Outbreak of Papaya ringspot virus in papaya orchards in St. Kitts

Fruit tree production has become increasingly more important in the agricultural industry of St. Kitts. This is because of an increasing demand for local fruits resulting from an expanding local tourism sector. Papayas (Carica papaya), along with bananas and mangoes, are commonly grown to provide the sector with the 'Kittian fruit plate'. In October 2002, mosaic symptoms on leaves and ringspot blemishes on fruits were observed on papaya trees in orchards at two locations along the northwest coast of St. Kitts (Brimstone Hill and Fahies). Samples were tested by double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA, Agdia Inc.) for Papaya ringspot virus (PRSV). In addition, crude sap extracts (1: 20) from affected leaf samples were mechanically inoculated onto papaya seedlings. Symptoms typical of PRSV (Purcifull et al., 1984), including vein clearing followed by mosaic development and leaf distortions, were observed in the inoculated plants within 2 weeks. All original samples and the indicator plants tested positive in DAS-ELISA. Reverse transcriptase polymerase chain reaction (RT-PCR) using primers to the capsid protein gene (Slightom, 1991) was performed. A single amplicon of the expected size (~ 996 bp) was obtained with samples from both locations. RT-PCR amplicons were subsequently cloned into the vector pEPT8 (Ling et al., 1997) and sequenced. The two sequences were 99% identical and showed high nucleotide identities (90 to 97%) with PRSV from Jamaica (DQ104812), Cuba (DQ089482), Florida (AF196839), and Brazil (AF344650) and a lower identity of 89% identity with an isolate from Puerto Rico (AF196838). This is the first confirmed report of PRSV in St. Kitts. Despite eradiction measures and destruction of the infected crop, the pathogen has subsequently spread throughout the island, wiping out approximately 90% of production.