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.