Determination of compatibility relationships between olive cultivars: an overview of available methods

Abstract

Olive (Olea europaea L.) is a wind-pollinated, preferentially allogamous species. However, inconsistent results are often reported for the classification of some cultivars as either self-compatible or self-incompatible, probably because of the influence of management and environmental conditions during bloom. Cross- pollination significantly enhances fertilization and fruit set in most olive cultivars. However, this improvement partly depends on the compatibility relationships between recipient and pollinizer trees in the species, where a few cases of cross- incompatibility have been reported recently. Different methods have been used to evaluate the success and inter-compatibility in pollination assays. The most common method for the determination of inter-compatibility is based on the observation of pollen-pistil interactions in cross-pollination trials. This method requires the usage of pollination bags to prevent the access of unwanted pollen grains to the stigmas of recipient flowers and the subsequent observation of pollen-pistil interaction features (pollen adhesion, pollen germination, pollen tube growth in the pistil and fertilization) and/or initial and final fruit set in response to experimental crosses. Lately, simple sequence repeats (SSRs) or microsatellites are increasingly becoming the markers of choice for paternity analysis of seeds to measure the success of crosses, especially when potential pollen donors are multiple and not applied by hand. SSRs offer a reliable way to test the paternity of seeds by checking the presence of parental alleles in the progenies. Knowledge of self-compatibility and cross-compatibility relationships of olive cultivars is a vital factor in the success of olive crosses and, therefore, of breeding programs. The advantages and drawbacks of the different methods to evaluate compatibility relationships within and between olive cultivars are presented in this work.