FIELD BEHAVIOR OF 32 DATE PALM CULTIVARS TOWARDS BAYOUD - A 25-YEAR SURVEY

Planting resistant cultivars constitutes the only efficient method available to control fusarium wilt (bayoud) in date palm. Twenty-five years ago, a trial was set up in naturally-infested open fields in Zagora (Morroco) to assess the resistance level of 32 cultivars. The observations reported in this paper enabled the cultivars to be ranked into several classes corresponding to their susceptibility to bayoud. The level of genotype resistance was characterized by the percentage of dead plants 25 years after plantation. However, in some cultivars, chronic symptoms were observed that did not necessarily induce plant mortality. Only 3 cultivars were totally resistant (Bou Sthammi-noire, Tadment and Bou Sthammi-blanche), all plants surviving without any symptom of disease. Four cultivars (Sair-Layalet, Iklane, Bou Feggous-ou-Moussa and Bou-Slikhene were tolerant to bayoud: a few plants showed symptoms of disease but did not die. Other cultivars showed a range of intermediate levels between total resistance and marked susceptibility. This continuous variation indicated a large diversity of genotypes and complexity of resistance determinism. Moreover, some cultivars were susceptible only when young, during the 10 first years of culture; in most of the cultivars however, the disease progression curve did not alter with plant age.