Squash breeding project

[jmsieglaff]

I posted this on another site a couple months back but have yet to get a reply. I'm guessing I'll get some thoughts here and very valuable thoughts--quite the group of knowledgeable and involved people here!


I'm starting a vining summer squash breeding project this summer and I'm looking for opinions regarding what to do with my F1 after this summer. Details about the project are below--but the long and short of it are do I backcross the F1 to one of the parents or self the F1 and grow out the F2?



The point of this project is to obtain the vining habit, vigor, and insect resistance of Tatume and the color, flavor, and production from the lemon squash (the flavor and production of Tatume wasn't bad--the lemon just a bit better). The other reason for this project is just for fun.
So my plan this year (2014) is to cross lemon squash with tatume squash (female) and save those seeds. As of now I'm planning on in 2015 planting the F1 seeds and backcrossing to Tatume (again female). I'll plant out the F1 x Tatume cross in 2016 and begin selecting for vining habit and yellow squash color (which should be 1/4 of the plants in 2016). Things probably won't be terribly exciting at least until 2016 because the F1 that I will grow out in 2015 I suspect will all have Lemon squash habit (semi-bush) and yellow fruit (at least if my assumption of simple dominance is right and that bush is dominate to vine habit and yellow fruit dominate to green). Over the years I hope to get a stable OP variety.



The other option is to self the F1 in 2015 and grow out the F2 in 2016 and select for vining yellow squash (3/16 of the plants).



The reason I'm not completely sold on the backcrossing to Tatume and thinking about the other method is 1) both varieties are already good squash, so it's not like I need to avoid the Lemon squash genetics, 2) vining yellow is 3/16 or 1/4 depending on the approach so no gain for all practical purposes, and 3) if nothing else the variety of growing out selfed F1s might be interesting.


I'm sure I'll learn a lot along the way and probably need to shift gears as I go, but in the end I'm hoping to having a vigorous vining summer squash that produces good amounts of yellow squash with good flavor-closer to the Lemon squash.


Any thoughts?

[peppero]

I have not done any of this sort of things but I want to wish you all of the success in the world. I am sure there are many ere who can offer suggestions based on experience.

jon

[Darren Abbey]

Backcrossing works when you're trying to transfer a single or few dominant traits from one line into another, with relatively few other impacts. This works for dominant traits because you can see them in the progeny at every stage. Recessive traits from the donor line will be hidden in the F1s and will remain hidden in the progeny of any backcrosses to the recipient line.

If you don't know the genetics of the traits you're interested in, you will have to grow out a reasonable number of progeny from the selfed F1s in order to characterize the genetics in the F2s. Growing 20 or so F2s from a selfed-F1 might not give you every combination you might expect, but it will allow you to examine the ratios of each of the traits you're interested in.
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The color genetics are relatively known, so we can examine them in detail:

Color genetics involved in your cross:
P : (wwgg) green "Tatume" x (wwGG) yellow "Lemon"
F1 : (wwGg) yellow
F2 : 3 (1 wwGG; 2 wwGg) yellow; 1 (wwgg) green

F1 x "Tatume" backcross:
P : (wwGg) yellow x (wwgg) green "Tatume"
F1 : (wwGg) yellow + (wwgg) green

Recurrent backcrosses of yellow progeny to "Tatume" will never clear out the recessive allele for green, but will convert more and more of other loci in the crossed line to the versions found in Tatume. After several generations (maybe 8? the more the better.) you will have produced a squash very much like "Tatume", except if will have the single selected dominant allele. At this time, selfing the line can then be used to produce a double-Dominant version.

"Tatume2" x "Tatume2":
P : (wwGg) yellow "Tatume2" x (wwGg) yellow "Tatume2"
F1 : 3 (1 wwGG; 2 wwGg) yellow; 1 (wwgg) green

At this stage, you will have to self each of the F1s and screen each set of F2s separately. 2:3 of the yellow F1s will produce green F2s… but that 1:3 won't. That 1:3 represents your final strain, "Yellow Tatume".

If you select for multiple traits at each step, you will generate a version of "Tatume" differing from the original only in those traits. Recessive traits in your final strain will match the version in "Tatume". The genetics of flavor and production are likely complicated and may involve recessive alleles. You will have to examine a batch of those first selfed-F1 F2s to determine this.
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If you're trying to carry over recessive traits using backcrossing, you will have to examine F2s at every step to ensure the backcrossed progeny you're working with still carry the recessive versions of the genes.

Hypothetical recessive flavor genetics:
P : (AA) bitter "Tatume" x (aa) sweet "Lemon"
F1 : (Aa) bitter
F2 : 3 (1 AA; 2 Aa) bitter; 1 (aa) sweet

F1 x "Tatume" backcross:
P : (Aa) bitter x (AA) bitter "Tatume"
F1 : (AA) bitter + (Aa) bitter

At this stage, you won't know which to use. You will have to grow out F2s from each to identify which line still has the 'sweet' allele. The more cycles of this, the more the resulting progeny will be like the original "Tatume", with the exception of the one recessive trait that you kept screening for.

"Tatume3" x "Tatume3":
P : (Aa) bitter "Tatume3" x(Aa) bitter "Tatume3"
F1 : 3 (1 AA; 2 Aa) bitter; 1 (aa) sweet

The final step of getting rid of that bitter allele from the original "Tatume" can then be done in one generation, giving you "Sweet Tatume".
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Backcrossing to carry over a single recessive trait will take roughly twice as many years as for a dominant trait.

