50 Years of Collecting Wild Sunflower
Wednesday, October 25, 2023
filed under: Research and Development
The October/November 2022 issue of The Sunflower carried a feature article focused on the retirement of Gerald Seiler, longtime USDA Agricultural Research Service botanist, Fargo, N.D. Seiler’s ARS career spanned 48 years, during which he played a major role in the collection, maintenance and distribution of sunflower wild species, both domestically and globally.
Why is this work so important to sunflower producers and the industry in general? Wild species — now commonly referred to among scientists as “crop wild relatives (CWR)” — constitute the essential foundation for the ongoing development of improved sunflower hybrids. Along with contributing tolerance and resistance to diseases like rust, downy mildew and Verticillium wilt, sunflower’s wild species offer ever-expanding access to traits such as salt, drought and insect tolerance, as well as increased tolerance/ resistance to diseases like Phomopsis and Sclerotinia.
Such traits don’t make the journey from their “wild state” into commercial hybrids easily. A host of scientists are involved at different stages during the multi-year process: from a seed collector/maintainer/distributor like Seiler, to plant pathologists, entomologists, agronomists, molecular geneticists — and, of course, public and private sunflower breeders. Some species cross more readily with Helianthus annuus, the predominant species in commercial hybridization, while other species are extremely difficult to cross with refined germplasm in order to retrieve, massage and utilize their sought-after trait(s).
An in-depth discussion of the long but vital collection journey appeared in a recent online issue of Helia, a publication of the International Sunflower Association. Authored by Gerald Seiler along with Tom Gulya* and Laura Fredrick Marek**, the article is titled “Fifty Years of Collecting Wild Helianthus Species for Cultivated Sunflower Improvement.” It’s an authoritative summary of the work by Seiler, Gulya, Marek and others across the past half century to seek out and preserve what is, essentially, a “gold mine” of sunflower diversity.
USDA established the wild Helianthus seed collection in 1976 at Bushland, Texas, “with the goal of collecting and conserving the broadest representative genetic diversity possible and serving as a central repository of germplasm and related information,” Seiler and his co-authors recount in the Helia article. This collection was transferred in 1985 to the ARS North Central Regional Plant Introduction Station at Ames, Iowa.
Across the past half century, 37 explorations were undertaken covering 175,000 km (nearly 109,000 miles) to collect seed populations of 53 Helianthus species from their varied distributional ranges. Those trips encompassed all 48 contiguous U.S. states, three Canadian provinces, Argentina and Australia. “The current wild CWR sunflower genebank contains 2,562 accessions of 53 species,” Seiler et al report, “with 1,065 Helianthus annuus accessions (42%), 617 accessions representing populations of the 13 other wild annual species (24%), and 880 accessions representing 39 perennial species (34%).
“This collection is the largest and most genetically diverse ex situ sunflower CWR seed collection in the world and is vital to the conservation of wild sunflower species for the global sunflower community,” the article in Helia stresses.
The Helia article points out that sunflower (H. annuus) is one of only a few modern-day crops whose center of origin is North America. That’s important for various reasons — but especially so because “crop wild relatives are typically adapted to different environmental conditions than their domesticated relatives.”
That means genetic material from these wild species “has the potential to play an important role in breeding for greater abiotic and biotic stress tolerance.”
Speaking to crops in general, including sunflower, Seiler, Gulya and Marek emphasize that genetic diversity “contributes to long-term preservation of species by allowing them to adapt quickly to changes in their environment.” Even secondary or tertiary gene pools in a wild species can be of real value, they add, because they “may contain genes that will protect crops with no or minimal host resistance against current pests or new pests in the future.”
The collection of wild species “not only preserves valuable germplasm, but also provides information about the diverse habitats occupied by wild sunflower and associated species,” Seiler et al continue. “The wild species are adapted to a wide range of habitats and possess considerable variability for most agronomic and achene quality characters, and reaction to insects and disease pathogens.” Being knowledgeable about a particular species’ native habitat and the population’s adaptation to its immediate environment means scientists can more accurately and efficiently select species that possess the unique traits being sought.
The Explorations: When, Where & What
Prior to 1976, when USDA formally established the wild Helianthus repository at Bushland, the sunflower collection was comprised of about 375 accessions housed at three locations: USDA/Texas A&M University at College Station, Texas (curated by Murray Kinman), USDA/ University of California at Davis, California (curated by Ben Beard) and USDA/ Fargo, North Dakota (curated by Bill Roath). Those collections consisted largely of annual species of sunflower, particularly wild H. annuus. Several individual scientists had undertaken collection trips in various U.S. regions through the years; but the collection had no real formal structure.
