Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 24, 2006
Publication Date: April 2, 2007
Citation: Porter, D.R., Burd, J.D., Mornhinweg, D.W. 2007. Differentiating greenbug resistance genes in barley. Euphytica. 153:11-14. Interpretive Summary: The greenbug is a devastating insect pest of barley production in the southern Great Plains. There are two resistance genes in barley (Rsg1a and Rsg2b) that provide protection from greenbug attack. However, the responses of these two genes have not been able to be separated by greenbug feeding damage. We conducted this study to show that a newly detected virulent population of greenbug can now differentiate the two resistance genes. One greenbug isolate used in this study (TX1) was able to differentiate Rsg1a from Rsg2b through dramatically different plant responses (Rsg2b conferred resistance, Rsg1a did not). This information is important to barley breeders as they decide which of the two genes to use in developing new pest resistant barley varieties. Also, based on the results of this study, the designations of these resistance genes were changed from Rsg1a to Rsg1, and from Rsg2b to Rsg2.
Technical Abstract: The greenbug [Schizaphis graminum (Rondani)] is an extremely damaging pest of barley (Hordeum vulgare L), particularly in the southern Great Plains of the USA. Two greenbug resistance genes, Rsg1a (in Post 90) and Rsg2b (in PI 426756), available for developing resistant barley cultivars, have similar phenotypes when challenged by various greenbug biotypes. This study was conducted to separate these two resistance genes via differential plant reactions to a recently collected field isolate of greenbug. Four barley entries and one wheat germplasm were challenged with two greenbug isolates and damage ratings were recorded for each combination. One greenbug isolate used in this study (TX1) was able to differentiate Rsg1a from Rsg2b through dramatically different plant responses (Rsg2b conferred resistance, Rsg1a did not). The results indicate a significant level of genetic diversity within greenbug for virulence, and points to the potential vulnerability of greenbug resistance genes in barley. Based on these and other reported results, we propose that gene symbol designations for greenbug resistance in barley be changed from Rsg1a to Rsg1 and Rsg2b to Rsg2.