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
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 RWA 2. RWA 1 and RWA 2 are both prevalent in Colorado and as such, resistance to RWA 1 is still a viable research effort. Of course, a new effort will consider resistance to RWA 2 as well as the even more important identification of resistance to both biotypes in single resistant sources. The original 115 unadapted RWA1 resistant lines were all tested against RWA 2 in replicated tests in the winter of 2004. Because of the precautions which must be taken when working with a new biotype with unknown adaptation potential, the RWA 2 screening conditions were stressful for barley. While all RWA 1 highly resistant lines also were highly resistant to RWA 2, some of the intermediate resistant lines appeared to be less resistant to RWA 2. This may have been due to the stresses of the testing. All prebred adapted lines being considered for release as germplasm or cultivars were also screened to RWA 2 and found to be resistant.
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 next step is increase of pure homozygous resistant seed prior to release as germplasm. Several lines selected through this process are being considered for cultivar release. 2003 field testing involved yield trials of potential germplasm and cultivar releases in Idaho, Colorado and Nebraska.
Field testing in 2003 was preformed in cooperation with Phil Bregitzer (spring barley) and Don Obert (winter barley) scientists with the USDA-ARS in Aberdeen, Idaho; Bob Hammon and Frank Piears, Colorado State University; and David Baltensperger, University of Nebraska. Preliminary Yield Trials were conducted at one location in Idaho on a total of 47 adapted RWA-resistant winter barley germplasm lines involving 2 susceptible winter barley backgrounds and 9 RWA-resistant sources. Another winter preliminary yield trial was conducted on 20 advanced generation winter barley germplasm lines in Fruita, CO involving 2 susceptible backgrounds and 9 RWA-resistant sources. Advanced yield trials were conducted at 4 locations in Idaho for 13 advanced generation adapted spring barley germplasm lines involving 3 susceptible backgrounds and 3 RWA-resistant sources. Preliminary yield trials were conducted on 13 advanced generation germplasm lines involving 9 susceptible backgrounds and 10 resistant sources at 3 locations in Idaho. A dryland preliminary yield trial was conducted at 5 locations in CO, 1 location in NE, and 1 location in ID on 10 advanced generation spring barley germplasm lines in an Otis background with resistance from 2 sources.
1,275 advanced generation adapted winter RWA-resistant barley germplasm lines were evaluated in headrows at Aberdeen, Idaho and rows selected for preliminary yield testing in 2004. Many of these lines are also resistant to greenbug E and I. Heads were selected from segregating rows for RWA and greenbug screening and further field testing in 2004. These lines involved 2 susceptible backgrounds and 11 RWA-resistant sources. 600 BC3F2 were increased in the greenhouse for possible field observation as BC3F3 in 2004 involving 6 susceptible backgrounds and 1 resistance source. 53 adapted RWA-resistant spring barley germplasm lines were increased for pure seed in the field in Idaho and in the greenhouse in Stillwater, OK.
A total of 1,966 winter barley lines and 2,731 spring barley lines were screened in support of the prebreeding effort.
Genetic Studies
Complete genetic analysis, using RWA 1, has been performed on nine out of a total of 108 RWA 1-resistant lines developed by the USDA-ARS in Stillwater. All nine lines showed multiple gene control for RWA 1 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 RWA 1. Multiple allelism testing requires 3 years for development of seed necessary for each test. Mapping of RWA resistance genes with molecular markers would greatly complement multiple allelism testing and, as such, cooperators to do this research will be sought whenever possible. 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 RWA 1. Lynn Dahleen, USDA-ARS Fargo, ND, is cooperating to map the genes for resistance in these 2 lines. Analysis is on going. 16 TC1F1 winter barley populations were increased for future genetic diversity studies.
Cooperative screening
Sixty-three advanced lines were screened for RWA 1 resistance for 1 barley breeder.
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. Several new screening techniques were tested on 20 barley accessions with 8 replications and 2 treatments in the early spring of 2003. Morphological measurements were made towards an understanding of aphid/host interaction and the identification of a previously undiscovered visual or measurable trait that would be applicable for future screening of barleys for BCOA resistance. Some interesting observations were made concerning delayed development of the inflorescence and stunting of seedlings given long day length and high temperatures to encourage plant maturation in a short period of time. Analysis is ongoing and a repetition of testing planned for the summer of 2004.
Two F2:F3 populations were increased from crosses between 2 greenbug biotype G (GBG) resistant lines and susceptible cultivars. These crosses were originally made to develop the genetic populations necessary to determine the inheritance of resistance to GBG in these lines. Six RXR crosses were made between 3 GBG resistant lines towards the development of populations for multiple allelism tests to determine the genetic diversity for resistance to GBG. Four hundred eighty seven BC3F4 lines, homozygous resistant for RWA 1 and GBI, were screened for resistance to GB biotype E. Lines with resistance to all 3 aphids would be advantageous in several southern barley growing areas.
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.