That began to change after the 1976 Bushland location development. Seiler and ARS Bushland colleagues Charlie Rodgers (entomologist) and Tommy Thompson (breeder), along with occasional foreign visiting scientists like Luka Cuk (Yugoslavia), began expanding the sunflower collection. For example:
• In 1980 Seiler and Cuk collected 400 accessions of wild sunflower over a three-month period. The accessions, which included 11 annual and 24 perennial species, were collected from locales in the southeastern, south central and southwestern United States.
• In 1981 Seiler and Rodgers went searching in the Great Plains, from Texas to North Dakota, collecting 34 new accessions of two annual sunflower species and nine perennial species.
• The following year, Ted Van Bruggen of the University of South Dakota added 61 accessions of several annuals from South Dakota and Iowa.
• A 1984 trip into southern Texas by Seiler resulted in 49 accessions of various annual species from wild populations.
Across ensuing years, Seiler and others traveled to several additional parts of the United States, including the Northeast and East (1985) and the Pacific Northwest (1987). The first exploration outside of the United States occurred in 1994 when Seiler and Mary Brothers, the then-curator of the Ames-based sunflower collection, undertook an exploration trip in the Canadian provinces of Manitoba, Saskatchewan and Alberta. Additional collection trips included the southwestern U.S. (2000), California (2002 and 2003), and the southeastern U.S. (2003).
After 2003, the Helia article recounts, the explorations made by Seiler and others became increasingly selective, focusing primarily on the collection of “underrepresented species from more restricted distributional ranges to fill gaps in the collection.” The varied geography on these trips was a strong reminder of the exceptional diversity of sunflower. For instance, a 2005 trip included the U.S.-Mexican border of southern California and the Pinta Sands area of Arizona, where the treasures included a population of a species with potential for drought tolerance.
Another collection trip that year focused on the high altitudes of Colorado and Wyoming. A 2006 trip explored the southeastern United States. Australia and Argentina were visited in 2007, with accessions of several naturalized wild sunflower species brought back and added to the ARS collection. Some collection trips amounted to a literal race against select populations’ disappearance due to urban development and/or other intrusions upon native habitats.
More collection trips, conducted mainly by Gerald Seiler and Laura Marek, continued through the decade of the 2010s. Again, the goal was to “fill in” gaps in the wild sunflower collection to reflect and utilize the outstanding diversity of sunflower. As illustrated in the photos accompanying this article, the Crop Wild Relatives of cultivated sunflower have very different physical appearances, exist in a wide range of natural habitats, from desert to tropical — and, as a group, possess a remarkable array of potentially useful traits.
Where We’re At
Since the formal establishment of the USDA sunflower CWR collection in 1976 explorations by Seiler and his USDA colleagues, along with scientists from several other national and international institutions, have added close to 2,800 accessions — including several new and endemic species — to the ARS Iowa genebank collection. As noted previously, this collection contained a total of 2,562 accessions as of early 2023, of which 1,682 are annual sunflower species and 800 are perennials. Of the 1,682 annuals, 1,065 are Helianthus annuus, the closest relative of cultivated sunflower. Growouts of most of those accessions have been conducted on a regular basis by Laura Marek in Iowa to increase seed populations to the point where they can continue to be distributed to interested parties, mainly sunflower breeders, both domestically and abroad.
Those are impressive numbers, together representing a remarkable treasure chest of sunflower genetic diversity. Equally important, because of the many years of successful population growouts, 97% of the annual accessions are available to sunflower breeders and other qualified scientists, as are 83% of the perennial accessions.
Still, as successful and enduring as the work of Seiler and others has been, “the need for continued, future explorations is apparent in the number of species with low accession numbers,” the Helia article states. Currently, there are five taxa with less than five available accessions; seven species with less than 10 available accessions; and another four that currently have no accessions in the ARS collection. “Some accessions do not have adequate seed for distribution at this time but will be increased and become available in the future,” the Helia article notes.
To what degree have private and public scientists utilized this collection? During the period 2001 to 2011, there were 520 requests from 430 recipients, totaling 10,683 accession items. For the period covering 2010 through 2019, however, a total of 36,000 accessions items from 1,214 orders (923 domestic and 291 international) were distributed. USDA-ARS National Plant Germplasm System sunflower accessions have become the basis of wild species research programs in a foreign countries such as Argentina, Bulgaria, China, France, Germany, Hungary, India, Italy, Romania and Russia, Serbia (former Yugoslavia), Spain and Mexico.
It’s all a wonderful gift that keeps on giving — and will continue doing so for many years to come. Plant breeders, sunflower growers and the industry in general are major direct beneficiaries. — Don Lilleboe
* Tom Gulya is retired research plant pathologist with USDA-ARS, Fargo, N.D.
**Laura Fredrick Marek, Iowa State University and USDA-ARS, is curator of the sunflower collection at the NCR Plant Introduction Station, Ames, Iowa.
Anyone interested in receiving a reprint of the Helia article is invited to contact firstname.lastname@example.org