First report of Hop stunt viroid infecting citrus orchards in Jamaica

Citrus fruit is one of the major traditional agricultural products of Jamaica. Fresh fruit is exported to the United Kingdom, United States, Canada, and Barbados but the domestic market accounts for approximately 85% of production. Constraints to fruit production are mainly related to tree decline caused by infection with Citrus tristeza virus (CTV). Exocortis has been described in Jamaica since the 1970s, but group II viroids including Hop stunt viroid (HSVd), the causal agent of cachexia, have not been reported (Naylor, 1974). Cachexia is a gumming and wood pitting disorder of citrus with severe infections characterised by stunting, chlorosis and eventual death of the tree (Duran-Vila et al., 2000).

In 2003 and 2004, a survey of six major citrus producing regions of Jamaica was conducted to evaluate the status of HSVd. A total of 24 samples of citrus varieties, without symptoms of viroid infection, were collected and indexed for viroids by inoculation of Etrog citron grafted on Citrus volkameriana and forHSVdusing Parson’s Special mandarin grafted on to rough lemon (Bennett et al., 2008). Within three months, typical viroid leaf symptoms were observed on Etrog citron inoculated with samples from four regions, Clarendon, St. Catherine, St. James, and St. Mary (Fig. 1). Within 18 months, gumming at the bud union, an indication of infection with HSVd, was observed on Parson’s Special mandarin inoculated with samples from the Clarendon region (Fig. 2). Total RNA extracted from the latter samples was subsequently used in reverse transcriptase-polymerase chain reaction (RT-PCR) with primers specific to HSVd (Elleuch et al., 2006). Single fragments (~ 283 bp) were amplified, cloned, and sequenced. BLAST analysis indicated high nucleotide identities (between 95 and 100%) with group II viroid species from Cuba (GenBank Accession Nos. AY594200, DQ014515), Mexico (DQ323934), Uruguay (AF416557, AF359274), North America (X69518, X69519), Spain (AF213483, EU559706), Israel (DQ269991, X13838), Japan (AB054609, AB054617), and China (EU131156, DQ371452).

This is the first confirmed report of HSVd infecting citrus in Jamaica. Apart from stunting, conspicuous HSVd symptoms are not observed in the field because of the prevalence of the tolerant sour orange rootstock. However, this pathogen may be a threat to the industry later on, given the recent initiation of replanting on CTV tolerant trifoliate rootstocks, most of which are susceptible to citrus viroids.Further work on other viroids infecting citrus is required, including their potential impact on the industry.