**1. Introduction**

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

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> Floral biology has important practical implications, in addition to its scientific relevance, given that flower characteristics and bloom affect fruit characteristics and yield. Yield derives from fruit quality (e.g. weight) and quantity (i.e. number), which, in turns, depend on flower quantity and quality: flowers must be suitable to become fruits, and then must be pollinated and fertilized, and must set fruits, which must then grow. Not all flowers can do all of this: some flowers, for instance, have aborted ovaries which are partially developed or absent at bloom, depending on when the abortion occurred. Even when still present, these aborted ovaries are not capable of becoming fruits. Normal pistils, may not be pollinated or fertilized, but also fertilized ovaries may drop after some growth, resulting in fruit drop. From 100 flowers, in olive, all the above phenomena result in one to few fruits (Hartmann, 1950). Because of this low fruit set, it is often believed that cultural practices aimed at improving pollination, increasing fruit set or reducing ovary abortion or fruit drop, may lead to increased olive yields.

> In the following paragraphs we will analyze in detail some of these passages (i.e. ovary abortion and fruit set) allowing fruit formation from the flower. We will conclude that, in olive, yield is affected mostly by the nutritional status of the tree and the environmental conditions affecting it, which determine the potential yield. To achieve this potential yield, the plant uses a series of compensating mechanisms which make the yield rather independent of flowering or any single subsequent passage (i.e. ovary abortion, fruit set, drop and size).

> Firstly, however, we will begin by describing how fruit characteristics, particularly fruit size, are mostly determined by the ovary characteristics at bloom. In the following paragraphs we will see how these ovary characteristics affect ovary abortion and fruit set. Finally we will discuss the apparent redundant flowering in olive, which produces many more flowers than necessary for the yield it can sustain.

© 2012 Rosati et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Rosati et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Floral Biology: Implications for Fruit Characteristics and Yield 73

*al.*, 2009). However, from the ovary to the mature fruit, the mesocarp grows much more than the endocarp (Rosati *et al.*, 2012), probably due to its longer growth period (i.e. up to fruit maturity) compared to the endocarp, which stops growing about eight weeks after bloom (Hammami *et al.*, 2011). However, both tissues grow in strict proportion to their initial cell number in the ovary. The greater growth of the mesocarp is related to its initial (i.e. in the ovary at bloom) greater number of cells of smaller size (Rosati *et al.*, 2012). These results agree with the hypothesis that cell number, rather than tissue mass, is related to the sink strength of an organ (Ho, 1992) even though this might be not always the case (Marcelis, 1996), because cell number is only one factor determining sink strength (Gillaspy *et al.*,

Mature fruit size correlates with flower and, particularly, ovary size at bloom (Rosati *et al.*, 2009). This is true for both the mesocarp and the endocarp independently, though, as stated above, the mesocarp grows proportionally more: the endocarp volume in the fruit is about 4000 times greater than its volume in the ovary, while the same ratio is about 800 for the

Both the endocarp and mesocarp contribute to the ovary size differences among and within cultivars and even the locular space is proportional to ovary size (Rosati *et al.*, 2012). Similarly, proportionality among the ovary and other flower parts was found both within trees (Cuevas & Polito, 2004) and between cultivars (Rosati *et al.*, 2009). Ovary size depends mostly on cell number rather than size, both across and within cultivars (Rosati *et al.*, 2011a). This is true both for the mesocarp and the endocarp, suggesting that similar mechanisms regulate cell division in different tissues. Cell size does differ among cultivar, but does not correlate with ovary size. Cell size differs greatly among tissues with bigger but fewer cells in the endocarp compared to the mesocarp, suggesting that cell growth patterns differ among tissues (Rosati *et al.*, 2011a). In fact, cell size in the ovary correlates with tissue relative growth (i.e. from bloom to fruit maturity), both across tissues and cultivars, suggesting that cell size at bloom reflects the stage of growth of a given tissue: the larger the cells, the less growth remains to be performed (Rosati *et al.*, 2012). This agrees with the observation that fruit growth is mostly achieved by cell expansion as mentioned above. The larger cell size of the endocarp at bloom suggests that this tissue is at a more advanced stage of growth, compared with the mesocarp and thus, its remaining growth, relative to its size at bloom, is less, at least in terms of cell expansion. This would also explain why the endocarp stops growing earlier than the mesocarp. It is possible that the endocarp might be in a more advanced stage of development at bloom, since it is inside this tissue that vital functions (e.g. fertilisation) take place soon after bloom and thus the endocarp needs relatively more differentiated cells. The mesocarp, on the contrary, does not perform particular activities at bloom, hence, it does not need advanced cell differentiation in this

In conclusion, genetic differences in fruit size, among olive cultivars, appear to arise from differences in cell division patterns occurring in the ovary (and probably in the whole flower) before bloom. Similar results have been found in other species where genes coding for cell division before bloom have been found to be responsible for differences in final fruit

1993).

period.

endocarp (Rosati *et al.*, 2012).

**Figure 1.** Flower size differs among olive cultivars: Nocellara del Belice, a large-fruited cultivar, on the left, and Koroneiki, a small-fruited cultivar, on the right.
