Greenbug has exhibited biotype development since the early 1960’s when biotypes A and B were identified. Biotypes are designated by their ability to damage resistant crop varieties. To date, 11 biotypes have been identified, four of which are important on sorghum. The reasons underlying biotype development are unclear and the question remains why some biotypes are virulent while others are not. Variability in characteristics such as virulence (damage) and fitness within greenbug clones could be important in biotype development. We examined the virulence and fitness of colonies of six greenbug biotypes grown on four sorghum genotypes. Seedlings were infested with approximately 30 greenbugs and placed in an environmental chamber. Colonies were counted at 3 day intervals until Tx7000 (susceptible check) was rating at a 7 or higher on a 9 point damage scale. All plants were then rated. Tx7000 incurred high levels of damage from all six biotypes, however biotype A caused significantly less damage than the other biotypes (F=3.07, p=0.03, N=32) and had large variability in damage rating (range 4 – 9). Mean colony size (82.2) 10 days post infestation for biotype A on Tx7000 did not differ significantly from the other genotypes (F=0.117, p > 0.05, N=20), due to large variability within biotype A. There was a significant biotype*genotype interaction (F=2.45, p=0.003, N=283) in virulence for all biotypes on all genotypes, suggesting a complex interaction between greenbug biotypes and their hosts. Plasticity for fitness and virulence measures was complex for the remaining greenbug biotypes and will be discussed. Large variability within biotype clones may be an important in biotype development. Susceptible plants may allow this variability to persist in nature and resistant plants would provide the selection necessary to allow the detection of “new” biotypes.
Species 1: Homoptera Aphididae Schizaphis graminum (greenbug)
Keywords: biotypes
The ESA 2001 Annual Meeting - 2001: An Entomological Odyssey of ESA