Pumpkin (Cucurbita maxima and C. pepo), a new host of beet pseudo yellows virus in California

In the summer of 2002, pumpkin plants (Cucurbita pepo L. and C. maxima Duchesne) with extensive leaf chlorosis similar to those observed in crinivirus infections were found in fields at two locations in Monterey County, California. Leaves of diseased plants were observed to have large populations of the greenhouse whitefly (Trialeurodes vaporariorum) present. Double-stranded RNA was extracted from symptomatic leaves of these plants and tested by northern hybridization for numerous criniviruses. A positive signal was identified exclusively with probes against the HSP70h gene of Beet pseudo yellows virus (BPYV) and confirmed by reverse transcription-polymerase chain reaction (RT-PCR) amplification of a 335-nucleotide section of the BPYV minor coat protein (CPm) gene (3). Similar symptoms were observed in additional fields in 2003, and BPYV was again confirmed. In addition, the CPm RT-PCR product was cloned into a TOPO pCR2 vector (Invitrogen, Carlsbad, CA) and sequenced. BLAST analysis of the cloned CPm RT-PCR product sequence corresponded to the published sequence of the CPm gene of BPYV (98%) (3) and Cucumber yellows virus (CuYV), a recently sequenced crinivirus considered to be a strain of BPYV (97%) (2). Incidence of BPYV in pumpkin appears to be variable and probably corresponds to the incidence of viruliferous whiteflies. On the basis of foliar symptoms, BPYV incidence varied from less than 50% in these fields in 2002 to nearly 100% infection of a large commercial field in 2003. BPYV is transmitted semipersistently by the greenhouse whitefly and has an extensive host range (1). The virus causes economic losses worldwide for greenhouse vegetable production and is becoming an increasing problem for field crops in areas of high greenhouse whitefly incidence (3). The impact of BPYV on pumpkin production remains to be determined; however, grower data suggests an increased incidence of fruit abortion and a substantial decrease in fruit weight. To our knowledge, this is the first report of BPYV infecting pumpkin.