Molecular Breeding - Genetics, Genomics and Breeding of Crop Plants - page 234

identification of natural allelic variation in populations or breeding material,
which is known as EcoTILLING (Comai et al. 2004). Its advantages over
other reverse genetics techniques include its applicability to virtually any
organism, its facility for high-throughput analysis, and its independence
from genome size, reproductive system, or generation time. TILLING has
been used successfully for the detection of both induced and natural
variation in several crops, including wheat (Slade et al. 2005), rice (McNally
et al. 2006) and maize (Till et al. 2004). Bauer et al. (2006) and Montemurro
et al. (2007) have proposed establishment of TILLING platforms in sunflower.
These authors describe the development of TILLING populations using
different ethylmethane sulfonate (EMS) treatments, establishment of
heteroduplex analysis for mutation detection, and a pilot screen on three
genes for fatty acid biosynthesis (Sabetta et al. 2008). Although no results
are currently available, the development of TILLING platforms will be a
valuable resource for future sunflower improvement.
7.5 Marker-assisted Selection
In a general sense, marker-assisted selection (MAS) involves the selection of
plants carrying genomic regions that are involved in the expression of traits
of interest using molecular markers. In sunflower, it is clear from other
chapters of this volume that there have been major advances in recent years
in the development of DNA markers, construction of genetic maps, and
mapping of important traits controlled by major genes and/or QTL. Whilst
the number of reports on mapped genes continues to grow rapidly, the
literature on the practical application of those markers in breeding programs
remains very limited. One reason for this is that there are several scientific
and logistical issues that must be resolved before a practical MAS strategy
can flow from a mapping study, and at each step there will be a certain level
of failure. Moreover, MAS programs in sunflower are mainly carried out by
private breeding companies, which may have restrictions on publishing
their findings. Therefore, in this section we will deal with factors that can
enhance the efficiency of MAS, and describe the few examples of practical
use of molecular markers in breeding programs that have been published in
this crop.
7.5.1 Marker Validation and Refinement
The efficiency of MAS depends on many factors associated with how the
underlying marker-trait associations were identified, including the size of
the mapping population, the nature of phenotyping, the design and analysis
of the experiment, the number and quality of markers used, the proximity
between markers and the trait of interest, and the proportion of the