Present status of virus and virus-like diseases of Citrus in Morocco

Abstract: Citrus is an important crop in Morocco, both economically and socially. Virus and virus-like diseases are a major factor in limiting production of Citrus fruits in the country. In order to assess the occurrence and distribution of Citrus virus and virus-like diseases, extensive surveys were conducted, between 2008 and 2017, in the main Citrus growing areas of the country: Gharb, Haouz, Loukkos, Moulouya, Souss and Tadla. Commercial Citrus groves, nurseries and varietal collections were inspected for symptoms of virus and virus-like diseases and a total of 5620 samples were collected for laboratory analyses. Direct tissue Blot immunoassay (DTBIA) was used to test for Citrus tristeza closterovirus (CTV), ELISA was used for Citrus psorosis ophiovirus (CPsV), Citrus variegation ilarvirus (CVV) and Spiroplasma citri, and imprint hybridization was used to test for Citrus exocortis pospiviroid (CEVd) and Hop stunt hostuviroid (HSVd). For confirmatory tests, representative positive and negative samples for each virus and virus-like agent were selected and submitted for additional PCR assays using specific primers for each agent. The obtained results showed that virus and virus-like diseases of Citrus were widely distributed in the country with an infection rate of 49%, especially in the region of Gharb where 57% of the tested plants were infected by at least one virus or virus-like agent. Average incidence of CTV was 2%, CPsV (33%), CVV (12%), S. citri (7%), CEVd (19%) and HSVd (11%), respectively. These results give a significant insight into the sanitary conditions of the Moroccan Citrus industry and should be considered for the development of control strategies for virus and virus-like diseases of Citrus in the country.