Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/18/2017
Publication Date: 8/28/2017
Citation: Mornhinweg, D.W., Armstrong, J.S., Puterka, G.J. 2017. New greenbug resistant sources in winter barley, Hordeum vulgare (L.). Southwestern Entomologist. 42(3):619-626.
Interpretive Summary: Greenbug is a serious pest of small grains worldwide and a persistent pest of wheat and barley in the western U.S., especially in the southern Great Plains. Central to the pest status of greenbug is the occurrence of resistance-breaking biotypes which can damage previously resistant plants. Resistant cultivars are much preferred over insecticide applications which are economically and environmentally costly. Two single dominant genes for greenbug resistance, Rsg1 and Rsg2, have been reported in barley. All greenbug resistant U.S. barley cultivars have Rsg1 resistance. U.S. barley is genetically vulnerable to biotype changes that often occur. Five lines with potentially new greenbug resistance genes were tested along with an Rsg1 cultivar and Rsg2 germplasm line against 14 greenbug biotypes. Four lines showed unique responses compared to Rsg1 and Rsg2 as well as each other. These new sources of resistance give breeders more genes for deployment in cultivars which are essential to reduce the vulnerability of barley to greenbug attack in the U.S.
Technical Abstract: Greenbug, Schizaphis graminum (Rondonai), is a chronic problem for small grains in the Southern Plains causing significant economic losses in outbreak years. Central to the pest status of greenbug is the occurrence of resistance-breaking biotypes. Rsg1 and Rsg2 are the only 2 genes for greenbug resistance in barley, Hordeum vulgare (L.), and only Rsg1 has been deployed in cultivars. Discovery of new resistant genes is essential to ensure resistance as biotypes continue to shift. Five winter barley accessions, PI 499276, PI 565657, PI 566459, CI 2458, and PI 565676, previously found to be resistant to greenbug biotype E, along with 'Post 90' (Rsg1), STARS 1501B (Rsg2), and susceptible cultivar 'Schuyler', were screened in isolated cages against 14 greenbug biotypes: B, C, E, F, H, I, TX1, WY4 A, WY4 B, WY10 MC, WY81, WY10 B, WY12 MC, and WY86. Visual damage ratings were based on the Starks and Burton chlorosis rating scale of 1 - 9 where 1 is resistant and 9 is dead. Damage means were classified as R or S and used to construct a response matrix which suggested unique genes for resistance in four of the five lines. Inheritance studies as well as multiple allele testing to determine the number of genes, gene, action and genetic diversity in these lines will be conducted in the future. These new sources of resistance have the potential to reduce the vulnerability of barley to future greenbug outbreaks.