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Synergism in Cereals Between Corn Leaf Aphid-Specific and Aphid-Nonspecific Isolates of Barley Yellow Dwarf Virus. C. C. Gill, Research Scientist, Agriculture Canada Research Stations, 195 Dafoe Road, Winnipeg, Manitoba, R3T 2M9; A. Comeau, Research Scientist, 2560 Chemin Gomin, Sainte-Foy, Québec, Canada, G1V 2J3. Phytopathology 67:1388-1392. Accepted for publication 16 May 1977. Copyright © 1977 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-67-1388.

In greenhouse experiments with Rodney oats and Herta barley, seed yields from plants inoculated simultaneously (doubly inoculated) with an aphid-nonspecific (7410) and a Rhopalosiphum maidis-specific (7413) isolate of barley yellow dwarf virus were significantly lower than yields from plants inoculated with only one or the other isolate. Five cereals also were tested in a field experiment in which plants were doubly inoculated either simultaneously with both isolates early (late tillering stage) or with both late (jointing stage), or with one isolate early and the second late in reciprocal treatments. Seed yields from doubly inoculated Rodney, Hudson, and FF64-74 oats and from Bonanza barley were lower than yields from both of the relevant singly inoculated controls, except for one of the four double-inoculation treatments with the tolerant oat, FF64-74. The differences were significant for three of the four double inoculations with Rodney and for one with Hudson. Synergism was not evident on Herta barley. The results from double inoculation of this cultivar may have been affected by a stimulatory effect on seed yield when the plants were inoculated early with isolate 7413 (38% higher yield than on noninoculated plants). When Herta barley was inoculated in a growth cabinet with either one of the isolates first and then, after a period of 4 or 10 days, with the other, both isolates were recovered from the inoculated plants, indicating lack of protection between the isolates.