Olive oil is a major economic resource of the Mediterranean region. Olive crop management can be improved by models that forecast the variable reproductive biology of olive tree. However, the processes controlling olive harvest are complex on large scales. Here, we study the parameters that influence olive fruit production for developing accurate forecasting models. Seventeen aerobiological sampling points have monitored olive pollen grains in Spain, Italy and Tunisia from 1993 to 2012. Six crop models have been developed at two provinces and country scales. The modelling has been done in two steps: (1) typification and (2) modelling by partial least square regression. Results show that higher pollen indexes and water availability during spring are related to an increase of final fruit production in all the studied area. Higher pollen indexes are also positively correlated with air temperature during early spring and autumn. Furthermore, a decrease of fruit production is related with increasing air temperature during winter and summer. To conclude, we have designed accurate models that allow accurate predictions of olive production.

The main characteristics of the heat accumulation period and the possible existence of different types of biological response to the environment in different populations of olive through the Mediterranean region have been evaluated. Chilling curves to determine the start date of the heat accumulation period were constructed and evaluated. The results allow us to conclude that the northern olive populations have the greatest heat requirements for the development of their floral buds, and they need a period of time longer than olives in others areas to completely satisfy their biothermic requirements. The olive trees located in the warmest winter areas have a faster transition from endogenous to exogenous inhibition once the peak of chilling is met, and they show more rapid floral development. The lower heat requirements are due to better adaptation to warmer regions. Both the threshold temperature and the peak of flowering date are closely related to latitude. Different types of biological responses of olives to the environment were found. The adaptive capacity shown by the olive tree should be considered as a useful tool with which to study the effects of global climatic change on agro-ecosystems.

In olive (Olea europaea L.), the formation of functionally staminate flowers rather than fully functional hermaphrodites is one of the major factors limiting fruit set, as flowers with aborted pistils are incapable of producing fruit. Studies conducted on various angiosperm species have shown a correlation between flower abortion and starch content. Thus, it is important to know if starch content plays a role in regulating pistil development in olive and if so, what mechanism regulates starch distribution. Cyto-histological observations of staminate and hermaphrodite olive flowers show that pistil development in staminate flowers is interrupted after the differentiation of the megaspore mother cell. At that stage, starch grains were only detected in the ovary, style and stigma of the hermaphrodite flowers. No starch was observed in the pistils of the staminate flowers. This finding suggests a tight correlation between starch content and pistil development. The secondary origin of starch within the flower is indicated by low chlorophyll content in the gynoecium, undetectable Rubisco activity in the pistils of these two kinds of flowers and by the ultrastructure of the plastids observed by transmission electron microscope analysis. The plastids have few thylakoid membranes and grana and in the staminate flowers appeared very similar to proplastids. Considering differences in starch content between staminate and hermaphrodite flowers and the secondary origin of the starch, differences in pistil development in the staminate and hermaphrodite flowers could be related to differences in the sink strength of these two types of flowers.

Olive trees have a plentiful bloom but a low percentage of normal fruit set. To improve fruit set, numerous investigations have sought to identify the obstacles that prevent full production. In this work, flower development in five DOP Umbria cultivars (Leccino, Frantoio, Moraiolo, Dolce Agogia and San Felice) was studied throughout different developmental phases, from before microsporogenesis and megasporogenesis to post-anthesis, by morphological and cytohistological observations. Dolce Agogia was the most precocious cultivar, while full flowering was simultaneous in Leccino, Frantoio, Moraiolo and San Felice. Frantoio and Leccino were also good pollen producers, having the highest percentage of pollen viability and germinability. Dolce Agogia can also be considered a good pollen producer in terms of the high quantity of released pollen, but it had the lowest levels of pollen viability and germinability and the highest percentage of aborted flowers and ovaries. Morphological and cytohistological observations on the number of flowers per inflorescence and the number of aborted flowers and ovaries suggest that fruit set was not influenced by the number of flowers per inflorescence, but rather by the number of inflorescences, which depends on the global fruiting potential of the tree.

No abstract