Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/30/2014
Publication Date: 6/3/2014
Citation: Seiler, G.J. 2014. Wild sunflower species as a genetic resource for resistance to sunflower broomrape (Orobanche cumana Wallr.). In: Proceedings of the Third Symposium on Broomrape (Orobanche spp.) in Sunflower, June 3-6, 2014, Cordoba, Spain. p. 156-162.
Interpretive Summary: Broomrape is a parasitic weed that infects sunflower roots causing severe crop losses in Central and Eastern Europe, including the Black Sea region, Middle East, Tunisia, Mongolia, and China. It is generally associated with drier climates. Since broomrape is a highly variable parasite, the breakdown of resistance is a frequent phenomenon, and multiple sources of resistance are needed to control the emerging races. Historically, sunflower breeders have been successful in developing broomrape resistant cultivars, but breeding programs are often based on a few dominant genes, and resistance breakdown caused by the appearance of new virulent races has occurred frequently in recent decades. Since the discovery of broomrape races beyond race E, available genes became ineffective in the mid-1990s, and the search for new resistance genes for the ever-evolving new broomrape races has been a major task for all major worldwide sunflower research programs. Wild sunflower species possess an abundance of valuable genes for improving cultivated sunflower, including broomrape resistance, but have long been neglected and under-utilized, especially the perennials due to the difficulties of crossing with cultivated sunflower. However, embryo rescue techniques have been developed that have made interspecific hybridization a routine process. The USDA-ARS, National Plant Germplasm System wild species collection with 53 species is preserving the genetic diversity of the genus Helianthus, but at the same time is making accessions available for screening for broomrape resistance. Wild species have provided genes that confer resistance to races E, F, G, and H, and others that have not been assigned a race designation. Cultivated sunflower has a narrow genetic background and is deficient in genes for resistance to broomrape. The diversity of wild sunflower species in the USDA-ARS wild species genebank offers breeders a diverse genetic pool from which to discover unique genes for existing and emerging new races of broomrape.
Technical Abstract: Broomrape (Orobanche cumana Wallr.) is a parasitic weed that causes economic damage in sunflower production in many countries, especially in Central and Eastern Europe, Spain, Turkey, Israel, Iran, Kazakhstan, and China. Genes for resistance to broomrape races A, B, C, D, and E are present in varietal populations of cultivated sunflower. Since broomrape is a highly variable parasitic weed, the breakdown of resistance is a frequent phenomenon, and multiple sources of resistance are needed to control the emerging races. Genes that confer resistance to races F, G, and H, and others that have not been assigned a race designation have been identified in wild sunflower species and incorporated into hybrid sunflower through interspecific hybridization. The USDA-ARS National Plant Germplasm System wild sunflower collection contains 2,239 accessions with 1373 annual accessions represented by 14 species and 866 perennial accessions represented by 39 species. Sunflower germplasm evaluations for resistance to broomrape races have demonstrated that the Helianthus species constitute a substantial reservoir of genes conferring resistance to new virulence races. The resistance to broomrape, including immunity reported in seven annual and 32 perennial species, provides breeders a broad genetic base from which to search for resistance to existing and newly emerging races.