OCCURRENCE AND PARTIAL CHARACTERIZATION OF A NEW MECHANICALLY TRANSMISSIBLE VIRUS IN MASHUA FROM THE ECUADORIAN HIGHLANDS

Mashua (Tropaeolum tuberosum) is a tuber crop indigenous to the Andean highlands and of economic value to its native people as a food and me dicinal crop. Field plants often exhibit symptoms typical of virus inf ection, including interveinal chlorosis, leaf cupping, distortion, and stunting. Using an herbaceous host range, at least 1 mechanically tra nsmissible virus was detected in each of 10 accessions. All virus isol ates tested reacted to potyvirus group antiserum in indirect enzyme-li nked immunosorbent assays (ELISA). Results of monoclonal antibody test ing using antigen coated plate (ACP) ELISA, where virions are disrupte d to expose cryptotopes, indicated that isolate Tt 4 has epitopes in c ommon with maize dwarf mosaic potyvirus A (MDMV-A). Polyclonal antiser um produced to purified preparations of the Tt 4 isolate reacted in in direct ELISA to Tt 4, the common strain of potato potyvirus Y (PVY-C), less strongly to tobacco etch potyvirus (TEV) and potato potyvirus A (PVA), but not to 11 other potyviruses, including MDMV-A. Conversely t he Tt 4 isolate reacted strongly in indirect ELISA to antisera to bean common mosaic potyvirus (BCMV) and watermelon mosaic potyvirus 2 (WMV -2), but not antisera to 12 other potyviruses. Our data suggest that i solate Tt 4 is a distinct potyvirus closely related to and sharing ext ernal epitopes with PVY-C, TEV, PVA, WMV-2, and BCMV, and buried epito pes with MDMV-A. The virus has been tentatively named Tropaeolum mosai c potyvirus (TropMV). A survey of T. tuberosum in Ecuador revealed tha t TropMV was widespread, being detected by ACP-ELISA in 34 of 46 acces sions at the National Institute for Agricultural Research's Santa Cata lina Research Station, Quite, and all eight production fields surveyed .