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68 linkage group codes were generated for the 17 sunflower chromosome
pairs in four different linkage group nomenclatures. By using probes from
three independent sources, Gedil et al. (2001) integrated 14 of 17 linkage
groups from two independent RFLP maps with an F
2
population derived
from two public sunflower lines, HA 370
HA 372. Thanks to the availability
of the mapped public SSR markers, almost all recently published maps are
now anchored by linkage group specific SSR markers and can be cross-
referenced.
3.7 Challenges
Satisfactory results have been achieved for sunflower genome mapping and
characterization, yet several challenges remain for the sunflower research
community. The first is data handling. Implementation of high-throughput
sequence-based markers in sunflower genome mapping in the near future
will generate enormous amount of data, which will be hard for individual
researchers to comprehend without help from a database. Therefore, there
is an urgent need to develop a public database of mapping information
from all mapping populations with cross-references.
The second challenge is the correlation of DNA sequence alterations
with the quantitative variations of economically important traits. Progress
has been made in locating many QTLs for traits of agronomic importance in
sunflower. However, previous QTL mapping was merely the identification
of anonymous markers in or near the chromosome regions affecting the
traits under study. The use of candidate gene-based markers in mapping
has just begun. With the rapidly advancing sequencing technology and the
fast reducing sequencing cost, most of the sunflower genes, or even the
whole genome, will eventually be sequenced. The observed phenotypic
variation of the mapping population is influenced by genotypes (G),
environments (E), and the interactions of G and E. The collection of phenotype
data will depend strongly on traditional quantitative genetic evaluation
systems which are time-consuming and labor-intensive. A coordinated,
cooperative effort on observing large mapping populations in various
environments is crucial to the sunflower crop. The ideal map will comprise
Figure 3-1 contd....
Figure 3-1
The public sunflower linkage map consisting of 577 SSR markers and 403
TRAP markers. The names of the SSP markers are in black. The names of the TRAP
markers amplified with fixed primers targeting the conserved telomeric repeat and
mapped to interstitial positions sequences are in green and mapped to the termini
positions are in red. The TRAP markers amplified with fixed primers designed against
selected sunflower ESTs showing homology with components of plant disease resistance
genes and homeobox genes are in blue (reprinted with permission from Dr. Dragan
Škori
'
, Editor-in-Chief of Helia, an international scientific journal published in Serbia).
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