Pathogenic comparison of highly virulent O. cumana affecting sunflower in Moldova, the South of Russian Federation, Serbia and Spain

The most effective method for controlling the parasitic weed Orobanche cumana (sunflower broomrape) is the incorporation of genetic resistance into cultivated sunflower. According to different genes of resistance that are overcome, several races of the parasite are pathogenically identified. Race G is the most virulent one because it infects the universal resistant inbred line P96. Besides, populations of O. cumana are molecularly clustered according to geographical origin, and pathogenic traits are secondary criteria for genetic differentiation. In this work highly virulent parasite accessions collected in Moldova, the South of Russian Federation, Serbia and Spain were pathogenically compared. Six accessions were inoculated onto differentials of highly virulent races of the parasite: NR5, L86 and P96. Plants were grown under shadehouse and glasshouse for ten weeks following a factorial on a completely randomised design. At the end of the experiment none of the accessions infected P96. According to the reactions of the inbred lines NR5 and L86, accessions from Moldova and Serbia were identified as race E, and accessions from Spain were identified as race F. Accessions from the Russian Federation showed intermediate pathogenic behaviour onto NR5 and L86. Since a highly virulent biotype of O. cumana is present in Rostov oblast and seed used in this work comes from individual broomrape plants, the presence of race F in this area might be confirmed through the study of genetically heterogeneous parasite accessions from the area. Our results show that, in order to efficiently manage the genetic resistance into cultivated sunflower, there is a need for a worldwide study of highly virulent populations of O. cumana.