2012 Annual Report
1a.Objectives (from AD-416):
The objectives of our proposed research are threefold: (1) To evaluate cultivated sunflower and wild Helianthus species for insect and disease resistance, concentrating on those diseases and insects which are of greatest impact to the U.S. sunflower industry, (2) to develop and phenotype segregating populations for DNA marker discovery, which will be used to supplement classical breeding methods to identify breeding material with improved agronomic, disease and insect resistance traits, and (3) to develop advanced germplasm which carry genes for insect and disease resistance.
1b.Approach (from AD-416):
To identify new sources of insect and disease resistance in sunflower we will evaluate, either under natural infestations (insects) or with artificial inoculations (diseases) a diverse selection of sunflower germplasm, including breeding populations, USDA Plant Introductions, and wild species (obtained from a companion research project 5442-21000-034-00D). For diseases, we will focus on Sclerotinia, downy mildew, and rust. The major insect pests in our studies are the sunflower stem weevil, sunflower moth, and banded sunflower moth. We have developed segregating populations for some insect and diseases, and are developing others. These populations will be used by the project molecular geneticist to identify markers for these traits. Phenotyping will be done at several locations, using either natural insect infestations or artificial inoculations for diseases. Finally, using field plots with natural insect infestations or artificial disease inoculations, and supplemented by marker-assisted selection, we will evaluate the new sources for resistance to the major insect pest species and disease pathogens and transfer that resistance into genetic stocks or advanced USDA germplasm for release to the public.
Identify new sources of disease resistance and map genes. One-quarter of the USDA PI collection of cultivated sunflower germplasm ( ~ 250 accessions) were phenotyped for Phomopsis stem canker resistance at four nurseries (ND, SD and MN) under natural infection and also tested for resistance to Sclerotinia head rot at two MN nurseries, using artificial inoculation. When completed in 2012, three diseases will have been phenotyped at four to six locations for each disease. These lines are the core of our association mapping effort to detect quantitative trait loci (QTL) for resistance to Sclerotinia and Phomopsis diseases. A candidate gene analysis indicated that COI1-like genes in sunflower are associated with resistance to stalk rot. Currently, we are awaiting the final field trial results to begin mapping of resistance QTL for the other two diseases. Forty downy mildew isolates were characterized to race, and four new races virulent on the Pl6 gene were identified, bringing the three-year total to nine new races. Ninety-five percent of commercial hybrids are susceptible to these new races, but four resistance genes available in 12 released USDA inbreds, remain immune to all U.S. mildew races. This information can be used by scientists and seed companies to further improve sunflower with the use of marker-assisted selection.
Find new sources of insect resistance and integrate into oilseed and confectionery lines. We evaluated more than 300 germplasm sources for resistance to key insect pests, including sunflower moth and sunflower stem weevil in Kansas, red sunflower seed weevil in South Dakota, and banded sunflower moth in North Dakota to find new sources of insect resistance. Several populations are under various stages of development in oilseed and confectionery backgrounds. A germplasm release is expected in 2012 for red sunflower seed weevil resistance. These releases will be used by commercial seed companies to produce hybrids requiring less pesticide use.
Based on testcross data, significant contributions to insect resistance in hybrids are being made by R-line parents (while previous breeding for insect resistance has focused on B-line development). Thus, we are testing additional testcross parents and R- and B-lines to better understand how both parents of a hybrid contribute to insect resistance.
Transfer new sources of disease resistance into high yielding backgrounds. Transfer of downy mildew (DM) resistance into multiple genetic backgrounds has continued, effectively combining it with resistance to IMI herbicide, Phomopsis, Sclerotinia stalk rot, Sclerotinia head rot, and insects, and altered fatty acid profiles in both confectionery and oilseed backgrounds. Rust resistant populations are in the early stages of development. We have F4 populations segregating for Verticillium wilt resistance genes, as well as other stacked traits, in both confection and oilseed background. This will further help seed companies by providing germplasm that can be used in conjunction with genetic markers.
Resistance to new infectious strains of sunflower downy mildew. Sunflower is an important oil and confection seed crop in the US. Downy mildew is a serious disease of sunflower. ARS scientists in Fargo, ND, identified a total of nine new infectious strains of downy mildew in the last three years that overcome two genes widely used in commercial downy mildew-resistant hybrids. More importantly, they determined that 12 released USDA lines remain resistant to all known U.S. downy mildew strains. This information allows sunflower seed companies to use effective resistance genes to downy mildew in their hybrids, thus protecting the U.S. crop from this ever-present disease.
Identification of new sunflower pathogens. Most sunflower pathogens are well known, and identified by classical methods. New species of the fungus Phomopsis have been identified in the U.S. which cause similar symptoms on sunflower, and are only distinguishable by complex DNA analysis. Precise identification of these new species will allow pathologists and breeders to refine inoculation/evaluation methods to specifically find resistance to each species. This information will make the development of resistant germplasm and commercial hybrids more effective and precise.
New sunflower genetic lines for disease resistance. Sunflower is an important oil and confection seed crop in the US. Sclerotinia is the major fungal disease of sunflower. ARS scientists in Fargo, ND, will release up to 8 oilseed sunflower genetic lines in 2012. Each contributes new genetic diversity for Sclerotinia resistance in a high yielding genetic background that possesses favorable genes for oil quality and herbicide resistance. These genetic lines will provide the sunflower breeding community and sunflower producers new sources of resistance against the nearly complete devastation of sunflower when it is attacked by Sclerotinia diseases.
Knodel, J.J., Ganehiarachchi, G.A.S.M., Beauzay, P.B., Chirumamilla, A., Charlet, L.D. 2011. Impact of planting dates on a seed maggot, Neotephritis finalis (Diptera: Tephritidae), and sunflower bud moth (Lepidoptera: Tortricidae) damage in cultivated sunflower. Journal of Economic Entomology. 104(4):1236-1244.
Prasifka, J.R., Bradshaw, J.D., Lee, S.T., Gray, M.E. 2011. Relative feeding and development of armyworm, Mythimna (Pseudaletia) unipuncta (Haworth), on switchgrass and corn, and its potential effects on switchgrass grown for biomass. Journal of Economic Entomology. 104(5): 1561-7.
Kang, J., Onstad, D.W., Hellmich II, R.L., Moser, S.E., Hutchison, W.D., Prasifka, J.R. 2012. Modeling the impact of cross-pollination and low toxin expression in corn kernels on adaptation of European corn borer (Lepidoptera: Crambidae) to transgenic insecticidal corn. Environmental Entomology. 41(1):200-211.
Hulke, B.S., Bushman, B.S., Watkins, E., Ehlke, N.J. 2012. Association of freezing tolerance to LpCBFIIIb and LpCBFIIIc gene polymorphism in perennial ryegrass accessions. Crop Science. 52:2023-2029.