Molecular Breeding - Genetics, Genomics and Breeding of Crop Plants - page 229

included Pl1 , Pl2 , Pl6 , and Pl7 , another one on LG 13 which included Pl5
and Pl8 , and a third one on LG 1 for Pl arg (Vear et al. 1997; Bert et al. 2001;
Bouzidi et al. 2002; Dussle et al. 2004). The Or5 gene was located on a
telomeric region of LG 3 (Lu et al. 1999, 2000; Tang et al. 2003; Pérez-Vich
et al. 2004). Other genes such as Ms6 , Ms7 , Ms9 , Ms10 , and Ms11 ,
determining nuclear male sterility, and S , controlling self-incompatibility,
were located on LG 16, 6, 10, 11, 8, and 17, respectively (Gandhi et al.
2005; Pérez-Vich et al. 2005; Chen et al. 2006; Capatana et al. 2008; Li et
al. 2008).
In addition, molecular mapping studies in sunflower have identified
genes or chromosomal regions that control quantitative traits, so-called
quantitative trait loci (QTL). Three to eight QTLs determining oil content
and its components (i.e., percentage of kernel weight in relation to whole
achene weight and kernel oil concentration) have been mapped (Leon et
al. 1995a, 2003; Mestries et al. 1998; Mokrani et al. 2002; Bert et al. 2003;
Tang et al. 2006a). The QTLs on LG 10, 16, and 17 were reported to be
centered on the phenotypic loci B (apical branching), hyp (pigmentation of
the achene hypodermis layer), and P (pigmentation of the achene
phytomelanin layer), respectively (Tang et al. 2006a). With respect to disease
resistance, lists of QTLs for resistance to white rot ( Sclerotinia sclerotiorum
[Lib.] de Bary), Phomopsis ( Diaporthe helianthi Munt-Cvet. et al.) and black
stem ( Phoma macdonaldii Boerma) are becoming available (Bert et al. 2002,
2004; Al-Chaarani et al. 2002; Micic et al. 2004, 2005a, b; Rönicke et al.
2005; Abou Alfadil et al. 2007; Darvishzadeh et al. 2007; Yue et al. 2008).
QTLs for other complex traits such as somatic embryogenesis and in vitro
organogenesis (Flores-Berrios et al. 2000) or photosynthesis and water
status (Hervé et al. 2001; Poormohammad Kiani et al. 2007) have also been
reported.
It is obvious that the targets for molecular breeding in sunflower do not
(and should not) differ markedly from those of conventional breeding. These
objectives may vary with specific programs, but the main emphasis is high
seed yield, high oil content, and improved oil quality for special markets.
Seed yield, and to a lesser extent, oil content depend on many factors
including a suitable agronomic type, tolerance to abiotic stresses, and
resistance to diseases and insects, and these, consequently, have also become
important marker assisted objectives.
7.3 Germplasm Characterization
Traditionally, germplasm characterization has been assessed by measuring the
variation in phenotypic traits. This approach has certain limitations, as the
number of traits that can be routinely measured is limited and they are subject
to environmental influences. Molecular markers circumvent these issues and