If you screen large numbers of F2s from the original "Tatume" x "Lemon" cross, you might find what you're looking for in the second year after starting. If you don't find it that second year, you will have a much better idea about the genetics of the traits you're interested in and can then plan how many more F2s you will need to grow to have good odds of finding it.

I prefer the idea of screening lots of F2s because you can find combinations of traits that were not obvious in the parents that result in a progeny plant which you like even better than either original plant.

[joseph]

I'd guess that bush habit is a recessive trait, because wild squash are vining. (It's harder to stabilize a dominant trait than a recessive.) I haven't paid close enough attention to estimate whether yellow skin is dominant or recessive.

There have been something like 8 genes identified that are directly involved in fruit color in pepo squash. So in the worst case scenario where they are all recessive and there are no common genes shared between the two parents the odds are 15 in a million of finding the right combination to get the same colors. Could be worse than that considering that we don't yet know all the genes that affect fruit color in squash. Could be much better if the two varieties share many of the same genes. Then there are the genes for productivity and vining habit and flavor to toss into the lottery.

I prefer selfing to back-crossing because I can let nature do the crossing and there is no work involved for me.

Also, with selfing I might find something close to the combination I'm looking for among the F2. If I do back-crossing then it takes a year longer.

It'd also be possible to do a back-cross in the F2 generation if the traits I'm looking for don't show up. Or to manually cross a few plants that have the traits that most resemble the end goal.

[jmsieglaff]

I really appreciate the feedback......I've read through it and will chew on it some more this weekend. It seems like there are some good reasons pointing me toward selfing the F1 and growing out the F2. Probably most important getting to a stable yellow color faster.

From the information I've found, and it sounds like there are some unknowns that remain, but generally bush habit tends to be dominate over vining and yellow fruit dominate to green (http://cuke.hort.ncsu.edu/cgc/cgcgenes/gene09squash.pdf)

When planting out the F2 seeds, I'm going to try a tip from Carol Deppe's Breeding Your Own Vegetable Varieties and plant out about 5 seeds in each spot and when ~4" tall select to the tallest plant--she found this is a good, not perfect, short cut to getting the vining habit without having more mature plants. Then later in the year I can select seed to save from yellow fruited plants (manually pollinating those of course).

I like the idea of growing out the F2 just to see what I end up with and the bonus of finding something that maybe I didn't exactly expect, but turns out to be something really good.

I'm starting with two varieties I like and do want certain genetics from both--not just one from one of the varieties--so again I think I've been convinced to not backcross. And I'll always want to strive for my end goal--but who knows maybe the F1 will be great!

[Darren Abbey]

I've got hundreds of seeds from one cross… so you really would only need to generate the F1s once in large numbers if you decide you really like it.

[jmsieglaff]

The Tatume are flowering and Lemon should do so on the next week or two. I am going to go with the growing F2 out and see what I get after selfing the f1 next year

[Darren Abbey]

My squash projects have been delayed due to my moving to a new location in midsummer. I look forward to hearing about the F1 next year.

[jmsieglaff]

Below are pictures of the parent plants, I'll post some pictures of the fruits as both varieties get more. These are both used as summer squash. The Tatume are more vining habit with oblong light green striped fruits, we pick them young for eating. The Lemon squash grow more of a single tall vine that needs tying up, but still has tendrils, I'd all it semi-bush or semi-vining. You can see the flowers taped up on both plants and I'll do my first attempt at the cross tomorrow. I often manually pollinate my squash to increase yields.

[jmsieglaff]

So I've got one cross done yesterday and one today. Below are pictures of the (hopefully) pollinated females all taped up with some shiny ribbon to mark the crossed squash.

[jmsieglaff]

The Tatume squash that will bear the F1 seeds is quite large and perhaps just starting to get some very small touches of yellow around the top (not necessarily obvious in this picture). The powdery mildew is coming on strong, but the vines are out growing it and still producing usable summer squash. Will be interesting to see how the LemonxTatume F1 does in 2015.

[Tracydr]

You may want to consider crossing zuchinni trombocino to lemon squash. Huge vines, resistant to borers and a dense meat, more similar to the lemon squash than tatume is.

[jmsieglaff]

I've grown Tromboncino and used them as a summer squash, but the production just wasn't adequate and we prefer the flavor Tatume and Lemon squashes. I thought the same thing you suggest about crossing Tromboncino with another variety, but from what I've read the cross species cross of C. Pepo with C. Moschata (Tromboncino) is not possible for a home gardener. Something about embryo transplanting or culturing or something to that effect was necessary.

[luigiwu]

I have nothing to offer except encouragement - go, go, GO!! I'm super interested in a vining squash (due to the small footprint of my garden, everything has to be trained upwards. While the tatume plant I'm growing this year is very nice, I do wish the flavor was more like traditional squashes. So I hope you are successful!

[jmsieglaff]

So here is the cross squash. I had to take the vines out as they were dead from powdery mildew. My plan is to ripen this on the table on our deck where the squash will receive a lot of sun (we've had very favorable powdery mildew weather lately, warm sunny days and rather cool moist nights). From what I've read I think this will let the squash mature and have viable seeds. Does/has anyone done this with squash/pumpkins?