Mechanisms of date palm resistance to Bayoud disease: Current state of knowledge and research prospects

The Bayoud disease, caused by Fusarium oxysporum f. sp. albedinis (Foa), represents a major limiting factor of date palm culture in Morocco and constitutes a serious threat to the date palm plantations in Algeria and all other countries. Efficient disease prevention requires the development of resistant cultivars. In Morocco, among the cultivars listed, only six appear to be resistant to Bayoud disease, but they produce poor quality fruit. Thus, the Moroccan program of date palm genetic improvement is based on directed crossing between resistant cultivars and susceptible cultivars with good date quality traits to select resistant genotypes producing high quality fruits. In addition to the separation of the resistance to Bayoud disease and quality of the fruits characters, this breeding program is really complex due to the sex separation in the date palm, the duration of juvenile phase which is very long, and the lifespan of the date palm which requires a durable polygenic resistance. Then, the selected genotypes must be of female sex, of good date quality, and possess effective defense mechanisms against the pathogen. Moreover, the selection of the date palm resistance must necessarily take into account the mechanisms of pathogen aggressiveness. In this review, we will present and discuss studies developed on the Bayoud disease of the date palm, particularly on the disease control, the biochemical and molecular markers of resistance, the program of date palm genetic improvement of resistance, the Foa pathogenicity factors, and host defense mechanisms. It will also highlight the recent studies that showed that differential behaviour of the resistant and susceptible cultivars was not related to a difference of induction of the defense mechanisms, but to the suppression of their elicitation in the susceptible cultivars. (C) 2010 Elsevier Ltd. All rights reserved.