1. The importance of maintaining/recovering olive biodiversity

In many olive-growing areas, despite the richness of olive varietal patrimony, most olive cultivars remain locally important and are progressively displaced by a handful of both traditional and new bred cultivars that meet the requirements of new olive-growing systems. In this sense, the present catalogue bears witness to the standardisation and the globalisation of olive oil, table olives and the plant market, within and beyond Mediterranean olive-growing areas. This trend entails a serious risk of genetic erosion of the crop through progressive abandonment, substitution and, finally, loss of traditional local cultivars. 

Nevertheless, traditional local cultivars represent an important and still largely unexplored, genetic heritage with potential value for growers and breeders. Traditionally cultivated under dry conditions, in harsh, marginal and/or mountain areas, local cultivars could be a very important source of diversity in the face of new or enhanced biotic and abiotic stresses associated with climatic change and in cases of outbreaks of new pests and diseases, such as the case of Xylella fastidiosa, as well as for obtaining new and better olive cultivars adapted to new cultivation techniques. Moreover, when displaying high nutritional and health values, many of these traditional varieties could provide added quality to monovarietal oils and those under PDO (Protected Denomination of Origin) and PGI (Protected Geographical Identification) denominations, thus contributing to the increase of their commercial value. In addition, traditional cultivars can contribute to solving problems that the olive groves may face in the future but that are unknown to us today. 

Therefore, their disappearance would not only mean the loss of the invaluable legacy of biodiversity of previous generations of farmers, but, most importantly, it would entail the reduction of the strategic reserve for the sustainable future of the crop. In this scenario, the exploration, collection, conservation, characterisation and evaluation of olive genetic resources are necessary steps to counteract the genetic erosion risk and enhance the diversification of olive orchards. In this sense, many local and national prospective surveys performed in the last century represented an enormous contribution to the collection and conservation of olive genetic resources in ex situ germplasm collections. However, recent identification studies have highlighted the presence of new and untapped local diversities in olive trees. It is expected that the chances of discovering and preserving this untapped diversity will be higher in olive-growing areas with less pressure of cultivar turnover and productivity. Along with their historical, landscape and cultural value, centennial olive trees also represent an important reservoir of unknown ancient cultivars. In addition, new and uncatalogued diversity may also be found in olive-growing countries beyond the borders of the Mediterranean basin. 

Accordingly, appropriate strategies for the prospection, collection and incorporation of this untapped diversity in olive germplasm collections is fundamental for their safeguard and further evaluation. Local genetic resources are strongly linked to the development of their growing areas, requiring the establishment of in situ/on farm strategies to avoid their irreparable loss. Overall, global and coordinated ex situ and in situ conservation programs are essential to preserve and evaluate the richness of the genetic legacy present in olive germplasms.