Crop Wild Relatives of Sunflower As a Genetic Resource for Resistance to Sunflower Broomrape.

Crop wild relatives (CWR) have been undeniably beneficial to modern agriculture dating back 100 years, providing plant breeders with a broad pool of useful genetic diversity. Sunflower CWR have been particularly valuable for the sunflower crop with an estimated contribution of 26% of the annual value of the crop. Much of this value is derived from disease resistance genes. The USDA-ARS, National Plant Germplasm System sunflower crop wild relatives collection contains 2,519 accessions with 1028 wild <i>Helianthus annuus </i>accessions (41%), 613 accessions representing populations of 13 other annual species (24%), and 878 accessions representing 39 perennial species (35%).This diverse collection of CWR provides potential resistance sources for broomrape (<i>Orobanche cumana Wallr.</i>), a parasitic weed that infects sunflower roots causing severe crop losses in many countries, especially in Central and Eastern Europe, including the Black Sea regions, and the Middle East. Broomrape is a highly variable parasitic weed controlled by vertical resistance of single dominant genes that leads to a rapid breakdown of the resistance and subsequently the continuous need for new and multiple sources of resistance to control new emerging virulent races. Sunflower germplasm evaluations for resistance to broomrape races have demonstrated that the <i>Helianthus</i> species constitute a substantial reservoir of genes conferring resistance to new virulence races. Resistance genes have been discovered in CWR conferring resistance to new virulent broomrape races F, G, and H, and others that have not been assigned a race designation. Broomrape resistance genes have been incorporated into hybrid sunflower through interspecific hybridization. The resistance to broomrape, including immunity has reported in seven annual and 32 perennial species, providing breeders with a broad genetic base from which to search for resistance to existing and newly emerging races.