ABSTRACT
Field observations of declining trees of “Mapo” tangelo, hybrid of “Avana” mandarin (Citrus deliciosa Tenore) and “Duncan” grapefruit (Citrus paradisi Macf.) topworked on “Comune” clementine having as rootstock the sour orange, allow the description of the symptomatology shown by this hybrid when infected with xyloporosis viroid. Both from the biological assays and from the symtomatology, it was established that the trees are infected with exocortis, xyloporosis, concave gum and cristacortis.
The symptoms of cristacortis and of concave gum are typical of these diseases.
The exocortis does not show any symptom in the infected trees as a result of the behaviour of the parents of “Mapo” tangelo regarding this viroid.
The xyloporosis in the intermediate stock of “Comune” clementine shows the typical symptomatology with pits on the bark correspondent to pegs on the wood, whereas on “Mapo” tangelo it causes a particular discolouration of the wood, enlarging more than in other species.
