Dieback and wilting symptoms caused by complex soilborne fungi are nowadays the most serious threatening disease affecting olive trees (Olea europaea) in Tunisia and presumably in many Mediterranean basin countries. Fusarium is one of the important phytopathogenic genera associated with dieback symptoms of olive trees. The objective of the present study was to confirm the pathogenicity of Fusarium spp. isolated from several olive-growing areas in Tunisia. According to the pathogenic test done on young olive trees (cv. Chemlali), 23 out of 104 isolates of Fusarium spp. were found to be pathogenic and the others were weakly or not pathogenic. The pathogenic Fusarium spp. isolates were characterized using molecular methods based on ITS PCR. Isolation results revealed the predominance of Fusarium solani (56.5%) and F. oxysporum species (21.7%) compared to F. chalmydosporum (8.7%), F. brachygibbosum (8.7%) and F. acuminatum (4.34%). Based on pathogenicity test, disease severity was highly variable among the 23 pathogenic isolates tested (P < 0.05) where F. solani was the most aggressive dieback agent. To the best of our knowledge, this is the first work that shows that Fusarium spp. might be a major agent causing dieback disease of olive trees in Tunisia.

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Forty-two isolates of Verticillium dahliae were recovered from stem and root samples of olive trees showing symptoms of verticillium wilt in various olive-growing regions in Tunisia. Each isolate was identified based on microscopic observations of morphological and cultural characteristics, pathogenicity tests, as well as PCR amplification using Vd1/Vd2 primers. Genetic diversity among the isolates was investigated using random amplified microsatellites (RAMS) and PCR-RFLP of intergenic spacer region (IGS) of ribosomal DNA (rDNA). A single fragment of approximately 1.7-2.