Russian Wheat Aphid (RWA) Resistant Germplasm Lines

One new RWA-resistant barley germplasm line has been selected and increased from a previously identified RWA-resistant accession from the National Small Grains Collection. R048 is a 6-row spring line highly resistant to RWA.

Prebreeding for adapted germplasm lines

The prebreeding program is designed to bring resistance genes from unadapted germplasm lines into adapted malting and feed barley backgrounds for all barley growing regions in the U.S. It involves repeated backcrossing with intermitent 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 is an ongoing process involving various resistant lines and adapted cultivars currently in all phases of the program. The summer of 1998 saw the first 28 lines in preliminary yield trials in the field in Aberdeen, ID with the cooperation of Darrell Wesenberg and Phil Bregitizer of the USDA-ARS. These lines were grown at two locations in Idaho with the potential for release of adapted germplasm lines or further testing and cultivar release. Of the 28 lines tested, 12 were greater than or equal to their adapted parent check for grain yield and plumps in Aberdeen, while in Tetonia, 22 lines were greater than or equal to their adapted parent check.

One-hundred seventy headrows, selected in the previous year involving 3 resistant lines and 3 adapted cultivars, were evaluated and 33 lines were selected for preliminary yield testing in 1999. Seven hundred eighty preliminary observation lines involving 23 different resistant sources and 7 adapted cultivars were evaluated for agronomics, and 263 lines were selected for head rows in 1999. Continuing with this program, 2,600 resistant BC3F2/BC3F3, involving 7 adapted cultivars and 18 resistant germplasm lines, were increased in the spring and summer of 1998 in the greenhouse in Stillwater and Aberdeen. A subset of 1,120 BC3F3/BC3F4 lines involving 7 adapted cultivars and 11 resistant germplasm lines were screened for homozygous resistance in the fall of 1998 and the resultant 702 homozygous resistant lines will be evaluated agronomically in Abdereen in the summer of 1999. Three hundred seedlings of each of 11 BC3F2 populations involving 3 winter barley cultivars and 10 RWA resistant germplasm lines were screened in the fall of 1998 and 100 BC3F3 plants from each population transplanted for increase in the greenhouse in the spring of 1999. Thirty-four spring barley BC3F1 populations, involving 13 cultivars and 13 RWA resistant germplasm lines, and 5 winter barley BC3F1 populations, involving 3 cultivars and 4 RWA resistant germplasm lines, were screened and 12 plants of each increased in the greenhouse in the fall of 1998. Seventy-one backcrosses were made towards future adapted RWA-resistant lines to be evaluated in the field in 2000, 2001, and 2002.

Genetic Studies

Complete genetic analysis has been performed on nine out of a total of 108 RWA -resistant lines developed by the USDA-ARS in Stillwater. All nine lines showed multiple gene control for RWA resistance. Eighteen F1 and 25 BC1 were made, and 300 F2-derived F3 families were increased for each of two populations for future genetic studies. Genetic diversity studies are planned all resistant lines to determine if these lines carry different genes for resistance to RWA. This type of analysis requires 3 years for development of seed necessary for each test. Sixty-one RXR F1, and 12 testcrosses of a resistant x resistant F1 on a susceptible were made, while 12 TC1F1 populations and 1,548 TC1F1-derived TC1F2 plants were increased for future genetic diversity studies.

Field studies

Previous field studies indicated that RWA feeding may have a negative effect on malting quality of RWA-resistant germplasm lines. Six agronomically adapted advanced generation RWA-resistant germplasm lines developed by Phil Bregitzer and Darrell Wesenberg with USDA-ARS in Aberdeen, ID in cooperation with the USDA-ARS lab in Stillwater, one unadapted RWA-resistant germplasm line developed by the Stillwater lab, and three adapted malting barley cultivars which were recurrent parents for the adapted germplasm lines were grown in Aberdeen, Idaho by Phil Bregitzer and Ft. Collins, CO with the cooperation of Frank Peairs and Colorado State Uninersity. Noninfested plots were kept RWA free with pre-plant seed treatment of Gaucho, while infested plots were artifically infested with RWA at an early or late date. The effect of RWA feeding on agronmics and malting quality of these lines was measured. Data analysis is on going and the study will be repeated in 1999.

Cooperative screening

Five hundred twenty-eight advanced lines were screened for resistance for two barley breeders.

Other aphids

The bird cherry oat aphid (BCO) is a perennial pest of barley throughout the U.S. Previously, the main agronomic concern associated with this aphid was transmission of a serious barley disease Barley Yellow Dwarf Mosaic Virus (BYDV), but recent reports have indicated yield loss due to the BCO. BCO damage to seedlings is not easily detected and it has proven extremely difficult, so far, to screen for resistance in the seedling stage. A new screening technique has been developed in Stillwater that can be quickly and easily performed on seedlings. Seeds are planted in transparent seed growth pouches in the greenhouse and germinating seedlings are infested with BCO. In addition, an identical control group is kept aphid free. A visual comparison of root length and secondary root hairs as well as plant height is made between the infested and noninfested controls and resistant plants selected. Resistance to BCO measured visually on roots and shoots of seedlings has not yet been correlated to grain yield. Approximately 163 accessions have been reported in the literature to have resistance to BCO, in terms of the effect of the plant on aphid biology, or to have resistance to BYDV. One hundred and ten potential BCO lines selected from these accessions on the basis of agronomics were screened with the new technique in the fall of 1997. 16 lines were selected for a replicated yield test in the greenhouse in the spring of 1998. Noninfested control plants were grown in pouches with Gaucho in the same greenhouse as the infested plants and plants were rescued from both the infested and noninfested pouches and transplanted to the greenhouse paired side by side in eight replications. Grain yield and yield components were measured and analysis is ongoing to determine the success of this new screening technique. At the same time, BCO- resistant lines, identified by this new screening technique, were rescued and transplanted to the greenhouse, and 102 backcrosses made to 13 adapted barley cultivars.

Personnel

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
Darrell Wesenberg, Research Agronomist, USDA-ARS, Aberdeen, ID
Phil Bregitzer, Research Geneticist, USDA-ARS, Aberdeen, ID
Berne Jones, Research Biochemist, USDA-ARS, Madison, WI
Frank Piears, Professor, Colorado State University

Publications