Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 160

male fertility restorer line) for mapping QTLs involved in resistance to S.
sclerotiorum ( Table 5-1 ) . For details on the parental lines, the population and
map construction see the section 5.2.2.3. Seven QTLs were identified for
Sclerotinia attacks on terminal buds, three were found for attack on capitolum
and four were identified for latenecy index. The LOD scores were from 2.85
to 12.79. FU parent contributed the positive alleles for six QTLs of the seven
detected for the attack on terminal buds. For attack on capitolum, FU parent
contributed the positive alleles for only one of the three QTLs. Both the
parental lines contributed equally the positive alleles for latency index QTLs.
The R 2 of QTLs was moderate varying from 2.5% to a maximum of 18.7%.
The authors showed also further evidence for additive gene effect for the
resistance to S. sclerotiorum in sunflower.
Micic et al. (2004) used an F 2 :F 3 mapping population (354 F 3 families)
from the cross between a resistant inbred line (NDBLOS) to stalk rot and a
susceptible line (CM625) to identify the QTLs controlling resistance to S.
sclerotiorum using artificial inoculation. The map was constructed by using
117 SSR markers with a total length of 961.9 cM and average interval length
of 9.6 cM. The LGs were numbered as sunflower reference map (Tang et al.
2002). Nine QTLs were identified for the leaf lesion on LG 1, 4, 6, 8, 9, 13 and
15; and seven QTLs were detected for stem lesion on LG 2, 3, 4, 6, 8, 15 and
16, among which those located on LG 4 are common for both the traits. The
total phenotypic variance explained by the QTLs for leaf lesion was 55.8%,
but it was 71.7% for the QTLs controlling stem lesion ( Table 5-1 ). The LOD
scores varied from 2.51 to 36.7 and a major QTL were identified for stem
lesion on LG 8, the position 20 cM from the north of LG. The authors showed
that a large number of QTLs with small effects are involved in resistance to
midstalk, which confirmed the polygenic nature of S. sclerotiorum resistance
in sunflower reported previously by Mestries et al. (1998). The authors also
identified significant QTLs for stem lesion on three of the four LGs reported
by Mestries et al. (1998). Cross-reference between two maps showed that
three QTLs identified for trait mycelium on leaves on LGs 6, 8, and 13 by
Bert et al. (2002), coincided with three QTLs for leaf lesion on LGs 13, 9, and
1, respectively of Micic et al. (2004).
Micic et al. (2005) identified three QTLs for stem lesion, leaf lesion and
speed of fungal growth, and validated some of them by selective genotyping
in an F 3 mapping population derived from the cross betwnn TUB-5-3234
and CM625, being resistant and susceptible parents, respectively ( Table 5-1 ).
Some of the QTLs for different disease resistance traits were overlapped on
linkage groups 4, 10 and 17, and two QTLs for stem lesion showed large
genetic effects and corroborated earlier findings from another cross
NDBLOS×CM625 (Micic et al. 2004). The QTLs explained up to 25% of the
phenotypic variance and in a simultaneous fit 75.9% of the genotypic
variance was explained for leaf lesion and 84.6% for speed of fungal growth.