Hulless seeded argyrosperma squash project

[Mike_Deyo]

I have been growing a population of hulless seeded pepo squash for a number of years, selecting for larger thicker seeds. Squash borers and squash bugs are always a problem though. After reading about Cucurbita interspecies crosses on OSSI, I decided to give it a try. I knew argyrosperma is pretty resistant to both pests, and some types have larger seeds.

In 2023 I grew Tennessee Sweet Potato and Mexican Wild Green Cushaw, both from Sand Hill Pres, and I crossed them. In 2024 I grew a F-1 plant that was TSP X MWG. The first female flower it had, I pollinated with my hulless pepo. There were no male flowers present on the argyr plant, but I still covered the flower before and after pollination. I first pollinated it the day before it was going to open, the again the next day. I had read this can give the pollen tube more time to grow. I think cool weather at the time was favorable for the pepo pollen. This was the fruit:

It had lots of seeds, but as they dried, they were all unfilled, except for 6 seeds.

This spring I planted two of the seeds. As seedlings they had the silver flecking of argyro, but the leaf outline of pepo:

The south plant had fruits like this:

The north plant had fruits like this:

Since it was the F-2 for the two argyro parents, they were segregating for argyro genes, at the same time being a F-1 argyro X pepo cross, so potentially showing showing something intermediate between the two species. For instance, the fruit skin pattern on the south plant looks much more like my hulless pepos than either argyro parent.

I made quite a few hand crosses, some selfing, some back crossing to either argyro or pepo. In general, selfing and backcrossing to argyro produced many well filled seeds, while backcrossing to pepo had only a few filled seeds (one exception).

The one exception was when I tried something new, pollinating the lobes (stigmas) of the female flower individually. With care, I could apply pollen to one lobe at a time. Here’s an example of what a female flower looks like (this one bee pollinated, pollen everywhere!):

My theory is that in the mature fruit, there are three “loops” of seeds, each loop produced from one of the three stigmas. This particular flower where the exception happened, I selfed two of the stigmas, and used pepo pollen on the third. I got ~45% filled seeds in two of the lobes (loops), and 23% in the third. Fruits that I pollinated solely with pepo pollen only had a few percent of filled seed. It can’t be fully confirmed until I grow out some seed, but it is worth experimenting with. Here’s how I marked them when harvesting seed (on a different fruit):

This was another one that seemed to show much higher seed set from pepo pollen than I would expect. It also had different pollen on different lobes. The seed sprouting in the fruit is something that happens with some of my hulless pepos, two lobes showed some seed sprouting, and I had pollinated two of the stigmas with pepo. This one had a pure argyro female parent. There was no seed sprouting in any other fruit of my argyro or argyro X pepo crosses.

[markwkidd]

Wow, what a cool project. Thank you for sharing your work.

[lyvasana]

I appreciate the level of detail and care that you put into your project – I hope you get more and more seeds each year. I hope to start my own project focused on small winter squashes that are perfect for small meals with no left overs.

[Mike_Deyo]

Thanks for your encouragement! I wish you luck in your project too. Which species of squash would you be working with?

[lyvasana]

Hello Mike,

I recently purchased tetsukabuto seeds and I intend to cross it with honeynut and koginut which are both really small. I am also looking to add in another small c maxima into the mix. I hope get a hybrid that readily crosses with c maxima and c moschata.

[Mike_Deyo]

I have 18 squash planted this summer that are various degrees of crosses between Curcubita argyrosperma and Cucurbita pepo. I made the crosses last year. If I use A for argyrosperma, and P for pepo, last year I grew two AxP plants (the A x P cross was done in 2024), as well as plain A and P plants. I made backcrosses (A x P) x P, (A x P) x A, also A x (A x P), and also selfed (A x P) x (A x P). The pepos that I used were all hull-less (naked) seeded. This is the first year that I should be seeing naked seed trait showing in some of the seeds. I am hoping to get the naked seed trait in an argyrosperma background, for their insect resistance.

One problem I anticipate, is the naked seeds might tend to sprout in the fruit. I had this come up in some crosses when in the past I crossed naked seeded and normal seeded C.pepo. I am doing more crosses this year, and labeling the fruits and keeping track of when the cross was done. The pepos seem to be ready to harvest for seed at about 45 days from pollination, while the argyrosperma take a bit longer, maybe 60 days. I don’t know what will happen with A x P plants. So I want to pick the fruits as soon as possible, but not so soon that the seeds aren’t sufficiently developed.

So far this year there have been only a few cucumber beetles, I saw two squash borer moths that I killed, and no squash bugs yet. Hopefully the crosses will show some resistance.

This is what the C.pepo naked seeded leaves look like:

This is what the argyrosperma leaves look like:

This is one of the (A x P) x P plants:

This is one of the (A x P) x (A x P) plants- slight silver flecking on leaves:

This is an (A x P) x A plant, shows less flecking that the straight A plants:

[Mike_Deyo]

Here are some of the developing fruits.

This is one of my naked seeded pepos. Notice there are two male flowers growing from the top of the fruits. I have never seen this before, although the same plant has some twin male flowers:

This is another line of my naked seeded pepos:

This is one of the (A x P) x (A x P) plants, I use a duct tape tag that I cut with scissors to make a pattern that I record, so I know which cross it is:

This is a different (A x P) x (A x P) plant:

This one is Campeche (an argyrosperma) x (A x P):

Some of the plants are growing as huge bushes before they start to vine, even though none of the parents grow like that:

There are also plants that seem stunted, like the one in the foreground. I’m putting in the little stakes with numbers, to help find the fruits in the jungle of leaves later when I go to pick.