Location: Sunflower and Plant Biology Research2010 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.
3. Progress Report
We evaluated about 440 germplasm sources including accessions, F4:5 lines and their testcrosses, and interspecific crosses for resistance to one or more key insect pests of sunflower, including the sunflower moth and sunflower stem weevil in Kansas, the red sunflower seed weevil in South Dakota, and the banded sunflower moth in North Dakota. Several different populations are under various stages of development for resistance to the four major insect pests. Each insect is also the subject of a separate phenotypic recurrent selection program. F5:6 lines and their testcrosses are currently being developed. Testcrosses of the F4:5 lines and the lines themselves are currently under evaluation in North Dakota and South Dakota. We are also making new elite x resistant donor crosses to continue a cycle of introducing new sources of resistance into elite germplasm. Studies were again conducted to evaluate selected commercial sunflower hybrids for tolerance to damage by the sunflower midge, sunflower seed maggot, and sunflower bud moth. We organized, for a third year, a network of cooperators to monitor flight activity of the sunflower moth from Canada to southern Texas using pheromone traps to provide a system to alert consultants and growers when moths are active in the area. Two hundred sixty diverse cultivated sunflower germplasms were evaluated for Sclerotinia stalk rot resistance in three environments in two years. This data has been summarized in preparation for regression in an association mapping project. Work is now underway to complete marker interrogation of the 260 germplasms using candidate gene and random SNP markers. There are also plans to use this population for other diseases, such as Sclerotinia head rot. A cross section of the USDA PI collection (260 accessions), previously tested over four environments for resistance to Sclerotinia stalk rot, is being phenotyped for head rot resistance in an inoculated field trial. Data from this multi-year study will be used to select germplasm with combined head and stalk rot resistance, and used in association studies. Wild sunflowers of 11 annual species, which have shown resistance to Sclerotinia stalk rot in greenhouse trials in Iowa, are being field tested under inoculated conditions, along with F1 crosses with cultivated sunflower. Field disease evaluations of the Sunflower Research Unit’s USDA breeding material for Sclerotinia head rot and stalk rot continue, with over 3500 rows at five off-station locations. Transfer of downy mildew resistance into multiple genetic backgrounds was continued, effectively combining this resistance with IMI herbicide resistance, Sclerotinia resistance, and altered fatty acid profiles. Rust resistant populations are in the early stages of development, and this resistance will be placed in an elite genetic background with other already stacked traits in both confectionery and oilseed backgrounds. We began work to investigate sources of resistance to Verticillium wilt, and have F2 populations segregating for Verticillium wilt resistance genes, as well as other stacked traits, in both confection and oilseed background.
1. Resistance among sunflower germplasm to sunflower insect pests. The banded sunflower moth, sunflower moth, and red sunflower seed weevil are significant insect pests of cultivated sunflower. All three cause yield loss because of larval destruction of seeds in the head. In five-year studies of the banded sunflower moth and sunflower moth, ARS scientists at the Sunflower Research Unit in Fargo, North Dakota, evaluated oilseed sunflower accessions, breeding lines, and interspecific crosses for resistance to infestation by naturally occurring populations of these insects in North Dakota, South Dakota, and Kansas. Eight accessions showed greatly reduced damage by the banded sunflower moth. Two accessions, three interspecific crosses, and two breeding lines demonstrated resistance to infestation and damage from larval feeding by the sunflower moth. Nine potential sources of resistance to attack by the red sunflower seed weevil were identified that showed low seed damage in two or more years of testing. Results from these investigations indicated that there is potential for developing resistant genotypes with reduced feeding injury that will help sunflower producers reduce yield loss due to these three major insect pests.
2. Identification of new virulent races of sunflower downy mildew. Downy mildew exists as different races, which are effectively controlled by single resistance genes. In 2009 ARS scientists in the Sunflower Research Unit in Fargo, ND, identified two new virulent races which overcome genes in USDA sunflower lines that are widely used to produce downy mildew-resistant hybrids. Of 49 downy mildew samples tested, 11 samples from North Dakota and Minnesota were able to overcome the Pl6 and Pl7 genes commonly employed in sunflower resistance to downy mildew. The ARS scientists determined that USDA lines with the Pl8 and Plarg genes remain resistant to all known U.S. downy mildew races. The information provided by this study will be critical to sunflower hybrid seed producers in order to incorporate effective genes for resistance to downy mildew in their hybrids.
3. Registration of germplasm with downy mildew and sunflower rust resistance. ARS scientists in the Sunflower Research Unit in Fargo, ND, registered three sunflower genetic stocks, HA 458, HA 459, and HA 460, in 2010. Each contributes a new gene available for incorporation of downy mildew resistance into a female parent for hybrid sunflower seed production. These three genetic stocks also provide the genes for high oleic acid content and good agronomic and yield characteristics. A sunflower germplasm, RHA 464, was also registered. This germplasm possesses genes for downy mildew and sunflower rust resistance. Both resistances have not been defeated, to our knowledge, by virulent races of either fungus. This will provide a valuable source of resistance to these two diseases in male parental lines, along with good yield and agronomic characteristics.
Hulke, B.S., Miller, J.F., Gulya, T.J., Vick, B.A. 2010. Registration of the Oilseed Sunflower Genetic Stocks HA 458, HA 459, and HA 460 Possessing Genes for Resistance to Downy Mildew. Journal of Plant Registrations. 4:93-97.