Morphological and molecular characterization of Fusarium spp. associated with olive trees dieback in Tunisia

Mariem Dammak,Sonia Kammoun,Rahma Trabelsi,Samira Krid,Aymen Mseddi,Manel Cheffi,Radhouane Gdoura,Yâakoub Gharbi,Mohamed Ali Triki,Hanen Sellami

doi:10.1007/s13205-016-0587-3

Abstract

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.

Highlights

Olive tree (Olea europaea) is the most widely cultivated tree species in Tunisia
Fusarium is one of the important phytopathogenic genera associated with dieback symptoms of olive trees
These observations together with the increase of inquiries received by the Olive Tree Institute of Tunisia, led us to investigate the etiology of this disease, to perform pathogenicity tests of the different Fusarium species recovered from olive orchards and their identification based on morphological and molecular features

Summary

Introduction

Olive tree (Olea europaea) is the most widely cultivated tree species in Tunisia. With a total cultivated area of about 1.7 million ha and more than 70 million olive trees (anonymous), Tunisia is ranked as the fourth producer of olive oil worldwide. The dieback and wilting symptoms induced by complex soilborne fungi has caused considerable economic losses in olive orchards in Tunisia (Boulila and Mahjoub 1994; Triki et al 2006, 2009, 2011; Gharbi et al 2014, 2015). Among these fungi, Fusarium species may cause disease in olive trees. Some species are known as common pathogens on olive trees, such as Verticillium dahliae (V. dahliae), and an increased frequency of isolates belonging to the genus Fusarium was noted. Some fluctuations have been recorded which were probably linked to climatic conditions and to the presence of some fungi especially in

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Conclusion