Location: Sunflower and Plant Biology Research2014 Annual Report
Objective 1: Identify gaps and acquire new wild species to fill gaps or deficiencies in the sunflower germplasm collection. Objective 2: Identify insect pests and pathogens of sunflower, develop effective screening methods to optimize assessment of resistance to sunflower pathogens, determine mechanisms of plant resistance, phenotype germplasm for resistance to major insect pests and pathogens, and introgress insect and disease resistance genes from the wild species into diverse cultivated germplasm. Subobjective 2A: Identify and monitor pathogens. Subobjective 2B: Develop effective screening procedures for Phomopsis and insect damage. Subobjective 2C: Identify and assess mechanisms of insect resistance. Subobjective 2D: Transfer disease resistance, insect resistance, and other agronomic traits from wild Helianthus species into cultivated sunflower and improve methods for interspecific hybridization and release of pre-breeding germplasm. Subobjective 2E: Characterize and map resistance to pathogens and insect pests, and other agronomic traits. Objective 3: Develop sunflower germplasm with high yield, high oil content, and desirable fatty acid concentrations, as well as novel resistance genes for diseases and insects. Subobjective 3A: Develop new inbred lines with novel fatty acid compositions, such as low saturated fatty acids, and high oleic acid. Subobjective 3B: Pyramid disease and insect resistance genes with high yield and oil content in a common germplasm.
Currently, there are a number of factors that reduce sunflower yield including a host of insects and diseases that require careful and costly management practices, reducing profitability. Research is proposed to reduce the input costs by developing durable pest resistance, herbicide resistance, oil content and quality increasing the oil per acre yield of sunflower. Specifically, we will collect wild sunflower relatives to broaden the crop’s genetic base. This germplasm will be phenotyped for resistance to major insect pests and pathogens, cytoplasmic male sterility, and fertility restoration. Methods for improving interspecific hybridization will focus on techniques to detect introgressed alien chromosome segments in interspecific crosses using the genomic fluorescence in situ hybridization technique. Interspecific gene transfer will be evaluated using molecular markers for desirable agronomic traits such as resistance genes to rust and downy mildew. Interspecific germplasm with useful genes will be introgressed into cultivated sunflower and released as enhanced pre-breeding germplasm. Current diseases will be monitored for shifts in virulence and races, and for newly emerged diseases. A field test will be developed to reliably test for the newly emerged Phomopsis stem canker pathogen. An efficient non-destructive screening method will be developed for detecting damage of banded sunflower moth, sunflower moth, red sunflower seed weevil, and sunflower stem weevil. Insect resistance mechanisms will be identified and assessed for sunflower moth. Resistance genes for pathogens and insects, and other agronomic traits will be characterized and mapped. DNA markers for selected traits will be developed and used for marker-assisted breeding. Enhanced sunflower germplasm with high yield, high oil content, and desirable fatty acids concentration, as well as novel resistance genes for diseases and insects will be developed and released. Accomplishing these objectives will provide producers with improved sunflower that will provide a stable supply of high quality oil and confectionery sunflower, improving on-farm profitability and providing the consumer with a reliable domestic supply of a healthy oil, a staple in the American diet.
