FIRST REPORT OF DIEBACK OF OLIVE TREES CAUSED BY NIGROSPORA sp IN TUNISIA
S. Krid HadjTaieb, M. Cheffi, A. Rhouma, M. A. Triki
During spring 2011, a new disease was observed on olive (Olea europea) cv. Chemlali in an orchard in Hencha (south east Tunisia). Inspection of the affected planting revealed reddish- brown necrotic lesions on the bark of dead twigs and branches. A fungus isolated on potato dextrose agar (PDA) from symptomatic twigs and branches had an initially white mycelium which turned gray with age. The fungus was identified as Nigrospora sp. based on morphological characteristics and analysis of the ITS gene region (White et al., 1990). A BLAST search of GenBank database revealed 100% homology with a reference sequence of Nigrospora sp. (strain P19E2, accession No. JN 207298.1). Pathogenicity tests were conducted on 10 two- year-old olive trees of cv. Chemlali by placing a mycelial plug in a shallow wound on the stem of each plant. Control plants were inoculated with sterile PDA plugs. Two months post inoculation, brown discolourations and necrotic lesions developed on inoculated stems whereas controls remained healthy. Nigrospora sp. was recovered from the necrotic lesion, fulfilling Koch's postulates.