Captivator is one kind of spineless gooseberry. I think there are a few other names that are spineless as well.
Nearly spineless cultivars have been developed, but the most popular cultivars, such as ÂWelcomeÂ, and ÂPixwell have short spines.

Here's a tidbit I found on the web:
One of the main goals of breeding is obtaining spineless gooseberry cultivars. The results of distant interspecific hybridization within genus Grossularia Mill. have been the most promising ones. In the result of crosses between European cultivars and derivatives of North-American species the following weak spiny and basically spineless cultivars have been obtained: Chernomor, Chernoslivovyi, Slaboshipovatyi 3, Shalun, Sirius, Yubilyar, Grossular, Serenada. Convergent crosses, backcross and inbreeding are considered to be the main up-to-date methods of breeding.
The most promising parents and cross combinations have been selected out of the 6700 seedlings. Spineless cv. Chernoslivovyi seems to be the best donor for spinelessness.
The analysis of spineless trait changes in ontogenesis has shown spiny seedlings predominance in the first year after seeds sowing. A significant increase of the share of seedlings with parents traits among hybrids from spineless and weak spiny cultivars is observed in the 2nd and 3rd years. Therefore a rigid discard of hybrids for spiny trait should not be made in the first year of vegetation.

I've got a question for you: Would I be wasting my time growing and maturing seedlings from my Josta plant? They would be josta F2's, since they developed without any other currants or gooseberries around.

What would you expect from such seedlings?

BTW, the seeds lasted the whole winter in the ground, then sprouted under my josta plant, I'd say these are pretty hardy :)

Could you arrive at another sort of 'josta' by crossing a spineless gooseberry with a red or white currant? I've always wondered about that. And why the true Josta had to be made with black currant?

Ribes are very interesting eh?

Besides
http://www.lsdi.lt/T20(3)-1_eng/T20(3)-1_eng_32.htm
I also found:
http://www.aif.ru:81/online/dacha/104/04_03
http://www.aif.ru:81/online/dacha/169/06_01
But I am unable to translate and I also don't know where to get those gooseberries, that are shurely worth testing. Those 'spineless' gooseberries seem to be derived mainly from Ribes oxyacanthoides?! Cultivars like Spinefree or Captivator have mostly weak spines but are not really spinefree. Secondly the branches are weaker therefore susceptible to wind damage, the yield is lower and the berries smaller. The second thing is that when they are micropropagated they develope a lot of spines. Josta never developes any spines. So my idea is to transfer genes from black currant to gooseberry to surpress spines totally. I made a crossing and found that triploid plants (one set black currant and two sets gooseberry) are also totally spinefree even directly after germination.
Breeding Josta in F2 is not interesting as most plants are nearly the same. The genetic variation is very small. To improve the genetic variation you either have to cross black currant (female) with gooseberry (male) and treat the resulting seedlings with Colchicine or cross Josta with either black currant or gooseberry and try to get seed from these triploid seedlings by pollinating them with Josta pollen.
Yes it is possible also to cross gooseberry with red currant but the seed set is very very low and you need embryo culture to get mature plants. I don't know anyone who tried to Colchicinate those plants to make the fertile.

Greetings
Martin

Are your 3X currant/gooeseberries fertile?

Yes and no. The triploid plants have a low fertility, but enough to get some seed when pollinated with diploid pollen.