An exploration of 3650 miles to collect populations of annual Helianthus bolanderi and perennial H. gracilentus crop wild relatives of sunflower from California and Oregon resulted in the addition of nine accessions of H. bolanderi and four H. gracilentus. Additionally, three accessions of a newly discovered species, perennial H. winteri were collected and added to the ARS National Plant Germplasm System wild crop relatives collection to fill gaps, making this species available for research for the first time for improving cultivated sunflower and preserving it for future generations. A survey of sunflower fields for downy mildew was undertaken in North Dakota, South Dakota, Minnesota, and Nebraska. A total of 120 fields were surveyed with 36% of the fields having one or more races present with the highest incidence of 58%, and 3.6% of the fields with economic damage levels. The prevalent race was 714, followed by races 774, 734 and 704. The commonly used genetic resistant PL6 gene was overcome by 72% of races found in the samples. The evolution and increasing spread of these races may account for the increase in downy mildew races noted in recent years. Three isolates of each of two Phomopsis species were inoculated onto a wounded sunflower stem at three different dates. Inoculation techniques consisted of an infected agar plug placed on the wounded stem and a Phomopsis-infected toothpick inserted into the stem. All inoculations at all dates were successful. Differences in virulence were observed in the isolates of the two species with the common species, P. helianthi slightly more aggressive. The toothpick method was just as effective as the agar plug in terms of infection, and was four times faster. Thus, for future germplasm testing for stem canker, the toothpick inoculation is both effective and time-efficient. Thirty public inbred lines were evaluated as part of a larger field trial for banded sunflower moth resistance in the field in Casselton, ND. Among these cultivated inbred lines, there was as much as a fourfold difference in seed damage by banded moth larvae and the best cultivated inbred lines appeared statistically similar to a resistant parent, PI 494859. PI 494859 (and other resistance sources that retain undesirable wild characteristics) is more difficult to use in breeding than existing inbred lines. The data from 2013 suggest some released inbred lines may provide useful resistance to banded moth with little additional breeding. Assessment of physical (pericarp hardness) and chemical resistance traits (sesquiterpene lactones) for sunflower moth indicate that significant amounts of variation exist for both within USDA germplasm. However, other germplasm sources (i.e., partially improved breeding material or wild sunflowers) have greater potential to reduce damage from sunflower moth than do available inbred lines. Work to document the relative value and inheritance of these traits is underway. Two wild H. strumosus, three H. tuberosus, and one H. hirsutus perennial species accessions showed total immunity to the predominant rust races in the U.S. These accessions were crossed with cultivated line HA 410 and progenies obtained via embryo rescue. Progenies were further backcrossed with cultivated line HA 410 and will be evaluated against rust races in the next generation. Advanced interspecific lines based on wild perennials crossed with cultivated lines screened for Sclerotinia stalk and head rot resistance in replicated field tests this year will be evaluated this fall to identify new sources of resistance to the new virulent races of rust. New crosses involving three accessions of H. tuberosus, two accessions of H. strumosus, and one accession each of H. hirsutus and H. simulans were successfully crossed and backcrossed with cultivated line HA 410. In addition, previous crosses involving H. hirsutus, H. salicifolius, H. occidentalis, and H. divaricatus were further advanced to identify chromosome addition lines, plants with reduced vigor, cytoplasmic male-sterility, and the plants with the same chromosome number as cultivated sunflower. Significant progress was made in completing a recombinant inbred line population derived from the cross of HA 89 with HA-R3 for QTL analysis of Phomopsis resistance. The banded sunflower moth population is currently at the F5 generation. A single seed descent F6 generation will be produced this field season. The F6 derived plants will be grown next year to produce large quantities of F6:7 seed for phenotyping purposes. Mapping of a rust resistance gene PH3 was completed. PH3 was released and registered in 2004 for rust resistance and is resistant to all rust races in the U.S. Molecular marker ORS 542 and a purple hypocotyl color gene linked to this rust resistance gene was identified, which will help select rust resistant lines derived from PH3 for hybrid sunflower development. F3 progeny confirmation of a downy mildew resistance gene in TX16R was completed, but rust resistance gene confirmation needs further clarification. Downy mildew resistance phenotyping of the F3 population of HA-R8 × RHA 468 together with the two parents was conducted. One hundred and ninety F2-derived F3 families were inoculated with DM race 734 and recorded for performance. Primary marker analysis indicated that the DM resistance gene in RHA 468 may be located on linkage group 13 of the sunflower genome. Cytoplasms of perennial Helianthus species cause vigor reduction in the absence of nuclear vigor restoration genes. Mapping populations with vigor restoration genes from cultivated sunflower and from wild sunflower species H. giganteus were established, and F3 progeny confirmations are in progress. A half diallel genetics population for low saturated fatty acids in a high oleic background was analyzed. F1 seed was tested for all matings to confirm that a cross was made (and not an accidental self pollination) using a cut-seed assay and gas chromatography. The F1 seeds of each mating that deviated in fatty acid composition from the female parent were selected for advancement. The seeds were planted in the field and will be self-pollinated for additional study of segregation in the next generation. Populations for combining yield, oil content, oil quality, agronomic traits, and biotic stress resistance were grown in both rural Santiago, Chile, during the winter season, and Fargo, ND, during the summer season. In all, three cage increases of near-release early maturing inbred lines were produced in Chile, along with a population that segregates for an insect resistance trait in an imidazolinone herbicide, Sclerotinia and Phomopsis resistant, and high oleic background. About 1000 progeny rows are being grown in Fargo, which includes both confectionery and oilseed lines at various stages before release. Two germplasm lines were released this year for confectionery sunflower that contain multiple rust resistance loci for durable resistance. Several other lines are planned for release in late FY-14 or early FY-15, pending data from our field nursery this summer.
