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Reduction of Disease Incidence in Small Field Plots by Isolate-Specific Resistance to Barley Yellow Dwarf Virus. Stewart M. Gray, Research plant pathologist, USDA, ARS, and associate professor, Cornell University, Ithaca, NY 14853; Dawn Smith(2), and Mark Sorrells(3). (2)research technician, Department of Plant Pathology Cornell University, Ithaca, NY 14853; (3)professor, Department of Plant Breeding and Biometry, Cornell University, Ithaca, NY 14853. Phytopathology 84:713-718. Accepted for publication 19 April 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994. DOI: 10.1094/Phyto-84-713.

Epidemics of two isolates, RMV and MAV, of barley yellow dwarf virus (BYDV) were studied in three spring oat genotypes. Two of the genotypes previously were found to possess varying levels of resistance expressed as a reduction in the accumulation of virus antigen titer in plants. The reduced virus antigen titer contributed to reduced virus acquisition and transmission efficiencies by aphid vectors. The third genotype was susceptible to the two BYDV isolates. Resistance was expressed at high levels against the RMV isolate; and in 1990 and 1991, the final disease incidence of RMV and rate of disease progress were significantly reduced in the resistant genotypes relative to the susceptible genotype. The resistance reduced both rate of disease progress and final disease incidence of the MAV isolate during both years of the study. The magnitude of the reduction in final MAV incidence relative to the susceptible genotype varied between the 2 yr and could be related to vector population intensity and environmental factors. Resistance expressed as reduced or suppressed virus accumulation in plants can be easily identified by serological or nucleic acid-based assays. The lower virus titer may reduce disease impact on plant growth and can reduce the efficiency with which aphid vectors acquire and transmit virus among resistant plants.