Other people below have covered fruits like watermelons. Seedless grapes though–I researched this and this is what I found: seedless grape varieties are propagated via cuttings. I’ve done this myself, in some cases it’s as simple as cutting off a branch with three buds on it and sticking it in the ground, and waiting for it to grow roots and become a vine. Also, apparently “seedless” grapes still have seeds sometimes, they’re just (mostly) soft so they’re not an issue to eat. I’m not sure if they’re viable or not, but it still allows for some cross-breeding of “seedless” grape varieties.
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