trying my hand over winter at a poblano x scotch bonnet cross,  but I would only want intermediate heat. I will probably still try it, but interspecific crosses affecting heat in unexpected ways is interesting.