Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 152

three, two and two QTLs were detected for Chl a , Chl b , Chl a /Chl b and Chlt
in the F 2 generation, respectively. Individual QTLs explained 8.8-49.5% of
the phenotypic variance and three QTLs for leaf greenness degree were
identified in the F 3 generation with R 2 from 10.8% to 27.2%. The authors
concluded that the genetic basis of morphological traits is very complex
and each trait is under the control of multiple genes. The authors confirmed
also one QTL for plant height on LG 17 ( ph6 ) to be linked to an SSR marker
ORS811, which had been reported earlier in the same genomic region by
Burke et al. (2002).
5.2.1.3 Oil Content and Yield-related Traits
Breeding of sunflower have focused mainly on yield and oil content. Seed
yield is known to be dependent on both additive and non-additive gene
actions, and genotype × environment interactions are important component
of variance leading to low heritability (Fick 1978). Furthermore, yield in
sunflower, as in all other crops, depends on many component characters,
which have polygenic mode of inheritance (Fick and Miller 1977). A polygenic
nature of inheritance has been indicated for oil content with heritability
estimates of 65 to 70% (Fick 1975). Oil content is determined by grain yield
and oil percentage in the grain. Therefore, both the characters are important
to be considered in breeding programs simultaneously. The use of molecular
markers provided additional information about the genetic basis of seed-oil
concentration.
Leon et al. (1995) used a genetic map of 201 RFLP markers and identified
six QTLs associated with 57% of genetic variation for oil content among the
F 2 progeny. Two QTLs were identified for seed oil concentration (LG C and
LG I), two for seed percentage (LG G and LG J) and the other two for both
traits (LG B and LG N); and additive effect was predominant for seed-oil
concentration. In a later study, the same mapping population was used for
mapping QTLs controlling seed oil concentration across four locations in
Argentina (Venado T, Daireaux, Balcarce) and USA (Fargo, ND) and the
measurements were recorded on F 3 plants. Eight QTLs on seven LGs (B, C,
G, I, L, M and N) were identified for mean values of the trait in the four
environments. These eight QTLs accounted for 59% and 86% of phenotypic
and genotypic variance, respectively. Alleles for increasing seed oil
concentration were all derived from HA89, the parent with higher values
for that trait. Gene action was additive for four QTLs on LGs B, C, I and M;
dominant for two QTLs on LGs G and N and overdominant for one QTL on
LG L. The authors confirmed five QTLs detected from a previous work by
Leon et al. (1995) in their study. These were located on LGs B, C, G, I and N.
QTLs for percentage of oil in grain and seed weight were also detected
by Mestries et al. (1998) in F 2 , F 3 and F 4 generations derived from an F 2