Identification of Russian Wheat Aphid (RWA) Resistant Barley Accessions

Previous screening of 23,070 accessions of Hordeum vulgare from the National Small Grains Collection in Aberdeen identified 114 accessions with some level of resistance to RWA. Of the 109 resistant lines selected out of these accessions, 44 are resistant based on Webster's scale of 1 to 9 where seedlings with chlorosis ratings of 1 to 3 are resistant, 4 to 6 are moderately resistant to moderately susceptible, and 7 to 9 are susceptible. An additional 62 lines were found to be moderately resistant to moderately susceptible. Moderately resistant lines are currently being selected from five accessions identified as segregating for a moderate level of resistant in 1994. One of the newly selected resistant lines is a 2-row barley. This is the first 2-row to be found with a resistance higher than 4-6 on Webster's scale.

New Release

RWA resistant germplasm line STARS-9577B was released to breeders in the spring of 1996. STARS-9577B is a 6-row spring barley with a greenhouse seedling resistance rating of 3 on Webster's scale of 1-9. Two years of field study in Wyoming has shown this line to have no significant yield reduction under artificial field infestations. Genetic analysis has shown RWA resistance of this line to be under the control of two genes. Both genes appear to be dominant with recessive epistasis. This inheritance differs from the inheritance in RWA-resistant barley germplasm line STARS-9301B. The primary mechanism of resistance in STARS-9577B appears to be tolerance.

Germplasm Enhancement

A total of 217 crosses were made in the greenhouse in 1995 with two main objectives (1) obtain populations for genetic studies and (2) prebreeding purposes. One-hundred and twenty-one BC's were make for prebreeding / future genetic studies, fifty-seven F1's and or RF1's between resistant lines and susceptible cultivars were made for prebreeding /genetic studies, twenty-one F1's between resistant lines were made for future tests for genetic diversity, and eighteen testcrosses were made between the F₁ of two resistant lines a susceptible cultivar for genetic diversity studies. One-hundred and eleven F2 populations were increased for future genetic analysis, as well as 300 F2-derived F3 families for each of 16 populations.

Genetic studies

Parents, F₁, F₂ and BC(s) to both parents as well as 300 F₂-derived F₃ families have been evaluated for two resistant lines. F₃ analysis indicates multiple gene control for both of these lines . Interpretation of gene action from the F₁, RF₁, F₂ and BC to both parents has yet to be completed.

Field Studies

Data collection and analysis on the second year of a field test to determine the level of seedling resistance in the greenhouse which translates to field resistance continued. Samples were sent to the USDA Cereal Crops Research Unit in Madison, WI for malting. Preliminary analysis suggests that RWA resistance may not exist in terms of malting quality. It appears the malting quality of lines quite resistant in terms of grain yield was negatively affected by RWA infestation. A new study is being designed for 1997 to test the effect of RWA feeding on malt quality. In preparation for this study, 65 resistant spring barleys and check plots of Harrington, Morex and Robust were grown in Aberdeen ID to determine malting quality under optimum growing conditions.

Mechanisms of Resistance

Analysis is ongoing for antixenosis, antibiosis and tolerance tests conducted for six RWA resistant lines including STARS-9301B. Tests to determine the mechanisms of resistance in five more lines, including STARS-9577B, is currently being conducted.

Cooperative Efforts

Screening of three-hundred twenty-eight advanced generation populations, three-hundred fifty-nine BC populations, and 64 doubled haploids was performed for a total of six breeders. Homozygous resistant lines were identified and resistant individuals from heterozygous lines were rescued and seed increased for rescreen next year.

Germplasm Enhancement

Dolores W. Mornhinweg, Geneticist

David R. Porter, Research Geneticist

Host Plant Resistance

James A. Webster, Research Entomologist

Keith A. Mirkes, Biological Science Technician

Cooperators at the University of Wyoming

Michael Brewer, Entomologist

Jane Struttmann, Entomology Technician

Chris Oswald II, Graduate Research Assistant

Mornhinweg, D.W., D.R. Porter, and J.A. Webster. 1995. Inheritance of Russian wheat aphid resistance in spring barley. Crop Sci. 35:1368-1371.

Mornhinweg, D.W., D.R. Porter, and J.A. Webster. 1995. Registration of STARS- 9301B Russian wheat aphid resistant barley germplasm. Crop Sci. 35: 602.

Mornhinweg, D.W., D.R. Porter, and J.A. Webster. 1995. Inheritance of RWA resistance in barley germplasm line STARS-9301B. Agron. Abst. American Society of Agronomy, Madison, WI. p. 88.

Mornhinweg, D.W., D.R. Porter, J.A. Webster, M.J. Brewer, and B.L. Jones. 1995. A serious pest of malting barley: Russian wheat aphid. ASBC Newsletter vol. 55 (2):31.