Survey of over 4, 500 monumental olive trees preserved on-farm in the northeast Iberian Peninsula, their genotyping and characterization

Abstract Inventorying, characterising and conserving on-farm ancient olive trees is a priority for safeguarding their genetic, natural and agricultural value and for protecting ancient genotypes threatened with extinction. In the “Taula del Senia” (M-TdS) area (northeast Iberian Peninsula) a highly important cultural landscape has been preserved, in which the olive groves play an outstanding social and economic role: the ancient olive trees, sustained by many local farmers, constitute a living heritage and provide a clear example of High Nature Value (HNV). A total of 4526 ancient productive olive trees, with a trunk circumference (PBH) larger than 3.5 m, were inventoried and their spatial localization and biometric measurements were collected. 41 olive trees have shown the highest category in monumentality (PBH >8.1 m). The outstanding trees might be 634–1082 years old. The endocarp morphology of a representative sample of the most ancient trees from this settlement resulted in 14 different profiles. The ancient trees genotyped, through eight simple sequence repeat (SSR) markers, revealed 43 SSR profiles. The use of SSR enabled us to verify that most of the trees (98%) belong to the local cv. ‘Farga’, a male sterile variety with a rare chlorotype, only a few trees corresponded with other local varieties, ‘Morrut’, ‘Canetera’ and ‘Sevillenca’, and ten hitherto unidentified genotypes were distinguished, some with chloroplast lineages different from the ‘Farga’ type. The M-TdS area holds a unique living and exploitable heritage with the highest concentration of ancient olive trees worldwide. On-farm conservation of this germplasm by the community of local growers is enabling preservation of this important source of genetic variation, potentially holding traits of resilience and adaptation to adverse soil and climatic conditions, demonstrated by the survival of these trees over the centuries. Farmers have undertaken initiatives to valorize the olive oil deriving from these M-TdS trees.