It took an extremely long time, but I now have two healthy young jackfruit seedlings growing! As far as I can tell it took longer than expected because the original seed leaves were damaged during irradiation and refridgeration of the fruit.
I'm thinking the plant on yhe left suffered even more damage. It sent up a bare stem with no leaves whatsoever. At least I've ended up with an odd bushy seedling that probably wouldn't have existed otherwise.
These are the only seeds I've successfully sprouted from irradiated fruit. The papaya sprouted but stop growing and eventually withered.