Abstract
The dagger nematode, (Xiphinema rivesi Dalmasso), a member of the X. americanum group, was first reported in 2002 in Chile (3). X. rivesi is a vector of at least four North American nepoviruses including Cherry rasp leaf virus (CRLV), Tobacco ringspot virus (TobRSV), Tomato ringspot virus (TomRSV), and Peach rosette mosaic virus (PRMV) (2). TomRSV, first reported in Chile in 1984, was associated with raspberry decline and lately with brownline disease in D'Agen prune trees (1), however none of the Xiphinema spp. found in Chile have been reported to transmit this nepovirus. Two virus isolates, TomRSV (prune brownline isolate PBL-08) and Grapevine fanleaf virus (GFLV) (Yellow mosaic isolate GFLV-012), from the virus collection of the Departamento de Sanidad Vegetal, Universidad de Chile were used in transmission tests with a population of X. rivesi found in Chile. X. rivesi is not known to transmit GFLV and this virus was included as a check. The nematodes were extracted from soil from a D'Agen prune orchard, and transmission tests were done in compliance with the criteria proposed by Trudgill et al. (4). Cucumis sativus cv. National Pickling were grown in a growth chamber at 25°C and used as acquisition hosts and transmission bait plants. Acquisition hosts were mechanically inoculated with GFLV or TomRSV, displaying systemic symptoms in 15 to 20 days. Noninoculated cucumber plants were included as controls. Virus infection was confirmed by double-antibody sandwich (DAS)-ELISA before the introduction of nematodes to the soil. After a 20-day acquisition feeding period, the nematodes were wet screened from the soil and added to the healthy bait plants and allowed a 20-day inoculation feeding period. X. rivesi transmitted TomRSV but not GFLV. TomRSV bait plants developed systemic symptoms 5 weeks after the nematodes were transferred. Transmission of TomRSV was confirmed by testing leaf and root sap of bait plants in a DAS-ELISA. High virus concentrations were detected in the roots and leaves of TomRSV symptomatic plants. Bait plants on which nematodes had been allowed to feed following virus acquisition from GFLV-infected or from virus-free control plants tested negative by ELISA. No symptoms appeared on bait plants used for GFLV transmission or the control bait plants. To our knowledge, this is the first report of transmission of TomRSV with a Xiphinema population from Chile and South America.
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