Hybridization in the genus Phoenix: A review

The genus Phoenix is composed of 14 species naturally distributed in the Old World. This genus comprises the date palm, Phoenix daetylifera L., cultivated for its fruits, the dates, while other species are grown for food, ornament and religious purposes. Phoenix species were, for these reasons, spread out of their natural distribution area. It is therefore common to find species not naturally sympatric, growing together, in cultivation or in the wild. Phoenix species are interfertile and crossing distinct species leads to fertile hybrid offspring (interspecific hybridization). The introduction of a species in the wild generates gene flows leading to the creation of new hybrids and has conservation implications. In cultivation, such crossings may be spontaneous or are the result of artificial pollination, as several reasons impel doing so. Crossing gives rise to beautiful hybrids and is also useful for the conservation of old palm groves threatened by pests. Moreover, artificial pollination of date palms using another Phoenix species can be of interest given the metaxenic pollen effects. In addition, this process may have some potential benefits in date palm improvements, by the creation of hybrid cultivars. Thus, an increasing need of hybrid detection and characterization exists, particularly as morphology alone is not sufficient for this task. Besides new methods such as traditional and geometric morphometrics that may bring new clues, the advent of genetic and molecular markers helps to detect hybrids, especially based on the combination of nuclear and chloroplastic data. The application of methods such as near-infrared reflectance spectroscopy is currently under examination to estimate their potential use for hybrid characterization.