First Report of Capsicum chlorosis virus Infecting Tomato in Taiwan.

Abstract

In December 2009, two samples from tomato plants (Solanum lycopersicum cv. Known-you 301) showing symptoms of chlorosis and necrosis on leaves were collected from two different fields that exhibited 5% disease incidence in Wufeng Township, Taichung County. Reverse transcription (RT)-PCR was applied to detect the presence of potential viruses in collected samples using three degenerate primers (3), gL3637/gL4435c for tospoviruses, Tob-Uni1/Tob-Uni2 for tobamoviruses, and Hrp5/Pot1 for potyviruses, and one specific primer, FJJ2001-7/FJJ2001-8, for the coat protein gene of Cucumber mosaic virus (3). An 816-nt DNA fragment was amplified from each of these two field samples by RT-PCR with the tospovirus degenerate primers, gL3637/gL4435c, designed from the conserved region of L RNA. One of the amplified fragments was cloned and sequenced. A homology search indicated that the new tomato-infecting virus in Taiwan might belong to Capsicum chlorosis virus (CaCV) since the partial L RNA shared more than 87% nucleotide and 99.6% amino acid identity with two CaCV isolates from Thailand (GenBank Accession Nos. DQ256124 and NC_008302). A virus culture isolated from the symptomatic tomato was established in Chenopodium quinoa through triple single-lesion isolation and designated as TwTom1. The partial L RNA and full-length nucleocapsid (N) gene of TwTom1 were obtained by RT-PCR with primer pairs gL3637/gL4435c and FJJ 2010-2 (5'-TTAAAT(C/T)ACAC(C/T)TCTATAGA)/N3534c (1), respectively. The 816-nt L RNA conserved region of TwTom1 (Accession No. HM021140) also shared 87% nucleotide and 99.6% amino acid identity with those of the above mentioned two CaCV isolates available in GenBank. The 828-nt N gene of TwTom1 (Accession No. HM021139) shared 85 to 98.1% nucleotide and 92 to 100% amino acid identity with those of 26 CaCV isolates available in GenBank. TwTom1 shared the highest N gene nucleotide and amino acid identity, 98.1 and 100%, respectively, with a gloxinia isolate (Accession No. AY312061). Sequence analysis results indicated that TwTom1 is an isolate of CaCV. The TwTom1 isolate was back inoculated onto three tomato (cv. Known-you 301) plants for pathogenicity test. The inoculated tomato plants showed symptoms of chlorosis at 13 days postinoculation (dpi) and symptoms of chlorosis plus necrosis on leaves at 20 dpi, which were similar to that observed in the field. A protein band measuring approximately 30 kDa in the crude sap of the TwTom1-infected tomato was observed in western blotting using the antiserum against the N protein of CaCV. In addition, CaCV was later detected by RT-PCR in two symptomatic tomato samples collected from another field. CaCV was first found in Australia, then Thailand, Taiwan, China, and India (2). Although CaCV was found to infect several species of ornamental crops in Taiwan, to our knowledge, this is the first report of CaCV that could naturally infect tomato, a nonornamental plant in Taiwan.