OKLAHOMA
Germplasm Enhancement for RWA Resistance
D.W. Mornhinweg, and D.R. Porter
USDA-ARS Wheat, Peanut and Other Field Crops Research Unit
Stillwater, Oklahoma
Prebreeding for adapted germplasm lines (RWA 1)
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 intermittent RWA screening, of developed resistant lines to cultivars adapted to barley production areas with a time commitment of approximately seven years from the first cross until homozygous resistant BC3F3 lines can first be evaluated as observation lines in the field. Spring lines can be developed at an accelerated pace because of the potential for 2 generations per season. Once selections have been made in applicable field locations, these lines enter replicated preliminary yield trials for several years before final selections are made for germplasm release. To date nearly 500 lines have been evaluated in preliminary yield nurseries including spring and winter barleys, feed and malt barleys resulting in the potential release of 60 germplasm lines. The final step is increase of pure homozygous resistant seed prior to release as germplasm. Many lines have been ready for release, however, the decision to release these 60 germplasm lines in four distinct groups has held up the release of some waiting for pure seed of lines that entered the process at a later date. Pure seed checks of 59 spring lines (screened as bulks) and 10 winter barley lines (screened as head selections) were conducted in the fall of 2005 resulting in the further increase of 100 plants each of 14 lines that were not pure. Thirty-five more winter barley germplasm lines are currently in the yield trial stage. These lines have been developed in a Post 90 background and are being developed to have both RWA and Greenbug resistance. They involve 10 sources of resistance to RWA and one source of resistance to Greenbug. Don Obert conducted a preliminary yield trial with these lines in Aberdeen, ID in the summer of 2004.
The first RWA-resistant barley cultivar, Burton, was released cooperatively by Phil Bregitzer, USDA-ARS, Aberdeen, USDA-ARS, Stillwater, University of Idaho, Colorado State University, University of Nebraska, and New Mexico State University. Burton is a 2 row, dryland feed barley. Several other lines selected through this process are being considered for cultivar release. Field testing of 10 drought hardy RWA resistant feed barleys was conducted in 6 locations in Colorado and one location in Nebraska in 2004 with the cooperation of Frank Peairs, Colorado State University; and David Baltensperger, University of Nebraska. These lines are in an Otis background with 2 sources of resistance to RWA1. They have been tested against RWA2 and are resistant to it as well.
RWA Biotypes
The summer of 2003 was a shocker for wheat growers in Colorado as RWA resistant wheat varieties showed heavy damage and incurred heavy losses from RWA. By the end of the summer of 2003 the thing feared most by plant breeders who work with insect resistance and growers who raise insect resistant crops was proven to have come to pass, a new biotype of the RWA was prevalent and doing damage in the field. All previous work towards resistance in barley was also potentially in jeopardy. Whereas all resistant wheat cultivars in Colorado had resistance from the same source, the emphasis in our barley breeding program in Stillwater has always been genetic diversity as a defense against just such a possible biotype adaptation. The original biotype is now designated RWA1 and the new biotype RWA2. RWA1 and RWA2 are both prevalent in Colorado and as such, resistance to RWA1 is still a viable research effort. Of course, a new effort will consider resistance to RWA2 as well as the even more important identification of resistance to both biotypes in single resistant sources. All prebred adapted lines being considered for release as germplasm or cultivars were screened to RWA2 and found to be resistant.
The original 115 unadapted RWA1 resistant lines selected in by the USDA-ARS in Oklahoma were all tested against RWA2 in replicated tests in the winter of 2004. Because of precautions which must be taken when working with a new biotype with unknown adaptation potential, RWA2 screening conditions were stressful for barley. While all RWA1 highly resistant lines also were highly resistant to RWA2, some of the intermediate resistant lines appeared to be less resistant to RWA2. Screening of 14 additional adapted germplasm lines to RWA2 was done in 2004. These lines held up to RWA2. Another biotype has been identified, RWA3, also in Colorado but has yet to be described in the literature. Resistance in 69 potential germplasm releases held up to RWA3 in screening tests in 2004. 20 new sources of RWA1 resistance were identified and plants rescued from screening for the NSGC. Only one accession had a high level of resistance.
Genetic Studies
Complete genetic analysis, using RWA 1, has been performed on nine out of a total of 109 RWA 1-resistant lines developed by the USDA-ARS in Stillwater. All nine lines showed multiple gene control for RWA1 resistance. Seed has been developed and future genetic studies planned for the remaining 99 lines.
