Location: Sunflower and Plant Biology Research2010 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.
3. Progress Report
The project on Sclerotinia resistance germplasm development utilizing wild perennial Helianthus species continued. Eight Sclerotinia-resistant diploid accessions, one hexaploid, and five interspecific amphiploids have been successfully crossed with Sclerotinia-tolerant cultivated lines, backcrossed and selfed to produce progeny families for field evaluation. In 2009, replicated field screening of 163 and 316 progeny families for head and stalk rot resistance, respectively, indicated good-to-excellent resistance among the progeny families suggesting successful gene introgression. A protocol using genomic in situ hybridization (GISH) to distinguish between chromosomes of perennial Helianthus species and cultivated sunflower has been established providing a new tool for studying gene transfer. A molecular tracking study utilizing SSR markers indicated a higher frequency of gene introgression from diploid perennials than from hexaploid or interspecific amphiploids, suggesting an advantage in using diploid perennials. The integration of classical genes onto the molecular map continues. We have completed the mapping of the fertility restoration gene Rf3 in the sunflower line RHA 280, and one major gene locus in HAR-4 conferring resistance to the predominant North American downy mildew races, including the recently identified aggressive downy mildew race. A survey of 104 sunflower breeding lines for resistance to new rust races was conducted. Nineteen sunflower lines were found to resist either rust race 336 or 777 or both. The interspecific line Rf ANN-1742 was identified as a new rust resistance source. Molecular mapping of this new gene is underway. Three selected rust resistance genes from oil sunflower, R2 in MC29, R4 in HA-R3, and R5 in HA-R2, were transferred to confection sunflower. We developed two molecular markers flanking the R4 gene to facilitate marker-assisted selection. A project initiated in 2009 was continued for transferring Sclerotinia resistance from wild annual species to cultivated sunflower. F1 hybrids from the crosses between cultivated lines with Sclerotinia stalk rot resistant wild annual species were highly resistant to stalk rot in a greenhouse test and were advanced to BC1.
1. Molecular mapping of rust resistance genes. Rust is a serious fungal disease in the sunflower growing areas worldwide, with increasing importance in North America in recent years. The most profitable and environmentally friendly strategy for farmers to control sunflower rust is to grow genetically resistant hybrids. Several genes conferring resistance to rust disease have been identified in sunflower, but few of them were genetically mapped. Rust resistance gene R4 in the germplasm line HA-R3 was derived from an Argentina open-pollinated variety, confers resistance to 88% of 300 rust isolates tested in the U.S. in the years 2007 and 2008, and is still one of most effective genes. ARS scientists in the Sunflower Research Unit in Fargo, North Dakota, mapped this gene to sunflower linkage group 13 within a large gene cluster which often associates with disease defense response. Two molecular DNA markers were identified that flank the R4 gene closely on both sides. The tightly linked markers to the R4 gene will facilitate gene pyramiding in rust resistance breeding of sunflower to attain a wide spectrum of resistance using molecular marker-assisted selection.
2. Exploration for wild sunflower species. Sunflower production continues to be challenged by several insect and disease pests. The production is also being shifted to marginal areas further challenging the crop. Genetic diversity is the key to an enhancing insect and disease resistance of a crop, as well as adaptability to dry or saline growing areas. The ARS scientists in the Sunflower Research Unit in Fargo, North Dakota, undertook an exploration for wild sunflower germplasm from the south central U.S. covering 4650 miles in Kansas, Oklahoma, Arkansas, and Missouri collecting 18 populations of H. salicifolius, 14 populations of H. pauciflorus, 10 populations of H. silphioides, 4 populations of H. x laetiflorus, 3 populations of H. occidentalis, and 2 populations of wild H. annuus. The value of this germplasm is the potential for modifying the fatty acid profile of sunflower. The addition of this germplasm to the ARS National Plant Germplasm System sunflower collection fills a gap in the wild sunflower collection making these species available for research for the first time for improvement of cultivated sunflower.
3. Sunflower oil with reduced saturated fat. Saturated fat in the diet continues to be a health concern for risk of cardiovascular disease. ARS scientists in the Sunflower Research Unit in Fargo, North Dakota, released a sunflower genetic stock (called RS5) of traditional high polyunsaturated sunflower with a seed oil composition of about 7.6% total saturated fatty acids, compared to about 13% saturated fatty acids for current conventional sunflower hybrids. The genetic source of this low saturated fatty acid trait is different from that in other low saturated fatty acid sunflower lines introduced in the past. The release of the RS5 sunflower line will allow public and commercial breeders to introduce the trait into their public and proprietary sunflower parental lines to produce hybrid seed for farmers to grow, resulting in sunflower oil with reduced content of saturated fat, benefitting the health conscious consumer.
Seiler, G.J., Jan, C. 2010. Chapter 1, Basic Information. In: Hu, J., Seiler, G., Kole, C., editors. Genetics, Genomics and Breeding of Sunflower. Enfield, NH: Science Publishers. p. 1-50.