Call of the Wilds
Wild sunflowers are somewhat of a paradox for cultivated sunflower. Concern about outcrossing or cross-pollination with wild species has held back biotech research in cultivated sunflower. At the same time, wild sunflower species represent a tremendous genetic resource for improving cultivated sunflower hybrids.
For example, it was genes from a wild species that led to cytoplasmic male sterility, the mechanism by which today's sunflower breeders develop new sunflower hybrids. And many of the genes for disease resistance introduced into cultivated sunflower were derived from wild sunflower species. USDA estimates that the economic value of traits already bred into cultivated sunflower from wild species is an estimated $267 million to $384 million annually.
Scientists with the USDA’s Agricultural Research Service have been collecting wild sunflowers since 1976. Accessions are placed in the ARS National Plant Germplasm System at Ames, Iowa, for safekeeping and distribution to sunflower researchers worldwide.
The USDA-ARS Sunflower Unit at the Northern Crop Science Laboratory (www.fargo.ars.usda.gov/sun/sun_home.htm) is a clearinghouse of sorts for newly collected specimens en route to being catalogued and stored at the germplasm bank in Iowa. Seeds are first evaluated for weight, oil content and fatty acid composition. The new accessions are then tested for possible resistance to economically important sunflower diseases.
H. annuus is the predominant Helianthus species kept at the wild sunflower germplasm bank, which has 2,163 accessions. H. annuus' preference for disturbed soils – like roadside grading and constructions sites – indicates the species’ tenacity and adaptability, notes ARS plant pathologist Tom Gulya.
Others are habitat-specific and vulnerable to human activity. In Texas, for example, road projects pushed aside populations of H. paradoxus. Fortunately, new ones were found in New Mexico. Now, H. paradoxus’ seed is in safe storage, including its genes for breeding salt- and drought-tolerant hybrids.
Gulya and ARS botanist Gerald Seiler collect wild sunflowers once or twice a year, typically driving 2,500 to 3,000 miles per trip across the U.S., much of that on back roads, to map and describe each new site so future collections of wild species can be made. They estimate at least one trip annually for the next 10 years will be needed to collect all remaining wild sunflower species native to the United States.
Collecting and cataloguing wild sunflowers is one thing, transferring useful genes to their cultivated sunflower cousins is another. Transferring genes can be difficult, especially when the transfer is attempted between annual and perennial species.
Recently, however, ARS geneticist Chao-Chien Jan discovered a gene from H. californicus, a wild perennial sunflower indigenous to central and southern California, that causes natural chromosome doubling in crosses with cultivated sunflower. The discovery may ultimately help facilitate transfer of useful genes from wild sunflowers into the cultivated crop.
Wild sunflower species was a major focus of this year’s annual Sunflower Research Forum, held recently in Fargo. Many facets of monitoring, managing, evaluating, and using wild species for the improvement of cultivated sunflower were discussed. Seiler notes that it was likely the most comprehensive discussions ever held regarding wild sunflower research involving the full spectrum of the sunflower industry, from researchers to growers and processors.
Detailed reports and proceedings from the 2005 Sunflower Research Forum will soon be posted online at www.sunflowernsa.com. Click on the “Research” link. – Tracy Sayler, with information from Brady Vick and Jan Suszkiw, USDA-ARS
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