Differential pathogenicity of two different recombinant PVY.sup.NTN .sup.isolates in Physalis floridana is likely determined by the coat protein gene

A previous study has identified two types of recombinant variants of Potato virus Y strain NTN (PVY.sup.NTN.sup.) in China and sequenced the complete genome of the variant PVY.sup.NTN.sup.-HN2. In this study, the complete genome of isolate PVY.sup.NTN.sup.-HN1 was fully sequenced and analyzed. The most striking difference between the two variants was the location of recombinant joint three (RJ3). In PVY.sup.NTN.sup.-HN1, like other typical European-PVY.sup.NTN .sup.isolates such as PVY.sup.NTN.sup.-Hun, the RJ3 was located at nucleotide (nt) 9183, namely the 3' proximal end of the CP gene (nt. 8571-9371), thus leading to most (the first 613 nucleotides from the 5' proximal end) of the CP gene (801 bp) with a PVY.sup.N .sup.origin and PVY.sup.N.sup.-serotype; whereas in contrast, the RJ3 in PVY.sup.NTN.sup.-HN2 was located at nt 8572, consequently leading to a CP gene of PVY.sup.O .sup.origin and PVY.sup.O.sup.-serotype. The varied genome composition among PVY.sup.O.sup., PVY.sup.N.sup., PVY.sup.N:O.sup., PVY.sup.NTN.sup.-HN1 and PVY.sup.NTN.sup.-HN2 made them useful for the investigation of possible roles of gene segment(s) in symptom formation on host plants. When Physalis floridana plants were infected with different PVY isolates, two types of symptoms were induced. PVY.sup.N .sup.and PVY.sup.NTN.sup.-HN1 induced mild symptoms (mainly mild mottling) whereas PVY.sup.O.sup., PVY.sup.N:O .sup.and PVY.sup.NTN.sup.-HN2 induced serve symptoms including leaf and stem necrosis, leaf-drop and stunting. These results, together with a previous study using artificial PVY chimeras, demonstrate that the CP gene, especially the 5' proximal segment (nt 8572-9183), and/or CP likely determine the pathogenicity of PVY in P. floridana.