Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2011
Publication Date: 9/15/2011
Citation: Kerlan, C., Nikolaeva, O.V., Hu, X., Meacham, T., Gray, S.M., Karasev, A. 2011. Identification of the molecular make-up of the Potato virus Y strain PVYZ: genetic typing of the PVYZ-NTN. Phytopathology. 101:1052-1060. Interpretive Summary: Isolates of Potato virus Y (PVY) are classified into strain groups either on the basis of biological characteristics of the virus or genetic characteristics by measuring disease reactions on a set of potato cultivars. The former is most often used in the United States, the latter in Europe. Here we report on the biological and genetic characterization of an unusual class of PVY isolates discovered during a study of the diversity of PVY infecting potato in the U.S. This new class of PVY resembles the tuber necrotic strain of PVY recently introduced into North America, but it also resembles a strain of PVY, PVYz, that was once described from Europe. The European isolates are no longer available for direct comparison, but we report on the complete characterization of what can now be described as PVYz and can now be used as a worldwide standard in the new classification of this group of viruses.
Technical Abstract: Potato virus Y (PVY) strains were originally defined by interactions with different resistance genes in standard potato cultivars. In the most recent classification, five distinct strain groups are defined that cause local and/or systemic hypersensitive response in the genetic background with a corresponding N gene, these were PVYO, PVYN, PVYC, PVYZ and PVYE. The nucleotide sequences of multiple isolates of PVYO and PVYN are known and differ from each other by about 8% along their genomes. Additionally, complete genome sequences of multiple recombinant isolates have been found to be composed of segments of parental PVYO and PVYN sequences. Here, we report that a recently found recombinant isolate PVY-L26 induces a hypersensitive response (HR) in the potato cultivar Maris Bard carrying the putative Nz gene, and is not recognized by two other resistance genes, Nc and Nytbr. These genetic responses in potato, combined with the inability of PVY-L26 to induce vein necrosis in tobacco, clearly define it as an isolate from the PVYZ strain group and provide the first information on genome structure and sequence of this PVYZ strain. The genome of the PVY-L26 isolate displays typical features of PVYEU-NTN isolates, i.e. European NTN type with three recombinant junctions, and thus the PVY-L26 isolate could be considered as PVYZ-NTN. Three typical PVYNTN isolates and two PVYN isolates, inducing vein necrosis in tobacco, were compared with PVY-L26. One PVYNTN isolate elicited HR reactions in cv Maris Bard, similar to PVY-L26, while two induced a severe systemic HR-like reaction quite different from the quasi-symptomless reaction induced by two PVYN isolates. Yukon Gold, a North American potato cultivar was shown to produce HR against several tested PVYNTN isolates, including PVY-L26, but only late and limited systemic necrosis against one PVYN isolate. Both PVYZ and PVYNTN isolates, consequently, according to symptoms in potato indicators appeared biologically very close and clearly distinct from PVYO and PVYN strain groups.