First report of Papaya ringspot virus infecting papaya in Côte d’Ivoire

Papaya (Carica papaya) is grown in Côte d’Ivoire for the export market and local consumption. Virus-like diseases constitute a major threat to papaya production; plants showing virus-like symptoms have been observed over the last few years with incidence reaching 100% in some fields.

In February 2006, papaya leaves with various symptoms including yellow dots along the veins (Fig. 1), yellow mosaic (Fig. 2 & 3) and shoe-stringing (Fig. 3), were collected from different papaya growing regions. On some green fruits symptoms were characterised by darker green ring spots or chlorotic spots, with darker green centres.

Extracts made from the papaya leaf samples were tested for the presence of Papaya ringspot virus (PRSV) by DAS-ELISA (Clark & Adams, 1977) using a commercial kit (Bioreba, Switzerland), according to the instructions of the manufacturer. PRSV was detected in nine out of fifty seven leaf samples. Examination of the ELISA-positive leaf samples, using a leaf-dip preparation for electron microscopy, with 2% phosphotungtic acid (PTA) as a negative stain, showed flexuous particles characteristic of potyviruses. For confirmatory testing, a 676 bp fragment containing a portion of the coat protein (CP) gene and the 3’-untranslated region (3’-UTR) was amplified by reverse transcription-polymerase chain reaction (RT-PCR) using a total RNA extract from one of the leaf samples that had previously tested positive for PRSV by ELISA. The primers used were Uni 3 (5’-ATG GTR TGG TGC ATT GAG AAT GG-3’) (W. Monger, personal communication) and Oligo dT. The nucleotide sequence of the PCR product (Genbank Accession Number DQ84023) showed 97% identity with PRSV strain W (Genbank Accession Number D00594) and 96% identity with PRSV strain P (Genbank Accession Number D00595). To our knowledge, this is the first report of PRSV infecting papaya in Côte d’Ivoire.