Tomatillos are a wonderful vegetable plant to grow. There are several distinct varieties available, but nowhere near the numbers we see for tomatoes, peppers, or other crops. What's the difference?
Tomatillos are almost exclusively out-breeders. You need two or more plants growing in an area to get good production of fruit. As a result, every plant is a new hybrid and a population will maintain a high degree of genetic diversity. This also makes it difficult for different varieties to be grown in the same area, as they will generally cross and meld into one diverse population.
A few years back I started an experiment with breeding tomatillos. I grew one plant of a variety with small purple fruit next to one plant of a variety with large green fruit. I had saved seeds from a CSA and the local grocer, so I don't have any specific variety names to give you. (If you want to replicate the experiment, the purple variety was similar to: https://www.edenbrothers.com/store/purple-tomatillo-seeds.html; the green to: https://www.edenbrothers.com/store/rio-grande-verde-tomatillo-seeds.html.)
Because the plants are such extreme out-crossers, every seed that year was expected to be a hybrid between the two different varieties. The next year I grew four plants, from seeds I saved from the purple plant. Each plant grew distinct fruit. (1-4, left to right in photo at right.) This diversity tells us that both parental varieties were highly heterogeneous, so the specifics of each hybrid plant depended on exactly which allele they inherited from each parent. As none of my neighbors were growing tomatillos, we can be pretty sure each one was pollinated by the other three.
The next year I planted seeds I had saved from plant #3. I grew 11 plants, but only 5 produced any fruit. The plants looked like they'd been exposed to an herbicide from the commercial garden soil I had added to the garden at the start of the season (Herbicide carryover). All the fruit were green, with some later developing some purple pigment as they ripened off the plant.
This year I planted seeds I had saved from plant #4. I grew 12 plants and all produced fruit. These showed a much wider range of pigment levels, including a pair of plants with visible purple pigment and large fruit.
One plant had a trait I didn't like at all. The fruit from spoiled very rapidly after picking. (Previous year's fruit stored for months.) That plant was one of two in an isolated garden, so I immediately culled all of the fruit from both plants. I didn't want to risk the genetics associated with spoilage turning up in the garden again next year.
One plant had fruit I really liked. The fruit were large and developed purple pigment, the traits I have been trying to combine in one plant. I wasn't expecting the fruit to develop stripes as they were maturing, however. These fruit are not lasting as long as I'd like, but the other good traits means I'll be saving seeds from them anyhow.
A couple other plants produced intensely dark purple fruit, appearing ink-black. This is the color I've been looking for, but the fruit aren't as large as I want. I'll save seeds from these as well.
Because the plants are out-crossers, I know they will have been pollinated by the others in the garden. Even though these two have trait combinations I really like, it will be unlikely to find offspring with the same traits because of all the other traits in the garden.
I've tried to diagram the overall history of the project so far. (I didn't have any photos of the original varieties, so they get cartoon representations.)
About this point I started thinking about how I might get around the issues caused by the potential for genes from every plant in a garden to turn up in the next generation. I don't want to have to cull everything from a garden when something strongly negative turns up in the population. Right now I only have two isolated garden spaces, so that strategy can only go so far.
References:
Tomatillos are almost exclusively out-breeders. You need two or more plants growing in an area to get good production of fruit. As a result, every plant is a new hybrid and a population will maintain a high degree of genetic diversity. This also makes it difficult for different varieties to be grown in the same area, as they will generally cross and meld into one diverse population.
A few years back I started an experiment with breeding tomatillos. I grew one plant of a variety with small purple fruit next to one plant of a variety with large green fruit. I had saved seeds from a CSA and the local grocer, so I don't have any specific variety names to give you. (If you want to replicate the experiment, the purple variety was similar to: https://www.edenbrothers.com/store/purple-tomatillo-seeds.html; the green to: https://www.edenbrothers.com/store/rio-grande-verde-tomatillo-seeds.html.)
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| #1. Medium purple fruit. #2. Small purple fruit. #3. Large green fruit, with purple dots. #4. Medium purple fruit. |
 |
| F2s from F1#3. |
The next year I planted seeds I had saved from plant #3. I grew 11 plants, but only 5 produced any fruit. The plants looked like they'd been exposed to an herbicide from the commercial garden soil I had added to the garden at the start of the season (Herbicide carryover). All the fruit were green, with some later developing some purple pigment as they ripened off the plant.
 |
| F2s from F1#4. |
One plant had a trait I didn't like at all. The fruit from spoiled very rapidly after picking. (Previous year's fruit stored for months.) That plant was one of two in an isolated garden, so I immediately culled all of the fruit from both plants. I didn't want to risk the genetics associated with spoilage turning up in the garden again next year.
A couple other plants produced intensely dark purple fruit, appearing ink-black. This is the color I've been looking for, but the fruit aren't as large as I want. I'll save seeds from these as well.
Because the plants are out-crossers, I know they will have been pollinated by the others in the garden. Even though these two have trait combinations I really like, it will be unlikely to find offspring with the same traits because of all the other traits in the garden.
I've tried to diagram the overall history of the project so far. (I didn't have any photos of the original varieties, so they get cartoon representations.)
 |
| Tomatillo project history so far. |
About this point I started thinking about how I might get around the issues caused by the potential for genes from every plant in a garden to turn up in the next generation. I don't want to have to cull everything from a garden when something strongly negative turns up in the population. Right now I only have two isolated garden spaces, so that strategy can only go so far.
For my solution, come back in a week for part 2!
References:
- Tomatillo varieties:
- Purple: https://www.edenbrothers.com/store/purple-tomatillo-seeds.html
- Rio Grande Verde: https://www.edenbrothers.com/store/rio-grande-verde-tomatillo-seeds.html
- Herbicide carryover: https://lee.ces.ncsu.edu/2016/03/herbicide-carryover-in-hay-manure-compost-and-grass-clippings/
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