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Title: FEEDING BEHAVIOR OF BIOTYPES E AND H OF GREENBUG (HOMOPTERA: APHIDIDAE) ON PREVIOUSLY INFESTED NEAR-ISOLINES OF BARLEY

Author
item Hays, Dirk
item Porter, David
item Webster, James
item CARVER, BRETT - OKLAHOMA STATE UNIVERSITY

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/16/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The greenbug aphid is a serious pest of small grains in the Southern Plains. Currently, the main line of defense against greenbugs is use of environmentally unfriendly insecticides. Development of greenbug-resistant small grains through traditional breeding practices offers the most economical solution. Presently, there are several sources of resistance to greenbugs in wheat and barley, but a mechanism of resistance to greenbugs has yet to be described. We used greenbug feeding behavior as the biological assay for determining the mechanism of resistance. Using an electronic feeding monitor, we examined the feeding behavior of virulent (lethal to plant) and avirulent (not lethal to plant) biotypes of greenbug following pre-infestation of the plant with greenbugs. A pair of barley lines that differ by the inheritance of greenbug resistance gene Rsg1a was used as the genetic model. When feeding on Rsg1a plants, biotype E ingested dfood from the phloem 4- to 8-fold less when compared with biotype E feedin on plants without the Rsg1a gene (Rsg1a-) or biotype H feeding on either isoline. When biotype H was monitored on Rsg1a plants that were pre-infested for 24 hours with biotype E, biotype H fed in the phloem 4-fold less often. This reduction did not occur for biotype H when monitored on Rsg1a- plants pre-infested with biotype E or on Rsg1a pre-infested with biotype H. These results suggest that like many plant resistance mechanisms to plant pathogens, the Rsg1a gene confers an induced form of resistance triggered by plant recognition of a nonlethal greenbug biotype. This knowledge may help in the development of new greenbug resistant cultivars of wheat and barley or an environmentally friendly alternative to insecticides.

Technical Abstract: The feeding behavior of virulent and avirulent greenbug biotypes following preconditioning of the plant with virulent and avirulent greenbug biotypes was examined. A pair of near-isolines of barley (Hordeum vulgare L.) which differ by the presence of the antibiosis greenbug-resistance gene Rsg1a was used. The Rsg1a gene confers resistance to all greenbug biotypes except biotypes H and J. When the data of a 7-h feeding monitor period were divided into two time periods (0 to 210 min and 210 to 420 min), differences in feeding behavior were noted during the second period. When feeding on Rsg1a+ plants, biotype E probed 3.5-fold more frequently and fed in the phloem 5- to 8-fold less when compared with biotype E feeding on Rsg1a- plants or H feeding on either isoline. The feeding behavior of biotype E was not improved by preconditioning Rsg1a+ plants with biotype H, indicating that biotype E did not lack the ability to condition the feeding gsite. However, when biotype H was monitored on Rsg1a+ plants that were pre conditioned for 24 h with biotype E, biotype H probed 2-fold and fed in the nonphloem 4-fold more often while feeding 4-fold less time in the phloem. This reduction did not occur for biotype H when monitored on Rsg1a- plants that had been preconditioned with biotype E or on Rsg1a+ that had been preconditioned with biotype H. These results suggest that the Rsg1a gene confers an induced form of resistance triggered by plant recognition of an avirulent greenbug biotype.