Barley Yellow Dwarf: A Multifacited Virus-Aphid-Plant Problem That Will Require an Integrated Solution
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Stewart M. Gray, USDA, ARS, Department of Plant Pathology, Cornell University, 334 Plant Science, Ithaca, NY 14853, USA

Barley yellow dwarf virus (BYDV) infects a wide variety of grain crops and countless wild grasses. The disease it causes, barley yellow dwarf (BYD), is a cosmopolitan problem and can be devastating to grain production in epidemic years and problematic in most other years. It is doubtful the true impact of BYD on cereal crop production is known for a majority of geographic regions. The disease may appear similar in most regions, but the fact is the dynamics and the components of the disease vary widely from region to region. Barley yellow dwarf virus is actually several different viruses and virus strains. Although they share some common features, the specificity of virus-plant and virus-aphid interactions can be very different. Each virus may have a different aphid vector species and/or the transmission efficiencies can differ. Similarly the ability to infect a plant or to avoid plant defense responses may differ among the various viruses or virus strains. Furthermore, all the BYDV's are totally dependent upon their aphid vectors to move about and this can have a profound influence on determining the virus host range and development of disease epidemics. BYD disease dynamics from two geographical regions will be discussed with particular emphasis on how intraspecific variability in viruses, aphids and plants can influence disease development and disease management. BYD is a controllable disease, however, some critical information that will identify the most important vectors and the characteristics of virus spread within the crop will facilitate the optimization of disease control practices. These critical pieces of information may differ in each geographical area, but fortunately, may be consistent over time.

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