Large Scale Survey of Citrus Tristeza Virus (CTV) and Its Aphid Vectors in Morocco

A large scale survey of Citrus tristeza virus (CTV) and its vectors was carried out in the main Moroccan citrus growing areas (Souss, Gharb, Moulouya, Tadla, Haouz and Loukkos). A total of 5,192 plants from commercial groves, nurseries and varietal collections were analyzed by DTBIA. In the groves, about 25% of the tested trees proved to be CTV-infected, with the highest incidence in the Loukkos region that showed a 60% of infection rate. Few infected trees were detected in the Souss and Gharb regions and no CTV infection was found in the remaining sites. A survey for CTV vectors in the Gharb and Loukkos regions showed that Aphis spiraecola and A. gossypii were the most abundant aphid species, accounting for 56 and 33% of the total aphid population, respectively, while no evidence for the presence of Toxoptera citricidus (Kirkaldy) was observed. Sequencing of the coat protein gene from six Moroccan CTV isolates revealed that five of them showed high nucleotide identity with the Spanish mild isolate T385 and the other, from Loukkos, had high similarity with the 19-21 severe Portuguese CTV strain.