Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 154

phenotypic variance and QTLs alleles for increased oil were transmitted by
the oilseed parent (RHA801). Five QTLs were identified on LG 5, 9, 10, 14,
and 17 for 100-seed weight. The QTLs collectively explained 73.4% of the
phenotypic variability. The RHA280 allele from four of the five QTLs
increased 100-seed weight, whereas the RHA280 allele for one of the five
QTLs decreased 100-seed weight. Results showed that three QTLs on LG 9,
10 and 17 control both the traits. An apical branching loci (B) and a
phytomelanin pigment loci (P) were linked to a QTL, which control both the
traits on LG 10 and 17, respectively. The B -liked QTL, which is located on
linkage 10, explained 22.5% and 52.5% of phenotypic variation for seed oil
concentration and 100-seed weight, respectively. The effect of B-linked QTLs
on seed oil concentration and 100-seed weight has been also reported in
two high-oil×high-oil mapping populations, GH×PAC2 (Mestries et al. 1998)
and XRQ×PSC8 (Bert et al. 2003). However, the effect of B -linked QTL on
seed oil concentration showed different direction in different genetic
backgrounds.
The seed oil of standard cultivated sunflower is composed primarily of
the saturated fatty acids palmitic (C16:0) and stearic (C18:0), and the
unsaturated oleic (C18:1) and linoleic acids (C18 : 2), with C18:1 and C18:2
accounting for about 90% of the total oil fatty acids (Dorrell and Vick 1997).
The quality of standard sunflower oil is defined by the relative content of
C18:2, which is high in most of the crop grown throughout the world. The
genetic control of the synthesis of stearic acid (C18:0) and oleic acid (C18:1)
in the seed oil of sunflower was studied through candidate-gene and QTL
analysis (Pérez-Vich et al. 2002). Two F 2 mapping populations were
developed using the high C18:0 mutant CAS-3 crossed to either HA-89
(standard, high linoleic fatty acid profile), or HAOL-9 (high C18:1 version
of HA-9). The HA-89 × CAS-3 map comprised 154 markers covering 1,808
cM with a mean spacing of 12.0 cM. The HAOL-9×CAS-3 map comprised
134 markers covering 1,642 cM with a mean interval of 12.5 cM between
markers. Two and four QTLs controlling stearic acid content were detected
in HA-89×CAS-3 (LG 1 and 7) and HAOL-9×CAS-3 (LG 1, 3, 8 and 14),
respectively. The two QTLs detected in HA-89×CAS-3 and four QTLs detected
in HAOL-9×CAS-3 for stearic acid content accounted for 79.3%, and 84.4%
of phenotypic variation, respectively ( Table 5-1 ) . One major QTL affecting
the C18:0 concentration (peak LOD 48.5) was identified on LG 1 in the HA-
89×CAS-3 F 2 population, explaining 78.6% of the phenotypic variation in
the C18:0 concentration. The CAS-3 allele at this QTL locus increased the
C18:0 content. In HAOL-9×CAS-3 F 2 population, two major C18:0 QTLs
were detected. The main C18:0 QTL was detected on LG 1 (peak LOD 50.6)
and it explained 81.3% of the phenotypic variance for this trait. A stearoyl-
ACP desaturase locus (SAD17A) was found to cosegregate with this locus
( Es1 ) controlling the high C18:0. A second major C18:0 QTL was located on