Mapping and Tagging of Simply Inherited Traits - Genetics, Genomics and Breeding of Crop Plants - page 126

largest and most complex cluster were identified and on LG 13 ( Pl 5 , Pl 8 ) the
second largest NBS-LRR cluster with TIR-NBS and non-TIR-NBS-LRR loci
were found. Thus, Radwan et al. (2008) allocated a source for identification
and cloning of R -genes like Pl 8 and R ADV (against rust). Furthermore, they
also showed the importance of wild species as a source of R -genes in
sunflower, because RGAs identified from wild species ESTs were linked to
several important R -genes like Pl ARG , OR 5 , Pl 8 , R 1 , R Adv (see Sections 4.2.2 and
4.2.4 for details).
4.2.2 Rust Resistance
Sunflower rust caused by the fungus Puccinia helianthi Schw. is a major
disease of sunflower that has been attributed to causing significant yield
losses in oilseed and confectionary crops grown in all regions of the world.
As gene pyramiding through traditional plant breeding can be a cumbersome
task because the presence of new genes introduced into the common
background is masked by genes already present, the use of genetic markers
is necessary for pyramiding of genes. Lawson et al. (1998) developed two
SCAR markers for the rust resistance genes R 1 and R Adv through conversions
of polymorphisms identified by RAPD-PCR and BSA. SCAR marker
SCTO6151 was tightly linked to the R 1 gene for resistance to rust race 1 and
was mapped to LG 8 close to a cluster of NBS-LRR resistance gene candidates
and the Pl 1 gene for resistance to downy mildew by Yu et al. (2003). SCAR
marker SCX20600 is linked to the R Adv gene and was mapped to LG 13 distal
to the fertility restorer locus Rf 1 (Yu et al. 2003).
4.2.3 Resistance to Sunflower Chlorotic Mottle Virus
Sunflower chlorotic mottle virus (SuCMoV), a member of the Potyvirus genus
within the Potyviridae family is one of the most widely distributed
potyviruses on cultivated and wild sunflowers in Argentina. SuCMoV
infection reduces yield parameters such as plant height, stem and capitulum
diameter, seed yield, and weight of 1,000 seeds significantly (Lenardon et
al. 2001). From 232 accessions tested, the line L33 exhibited the highest level
of resistance, characterized by an isolated chlorotic pinpoint which
resembles hypersensitive reactions, accompanied by a delay in the beginning
of viral replication. Linkage analysis in the F 2 plants from the cross L2 x L33
detected a single locus ( Rcmo-1 ) for resistance located on LG 14, flanked by
the markers MS0022 (5 cM) and ORS307 (4 cM) (Lenardon et al. 2005).
4.2.4 Broomrape Resistance
Broomrape ( Orobanche cernua Loelf.) is a parasitic plant that feeds on
sunflower roots, causing severe economic damage. The first reports of this