Stone diversity in wild and cultivated olive trees (Olea europaea L.)

Abstract

The olive tree is represented in Tunisia by two varieties: var. sylvestris (wild olive trees) and var. europaea (cultivated olive trees including diverse cultivars). Seed (stone) size and shape analysis may provide the basis for relationships between varieties and cultivars as well as to study the responses to environmental conditions. A semi-automated method of image analysis allows to obtain data related with magnitudes descriptive of stone size and shape and to compare between wild and cultivated olives. Also, the effect of bioclimate on size and shape was analyzed in some cultivars. Stone size and shape presents high variability. In cultivated trees stones are larger. Mean seed image area is 0.38 and 0.75 cm² for wild and cultivated plants respectively. Roundness and circularity were compared as to their potential to define seed shape. Mean values were higher for circularity, but roundness is more variable reaching higher values in some individuals and varieties. Roundness is more useful to compare seed shape variations. In addition, climate factors affect the stone characteristics in cultivars; those of sub-humid region having larger stones. Phenotypic parameters of stone are discriminating parameters for the analysis of intra-specific, intra-varieties and intra-cultivars variability in Olea europaea.