Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 162

5.2.2.5 Resistance to Orobanche cumana
Under semidry conditions (Spain, Israel, Northern Africa), Orobanche cumana ,
a root parasite of sunflower appears to be one of the most important
constraints of sunflower production. Different races from A to E of broomrape
( Orobanche cumana ) have been described (Alonso 1998), and a monogenic
dominant inheritance of resistance to races A to E was found in most of the
genetic studies (Pogorletsky and Geshele 1976; Vranceanu et al. 1980; Ish-
Shalom-Gordon et al. 1993; Sukno et al. 1999). However, some reports pointed
to a more complex inheritance of the trait, including two dominant genes
(Domenguez 1996), one recessive gene (Ramaiah 1987), double recessive
epistasis (Kirichenco et al. 1987) or even quantitative inheritance (Pustovoit
1966).
Genetic mapping of several sources of resistance to Orobanche cumana
were described (Lu et al. 1999, 2000) leading the way to putative breeding
for appropriate sunflower inbred lines. In the late 1970s, five pathogenic
races named A through E, with a set of sunflower differentials carrying the
dominant resistance genes Or1 through Or5 have been identified. Pérez-
Vich et al. (2004) identified five QTLs for resistance to the race E and six
QTLs for resistance to the race F (identified later in the mid 1990s in Spain)
of broomrape on seven out of the 17 linkage groups ( Table 5-1 ) . Phenotypic
variance for resistance to the race E was mainly explained by a major QTL
(R 2 = 59%), while the race F resistance was explained by QTLs with small to
moderate effects (R 2 = 15.0-38.7%). The results suggested that resistance to
broomrape in sunflower is controlled by a combination of qualitative, race-
specific resistance affecting the presence or absence of broomrape and a
quantitative non-race specific resistance affecting their number. However,
the nature of the Or1 to Or5 genes involved in this interaction is not known.
Marquez-Lema et al. (2008) investigated the nature of the Or5 gene through
a candidate gene approach, and identified markers close to the gene in
order to facilitate map-based cloning strategies. Using an F 2 population
from the cross between a resistant line to races E and F of broomrape (P-21)
and a susceptible line (P-96), several SSRs, TRAPs and candidate gene
markers were genotyped and the linkage map was constructed. The authors
mapped the Or5 gene on LG 3 close to TRAP marker, TRC27133 and SSR
marker, CRT392c. Unfortunately, among the 12 candidate genes tested, three
were mapped on LGs 7, 9 and 17, but none of them was located close to the
Or5 gene, which needs further investigation (Marquez-Lema et al. 2008).
Linkage of molecular markers with resistance genes to rust was also
described in sunflower (Lawson et al. 1998). Thus, several tools are already
available to breeders for the improvement of breeding processes for disease
resistance in sunflower.