Location: Sunflower and Plant Biology Research2013 Annual Report
1a. Objectives (from AD-416):
1. Collect and evaluate wild and interspecific germplasm for useful agronomic traits. 2. Introgress useful genes into cultivated sunflower through interspecific hybridization and release the enhanced germplasm. 3. Develop DNA markers and apply them to genetic studies and marker-assisted selection.
1b. Approach (from AD-416):
We will collect nine underrepresented wild Helianthus species to fill gaps in the sunflower collection. Wild species will be evaluated for various agronomic traits, such as insect and disease resistance, saturated fatty acid content, cytoplasmic male sterility, and fertility restoration. DNA markers will be identified and used to reveal genetic diversity in the wild Helianthus collection. Once useful germplasm is identified, we will introgress the genes of interest into cultivated sunflower through interspecific hybridization. We will concentrate on transfer of Sclerotinia head and stalk rot resistance genes from wild perennial species into cultivated sunflower. Other traits we will identify and transfer are resistance to sunflower rust, downy mildew, and insects. Additional EST-based and SNP DNA markers will be developed for further saturation of the sunflower genetic map, and markers tightly linked to traits such as resistance to downy mildew, rust, and Sclerotinia, as well as to fertility restoration, will be used to expedite the process of sunflower germplasm enhancement via marker-assisted selection. We will use association mapping to identify DNA markers associated with insect resistance. BAC and BIBAC clones will be used to identify trisomics for the purpose of assigning individual linkage groups of the sunflower genetic map to single chromosomes of cultivated sunflower. BSL-1, 7/3/07.
3. Progress Report:
Explorations to fill gaps in the USDA-ARS wild sunflower species collection were undertaken over the past five years. Explorations covered 17 Midwest, South-central, and Southeast states covering 25,500 miles with the collections of 201 populations of 38 Helianthus species. The addition of this germplasm to the wild sunflower collection makes several wild species available for research for the first time in 40 years to be evaluated for useful traits for the improvement of cultivated sunflower and also preserves them for future generations. Over 1000 populations of wild sunflower species were analyzed for oil concentration and fatty acid composition represented by six annual and 16 perennial species. Of particular interest was the high concentration of the polyunsaturated fatty acid, linoleic acid in one population of annual H. porteri from Georgia with a linoleic content of 83.4%, the highest ever reported for a wild species. One population of Helianthus anomalous from the desert southwest in Utah had an oil concentration of 44.5%, the highest even report for any wild sunflower species. Knowledge of the oil and oil quality traits will facilitate the use of the wild species in breeding programs for these and other traits. A new tool, genomic in situ hybridization has been developed that is able to distinguish chromosomes of wild perennial species from cultivated sunflower facilitating the study of gene transfer. This technique indicated a higher frequency of gene introgression from diploid perennials than from hexaploid or interspecific amphiploids. Another tool was developed using chromosome-specific cytogenetic markers based on bacterial /binary bacterial artificial chromosome (BAC/BIBAC) clones that encompass the 17 sunflower linkage groups providing a valuable tool for identifying sunflower cytogenetic stocks (such as trisomics) and tracking alien chromosomes in interspecific crosses. This work also demonstrates the potential of using a large-insert DNA library for the study of sunflower genomic relationships. Several new sources of disease resistance genes have been discovered in wild sunflower species. A multi-strain rust and downy mildew resistant genes from wild annual sunflowers offers durable resistance to the predominant and most virulent races. Additionally, sources of resistance to Sclerotinia stalk and head rot have been discovered in five annual, and ten perennial species with interspecific germplasm developed which will be released to the sunflower breeders to diversifying the available genes for this devastating disease. Significant progress was made in developing a high-density genetic map of sunflower with 5,018 SNPs and 118 SSR markers which were used to orient the linkage groups on the previous public sunflower map. This map also combines two disease resistance genes; one for rust R-gene R12, and another for downy mildew R-gene Pl ARG. Closely linked SNP markers to these two genes facilitate high-throughput marker assisted selection in sunflower breeding programs. Classical genes were also mapped including white cotyledon, nuclear male sterility, fertility restoration genes, and gene clusters for disease resistance.
1. Exploration for wild sunflower species. Solving insect and disease pests and production problems requires new sources of genetic diversity. ARS scientists in Fargo, North Dakota discovered new germplasm from the southwest US. This germplasm has the potential to develop salt tolerant sunflower that can be grown on salt impacted lands and with saline irrigation water and adds to the ARS National Plant Germplasm System wild sunflower collection for research and preservation.
2. A durable sunflower rust resistance gene. Sunflower is grown as a confectionary seed crop in the US. Sunflower production in North America is constantly being threatened by the development of new virulent races of sunflower rust. ARS scientists in Fargo, North Dakota discovered a novel rust resistance gene, termed R13a, from a genetic line of sunflower that provides resistance to the newly emerged virulent rust races. This multi-strain rust resistant gene has been mapped on the public sunflower map using DNA markers allowing breeders to improve rust resistance in commercial confectionary sunflower. Enhanced resistance to devastating rust disease will sustain sunflower production in large portions of the US, improve net returns for sunflower growers, and provide food processors with abundant source of a healthy snack for the American consumers.
3. Molecular mapping of a novel rust resistance gene in sunflower. Sunflower is an important oil seed crop in the US. Change in infectiousness of the sunflower rust populations in North America has rendered most of the commercial hybrids susceptible to new strains. Molecular markers are a new tool that can be used for marker assisted selection. ARS scientists in Fargo, North Dakota discovered the R13b gene that confers resistance to the most predominant and most virulent rust races in the US Northern Great Plains. Discovery of the R13b novel rust resistance locus in sunflower and associated markers will support the introduction of the rust resistance gene, R13b into oilseed sunflower breeding lines. Ultimately, durable rust resistance will reduce chemical applications and will sustain and improve production in an environmentally friendly manner, and will enhance net returns for sunflower growers and processers.
Kane, N.C., Burke, J.M., Marek, L., Seiler, G., Vear, F., Baute, G., Knapp, S.J., Vincourt, P., Rieseberg, L.H. 2013. Sunflower genetic, genomic, and ecological resources. Molecular Ecology Resources. 13:10-20.