'Arbequina' olive is self-incompatible

'Arbequina' is the olive cultivar preferred by growers for the design of the trendy high-density orchards due to its low vigor, high yield, and extraordinary oil quality. Although, 'Arbequina' is considered by many authors as self-compatible, increasing evidence questions its full self-compatibility. Our results clearly illustrate that, contrary to earlier assumptions, 'Arbequina' olive behaves as a self-incompatible variety. Self-pollen rejection in the style, low levels of self-fertilization and decreased initial and final fruit set after self-pollination in comparison to cross-pollination treatments clearly indicate that 'Arbequina' is self-incompatible. Furthermore, even seed and fruit size were depressed in response to self-pollination, despite the lighter crop produced in self-pollinated shoots. This was observed in both 'on' and 'off' 'Arbequina' trees. Both pollinizers tested, 'Manzanillo' and 'Picual', matched results obtained under free open-pollination and significantly increased the yield obtained under self-pollination. Our results suggest the convenience of establishing pollinizers for large, high-density 'Arbequina' orchards, especially in new areas of olive cultivation, where wind pollination may be not enough to ensure beneficial cross pollen flow.