Genetic diversity within an isolated olive (Olea europaea L.) population in relation to feral spread

Genetic variability within and between groups of olives (Olea europaea L.) in an isolated population within an area of about 1 km(2) was investigated using the random amplified polymorphic DNA (RAPD) technique. Based on visual observation, three putative groups were identified: nine trees that appeared to be an original grove, 12 trees that were assumed to be planted progenies of the original grove, and 24 feral trees in the surrounding hills and valleys. The DNA fingerprints of these 45 trees were compared, and the genetic variability within and between groups within the population was partitioned using analysis of molecular variance (AMOVA). The AMOVA showed high genetic variation within each of the three putative groups of the population but there were no significant genetic differences between them. A dendrogram constructed using the simple matching coefficient with unweighted pair group mathematical average (UPGMA) clustering showed the presence of three clusters that persisted when the data were subjected to multi-dimensional scaling (MDS). The three clusters obtained from molecular data were significantly different from one another. Each cluster consisted of at least one or more trees from the original grove and others from the population. Estimates of tree age were highly variable, but the overall trend supported the derivation of feral trees from the original grove. The distribution of these clusters within the population suggests that the predominant mode of feral spread was by fruit drop close to the parent trees, with occasional wider dispersal by animals or birds. (C) 2002 Elsevier Science B.V. All rights reserved.