Yacon seed looks exactly like the Smallanthus uvedalius seed that I’m trying to germinate. A native seed website gave me some tips on germinating the S. uvedalious (Hairy Leaf Cup) seed. Instructions said to try scarification with light sand paper OR to stick them in damp (not wet) sand in the fridge at 33-38F for 1 to 3 months then planting out in trays in the greenhouse… Maybe both methods can be combined.
The Cultivariable Growing Guide said some yacon varieties like Morado have very low seed set. It makes me wonder if the embryo is dying shortly after development. Something similar happens with hybrid lily embryos with weird ploidy . Such lily embryos can be extracted before they die in the seed and propagated.