A novel type of potato virus Y recombinant genome, determined for the genetic strain PVYE

Abstract

Two Potato virus Y (PVY) isolates collected in Brazil, PVY-AGA and PVY-MON, were identified as recombinants between two parent genomes, PVYNTN and PVY-NE-11, with a novel type of genomic pattern. The new recombinants had an ordinary PVYNTN genome structure for approximately 6·7-kb from the 5′-end of the genome whereas the 3′-terminal 3·0-kb segment had two fragments of NE-11-like sequence separated by another small PVYNTN-like fragment. PVY strains are defined based on the hypersensitive resistance (HR) response in potato indicators. Both PVY-AGA and PVY-MON isolates did not induce the HR in potato cultivars carrying Ny, Nc, or (putative) Nz genes and thus were able to overcome all known resistance genes to PVY. Only one of the two isolates, PVY-AGA, induced a vein necrosis reaction in tobacco. The biological responses of the potato indicators and tobacco defined PVY-MON as an isolate of the PVYE strain. To distinguish PVY-AGA and PVY-MON from other PVYNTN isolates, an RT-PCR test was developed utilizing new specific primers from the capsid protein gene area and producing a characteristic 955-bp band. Serological profiling of these PVY isolates with three monoclonal antibodies revealed an unusual reactivity, where one of the two commercial PVYN-specific monoclonal antibodies did not recognize PVY-AGA. The ability of these new PVY recombinants to overcome resistance genes in potato producing mild or no symptoms, combined with the lack of serological reactivity towards at least one PVYN-specific antibody may present a significant threat posed by these isolates to seed potato production areas.