FIRST REPORT OF DIEBACK OF OLIVE TREES CAUSED BY NEOFUSICOCCUM AUSTRALE IN TUNISIA
M.A. Triki, S. Krid HadjTaieb, M. Cheffi, Y. Gharbi, A. Rhouma
In spring 2011, a severe disease resulting in tree dieback of olive tree cv. Chemlali was observed in an orchard in Hencha (south-east Tunisia). Symptomatic trees exhibited plenty of dead twigs and wilted leaves. On potato dextrose agar (PDA), a fungus isolated from symptomatic twigs and branches has an initially white mycelim that turned glaucous grey to greenish grey on the upper surface. The fungus was identified as Neofusicoccum australe, based on morphological characteristics and analysis of the ITS gene region (White et al., 1990). The sequence analysis of ITS region of the isolate revealed 100% homology with a reference sequence of N. australe (Strain E54 ML, GenBank accession No. KF702388.1). Pathogenicity tests were conducted on 10 two-year-old olive trees of cv. Chemlali. A mycelial plug was put in a shallow wound on the stem of each plant. Control plants were inoculated with sterile PDA plugs. All plants were kept in a greenhouse. Two months post inoculation, symptoms appeared with stems showing brown color. No symptoms developed on the control plants. Neofusicoccum was isolated from inoculated stems, thus fulfilling Koch's postulates. N. australe has been reported as responsible for cordon grapevine dieback in Italy (Linaldeddu et al., 2010). To the best of our knowledge, this is the first report of N. australe as a causal agent of dieback of olive trees in Tunisia.