First report of Tomato chlorosis virus infecting tomato crops in Sinaloa, Mexico

Starting in 2005, abnormal yellow leaf symptoms were observed in tomato (Lycopersicon esculentum) fields in the Guasave, Ahome and Culiacán counties of Sinaloa state, in northern Mexico. In affected fields, symptomatic plants occurred at random and resembled previous descriptions of crinivirus infections in tomato (Wisler et al., 1998; Fig. 1. The symptoms and the presence of whiteflies (Bemisia tabaci) in the affected fields suggested a viral etiology.

Leaf samples of 62 tomato plants with symptoms and four weeds samples (Solanum nigrescens, Datura stramonium, Amaranthus retroflexus and Parthenium hysterophorus) were collected. Total RNA was extracted and analyzed by RT-PCR. First, the degenerate primers MA59/MA60 were used for amplification of a 587 bp fragment of the HSP70 gene of Tomato infectious chlorosis virus (TICV) and Tomato chlorosis virus (ToCV) (Nava-Castillo et al., 2000). A fragment of the expected size was amplified in 10% of the tomato samples. Second, degenerate primers (HS-11/HS-12) were used in combination with specific primers (TIC-3/TIC-4 and ToC-5/ToC-6) for detection of TICV and ToCV by nested-PCR (Dovas et al., 2002). In this assay, 60% of the tomato samples, along with the Solanum nigrescens and Datura stramonium samples, produced amplicons of the expected size for ToCV (463 bp). However, none of the samples tested positive for TICV (Fig. 2).

Four amplicons from RT-PCR of tomato field samples were directly sequenced. One amplicon (accession No. DQ377368) was compared with the sequences of other criniviruses in the NCBI/GenBank database using the Clustal V alignment method (MegAlign, DNASTAR software, London). The highest sequence similarity (99.4% identity) was obtained with a ToCV isolate from the USA (accession No. AY903448). Our data proves the presence of ToCV in some of the tomato plants with symptoms. To our knowledge, this is the first report of Tomato chlorosis virus infecting tomato crops and two weeds, Solanum nigrescens and Datura stramonium, in Mexico.