Peach (Prunus persica (L.) Batsch) is one of the most important fruit crops in the temperate regions of Mexico. In 2006, during a survey conducted in commercial peach orchards in Puebla, Mexico for viral diseases, many trees were observed with foliar symptoms that included yellow mottle, ringspot, line patterns, and mosaic. Samples (flowers, young shoot tips, and leaves) were collected from 120 symptomatic trees in three locations (San Martin Texmelucan, Domingo Arenas, and Tepetzala). All samples were tested using double-antibody sandwich (DAS)-ELISA kits (Agdia, Inc., Elkhart, IN) for the presence of the following viruses: Apple mosaic virus, Plum pox virus, Prune dwarf virus, and Prunus necrotic ringspot virus (PNRSV). Sap extracts from young symptomatic leaves and shoots were used to mechanically inoculate Chenopodium quinoa, C. amaranticolor, Gomphrena globosa, Nicotiana tabacum cv. Xanthi, N. glutinosa, N. clevelandii, N. benthamiana, Datura stramonium, Capsicum annuum, and Solanum lycopersicum. Plants were kept in a greenhouse with approximate temperatures of 25 to 35°C, humidity of 70%, and 12 h of light. Sap extracts were also used for dsRNA extraction and analyses (2) and RNA extraction for use in reverse transcription (RT)-PCR with the Access RT-PCR system (Promega, Madison, WI) and primers that annealed to a conserved region in the PNRSV coat protein gene (1). The expected size amplicons of approximately 450 bp were generated from all field-collected samples. The PCR products from three geographically distinct PNRSV isolates (Domingo Arenas [Accession No. DQ979004], Tepetzala [Accession No. DQ979005], and San Martin Texmelucan [Accession No. EF456771]) were directly sequenced with a Genetic Analyzer 3100 (Applied Biosystems, Foster City, CA) and their nucleotide and deduced amino acids sequences were more than 93% identical to corresponding sequences of PNRSV available in the NCBI/GenBank database. PNRSV was the only virus detected by DAS-ELISA in flowers and young shoots from 60 of the symptomatic field samples tested from the three locations. DsRNA banding patterns were obtained from 40 field-collected symptomatic samples; all showed three bands of approximately 3.6, 2.5, and 1.8 kb, the expected sizes for RNAs 1, 2, and 3 of PNRSV, respectively. DsRNAs were not detected in asymptomatic plants. PNRSV transmission by mechanical inoculation induced mosaic symptoms in N. tabacum cv. Xanthi and necrotic local lesions in G. globosa. Although G. globosa is reported to be a systemic host of PNRSV and N. tabacum is not reported to be a host, symptomatic plants were positive for PNRSV in DAS-ELISA tests. It is possible that there was an additional virus not detected in our assays that was responsible for the unexpected reactions in the host range studies. To our knowledge, this is the first report of PNRSV in peach in Mexico.
References: (1) D. J. MacKenzie et al. Plant Dis. 81:222, 1997. (2) R. A. Valverde et al. Plant Dis. 74:255,1990.
