Molecular Mapping of Complex Traits - Genetics, Genomics and Breeding of Crop Plants - page 163

5.2.3 Self-incompatibility and Seed Dormancy
Self-pollination (SP) and seed dormancy (SD) are genetically complex traits
and a number of self-incompatibility (SI) loci has been disputed (Gandhi
et al. 2005). Wild populations of common sunflower ( Helianthus annuus L.)
are self-incompatible (Heiser 1954; Heiser et al. 1969) and have high seed
dormancy (Heiser 1976; Seiler 1988, 1996, 1998), whereas modern cultivars,
inbreds, and hybrids are self-compatible and partially-to-strongly self-
pollinated (Luciano et al. 1965; Fick and Zimmer 1976; Fick and Rehder
1977; Fick 1978), and have short-lived seed dormancy (Alissa et al. 1986;
Corbineau et al. 1990). Self-incompatibility (SI) and seed dormancy (SD)
complicate breeding in elite × wild hybrids (Seiler 1992), and the genetic
mechanisms underlying SI, SP, and SD in sunflower are either unknown or
superficially known. Gandhi et al. (2005) mapped the QTLs controlling SP,
SI and SD in a backcross mapping population from the cross between an
elite, self-pollinated, non-dormant inbred line (NMS373) and a wild, self-
incompatible, dormant population (ANN1811) ( Table 5-1 ). A population
consisting of 212 BC 1 progeny was subsequently produced by backcrossing
a single hybrid individual to NMS373. The authors identified one QTL for
SI (R 2 = 66.2%) and three QTLs for each SP (R 2 = 63.9%) and SD (R 2 = 38.3%)
on different linkage groups. The results differentiated successfully between
loci governing SI and SP and identified DNA markers for bypassing SI and
SD in elite × wild crosses through marker-assisted selection.
5.2.4 Fertility Restoration and Male Sterility
Hybrid breeding in sunflower is based on a single source of cytoplasmic
male sterility (CMS), which is present in all the female but male-sterile plants.
To produce the hybrid seeds, the CMS plants are crossed with restorer lines
that have the Rf1 (restorer of fertility) gene to obtain fertile plants. A novel
fertility restoration gene has been recently mapped in relation to disease
resistance loci, downy mildew and black rust (Abratti et al. 2008). Using an
F 2 segregating population from the cross RHA340×ZENB8, the authors
reported a new restoration gene on linkage group 7. The ability of molecular
markers linked to this locus facilitates the introgression of this gene in
different lines of breeding programs for developing new restorer lines.
However, map-based cloning of the Rf genes may also help to clarify the
mechanism behind the expression of the CMS-associated mitochondrial
gene.
Two new single recessive nuclear male sterility (NMS) genes ' ms 6 ' and
' ms 7 ' were also identified and mapped using molecular marker approaches
(Capatana et al. 2008; Li et al. 2008). An F 2 population from the cross between
nuclear male sterile mutant NMS HA89-872 and the male fertile line RHA271