Pollen limitation and dependence on cross-pollination in borage (Borago officinalis L.) in the Pampas region of Argentina

Borago officinalis L. is an insect-pollinated crop valued for its seed oil. While described as self-compatible, the extent to which its reproductive success depends on pollinator-mediated cross-pollination and whether it experiences pollen limitation in agricultural settings remain key questions for its sustainable cultivation. We experimentally evaluated the effect of five pollination treatments (natural pollination, autonomous self-pollination, artificial cross-pollination, anemophily, and apomixis) on fruit set and nutlet number in a borage experimental population in the Pampas region of Argentina. Artificial cross-pollination yielded the highest reproductive output, while autonomous self-pollination (including possible geitonogamous pollen transfer) and anemophily produced intermediate and similar results. Artificial cross‑pollination increased fruit set by 284% and nutlet number per fruit by 338% compared to natural pollination, demonstrating strong pollen limitation despite the presence of managed honeybees. Apomixis was negligible. Our findings demonstrate that B. officinalis relies on cross-pollination to maximize reproductive success and that even in the presence of managed honeybees, pollen limitation can significantly reduce yield. This highlights the need to ensure adequate pollinator services for the cultivation of this species.