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An Isolate of Barley Yellow Dwarf Virus Transmitted Specifically by Schizaphis graminum. Rebecca A. Johnson, Graduate Assistant, and Research Plant Pathologist, Plant Science Research Division, ARS, USDA, Cornell University, Ithaca, New York 14850; W. F. Rochow, Professor of Plant Pathology, Cornell University, Ithaca, New York 14850. Phytopathology 62:921-925. Accepted for publication 28 February 1972. DOI: 10.1094/Phyto-62-921.

An isolate of barley yellow dwarf virus (BYDV), SGV, differed from those previously studied in New York because it was transmitted specifically by Schizaphis graminum. Specificity of SGV was relative, not absolute; Rhopalosiphum padi was more likely to effect an occasional transmission of SGV than was R. maidis or Macrosiphum avenae. Rearing aphids on SGV-infected plants increased chances for such occasional transmissions. Specificity of SGV was not altered after occasional transmissions by “nonvector” aphids, by feeding any of the aphid species at 20, 25, or 30 C, by passage of SGV through several varieties of oats, wheat, or barley, or by mixed infections with other BYDV isolates. Injections of a concentrate of SGV into S. graminum and subsequent daily serial transfers of individual aphids showed that SGV has a typical circulative or persistent relationship with its vector. S. graminum was more likely to transmit SGV as length of acquisition feedings on detached leaves was increased (1-5 days), and as longer inoculation test feeding periods (1-5 days) were used. The aphid was more likely to transmit SGV when fed on seedlings at 20 or 25 C than at 30 C. A major factor affecting transmission of SGV was the age of S. graminum. Individual first- or second-instar nymphs transmitted virus to 56 of 164 plants; only 8 of 164 plants became infected in parallel tests with adults.