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Importance of Virus Source Leaves in Vector Specificity of Barley Yellow Dwarf Virus. M. J. Foxe, Former Graduate Research Assistant, Department of Plant Pathology, Cornell University, Ithaca, New York (Currently Lecturer, Department of Plant Pathology, University College, Dublin, Ireland); W. F. Rochow, Research Plant Pathologist, Crops Research Division, Agricultural Research Service (ARS), U.S. Department of Agriculture (USDA), and Professor of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 65:1124-1129. Accepted for publication 29 April 1975. DOI: 10.1094/Phyto-65-1124.

The age of leaf from which aphids acquired virus affected virus transmission in tests with two isolates of barley yellow dwarf virus, but not with a third. Although the vector Macrosiphum avenae transmitted the MAV isolate efficiently from all leaves, Rhopalosiphum padi was much more likely to effect an occasional transmission of MAV from young leaves than from old. In tests with the PAV isolate, R. padi transmitted virus efficiently from all leaves, but M. avenae transmitted PAV regularly only from young leaves. When concentrated preparations were made from the two kinds of leaves, virus titers were higher for both MAV and PAV in preparations of young leaves than in those of old. The average yield of MAV (per 100 g of tissue) was 89 µg from young leaves and 9 µg from old. Corresponding yields of PAV were 20 µg from young and 6 µg from old leaves. When fed through membranes, M. avenae more frequently transmitted PAV acquired from preparations of young leaves than of old ones; the relationship was similar for occasional transmission of MAV by R. padi. In corresponding tests with the RPV isolate, R. padi transmitted the virus regularly from all leaves, but M. avenae was no more likely to transmit RPV from young than from old leaves. Differences were not consistent in virus titer of preparations made from each kind of leaf. The average yield of RPV was 29 µg from 100g of young leaves and 23 µg from old ones. When aphids were fed on concentrates of each kind of leaf, M. avenae was no more likely to effect an occasional transmission from one kind than the other. Virus concentration affected vector specificity, but the amount of virus needed to alter specificity varied with each virus isolate and aphid species. In tests to evaluate use of liquid nitrogen in extraction of BYDV from plants, no more virus was found in RPV preparations made from tissue extracted with liquid nitrogen than in those from parallel preparations made without it. Preparations of the MAV isolate made without liquid nitrogen contained about 47% more virus than parallel preparations made with it.