First Identification of an Unusual Recombinant Potato virus Y Strain in Potato in Mexico.

Potato virus Y (PVY) has been reported in potato crops in Mexico (3), with tobacco necrotic variants found in the central State of Mexico (4). Nevertheless, many individual states are currently declared PVY free and distribution of individual strains of PVY in potato in different states of Mexico and in different solanaceous crops had not yet been studied. A limited field PVY survey was conducted on potato in the State of Chihuahua in August 2009. More than 900 random potato leaf samples were collected from cvs. Snowden, Atlantic, FL1867, Felsina, Fianna, Gigant, and Alpha. Seven were found to be PVY-positive and had been collected from cvs. Fianna, Snowden, and FL1867. The PVY status of the collected samples was initially determined with the PVY-specific Immunostrips (Bioreba, Reinach, Switzerland) and by double-antibody sandwich-ELISA using the polyclonal PVY detection kit (Agdia, Elkhart, IN). To determine the strain specificity of these PVY isolates following ELISA tests, the infected original samples were inoculated onto tobacco plants at the four-leaf stage and symptom appearance and development were observed for 8 weeks side-by-side with control isolates PB-Oz (PVYO), N4 (PVYNTN), and Mont (PVYN) (1), followed by the standard PVY strain typing by reverse transcription (RT)-PCR (2). Only one of the PVY-positive samples, originally from symptomless potato cv. Fianna, induced systemic PVY infection in tobacco by producing stunting, mosaic, and vein clearing. No systemic vein necrosis, characteristic of isolates Mont and N4, was observed in Nicotiana tabacum cvs. Burley, Xanthi, or Samsun after inoculation with this isolate during all 8 weeks of observation. This isolate, PVY-M3, was typed as a PVY recombinant by RT-PCR, with two recombinant junctions characteristic of European PVYNTN strains (2). It was further analyzed by triple-antibody sandwich-ELISA using four PVYO and PVYN strain-specific monoclonal antibodies. Monoclonals 1F5 (Agdia) and SASA-N (Scottish Agriculture Science Agency [SASA], Edinburgh) reacted to this isolate and identified PVY-M3 serologically as PVYN serotype, characteristic of other PVYNTN recombinants. Monoclonals MAb2 (Agdia) and SASA-O (SASA), specific to PVYO and PVYC strains, did not react to PVY-M3. Taken together, the combination of biological, serological, and molecular characteristics define this recombinant isolate from Mexico as belonging to the same PVY strain group represented by the isolate PVY-L26 (1). To our knowledge, this is the first report of such an unusual PVYNTN recombinant strain from Mexico. Presence of this isolate, with no vein necrotic symptoms induced on tobacco and with PVYNTN genome, will necessitate development of new detection methods for the seed potato industry in Mexico. References: (1) X. Hu et al. Virus Res. 143:68, 2009. (2) J. L. Lorenzen et al. Plant Dis. 90:935, 2006. (3) L. P. Moreno et al. Rev. Mex. Fitopatol. 22:187, 2004. (4) V. R. Ramirez-Rodriguez et al. Virol. J. 6:48, 2009.