Selection of wild and cultivated sunflower for resistance to a new broomrape race that overcomes resistance of the Or5 gene

Broomrape (Orobanche cernua Loefl., syn. O cumana Wallr.) populations belonging to a new race F in Spain have overcome all known resistance genes Or(1) to Ol(5) in cultivated sunflower (Helianthus annuus L.) and are spreading rapidly. All hybrids currently grown in Spain are susceptible to race F, and sources of resistance genes for this race are needed to develop new resistant cultivars. The objective of this study was to evaluate sunflower germplasm for resistance to race F (virulent population SE296). Using artificial inoculation with broomrape seed, 54 accessions of wild Helianthus spp. representing 27 perennial and four annual species and 55 cultivated accessions of sunflower were evaluated after incubation for approximate to 1 mo in a growth chamber. Helianthus seedlings were transplanted to the greenhouse for an additional approximate to 3 mo to evaluate the broomrape infection. Most perennial species of wild Helianthus were completely resistant to race F, but some accessions of the species H. divaricatus, H. maximiliani, and H. pauciflorus subsp. pauciflorus showed different proportions of susceptible plants, with a disease incidence varying from 10 to 80%. The annual wild species, H. anomalus and H. agrestis, were fully resistant, while segregation was observed in H. debilis subsp. cucumerifolills and H. exilis. Only 7.2% of the accessions of cultivated sunflower tested were fully resistant, with 20% of them segregating for resistance. The high frequency of broomrape resistance to race F observed in the perennial wild species, as well as the resistance found in wild annual and cultivated germplasm, indicates that development of sunflower cultivars resistant to this new race of the parasite is feasible.