Hi! I want to start landracing with spaghetti squash, but there are only one or two varieties available where I live. I’m wondering if selecting for the spaghetti texture is too narrow a criteria for landracing, even if there are other traits that can vary (color, shape, etc.).
There’s a lot of talk about not introducing unwanted traits, but do you think I should still introduce other (non-spaghetti) squashes to add genome variety and just start to deselect the non-spaghetti texture away in the later years, in favor of just trying to work with the two spaghetti varieties available here?
I originally posted this question in the course’s discussion panel and was asked to repost here. I saw a good post here about spaghetti squash, but I’m also interested in trait criteria as a more general concept. Sure, the texture is only one variable, but unavoidably there will be other criteria as well (disease resistance, growth speed, taste, etc). What I’m worried about is if the spaghetti trait will narrow down the selection too much in the long run, ‘forcing’ me to keep adding variety and continuously struggle with the texture.
The spaghetti trait is a recessive. However, when I did my initial spag x pump x zuc cross, I got the spaghetti trait in both the surviving f1 (pumpetti and zucchetti) fruits. So either the trait is genetically more complex than the experts know, or it’s in many pepos.
I would suggest a trial. Do one population with your two varieties, and another with spaghetti squash mixed with other pepos with traits you like.
When both are stable, selectively breed the other pepo mix into your original population.
Several of us are working on spaghetti squash crosses. My own inclination is toward as much mixing as possible, as long as your goals are met.
I like that idea. I seem to recall Joseph Lofthouse said that if he could do it all over again, he would have grown Solanum habrochaites as a separate population, and selected it for the best, before mixing it with his domesticated tomato population. Then he wouldn’t have needed to select out some of the traits he disliked.
That seems like a good principle for other landraces, too.
Landrace Gardening works wonderfully if a few traits get favored while other traits float freely.
For example, selecting for productivity, stringiness, and flavor works well.
We could allow leaf-shape, to float freely without affecting stringiness. We could allow variation in skin color, rind texture, and (perhaps) shape without affecting stringiness. A zucchini/marrow/spaghetti could be really clever, especially if someone managed to get high levels of yellow/orange pigments into the flesh.
A huge infusion of genetic diversity would occur even if we crossed spaghetti with other varieties, and then re-selected for the classic spaghetti fruit phenotype.
Good point! Maybe you could choose some varieties of pepo that you really like for other reasons and cross them with spaghetti squashes, then do recurrent backcrossing and mass selection to try to create a population of all spaghetti squashes that also has traits you love that are unusual for the variety.
It’s really easy to select for recessive traits, even multiple recessive traits at the same time.
For example: With tomato the difference between red or yellow fruits depends on one gene. Therefore 1 in 4 plants of the F2 will be that phenotype. And with recessive genes, the trait becomes fixed when you find it (as long as no further crossing occurs to plants with dominant genes).
With two recessive traits, 1 plant in 16 will show the desired phenotype. In sweet corn crossed to flour corn, that would be equivalent to selecting for the su sweet gene and the se sugary enhanced gene. That works out to about 18 kernels per cob. Very doable.
With three recessive traits, 1 plant in 64 will show the desired phenotype. Say we double that to 128, just to make sure the math works out in our favor. Say I plant squash seeds in a row spaced at 6". I’d only have to grow a row 64 feet long to have a really good chance of finding the desired phenotype.
If there is one gene for stringiness, and one gene for oblong shape, and one gene for hard shell, and they are all recessive, then the desired outcome could be selected in the F2 generation.
The main challenge is that, if you have space for only 10 plants, growing 128 in one year to find the right phenotype can be challenging. It’s an even bigger deal if you’re trying to select for four or more recessive traits – then you’d need to grow about 256 plants (512 for safety) to recover one plant with the desired genotype in the F2 generation.
Happily, if you need to work with a smaller population, you can choose to select for only one or two traits per year. The nice thing about recessive traits is that, once you’ve got them fixed in a population, you know they’ll stay stable (barring accidental crosses or random mutations). So you could do them two per year, and you’d only need to grow 16 plants (32 for safety) to find what you’re looking for that year.
Backcrossing can be a valuable tool, too. If there are ten recessive traits you want, and one of the varieties contains eight of them, the best way to get what you want would be to select your F2 generation for the two recessive traits that aren’t in that variety, and then backcross the F3 generation to that variety. You could select two or three of the traits you’re looking from that backcross, backcross again, select again for a few more, etc.
This is something I’ve done a fair amount of thinking about because quite a few of the traits I value in pepos are recessives, but I only want to grow about 8-10 plants per year. Happily, Carol Deppe gave me lots of great ideas to breed what I want within a reasonable number of years in her books.
There’s also incomplete dominance, which can be super helpful. When there’s incomplete dominance, you may not be able to get what you want in one year, but if you get partway there, you can tell the difference.
I want to breed my pepos to be completely thornless, which seems to be a recessive trait controlled by two genes. In theory, that means I’d have to grow sixteen plants (thirty-two for safety) to get what I want.
Happily, however, it seems to exhibits incomplete dominance, so I can guess pretty easily which plants have the alleles I want. It seems to be:
Four dominant alleles: Huge, hard, sharp, nasty thorns.
Three dominant alleles: Pretty big thorns.
Two dominant alleles: The typical thorns most pepos have.
One dominant allele: Very small and soft thorns.
Zero dominant alleles: No thorns whatsoever.
I want zero, but if the best I can get is one or two, I can identify those easily because they seem to be incompletely dominant and cumulative. So helpful!
From what I’ve read, disease resistance and flavor often work similarly, which is great because they tend to have way more recessive genes you’re selecting for.