Most Spanish olive orchards are monovarietal as a result of the farmer's belief that the species does not require cross-pollination. Paradoxically, accumulated evidence from controlled experiments demonstrates that olive is partially self-incompatible and that cross-pollination increases yield and fruit quality in this wind-pollinated crop. With the aim of assessing cross-pollination deficit in large plots of the most widespread olive oil cultivar in Spain, fruit set was compared in two solid orchards of ‘Picual’ in response to self-, open-, and artificial cross-pollination. In both orchards, ‘Picual’ behaved as a self-incompatible cultivar with reduced fruit set under self-pollination (index of self-incompatibility = 0.21). However, cross-pollination rarely increased fruit set in comparison with open-pollination. Bagging experiments demonstrated that open-pollination provided enough cross-pollen to induce high levels of fruit set. The increase in fruit set in response to mechanical application of cross-pollen was limited to the trees directly receiving the pollen flow and only in one orchard. Consistently, airborne pollen concentration after a single terrestrial application significantly fits a decay curve with a short dispersal. In contrast with the limited dispersal of single mechanical applications, open-pollination results suggest that trees from plantations at least 250 to 500 m away are acting as unsuspected pollenizers. This is probably taking place to some extent in most traditional olive districts in Spain, and it explains why farmers have never demanded pollination designs in this crop. Modern homogeneous plantations can, however, change this situation dramatically and give rise to pollination deficits.

The fluorochromatic reaction that viable pollen grains exhibit when exposed to fluorescein diacetate (FDA) is an easy, quick and accurate tool for assessing pollen viability in many plants. Despite its widespread use, the method as initially proposed by Heslop-Harrison and Heslop-Harrison lacks specificity in some respects that are essential for comparing simultaneously the viability of different pollen sources. We have determined the time needed for the fluorochromatic reaction to take place and fade, and the lifetime and most effective concentration of the FDA working solution. Our results show that consistent records of pollen viability in samples of olive (bicellular pollen grains) and cherimoya (tricellular pollen grains) can be obtained within minutes, but that measurement must be completed in the first hour after pollen exposure to FDA. The lifespan of the FDA working solution is 1 h, whereas concentrations between 1.5x10(-5) M and 1.8x10(-3) M are equally valid. Pollen grains of both species responded similarly, although some differences were observed in the persistence of fluorochromasia.