Russian Wheat Aphid (RWA) Resistant Germplasm Lines

Four RWA-resistant barley germplasm lines have been selected and increased from newly identified RWA-resistant accessions from the National Small Grains Collection (NSGC). R044, a 2-row line, and R045, a 6-row line are both highly resistant while MR055 and MR058 are both 6-row lines with a moderate level of RWA resistance. Some potential new sources of resistance were identified in a screening of genetic stocks recently donated to the NSGC by Colorado State University.

Prebreeding for Adapted Germplasm Lines
 

A prebreeding program continues in an attempt to bring resistance genes from unadapted germplasm lines into adapted malting and feed barley backgrounds for all barley growing regions in the U.S. The main thrust is repeated backcrossing with intermittent screening with a time commitment of approximately seven years from the first cross until homozygous resistant BC3F3 lines can be evaluated in the field. This ongoing process involves various resistant lines and adapted cultivars currently at all phases of the program. The summer of 1997 will see the first 300 lines from this program in the field in Aberdeen, ID with the cooperation of Darrell Wesenberg and Phil Bregitizer of the USDA-ARS. These lines involve three different resistant sources and three adapted cultivars, Morex, Crystal and Targhee, and will be evaluated both for agronomics and malting quality. To this end, 200 BC3F2 and 300 BC3F3 were increased in the summer of 1996 both in Aberdeen and Stillwater and the resultant 583 BC3F3/BC3F4 lines were screened for homozygous resistance. Another 18 BC3F1 populations were screened, resistant plants increased and BC3F2 progeny screened again, with 100 resistant BC3F2 identified and transplanted for increase this spring in Stillwater and Aberdeen. Eleven BC3F2 populations were screened and 100 resistant plants transplanted for increase in Stillwater in the spring of 1997. These 29 populations involve eight cultivars and 23 different resistant lines. Nine BC3F1 populations were screened and resistant seedlings transplanted in the greenhouse in Stillwater for increase in the spring of 1997. Twenty-nine BC3, 57 BC2, 43 BC1 and 5 F1 crosses were made towards future adapted RWA-resistant lines to be evaluated in the field in 1999, 2000, 2001 and 2002.

Genetic Studies

Parents, F1, RF1, 150 BC to each parent, 200 F2, and 300 F2-derived F3 families were evaluated for two resistant lines to determine the number of genes and genetic control for RWA resistance in these lines. Analysis is on going. Complete genetic analysis has been performed for eight out of a total of 108 RWA -resistant lines developed by the USDA-ARS in Stillwater. All eight lines have shown multiple gene control for RWA resistance. Seventy-three crosses between homozygous resistant F3 lines and a susceptible were made in an attempt to isolate a single dominant gene for resistance. Sixteen F1 and 46 BC1 crosses were made, 42 F2 populations were increased, and 300 F2-derived F3 families were increased for each of 15 populations for future genetic studies.

Genetic diversity studies are planned for resistant lines to determine if these lines carry different genes for resistance. This type of analysis requires three years for development of seed necessary for each test. One F1 and 19 testcrosses of a resistant x resistant F1 on a susceptible were made and 18 TC1F1 populations were increased to TC1F2 for future genetic diversity studies. Mechanisms of resistance tests also were performed for seven RWA-resistant germplasm lines.

Field Studies

Sixty-five RWA-resistant lines were grown in cooperation with Darrell Wesenberg and Phil Bregitzer, USDA-ARS, in Aberdeen, Idaho and evaluated for agronomics as well as malting quality. These lines were malted by Berne Jones, USDA-ARS in Madison, WI. Previous field studies indicated that RWA feeding may have a negative effect on malting quality of RWA-resistant germplasm lines. Data from this field test was used to select RWA-resistant lines to be grown in a randomized test this spring at two locations in Idaho to determine the effect of RWA feeding on malting quality.

Cooperative Screening

Four hundred-thirty lines and 216 doubled haploids were screened for homozygous resistance for five barley breeders. Two hundred and two advanced generation populations were screened for three breeders for RWA resistance and resistant plants saved for increase in Stillwater or sent back to the breeders for increase.

Personnel

Germplasm Enhancement

Dolores W. Mornhinweg, Geneticist
David R. Porter, Research Geneticist

The germplasm enhancement team welcomed a new postdoctoral researcher, Dirk B. Hays, who will work in the area of biochemistry and physiology of aphid resistance in barley.
 

Host Plant Resistance

James A. Webster, Research Entomologist
Keith A. Mirkes, Biological Science Technician

Cooperators

Darrell Wesenberg, Research Agronomist, USDA-ARS, Aberdeen, ID
Phil Bregitzer, Research Geneticist, USDA-ARS, Aberdeen, ID
Berne Jones, Research Biochemist, USDA-ARS, Madison, WI
 

Publications

Mornhinweg, D.W., D.R. Porter, and J.A. Webster. 1996. Inheritance of Russian wheat
aphid resistance in spring barley germplasm line STARS-9577B. Preceedings of the V International Oat Conference and the VII International Barley Genetics Symposium, Poster Session, Voume 2, University of Saskatchewan, University Press, Saskatoon, Saskatchewan, Canada, p. 533.

Mornhinweg, D.W., D.R. Porter and J.A. Webster. 1966. Effect of constant Russian
wheat aphid infestation on yield and yield components of RWA-resistant and susceptible barleys. Agron. Abst. American Society of Agronomy, Madison, WI. p. 273.