Characterization of a Single Clonal Lineage ofFusarium oxysporumf. sp.albedinisCausing Bayoud Disease of Date Palm in Morocco

Abstract

Bayoud, the Fusarium wilt of date palm, was first detected in southern Morocco (Draa Valley), after which it spread to most of the Moroccan palm groves. To assess whether the epidemic results from the spread of a single virulent clone, 42 isolates of Fusarium oxysporum f. sp. albedinis were collected from several cultivars of wilted palms at different locations in Morocco; two isolates were included from Algeria, where the disease also occurs. The isolates were tested for vegetative compatibility group (VCG), restriction fragment length polymorphism (RFLP), and random amplified polymorphic DNA (RAPD). No polymorphism was observed either in RFLP studies on mitochondrial DNA or in RAPD analysis, and all strains belonged to a single VCG (0170). Sequences homologous to the DNA transposable element Fotl were found in the genome of the F. oxysporum f. sp. albedinis strains. Repetitive DNA patterns were produced when EcoRI-digested DNA of the isolates was probed with Fotl; 23 distinct hybridization patterns were established among the 44 isolates. Of these patterns, 4 accounted for more than 50% of the isolates, 1 was found twice, and 18 were represented by a single isolate each. Common hybridization patterns were found in the Moroccan palm groves surveyed; the two Algerian isolates had a pattern that also was found in the Draa Valley. Cluster analysis grouped most of the F. oxysporum f. sp. albedinis strains at a genetic distance of 0.11. Such close genetic relationships between the isolates provides evidence that Moroccan F. oxysporum f. sp. albedinis populations may belong to a single clonal lineage that originated in Moroccan palm groves and eventually reached the Algerian oases.