2011 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.
We evaluated 400 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 and integrate into oilseed and confectionery lines. Several populations are under various stages of development for resistance to the four major insect pests, in both oilseed and confectionery genetic background. Germplasm releases are expected in 1 to 2 years. These will be used by commercial seed companies to eventually produce hybrids requiring less pesticide use.
A recombinant inbred line population is being developed and phenotyped for Banded Sunflower Moth resistance. Concurrently, a study will conclude next year to determine whether insect resistances for all four of above species is dominant or additive. The genetics will determine whether one or both parents of a hybrid need to contain resistance.
A portion of the USDA PI collection previously tested for Scleortinia stalk rot (SR) is being tested for Sclerotinia head rot (HR) at two locations to identify new sources of disease resistance and map genes. Data from this multi-year study will be used to select germplasm with combined HR and SR rot resistance. These lines are the core of our association mapping efforts to detect quantitative trait loci (QTL) for resistance to all diseases. About 8,000 SNP markers and sequences from host plant defense-related genes in these lines will be used in an analysis to determine the location of QTL for Sclerotinia SR resistance by September 2011. Wild sunflowers of 11 annual species, shown to have SR resistance in greenhouse trials, are being field tested. Field disease evaluations of the unit’s breeding material for Sclerotinia HR and SR continue, with over 5000 rows at five locations. Three new virulent races of downy mildew (DM) were identified in 2010, bringing the total of races overcoming the Pl-6 gene to five. Ninety percent of commercial hybrids marketed as DM-resistant were susceptible to one or more of these races. At least four released USDA lines confer resistance to all new virulent DM races. This information can be used by scientists and seed companies to further improve sunflower with the aid of marker-assisted selection.
Transfer new sources of disease resistance into high yielding backgrounds continued. We transferred DM resistance into multiple genetic backgrounds, effectively combining it with resistance to IMI herbicide, Sclerotinia SR, and insect resistance, 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 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 five new infectious strains of downy mildew that overcome two genes widely used in commercial downy mildew-resistant hybrids. More importantly, they determined that some USDA genetic lines remain resistant to all known U.S. downy mildew strains, including the five new infectious strains. The information allows sunflower hybrid seed producers to incorporate effective genes for resistance to downy mildew in their hybrids.
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, released four oilseed sunflower genetic lines. 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 a new source of resistance against the nearly complete devastation of sunflower when it is attacked by Sclerotinia diseases.
Hulke, B.S., Miller, J.F., Gulya, T.J. 2010. Registration of the restorer oilseed sunflower germplasm RHA 464 possessing genes for resistance to downy mildew and sunflower rust. Journal of Plant Registrations. 4:249-254.
Charlet, L.D., Gavloski, J. 2011. Insects of sunflower in the northern Great Plains of North America. In: Floate, K.D., editor. Arthropods of Canadian Grasslands (Volume 2): Inhabitants of a Changing Landscape. Biological Survey of Canada. p. 159-178.
Ode, P.J., Charlet, L.D., Seiler, G.J. 2011. Sunflower stem weevil and its larval parasitoids in native sunflowers: Is parasitoid abundance and diversity greater in the U.S. Southwest?. Environmental Entomology. 40(1):15-22.