Variation in transmission efficiency among Barley yellow dwarf virus-RMV isolates and clones of the normally inefficient aphid vector, Rhopalosiphum padi

The RMV strain of Barley yellow dwarf virus (BYDV-RMV) is an unassigned mem ber of the Luteoviridae that causes barley yellow dwarf in various cereal c rops. The virus is most efficiently vectored by the aphid Rhopalosiphum mai dis, but can also be vectored with varying efficiency by R. padi and Schiza phis graminum. Field collections of alate aphids migrating into the emergin g winter wheat crop in the fall of 1994 in central New York identified a hi gh proportion of R. padi transmitting BYDV-RMV. This prompted a comparison of the BYDV-RMV isolates and the R. padi populations found in the field wit h type virus and aphid species maintained in the laboratory. A majority of the field isolates of BYDV-RMV were similar to each other and to the type B YDV-RMV isolate in disease severity on oar and in transmission by the labor atory-maintained population of R. maidis and a field-collected population o f R. maidis. However, several field populations of R. padi differed in thei r ability to transmit the various BYDV-RMV isolates. The transmission effic iency of the R. padi clones was increased if acquisition and inoculation fe eding periods were allowed at higher temperatures. In addition, the transmi ssion efficiency of BYDV-RMV was significantly influenced by the aphid that inoculated the virus source tissue. In general, BYDV-RMV transmission by R . padi was higher when R. padi was the aphid that inoculated the source tis sue than when R. maidis was the inoculating aphid. The magnitude of the cha nge varied among virus isolates and R. padi clones. These results indicate that, under certain environmental conditions, R. padi can play a significan t role in the epidemiology of BYDV-RMV. This may be especially significant in regions where corn is a major source of virus and of aphids that can car ry virus into a fall-planted wheat crop.