1. Durable sunflower rust resistance genes. Sunflower is a confectionery seed crop grown in the US where leaf rust is a serious disease that has been increasingly prevalent in much of the production area with the development of new virulent races. Few suitable inbred confection sunflower lines exist that have a high level of rust resistance, which poses risks of a potential disease epidemic from the use of a single resistance gene. ARS scientists in Fargo, North Dakota released two confectionery sunflower germplasms with rust resistance controlled by two genes, R4 and R5. These genes will enhance durable resistance to this devastating rust disease in confectionery sunflower, sustaining sunflower production in large portions of the US, improving net returns for sunflower growers, and providing food processors with an abundant source of a healthy snack for the American consumers.
2. New cytoplasms for hybrid sunflower production. Globally, sunflower is the fifth largest hybrid crop. Sunflower is currently based on a single female cytoplasm parent CMS PET1 developed in 1969 derived from a wild prairie sunflower. This leaves sunflower very vulnerable to attack by pathogens similar to the disaster seen in corn in the 1970s. A newly identified female line, CMS GIG2, derived from a wild perennial sunflower and an associated male line are clearly different from the CMS PET1 cytoplasm and the male lines. The new combination could be used to substitute for the older CMS PET1 cytoplasm currently used in hybrid sunflower production. Additionally, closely linked molecular markers were discovered for the male line that can be used to speed up the breeding process, facilitating marker-assisted selection. The new CMS and male fertility restoration line will provide an alternative source for parental line development for hybrid sunflower production.
3. High density molecular map for sunflower rust. Leaf rust is a serious disease of sunflower that has been increasingly prevalent in much of the production area with the development of new virulent races. Molecular markers and high density genetic linkage maps are important tools for understanding genome organization. ARS scientists in Fargo, North Dakota developed a high-resolution genetic map of sunflower. The map consists of 5,019 single nucleotide polymorphism (SNP) DNA markers derived from random amplified polymorphic DNA tag sequencing and 118 publicly available single sequence repeat (SSR) markers distributed in 17 linkage groups. Fine mapping and marker validation of the rust resistance gene R12 were performed, providing closely linked SNP markers for marker-assisted selection in sunflower breeding programs. This high resolution genetic map will serve as a valuable tool for the sunflower community for studying marker-trait association of important agronomic traits, marker- assisted breeding, map-based gene cloning, and comparative mapping.
4. Exploration for sunflower wild crop relatives. Solving insect and disease pests and production problems in sunflower requires new sources of genetic diversity. ARS scientists in Fargo, North Dakota collected new sunflower crop wild relatives from California and Oregon. Collections were made for a newly discovered perennial species in California, Winter’s sunflower, representing the first germplasm of this species to be publicly available. Other germplasm collected has the potential to develop salt-tolerant sunflower that can be grown on salt-impacted lands and with saline irrigation water. The collection of the crop wild relatives for the ARS National Plant Germplasm System not only makes them currently available for improvement of the sunflower crop, but also fills gaps in the collection and preserves them for future generations.
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