**6. Conclusions**

76 Olive Germplasm – The Olive Cultivation, Table Olive and Olive Oil Industry in Italy

**5. Redundant flowering, andromonecy and fitness** 

appears to be the adjustment of fruit set.

more for wind pollinated species, like the olive.

suggests compensation between fruit number and size. The genetic effect on fruit set, appears thus to result from different degrees of competition for resources among ovary/flowers of different sizes. This would explain why small-fruited cultivars like Arbequina and Arbosana tend to produce several fruits per inflorescence, while table-olive (i.e. large-fruited) cultivars typically produce only one, but bigger fruit. Nor can it be argued that the small size in small-fruited cultivars is the result of a higher fruit set and consequent source limitations. In fact, aside from the fact that the fruit of these small-fruited cultivars is smaller already at bloom (i.e. the ovary), well before fruit set is decided, thinning fruits to reduce competition increases fruit size minimally, but does not result in fruit size comparable to that of large-fruited cultivars (Rosati *et al.*, 2010). This suggests that differences in fruit size are mainly of genetic origin. Clearly, the ultimate fruit size depends also on resource availability, and varies up to more than 100% within the same cultivar, but among cultivars fruit size may vary much more than that (Barranco, 1999), up to 600% (Rosati *et al.*, 2009). Hence, adjusting fruit load across cultivars with extremely different fruit size needs a wider compensation mechanism than just adjusting fruit size: this mechanism

As stated above, the olive produces redundant flowers relative to its yield potential and fruit set is very low. We have seen how ovary abortion increases under conditions that increase competition for resources. In fact, ovary abortion is a means to save resources, balancing the number of ovaries to the resources available (Primack & Lloyd, 1980; Bertin, 1982; Stephenson & Bertin, 1983). Plants, like the olive, that abort part of the ovaries in otherwise hermaphrodite flowers are called andromonoecious (about 4000 species are estimated to be andrommonoecious). From an evolutionary point of view, andromonoecy is considered an intermediate step towards dioecy, and allows saving of resources without affecting the total number of flowers and thus the male function and fitness (Vallejo-Marín & Rausher, 2007). Aborting the ovary does not affect pollen production in olive (Cuevas & Polito, 2004). In this species, large-fruited cultivars have greater ovary abortion, but similar number of flowers (Rosati *et al.*, 2010, 2011b), leaving the male function probably unaltered (although differences in pollen production per flower, among cultivars with different fruit/ovary/flower size have not been studied). Leaving the male function (and fitness) unaltered might explain why only the ovary is aborted instead of the whole flower, which would save more resources, given that the flower is several times bigger than the ovary alone (Rosati *et al.*, 2009; Cuevas & Polito, 2004). It would also explain why the flower production is so redundant compared to the fruiting potential. Producing pollen is less expensive than producing fruits and seeds, while still increasing the plant's fitness, making it more convenient to produce more (male) flowers that fruits. Modeling work demonstrates that fitness is maximized, under limiting resources, when many more flowers than fruits are produced (Morgan, 1993). This author finds that the optimal flower/fruit ratio increases for andromonoecious and monoecious species compared to dioecious ones, and increases even We have seen how competition for available resources among developing flowers and fruits plays a continuous role during the whole developmental cycle of the reproductive organs (Lavee *et al.*, 1999). Hence, pistil abortion first, and fruit set afterwards, appear to be part of a single mechanism that adjusts maternal investments to available resources. Even the genetic component affecting fruit size (i.e. cultivar differences) may be explained with the competition theory, based on the related differences in flower and ovary size (which correlates with fruit size), implying different energetic costs for the development of one fruit. In the absence of catastrophic events that might impair production (e.g. lack of pollination, severe drought or nutrient deficiency, etc.), the olive tree appears to produce fruits according to its potential, independent of the amount of flowers produced. To achieve this potential, the tree uses the different compensatory mechanisms available at any given developmental stage (i.e. pistil abortion, fruit drop, fruit size). Hence, studies reporting positive correlations between abundance of flowering (or pollen in the air) and yield (Moriondo *et al.*, 2001; Fornaciari *et al.*, 2002, Galán *et al.*, 2004), would imply not a causal relationship but simply correlated phenomena: bloom and yield both represent an expression of the tree yield potential. The redundant flowering in olive, may serve the purpose of increasing the mail and the overall fitness, which is advantageous from an evolutionary point of view, but wasteful from an agronomical perspective. For the olive grower, selecting for reduced mail fitness (i.e. fewer flowers) to benefit the female fitness (i.e. yield) might prove beneficial.
