The germinability of fermented seeds could represent an inadvertent selective bottleneck during grapevine domestication

Propagation techniques played a significant role in the early domestication of grapevines. Considering the morphological features of wild grape berries and the nutritional properties of grape seeds, it is unlikely that these were spat out by ancient agriculturists: it is much more likely that they were eaten, or they were disposed of with the winemaking residues. In this study, we tested whether seed exposure to different processing methods-fresh, dried, and fermented-affected germination in Vitis vinifera L. Trials were conducted in 2024 at two ampelographic collections in Lizzano (Italy) and Jighaura (Georgia). We sampled 6 accessions of V. vinifera subsp. sativa in Italy and 19 accessions-5 wild V. vinifera subsp. sylvestris and 14 cultivated V. vinifera subsp. sativa-in Georgia. Grapes were processed as fresh, dried, and fermented berries. Germination was assessed for 15 days, using 4 to 8 replicates of 25 seeds each. A total of 13200 seeds was observed. Our results indicated that seeds from fresh and dried berries exhibited similar and higher germination potential, while fermented seeds showed a significant reduction in germination-only two fermented accessions (one subsp. sylvestris, one subsp. sativa) showed limited germination capacity. Ethanol exposure during fermentation may damage the seed embryo, reducing its germination ability. In general, the germination rate of the unfermented seeds of subsp. sylvestris were noticeably higher than the ones of subsp. sativa, suggesting potential differences due to their divergent propagation strategies. Collectively, these findings indicate that during grapevine domestication, grape propagation by fresh and dried seeds could be successful, while fermentation imposed an inadvertent selective bottleneck against sexual propagation. Only occasional ethanol-tolerant seeds may have survived. This may have eventually decreased the cultivated grapevine's biodiversity.