Greenbug is a key insect pest of small grains and sorghum throughout many parts of the world. Biotypes can overcome host plant resistance, which is the most cost effective means of greenbug control in sorghum. Although larger colonies may generally be associated with greater plant damage, the interaction is biotype/plant genotype dependent. The present study identified the relationship between aphid colony size and plant damage in 4 greenbug biotype and 5 sorghum genotype combinations in a full factorial design. Non-choice tests were initiated by growing plants to the 3-leaf stage and infesting with ~ 30 adult and nymphal greenbugs. Pots were then covered with cages and placed in environmental chambers. Colony sizes were determined by counting aphids at 3 day intervals beginning 1 day post infestation. Plant damage was determined using a 9 point rating scale at the time when the susceptible check was rated at 7. Pooled data suggested that damage was higher in sorghum plants supporting larger colonies, however this was highly dependent on the biotype/genotype combination. Significant interaction effects were identified, indicating that some combinations did not follow the overall positive trend. These results show that although large colonies may be associated with higher plant damage in general, aphid/plant interactions are more complex than may seem initially “to be the case.”
Species 1: Homoptera Aphididae Schizaphis graminum (greenbug)
Keywords: biotype, host plant resistance
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