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A Begomovirus Associated with Leaf Curling and Chlorosis of Soybean in Sinaloa, Mexico is Related to Pepper golden mosaic virus

Since June 2001, symptoms of yellowing, leaf curling, crumpling, and stunted growth were observed on soybean (Glycine max Merr.) plants in Sinaloa, Mexico. These symptoms and the presence of whiteflies (Bemisia tabaci Gennadius) in the affected fields suggested a viral etiology. Samples from symptomatic plants were collected from commercial fields and analyzed for the presence of begomoviruses using DNA hybridization, and as a probe, the DNA A of Pepper huasteco virus at low stringency (2). Thirty-five positive samples were subsequently used for polymerase chain reaction (PCR) amplification with the degenerate primers RepMot and CPMot (1). These primers direct the amplification of a DNA A segment comprising the entire intergenic region (IR) and the first 210 bp of the coat protein (CP) gene, which is highly variable in size and nucleotide sequence among begomoviruses. PCR products were obtained for 25 of 35 samples and five of these were cloned into the pGEM-T easy vector (Promega, Madison, WI) and sequenced. The 571-bp DNA sequence (GenBank Accession No. AY905553) was compared with sequences of other begomoviruses in GenBank using the Clustal alignment method (MegAlign, DNASTAR software, London). The sequence was 74 and 70% identical to the Pepper golden mosaic virus (PepGMV; GenBank Accession No. U57457) and Cabbage leaf curl virus (CaLCuV; GenBank Accession No. U65529) sequences, respectively. Interestingly, the partial coat protein gene sequence (210 nt) of this soybean-infecting virus was 98% identical to the CP gene of Tobacco apical stunt virus (TbASV; GenBank Accession No. AF076855). Nonetheless, the known sequence of TbASV intergenic region (GenBank Accession No. AF077744) is very different from the homologous region of the soybean virus (34% of nucleotide identity). Analysis of the soybean virus intergenic region revealed that it harbors almost identical iterons (i.e., Rep-binding sites) to PepGMV, suggesting a close relationship between these two viruses. Soybean-infecting geminiviruses have been previously reported only from Asia; however, the partial sequence of a begomovirus isolated from soybean in Brazil was recently deposited in Genbank (Accession No. AY436328). Sequence comparisons between the Brazilian and Mexican isolates showed these viruses are less related with a nucleotide identity of 46%. Taken together, our data indicate that the virus identified in this study might be either a different strain of PepGMV adapted to leguminous plants or a new begomovirus species. To our knowledge, this is the first report of a begomovirus infecting soybean in Mexico.

References: (1) J. T. Ascencio-Ibañez et al. Plant Dis. 86:692, 2002. (2) J. Méndez-Lozano et al. Phytopathology 93:270, 2003.