Genetic diversity studies are also planned for all resistant lines to determine if these lines carry different genes for resistance to RWA1. Multiple allelism testing requires 3 years for development of seed necessary for each test. The first test for multiple allelism was preformed in the winter of 2004 on STARS-9301B and STARS-9577B. Parents, F1, reciprocal F1, F2, TC1F2, and TC1F1:F2 families were screened with RWA1. Lynn Dahleen, USDA-ARS Fargo, ND, is cooperating to map the genes for resistance in these 2 lines. As a part of that project, 300 F2:F3 families were grown and screened for RWA1 resistance. Remnant seed was sent to North Dakota for mapping. Analysis is on going. Populations of 17 RXR TC1F1 were increased for future genetic diversity studies. Five testcrosses were made for genetic diversity studies of the Greenbug.
Cooperative screening
Two hundred and forty-five advanced lines were screened for resistance to RWA1 for one barley breeder, 82 lines were screened for Busch Agricultural Research, Inc., and 168 accessions were screened for the National Small Grains Collection.
Bird Cherry oat aphid
BCOA damage to barley seedlings is morphologically symptom-less. As a result, traditional seedling screening techniques are not successful in identifying BCOA resistant barleys. Development of a greenhouse seedling screening test would make screening of large barley collections fast and effective for identification of BCOA-resistant barleys. A new screening technique was tested on 20 barley accessions with 8 replications and 2 treatments in the summer of 2004. This technique was unique in that the screening occurred under high temperatures and long day lengths. All lines tested were killed by the aphids while the non-infested controls grew normally. Repeated tests are planned for 2005 with small adjustments in temperature and level of aphid infestation.
Four hundred and eighty-three winter barley lines, previously determined to be RWA resistant, were screened with GBE. Homozygous resistant plants were increased in the greenhouse. In cooperation with USDA-ARS in Aberdeen ID, a preliminary yield nursery was conducted on 35 BC3F3 lines with GB and RWA resistance for potential germplasm release. These lines involve 10 RWA resistant sources in a Post 90 background.
Hulless Feed Barley
There is new interest in hulless barley production in Oklahoma for ethanol production. Byproducts have the potential to be used for cattle, hog, or chicken feed as well as human nutrition. Winter barley production in OK would be dryland and resistance to GB as well as RWA would be desired. 831 hulless barleys obtained from the NSGC were evaluated in single rows at two locations in northern OK. 920 previously developed RWA and GB resistant BC3F4 hulled barley lines were also evaluated at each location. These lines involved 10 different RWA1 resistant sources in a Post 90 background. Post 90 is resistant to all known biotypes of GB. If a hulless line cannot be found that is adapted to OK growing conditions then a crossing program will begin in 2005 to bring the hulless gene into RWA/GB resistant lines adapted to OK. 987 RWA1 resistant BC3F3 were screened to GBE and 1,218 lines to GBI. Resistant plants were rescued and increased in the greenhouse.
Germplasm Enhancement
Dolores W. Mornhinweg, Geneticist
David R. Porter, Research Geneticist
Cooperators
Don Obert, Research Geneticist, USDA-ARS, Aberdeen, ID
Phil Bregitzer, Research Geneticist, USDA-ARS, Aberdeen, ID
Frank Piears, Professor, Colorado State University
Bob Hammond, Professor, Colorado State University
Dave Baltensperger, Professor, University of Nebraska
Bregitzer, P, D.W. Mornhinweg, and B.L. Jones. 2003. Resistance to Russian Wheat Aphid Damage Derived from STARS-9301B Protects Agronomic Performance and Malting Quality When Transferred to Adapted Barley Germplasm. Crop Sci. 43: 2050 – 2057.
Mornhinweg, D.W., L.H. Edwards, E.L. Smith, G.H. Morgan, B.F. Carver, J.A. Webster, and D.R. Porter. 2004. Registration of Post 90 Barley. Crop Sci. 44: 2263.
Porter, D.R., and D.W. Mornhinweg. 2004. New sources of Greenbug Resistance in Barley. Crop Sci. 44: 1245-1247.
Porter, D.R., and D.W. Mornhinweg. 2004. Characterization of greenbug resistance in barley. Plant Breeding 23(5): 493-494.