Comparing the historic olive trees (Olea europaea L.) of Santa Cruz Island with contemporaneous trees in the Santa Barbara, CA area: a case study of diversity and structure in an introduced agricultural species conserved in situ

ABSTRACT: Historic populations of crop species outside their centers of origin and diversity, like the domestic olive (Olea europaea L.) in North America, are genetic resources for contemporary agriculture, including genotypes that could be readily evaluated for, and may be adapted to, local conditions. The primary goal of this study was to describe the diversity and structure of several significant, adjacent, contemporaneous historic olive plantings in central coastal California, USA with reference to the USDA ex situ Olea europaea germplasm, and test the hypothesis that physical and chronological proximity are predictive of genetic similarity in those trees. The groups studied using 14 SSR markers were dominated by a limited number of genotypes represented in the USDA collection, but also four unique cultivar genotypes not in that collection. Historical socioeconomic networks appear to have had an important influence on the source and kind of material planted. This is the first study of historic olive trees conserved in situ in North America and provides the basis for a larger regional study integrating genetic, historical and geographic data to describe the structure and diversity of remaining historic olive plantings in California.