Increased Virulence in Sunflower Broomrape (Orobanche cumana Wallr.) Populations from Southern Spain Is Associated with Greater Genetic Diversity
Genetic resistance to broomrape (Orobanche cumana Wallr.) in sunflower is mainly monogenic and dominant. Massive use of vertical resistance has led to the progressive extension of increasingly virulent races of the parasite. Additional introduction of horizontal resistance genes is crucial to develop more durable resistance. The objective of this research was to study the inheritance of resistance to broomrape race F in sunflower line K-96 and to identify QTL of potential value for marker assisted pyramiding of resistance genes. The inheritance of broomrape resistance was studied in crosses with the susceptible line P-21 and the line P-96, with oligogenic recessive resistance. Crosses with P-96 revealed broad transgressive segregation for susceptibility in the F2, indicating that both lines possess different resistance alleles. Crosses with P-21 suggested that the trait is mainly controlled by a dominant-recessive epistasis at two loci. Additionally, segregation for plant height was identified and measured in a non-inoculated F2 population. Five QTL on LG 2, 3, 4, 5, and 6 were associated with broomrape resistance traits. Two of them at LG 4 and 5 were also associated with plant height, suggesting an alleged pleiotropic effect of plant height on broomrape resistance. The latter two QTL had been previously identified in the cross P-21 × P-96, whereas the other QTL seem to be involved in K-96 but not in P-96 resistance. This study concluded that K-96 and P-96 have complementary QTL with minor effect on broomrape resistance. They are, therefore, good donor sources for marker-assisted pyramiding programs.