FIRST REPORT OF NECTRIA HAEMATOCOCCA ASSOCIATED WITH DIEBACK OF OLIVE TREES IN TUNISIA
S. Krid Hadj Taieb, M.A. Triki
During a routine survey for olive diseases conducted in autumn 2013 in southern Tunisia (Bir Ali region), wilting and chlorosis of the leaves accompanied by brown-to-black discoloration of the wood in cross-sectioned twigs were observed on 3- to 10-year-old olive trees. On potato dextrose agar (PDA), a fungus was isolated from symptomatic twigs and branches with an initially white mycelium that over time became light gray-brown. This fungus was identified as Nectria sp. based on morphological characteristics and analysis of the ITS gene region (White et al., 1990). A BLAST search of GenBank database revealed 99% homology of the amplified product with a reference sequence of Nectria haematococca (strain HLJ_14, accession No. JN088237.1). 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, symptoms appeared, with stems showing brown discolorations and necrotic lesions. Controls remained healthy. N. haematococca was recovered from necrotic lesions, thus fulfilling Koch's postulates. N. haematococca was held responsible for root rot of olive trees in Argentina (Barreto et al., 2003). To our knowledge this is the first report of N. haematococca as a causal agent of dieback of olive trees in Tunisia.