Location: Sunflower and Plant Biology Research2013 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:
Identify new sources of disease resistance and map genes. One-sixth of the USDA Plant Introduction Station collection of cultivated sunflower germplasm (~ 250 accessions) was tested at multiple field sites in ND, SD and MN over the 5-yr period to identify new sources of resistance to Sclerotinia head rot (SHR), Sclerotinia stalk rot (SSR) and Phomopsis stem canker (PSR). The 19 trials, using artificial inoculation, totaled 13,000 rows, and the data were also used in association mapping analysis to detect quantitative trait loci (QTL) for the three diseases. A candidate gene analysis indicated that COI1-like genes are associated with resistance to SSR. During the 5-yr period we planted 18,000 rows to evaluate unit breeding material for SSR and SHR. A new virulent race of downy mildew (DM), able to attack the Pl6 gene, was found in 2009. We examined 400 DM isolates over the 5-yr period, and identified nine virulent races, which comprised 30% of DM population in ND, SD, and MN. Four resistance genes, available in 12 USDA inbreds, remain immune to all DM races. A 4-yr study of rust races was finished in 2009, and revealed that 39 rust races exist in the U.S., with two races comprising 45%. Nine USDA lines are resistant to all U.S. races. Find new sources of insect resistance and integrate into oilseed and confectionery lines. Over the 5-yr period, > 500 germplasm sources were tested for resistance to major sunflower insect pests under field conditions. Greatest progress was made for the red sunflower seed weevil. Germplasm developed for the weevil is agronomically very good and reduces weevil damage by ~ 75%. For the banded sunflower moth, a recombinant inbred line population was developed and is being evaluated for resistance. The first populations developed for the sunflower moth and sunflower stem weevil showed inconsistent results, suggesting these sources are not suitable for future breeding work. This has focused our future work on discovering resistance mechanisms which can be tested under lab and greenhouse conditions, thus increasing our efficiency. Work on the inheritance of two sunflower moth-specific resistance traits is underway. Transfer new sources of disease resistance into high yielding backgrounds. Over the 5-yr period, our germplasm enhancement project has formed 162 breeding populations and developed new inbred lines with disease and insect resistance traits. From these populations, around 8,000 yield trial plots have been planted across the sunflower growing region (ND, SD, MN, KS, TX) to assess yield and agronomic quality, as well as disease and insect resistance. Four germplasm releases were made in 2011 and nine are planned for 2013, combining multiple disease resistances (SSR, SHR, PSC and DM) with yield and agronomic traits of importance. These releases will help seed companies by providing germplasm that can be used in conjunction with genetic markers. This and companion project 5442-21000-034-00D have been merged into a new project 5442-21000-039-00D titled "Sunflower Genetic Improvement with Genes from Wild Crop Relatives and Domesticated Sunflower."
1. Markers for Sclerotinia Stalk Rot resistance in sunflower. Sclerotinia stalk rot is one of the most important diseases in sunflower in terms of losses. ARS scientists were able to find 25 SNP loci including those in two COI1-like genes that associate with resistance in breeding germplasm and the Plant Introduction collection. These markers should translate well to other breeding germplasm and provide additional information on the Plant Introduction germplasm resources.
2. 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 foure years that overcome two genes widely used in commercial downy mildew-resistant hybrids. More importantly, they determined that 12 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.
3. Identification of new sunflower pathogens. Most sunflower pathogens are well known, and identified by classical methods. Three additional Phomopsis species (P. stewartii, P. longicola, and P. gulyae, in addition to P. helianthi), all causing similar stem lesions, have been identified on sunflower in the U.S and are only distinguishable by complex DNA analysis. The above Phomopsis spp. have now been identified on soybeans and several weeds, which increases the host range and presents a larger reservoir of inoculum. This is a collaborative effort between our unit and North Dakota State University. 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.
4. Identification of physical resistance in developing sunflower germplasm. The resistance source PI 170415 has been shown to have an unusually strong pericarp 2-3 weeks after fertilization, reducing damage from larvae of the sunflower moth. The ability to screen germplasm derived from this source using a simple physical trait will allow more efficient selection of breeding material with the desired trait, eliminating the need to rely only on field trials, in which populations of insects are inconsistent. The simplified screening method should allow for the trait to be mapped and utilized by public and private breeders in the development of hybrids with sunflower moth resistance.Gulya Jr, T.J., Rooney-Latham, S., Miller, J.S., Kosta, K., Murphy-Vierra, C., Larson, C., Kandel, H., Vaccaro, W., Nowatzki, J.F. 2012. Sunflower diseases remain rare in California seed production fields compared to North Dakota. Plant Health Progress [online]. Available: http://www.plantmanagementnetwork.org/pub/php/research/2012/sunflower. DOI:10/1094/PHP-2012-1214-01-RS.