Chile breeding

Plant breeding involves a great deal of luck and you can have some really good success with that. Luther Burbank produced numerous amazing plant varieties, but at the same time, he never believed in genetics. The key aspects of his method were to just try things, to grow large numbers at every stage, and to pay close attention to every plant (to find the differences). He tried crossing a strawberry and a raspberry... and actually got something.

With some knowledge, you can make predictions about what is more likely to work. To that end, plant breeders have researched what techniques are needed to hybridize different species. Usually there is limited success with hybridizing species in different genera, where the plants are less closely related, but there are exceptions. In the end, species labels are things we make for our convenience. Nature is under no obligation to follow what we think a species is or should be.

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In peppers there are several domesticated or partially domesticated species:

• Capsicum annum : common sweet & hot peppers in North America.
• C. baccatum : more common in South America.
• C. chinense : habanero type peppers.
• C. frutescens : generally smaller, less common peppers. 
• C. pubescens : rocoto, manzano, locoto; tropical peppers with black seeds.

There are many more wild species that are only occasionally or rarely grown by gardeners. Those species contain a wealth of potentially useful genes though. Disease resistances, agronomic traits, and novel flavors can all potentially be moved from the crop wild-relatives into domesticated peppers. Towards that end, researchers have tried crossing almost any pair of species related to domesticated peppers. The following figure shows a crossability polygon, summarizing the results from attempts to hybridize between eleven species in the pepper genus.

I found the figure several years ago at: www.plantsciences.ucdavis.edu/vc221/pepper/PEPPERrd.htm. I have not yet been able to find the paper in which this figure was first published.

There are other wild pepper species, which could maybe be included in a more recent version of the figure.

• C. lanceolatum: a cloud-forest species sharing the trait of black seeds with C. pubescens.
  C. rhomboideum: a species barely considered to belong to the genus Capsicum, with yellow flowers, sweet berries, and brown seeds.
• C. annum var glabriusculum : tiny, very hot, wild pepper of the desert southwest US.
• And many others...

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What this diagram suggests is that you could transfer an interesting trait from any one of these species into any other species you're interested in working with, either directly or through intermediaries. It would just take motivation, time, and money to do so. More generally, hybrids between the species would let one introduce much more genetic diversity into their pepper breeding projects, even if there wasn't a specific trait of interest.

I'm working with lines that include C. annum var glabriusculum in their recent ancestry. This was the wild pepper which grew in San Antonio and Austin Texas where I grew up. I started by growing seeds for the species which I (or friends and family) had collected from the wild. At one point, a few seeds collected from a large, seemingly wild plant grew up showing the parent plant had been a hybrid with some unknown domesticated type. I've been growing the descendants of those plants since.

At left is an side view of a patch of miniature pepper plants grown in 2022. Here they're about 4.5 inches tall and the tallest matured to about 8 inches in height. The smallest stayed under an inch (and didn't mature any pods). This line has the small leaves and pods of its wild ancestor, but has a far more dense branching structure and short stems. They produced more and more dark purple/black pigment in the leaves as the season went on. The pods matured from black to bright red at final maturity. The pods range from very hot to volcanic. The plants were covered in black and red pods at the end of the season.

Other plants derived from that initial wild hybrid had larger, more typical forms, though they were still small in size compared to many garden types. Among those, one plant (at right) stood out as extra productive in 2021. I had been hoping to select up a productive hot pepper type since the more standard types have been not doing so well with my short growing season. I grew 25 plants in 2022 from seeds saved from this plant.

Those plants made it clear the productive parent plant had been a new hybrid, between the wild hybrid derived plants I was growing and the Pimenta da Neyde pepper I had been growing the year before. In addition to a wild range of leaf color and plant growth habit in these F2 plants, I also found several with decently large pods at various heat levels.

The split pod at left came from a single plant which seemed to mimic a habanero. The pods had very thin walls and had a heat comparable or higher than habaneros. The internal membranes look so enriched in capsaicin oils that I was hesitant to try tasting them. Other plants seemed to mimic jalapenos, with their thick flesh and corked skin. These peppers are smaller than real jalapenos with a moderate heat level. The plants with both types of pods were far more productive than any habanero or jalapeno I had grown in my gardens, so I took this as a win.

Though I can't be sure, I have a pretty good feeling that all of these peppers are able to grow as well as they do for me in part because of some genes inherited from their recent wild ancestor. They handle the poor soil and limited water in my garden far better than usual garden types. The miniature peppers absolutely have their size and growth habit in part due to their wild ancestry.

In the next several years I hope to stabilize several new varieties from this project. Even if I don't, I'll be getting plenty of hot peppers along the way.

References:

• Burbank's strawberry/raspberry hybrid: https://the-biologist-is-in.blogspot.com/2015/01/hybrid-sterility-and-speciation.html
• Intergeneric hybrid orchids: https://www.aos.org/orchids/additional-resources/intergeneric-hybrids.aspx