Molecular Breeding - Genetics, Genomics and Breeding of Crop Plants - page 228

between alleles of a gene underlying a given phenotype. Examples of this
type of markers in sunflower are currently rare, but they have been developed
for traits determining oil quality (Tang et al. 2006b) and herbicide resistance
(Kolkman et al. 2004).
The ideal DNA marker system for molecular breeding should meet
the following requirements: the ability to detect high level of
polymorphism, codominance, abundance (i.e., whole genome coverage),
high reproducibility, suitability for high-throughput analysis and
multiplexing, technical simplicity, cost effectiveness, require small
amounts of DNA, and be user-friendly (such as their suitability for use
in different genotyping systems and facilities). The second and third
generation of sunflower markers including SSRs, gene-targeted and
functional markers generally satisfy these requirements, thus providing
an excellent platform for molecular breeding programs. In addition, the
development of a reference map using both an internationally accepted
linkage group nomenclature system and publicly available markers, for
cross-referencing maps and mapped gene locations, is also an essential
prerequisite. In sunflower, the reference genetic map is the one reported
by Tang et al. (2002) based on a recombinant inbred line (RIL) population
derived from RHA280 x RHA801, which comprises a critical mass of
public SSR markers. Additionally, the “immortal” RIL mapping resource
enables the on-going placement of new markers, such as InDels derived
from RFLP cDNA probes (Yu et al. 2003), SNPs based on ESTs (Lai et al.
2005) or telomere sequence repeat-derived markers (Hu 2006). It should
be noted that the linkage group nomenclature of this reference map will
be used throughout this chapter.
Determination of significant marker-trait associations is essential
for any molecular breeding program. A number of major genes underlying
simply inherited traits have been mapped in sunflower, and molecular
markers linked to them or based on candidate genes have been described.
For oil quality, the Es1 , Es3 , and Ol genes controlling modified fatty
acid profiles, and the Tph1 and the Tph2 genes, associated with altered
tocopherol profiles, were located on linkage groups (LGs) 1, 8, 14, and 1,
and 8, respectively. Markers based on stearoyl-acyl carrier protein desaturase
(for Es1 ), oleoyl phosphatidyl-choline desaturase (for Ol ), 2-methyl-6-
phytyl-1,4-benzoquinone/2-methyl-6-solanyl-1,4-benzoquinone
methyltransferase (for Thp1 ) and gamma-tocopherol methyltransferase (for
Tph2 ) genes were subsequently developed (Pérez-Vich et al. 2002, 2006;
Hass et al. 2006; Schuppert et al. 2006; Tang et al. 2006b). For disease
resistance, the major Pl genes conferring resistance to downy mildew
( Plasmopara halstedii [Farl.] Berl. and de Toni), and the Or5 gene associated
with resistance to race E of broomrape ( Orobanche cumana Wallr.) have been
mapped. The Pl genes were mapped to different clusters, one on LG 8 that