Squash backcross to a parent or self F1s?

jmsieglaffDecember 27, 2013


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.

Any thoughts?

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Hi jmsieglaff,

Based on my last several years of breeding zinnias, I do have some thoughts. The power of F2 recombination is impressive, but the more plants you can grow, the greater is that power. It is a little bit like playing a slot machine, the more tries, the better your chance of a jackpot.

I don't know your zone or growing season, so I don't know whether you have your Tatumes and Lemons growing yet. I would try to accelerate things by trying to get more than one generation in a year. One technique that has helped immensely with my zinnia growing is planting green seeds or even naked embryos. I can pluck green seeds from a still blooming zinnia flower, and breach the living seed coat so the embryo can absorb some water. A living seed coat is impermeable to water, so if you plant a green seed without breaching the coat the seed won't germinate until the seed coat dies and becomes water permeable. That can take weeks. The fastest way is to harvest some green seeds and use an X-Acto knife to remove the seed coat and just plant the embryos. That lets you get seedlings in a very few days. I got four generations of zinnias this last year by planting the green seed/embryos and growing two generations indoors under fluorescent lights.

I recommend that you try to get green seeds from your crosses, and grow your F1 hybrids this year and save F2 seeds from them this Fall. You can also save those F2 seeds as green seeds, only to store them you will need to spread them out on a newspaper and dry them for a couple of weeks. With my zinnias, dried green seeds work as well as waiting an extra month or two for the seed heads to turn brown and dry in the field.

I don't know how much ground you have available for your project. If you are area limited, you might try going vertical, and grow your squash rather like they grow grape vines. There are advantages to growing squash vertically, besides being able to grow more vines in a limited area. Weed control is easier, and access to the blooms and squashes is more convenient. And it's easier to watch for pests and control them.

I grew some Costata Romanesco squash in a tall wide tomato cage instead of on a fence and got three large plants in only a few square feet that way. It was easy to harvest the squash and the squash blossoms. Squash blossoms can be tasty battered and deep fat fried, and the Costata Romanesco produced a lot of big squash blossoms. If you are space limited, vertical growing could be a solution. The more F2 plants you can grow, the more recombinant variations you can get.

It would be an interesting challenge to try to grow a few squash indoors under fluorescent lights or HID lights. There are plant growth regulators that could keep the inter-nodal length of your vines under your control. And you might try vertical growth indoors as well. One indoor F1 squash vine could supply an abundance of F2 seeds for planting next Spring. Zinnia growing indoors has its problems, but I am a big fan of surmounting those problems for extra generations. Last Fall, rather than bringing in cuttings as I usually did, I brought in green seeds and planted them and/or embryos to have a new generation of zinnias blooming by Christmas, and green seeds from them produced a second generation whose seeds and seedlings are going in the garden now. This last year accomplished four years worth of breeding for me. Two generations outdoors and two generations indoors. I am not suggesting a factor of four for your squash, but a factor of two is probably feasible outdoors. And indoor or greenhouse culture could make a factor of three or four possible.


    Bookmark   May 14, 2014 at 3:18AM
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