Author
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BURD, JOHN |
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Submitted to: Workshop Proceedings
Publication Type: Proceedings Publication Acceptance Date: 7/1/2009 Publication Date: 8/11/2009 Citation: Burd, J.D. 2009. Management of greenbug biotypes in wheat-sorghum cropping systems. In: National Sorghum Producers Research Conference, August 10-12, 2009, Amarillo, TX. Interpretive Summary: Technical Abstract: Strategies for deploying crop cultivars with durable resistance to insects have for years been the focus of considerable debate and speculation. Interpretation of elaborate simulation models used to predict durability of resistance has led to the generally accepted paradigm that the widespread use of an insect-resistant cultivar with a single, major gene for resistance will be selective for new, virulent biotypes. Research has shown that this breeding tenet does not hold for the greenbug (Schizaphis graminum). A greenbug biotype is defined as an infraspecific population, independent of geographic distribution that is able to injure a plant containing specific resistant gene(s) that are resistant to other infraspecific populations. Moreover, there is no presumption of the genetic basis within the greenbug for the ability to cause injury, nor is any evolutionary or taxonomic status implied. Obviously, there are genetic differences among greenbug biotypes, which affect feeding behavior and the phenotypic response of the plant. However, the term biotype does not describe those differences, nor does it require knowledge of the biotype-specific traits that induce the damage symptoms. Thus, we conclude that a greenbug biotype is merely a plant phenotypic expression elicited by an indefinite number of genotypes. Greenbug virulence on crops does not coincide with greenbug fitness, and the use of plant resistance has not selected for more virulent biotypes. Instead, the greenbug species complex is made up of host-adapted races that have diverged on non-cultivated grass species well before the advent of modern agriculture, and biotypes are comprised of genetically diverse individuals among different host races that merely share similar virulence genes. Plant resistance to greenbugs will continue to be an important strategy in pest management; however, we question the tenet that places an emphasis on releasing tolerant, multigenic cultivars and deemphasizes antibiotic, simply inherited greenbug resistance. |
