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Barley Yellow Dwarf: Dependent Virus Transmission by Rhopalosiphum maidis from Mixed Infections. W. F. Rochow, Research Plant Pathologist, Northeast Region, Agricultural Research Service, U.S. Department of Agriculture, and Professor of Plant Pathology, Cornell University, Ithaca, New York 14850; Phytopathology 65:99-105. Accepted for publication 1 August 1974. DOI: 10.1094/Phyto-65-99.

Rhopalosiphum maidis very rarely transmitted the MAV isolate of barley yellow dwarf virus from MAV-infected plants, but it often transmitted MAV, together with the RMV isolate, from plants doubly infected by RMV and MAV. This dependent transmission of MAV by R. maidis occurred from barley and oats, from oats at intervals from 2 and 6 weeks after inoculation of the doubly infected source plants, and from oats infected by either of the virus isolates 12 days before the other was introduced. Serological tests confirmed the identity of MAV transmitted dependently by R. maidis. No dependent virus transmission occurred when R. maidis first fed on plants infected by one virus isolate before feeding on plants infected by the other virus isolate. Although the dependent transmission of MAV by R. maidis is similar to the previously studied dependent transmission of MAV by R. padi (in the presence of RPV), there are two main differences. Mixed infections are not maintained indefinitely in serial transfers by R. maidis, as they are by R. padi, and the phenomenon has not occurred to date in tests of purified preparations made from plants infected by RMV and MAV. The helper viruses were specific for each vector–R. padi did not transmit MAV from plants infected by RMV and MAV, nor did R. maidis transmit MAV from plants infected by RPV and MAV.