open access

Abstract

Viroids are the smallest known pathogens of plants. They are single-stranded, circular, rod-like RNAs with no protein capsid no any detectable messenger activity. Citrus species are natural hosts of at least seven viroids in the family Pospiviroidae. Exocortis and cachexia are the most important viroid diseases of citrus in Morocco. In order to assess the incidence and distribution of Citrus exocortis viroid (CEVd) and Hop stunt viroid (HSVd), extensive surveys were conducted, between 2008 and 2018, in the main citrus growing areas of the country. A total of 100 commercial citrus groves of different varieties were inspected for symptoms of exocortis and cachexia, and 5390 samples were collected for laboratory analyses, using imprint hybridization. Representative positive and negative samples for each viroid were selected and submitted for additional confirmatory RT-PCR assays using specific primers. The incidence of infection by viroids was about 28,9 %, regardless of citrus species and location, although a slightly higher number of infected trees were located in the Gharb region (41,5 %). CEVd was detected in 11,3 - 18,2 % of the tested samples, while HSVd was detected up to 10,8 % of the samples tested. Since CEVd and HSVd are readily mechanically transmissible via working tools, they affect both old and young plantings in all the regions surveyed.

Key words: Citrus exocortis viroid, Hop stunt viroid, citrus, survey, Morocco.