| Summary: | Virus-host and virus-vector studies were carried out with several vectors and isolates of barley yellow dwarf virus (BYDV) from Manitoba. Interference between certain isolates of BYDV was observed in the plant and, possibly, also in the vector. Serial transfers on test plants of aphids infected with certain isolates of BYDV revealed differences in the pattern of transmission by nymphs and adults. Interference studies were carried out in the plant with a Macrosiphym avenae-specific, a Rhopalosiphum padi-specific, and a non-specific isolate of BYDV. There was reciprocal interference between the M. avenae-specific and the non-specific isolates, both when the isolates were inoculated simultaneously into the plant and when there was a time interval between inoculations. Although no cross protection was evident, the fact that interference occurred between these two isolates in the plant suggested that they were related... In a limited study with a number of different BYDV isolates, three types of effect were observed in the aphid vectors when they were allowed access in succession to a given pair of the isolates... With both of the S. graminum-specific isolates, aphids that acquired virus as nymphs usually lost their ability to transmit after the final moult. With one of these isolates, adults that had access to the virus as nymphs, were less efficient vectors than aphids which had access to the virus as adults.
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