Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 142

factors with major qualitative effects (Jan 1986). Additive gene action has
the greatest influence on flowering (Miller et al. 1980; Alvarez et al. 1992),
but dominant effects have also been noted (Jan 1986).
Since flowering date is an important agronomic trait for adaptation,
several QTL analysis have been carried out on crop species including
sunflower. Understanding genetic factors influencing DSF could improve
the breeding method and ability to investigate and manipulate other traits
in selection programs. An RFLP/isoezymes F 2 :F 3 mapping population (162
F 3 plants) from a cross between two inbred lines (GH and PAC2) developed
by INRA-France with 82 markers was used for mapping DSF, and three
QTLs were detected on linkage group LG A, LG G and LG L (Mestries et al.
1998; Table 5-1 ). The three QTLs explained 30% of the total phenotypic
variation (R 2 ) and the type of gene action observed was consistent with
partial dominance on LG L and overdominance on LG A and LG G. For the
QTLs on LG A and LG G, the parent, GH, contributed to positive alleles and
for the QTL on LG L, PAC2 alleles increased the trait.
Leon et al. (2000) used 235 F 2 :F 3 progeny from the cross between two
non-restorer (B) photoperiod sensitive lines ZENB8 (female) and HA89
(male), and mapped QTLs controlling DTF in four different environments
(Fargo, ND, and Venado Tuerto, Daireaux and Balcarce in Argentina). An
RFLP genetic map from the same cross with 205 markers and 1,380
centiMorgans (cM) genome coverage was used in their studies. Five QTLs
were identified on LGs A, B, H, I and L that accounted for 73% of the
phenotypic and 89% of the genotypic variation in the mean environment
with LOD scores ranging from 2.7% (LG H) to 38.4% (LG B). The authors
reported that the genetic variation and parental effects of the QTLs were
highly consistent across environments and generations. Two QTLs were
environment-specific on LG H and I, and the others were detected in all
environments (environment-non-specific). Using the same mapping
population, Leon et al. (2001) detected QTLs controlling growing degree
days (GDD) to flowering in six different environments with 12.1, 13.1, 14,
15, 15.5 and 16.4 h photoperiods (PP). Six QTLs associated with GDD
flowering were detected on LGs A, B, H, I, J and L, contributing 67% and
76% of the phenotypic and genotypic variation in the mean environment.
Gene actions were mainly additive and genetic effects for higher values of
GDD to flowering were derived from both parents. QTLs with additive effect
for higher GDD to flowering were derived from HA89 in the LGs A, F and J,
while from ZENB8 in LGs B, I and L. Four of the six QTLs for GDD to
flowering (LGs A, B, F and J) had significant QTL × environment interactions.
The LOD scores for QTLs in LGs A and B were highly dependent on PP. The
LOD scores of QTLs in LG A decreased, while the LOD values of QTLs of LG
B increased, as the PP increased from 12.1 to 16.4 h. Moreover, the LOD
scores for QTLs in linkage group B were not significant at a PP of 12.1 and