In May 2005, the Plant Protection Service in the Netherlands received two tomato (Lycopersicon esculentum) plant specimens for diagnosis from a protected crop production facility of 2.5 ha near Kebili in Tunisia. Growth of the plants was reduced and leaves were chlorotic and brittle. Ripening of the fruits was delayed and their storage life was reduced from 3 weeks to 1 week. The grower reported that initially only 5% of plants showed symptoms; however, the number of symptomatic plants increased quickly to 100% as a result of increasing temperatures in the production facility. Test plant species Chenopodium quinoa, Datura stramonium, Nicotiana glutinosa, N. hesperis-67A, N. occidentalis-P1, and L. esculentum ‘Money-maker’ were mechanically inoculated with sap from the affected plants. Symptoms including chlorosis and stunting were observed only on L. esculentum. Reverse transcriptase-polymerase chain reaction (RT-PCR) with universal pospiviroid primers Pospi1-RE/FW (2) yielded amplicons of the expected size (196 bp) for each of the two samples. One of these amplicons was sequenced and showed the highest identity to the four isolates of Tomato apical stunt viroid (TASVd) in the NCBI Gen-Bank. Subsequently, the complete sequence of the Tunisian isolate (Gen-Bank Accession No. DQ144506) was determined by sequencing the am-plicon obtained after RT-PCR using primers developed for the detection of Citrus exocortis viroid (CEVd) (1). The isolate consisted of 363 nucleotides and showed the highest sequence identity (96.7%) to tomato isolates of TASVd from Indonesia and Israel (GenBank Accession Nos. X06390 and AY062121, respectively), 92.6% to a tomato isolate from the Ivory Coast (GenBank Accession No. K00818), and 87.7% to an isolate from Solanum pseudocapsicum (GenBank Accession No. X95293). The next highest sequence identity was 81.5% to an isolate of CEVd (GenBank Accession No. X53716). On the basis of these results, the viroid was identified as TASVd. To our knowledge, this is the first report of TASVd in Tunisia.
Reference: (1) N. Önelge. Turkish J. Agric. For. 21:419, 1997. (2) J. Th. J. Verhoeven et al. Eur. J. Plant Pathol. 110:823, 2004.
