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The Relationship Between Aphid-Transmissibility of Potato Leafroll Virus and Surface Epitopes of the Viral Capsid. J. F. J. M. van den Heuvel, DLO Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW Wageningen, The Netherlands; M. Verbeek(2), and D. Peters(3). (2)DLO Research Institute for Plant Protection (IPO-DLO), P.O. Box 9060, 6700 GW Wageningen, The Netherlands; (3)Department of Virology, Wageningen Agricultural University, P.O. Box 8045, 6700 EM Wageningen, The Netherlands. Phytopathology 83:1125-1129. Accepted for publication 15 June 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/Phyto-83-1125.

A panel of nine monoclonal antibodies (MAbs) was used to investigate the relationship between aphid-transmissibility and surface epitopes of the capsid of potato leafroll virus (PLRV). In immunoblocking experiments, mixtures of purified PLRV and MAbs were fed to 1-day-old Myzus persicae nymphs, and their transmission efficiency was then studied. The MAbs were applied in triple-antibody sandwich enzyme-linked immunosorbent assay (TAS ELISA) to characterize antigenically two phenotypic variants of the Wageningen isolate of PLRV (PLRV-Wag) that differ in transmissibility and a highly aphid-transmissible isolate of PLRV. It was previously established that these MAbs reacted with epitopes exposed on the surface of the virion. However, the MAbs can be separated into two groups on the basis of their reactivity with intact and disrupted particles of PLRV. One group of six MAbs identified epitopes located on individual subunits of the viral capsid, since they reacted equally well with either conformational state of the virus. Four of these MAbsóWAU-A5, -A6, -A7, and -A13óaffected the transmission of PLRV in immunoblocking experiments by significantly increasing the latency period of the virus in the aphid. The epitopes to which they are directed were previously found to be closely related topologically. WAU-A13 reacted significantly more strongly in TAS ELISA with the readily transmitted phenotypic variant of PLRV-Wag isolated from upper leaves of Physalis floridana than with the poorly transmissible variant from lower leaves. The other MAbs did not differentiate between these variants. Only WAU-A13 detected a highly aphid-transmissible isolate of PLRV (hat-PLRV) obtained after a selective transmission pressure was exerted on PLRV-Wag. Thus the epitope delineated by this MAb or topologically related capsid domains might be associated with the aphid transmission of PLRV. Western blot analysis of purified PLRV revealed the presence of two proteins with molecular masses of 23 and 56 kDa. Since WAU-A13 tagged both capsid-associated proteins, this MAb is specific for the major coat protein species of 23 kDa. The second group of MAbsóWAU-A12, -A24, and -B9óreacted exclusively with intact particles of PLRV, which suggests that they are directed to epitopes that depend on the quarternary protein structure. These MAbs did not interfere in PLRV transmission in the immunoblocking experiments, did not detect hat-PLRV, and were hardly reactive to the readily transmissible variant of PLRV-Wag compared to the poorly transmissible one. The epitopes delineated by these MAbs therefore could not be associated with aphid-transmissibility.

Additional keywords: luteovirus, persistent virus transmission.