Location: Sunflower and Plant Biology Research2011 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 integration of classical genes onto the sunflower molecular map continues. Studies mapping two rust resistance genes from sunflower germplasm, HA-R2 and RHA 464, were completed. Progress was made on our genetic and molecular mapping studies developing four mapping populations for new rust resistances genes in the lines Rf-ANN 1742, HA-R6, HA-R8, and RHA 397. A new downy mildew resistance gene from wild annual species of H. argophyllus was transferred into cultivated sunflower. Genotyping of the two parents with 869 simple sequence repeat markers was completed and phenotyping samples from a large BC1F3 population to identify genomic region associated with downy mildew resistance was begun. Progress was made on studies deploying novel sources of Sclerotinia stalk rot resistance in sunflower. BC2F1 and BC2F2 populations from the crosses of cultivated sunflower with Sclerotinia resistant plants selected from wild annual species of H. argophyllus, H. debilis, H. praecox, and H. petiolaris will continue to be evaluated to identify resistant introgressed lines. We screened 8,000 SNP markers in an F2 population from the cross between HA 89 and rust resistant RHA 464. About 2,800 SNPs showed polymorphism in this population. The project on Sclerotinia resistant germplasm development utilizing wild 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 2010, replicated screening of 323 progeny families for stalk rot resistance indicated good-to-excellent resistance among progeny families suggesting successful introgression of resistance genes. 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. Molecular tracking using SSR markers suggested a higher frequency of gene introgression from perennial diploids species than from hexaploid or interspecific amphiploids. In 2010, eight accessions from three diploid and one tetraploid perennial species were crossed with HA410 and HA451 and are being backcrossed. The new crosses will provide more diverse resistance genes for developing Sclerotinia resistant germplasm. Over 200 populations of wild sunflower were analyzed for oil concentration and fatty acid composition. They were represented by 1 annual and 6 perennial species. Two of these species are rare providing valuable information about their oil profiles. Of particular interest was the high linoleic acid concentration in one population of H. porteri of 81.5%, the highest ever reported for a wild species. It is very unusual for species from the southeast US to have such high levels of linoleic acid. This could allow traditional sunflower to be grown in southern latitudes and still maintain its high quality polyunsaturated oil. The oil and fatty acid contents of a recently rediscovered rare species, H. verticillatus were reported for the first time.
1. Exploration for wild sunflower species. Sunflower is an important oil and confection seed crop in the US. Solving insect and disease pests and production problems for sunflower requires new sources of genetic diversity. The ARS scientists in Fargo, North Dakota, discovered new germplasm from the southeastern US. This germplasm has the potential to improve the fatty acid profile of sunflower grown on marginal lands and adds to the ARS National Plant Germplasm System wild sunflower collection for research and preservation. Ultimately, enhanced genetic resources sustain and improve production and enhance net returns for sunflower growers and processers.
2. A durable rust resistance gene in sunflower. Sunflower is an important oil and confection 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. A genetic line of sunflower carrying the rust resistance gene R5 was released in 1985, but has not been widely used in commercial hybrid production; it still remains effective against prevalent rust strains in North America. ARS scientists in Fargo, North Dakota, genetically mapped a multi-strain rust resistant gene from the genetic line of sunflower called HA-R2 and identified two DNA markers. DNA markers in close proximity to the R5 gene allow breeders to improve rust resistance in commercial hybrid sunflower. Enhanced resistance to devastating diseases like rust will sustain sunflower production in large portions of the US, improve net returns for sunflower growers, provide food processors with abundant source of healthy oil, and American consumers and recreationalists with sunflower seeds for direct consumption.
3. Development of sunflower broomrape resistant germplasm. Broomrape is a parasitic weed that constrains sunflower cultivation in Europe and Asia. A broomrape population race G has overcome all known resistance genes. ARS scientists in the Sunflower and Plant Biology Research Unit in Fargo, North Dakota, used the USDA-ARS North Central Regional Plant Introduction Station, Ames, Iowa, wild sunflower germplasm collection to develop interspecific hybrids that can be utilized to introgress resistance genes into elite sunflower hybrids. This research provides a source of durable resistance to broomrape for sunflower.Qi, L.-L., Gulya, T.J., Seiler, G.J., Hulke, B.S., Vick, B.A. 2011. Identification of resistance to new virulent races of rust in sunflowers and validation of DNA markers in the gene pool. Phytopathology. 101:241-249.