Ripening indices and harvesting times of different olive cultivars for continuous harvest

This research was performed in order to assess the optimal harvesting time of four olive cultivars for continuous harvest, by following the seasonal changes of the most reliable ripening indices and by developing a model to find out the detachment index by the most quick colourimetric index. In the literature there are no works on these topics. A two-year field experiment was carried out in a super high-density olive orchard on Arbequina, Arbosana, Coratina and Urano® cultivars. Fruits firmness, detachment index, colourimetric index, pigmentation index, oil and polyphenol contents were compared and it used a model coming from a non-linear regressions to determine the detachment index by the colourimetric index. For all the cultivars the maximum oil content was observed in a more concentrated period with respect to the maximum mechanical efficiency, between the 60th and the 75th day after the start of the ripening process. Moreover the oil content maximum values occurred about 1 month after the maximum detachment indices. For Arbosana the relations between colourimetric and detachment index were not significant, both as a linear correlation and non-linear regression, because of the skin pigmentation occurred very slowly and never completely. So, it can be suggested to use the firmness or detachment index as reliable ripening indices for this cultivar. On the contrary, for the remaining cultivars colourimetric index could represent an useful ripening index. The sigmoid model could be reliable for the cultivars that veraison quickly, as Arbequina, Coratina and Urano® do.These first data collected on four cultivars could contribute to highlight their ripening processes and they could be useful for harvesting management in super high-density orchards. The ripening processes showed fundamental differences among the cultivars. Moreover, data obtained in this study are the first ones available in the literature for the new Italian cultivar Urano®. Our results emphasize the importance of setting a priority of criteria for choose the harvesting time for continuous harvest that will take into account first of all the maximum mechanical efficiency, so the maximum oil harvestable and then the maximum oil quality. The question on which better ripening index it could be used in order to detect the optimal harvesting time depend on the rapidity of the ripening process of a cultivar. The sigmoid model obtained is applicable only for Arbequina, Coratina and Urano®, for which it could represent a very reliable instrument to evaluate the optimal harvesting date.

► The better ripening index choose depends on the rapidity of the ripening process of a cultivar.
► For Arbosana, a very slow and late ripening cultivar, destructive indices should be used.
► The sigmoid model could be a very reliable instrument to evaluate the optimal harvesting date.
► The model could be reliable for the cultivars that veraison quickly as Arbequina, Coratina, Urano.
► For continuous harvest there is priority of criteria for determining harvesting time.