In early 2004, severe yellowing and chlorosis were observed in field-grown cucurbits in Costa Rica. Symptoms resembled those of the genus Crinivirus (family Closteroviridae), and large populations of whiteflies were observed in the fields and on symptomatic plants. Although the identity of the whiteflies on the curcurbits was not determined, the greenhouse whitefly, Trialeurodes vaporariorum (Westwood) is known to be present in the region from where the samples were obtained. To identify the causal agent of the disease, leaf samples of symptomatic plants were collected from several farms. The leaf samples were dried with silica gel. Total RNA was extracted from leaf tissue of eight representative samples (two from healthy plants and six from symptomatic plants) using TRI Reagent (Molecular Research Inc., Cincinnati, OH). Reverse transcription-polymerase chain reactions (RT-PCR) containing one primer set at a time were performed using the Titan One-Tube RT-PCR kit (Roche Diagnostics Corp., Chicago IL) and primers specific for genes of cucurbit-infecting criniviruses, including the coat protein gene of Cucurbit yellow stunting disorder virus (3) and the minor coat protein gene (CPm) of Beet pseudoyellows virus (BPYV) (4). Primers specific for the heat shock protein (HSP) gene (CYHSPF 5′ GAGCGCCGCACAAGTCATC 3′ and CYHSPR 5′ TACCGCCACCAAAGTCATACATTA 3′) of Cucumber yellows virus (CYV, a strain of BPYV) (1) were designed based on published sequence data. In addition, primers specific for Cucurbit aphid-borne yellows virus (2) and melon yellowing-associated flexivirus (MYVF 5′ GGCTGGCAACATGGAAACTGA 3′ and MYVR 5′ CTGAAAAGGCGATGAACTA TTGTG 3′) were used in RT-PCR reactions. Amplified DNA fragments of 333 and 452 bp were obtained in each of two samples obtained from symptomatic plants and only in separate reactions containing BPYV and CYV primer sets, respectively. Nucleotide sequence analysis of all purified PCR products verified their identity as variants of BPYV, with 97 and 99% sequence identity with reported CPm and HSP sequences, respectively. The two samples from Cucurbita moschata Duch. (ayote or squash) and Cucurbita pepo L.(escalopini or sunburst squash) were taken from a region around Paraiso, Cartago, Costa Rica. To our knowledge, this is the first report of BPYV in Costa Rica. The economic impact on cucurbit production has not yet been determined. Studies are underway to determine the prevalence and genetic variability of BPYV isolates in Costa Rica.
References: (1) S. Hartono et al. J. Gen. Virol. 84:1007, 2003. (2) M. Juarez et al. Plant Dis. 88:907, 2004. (3) L. Rubio et al. J. Gen. Virol. 82:929, 2001. (4) I. E. Tzanetakis et al. Plant Dis. 87:1398, 2003.
