**3. Ovary (or pistil) abortion**

Ovary or pistil abortion indicates the presence of flowers with absent or only partly formed and non-viable ovaries: that is, ovaries incapable of becoming fruits and destined to drop. Flowers with aborted ovaries are often called staminate flowers since only the male organs are complete and functional. Normal flowers with both male and female organs complete and functional are called hermaphrodite flowers. Ovary abortion varies greatly with year, cultivar, individual tree, branch and shoot, and even among and within inflorescences (Morettini, 1939; Bottari, 1951; Badr & Hartmann, 1971; Fabbri *et al.*, 2004; Martin & Sibbett, 2005). Ovary abortion occurs early during flower development, (Pirotta & De Pergola, 1913), mostly 30-40 days before bloom (Uriu, 1959; Cuevas *et al.*, 1999; Reale *et al.*, 2006).

Ovary abortion in olive appears to results mostly from competition among flowers (and ovaries, the future fruits) for resources, which are insufficient for all flowers to develop, given the redundant flowering. The onset of this competition occurs very early and affects both pistil abortion and fruit set, as we will see later (Hartmann, 1950; Uriu, 1959; Cuevas *et al.*, 1994; Perica *et al.*, 2001; Levin & Lavee, 2005). Conditions that affect competition among flowers/fruits or that decrease available resources, usually result in increased abortion and decreased fruit set. Among such conditions are: N deficiency, foliar diseases and low leaf-tobud ratio, (Petri, 1920; Morettini, 1951; Uriu, 1953, 1959; Fernandez-Escobar *et al.*, 2008); water stress (Melis, 1923; Brooks, 1948; García Gálvez, 2005); insufficient light (Bottari, 1951; Dimassi *et al.*, 1999); adverse climactic conditions and high yield in previous year (Rallo *et al.*, 1981; Rapoport & Rallo, 1991; Lavee, 1996; Cuevas *et al.*, 1994); abundant flowering in current year (Reale *et al.*, 2006); and unfavorable inflorescence position in the canopy (Cuevas & Polito, 2004; Seifi *et al.*, 2008). Aborted flowers do not contain starch, suggesting a link between nutrient availability and pistil abortion (Reale *et al.*, 2009). Removing part of the inflorescences reduces drastically the ovary abortion in olive (Seifi *et al.*, 2008).

On the other hand, pistil abortion is known to be under genetic control, varying with the cultivar (Campbell, 1911; Morettini, 1939, 1951; Magherini, 1971; Lavee, 1996; Lavee *et al.*, 2002). In a recent paper it has been demonstrated that even the genetic component can be interpreted with the competition theory (Rosati *et al.*, 2011b). In fact, as described above, fruit size differences are related to ovary size differences among cultivars. Large-fruited cultivars tend to have bigger flowers, not just ovaries (Rosati *et al.*, 2009). This implies greater energetic costs for the same number of flowers, and thus greater pistil abortion, which in fact tends to be higher in larger-fruited cultivars (Morettini, 1939; Magherini, 1971; Acebedo, 2000; Rosati *et al.*, 2011b). In the previous paragraph we have seen that greater ovary size in large-fruited cultivars results from greater cell number (not greater cell size) and cell number appears to be a key factor in determining the sink strength of an organ (Marcelis, 1996). Larger ovaries with more cells, therefore, might have a greater ability to compete for resources than smaller ovaries, determining both greater abortion and lower fruit set.
