Genetics and Gene Mapping of Disease Resistance in Brassica - Translational Genomics for Crop Breeding: Biotic Stress - page 339

B. rapa chromosome fragment between these
two blackleg-resistance genes was eliminated,
were developed using molecular markers for
one cloned gene and one fine-mapped blackleg-
resistance gene (unpublished data).

basis for the pyramiding of different resistance
genes into single lines and this may facilitate the
development of durable resistance to blackleg
disease in canola breeding. As described previ-
ously, good progress has also been made in con-
trolling other diseases, such as downy mildew
and turnip mosaic virus, via the development
of resistant cultivars, since sources with high
levels of resistance to these diseases are avail-
able. Finally, genome sequencing will facilitate
gene mapping and gene cloning and in turn,
promote the development of high quality and
high throughput molecular markers. Undoubt-
edly, molecular marker-assisted selection is play-
ing and will increasingly play a very important
role in modern breeding in Brassica species.

Summary

Disease resistance is a very important trait in
plant breeding, since deployment of resistant
cultivars is almost always an effective and effi-
cient method for reducing losses caused by dif-
ferent diseases. Therefore, resistance to most
major diseases such as sclerotinia stem rot,
clubroot, and blackleg in Brassica species has
been extensively studied and significant progress
towards the development of resistant cultivars
achieved. Although it is not easy to iden-
tify sources with high levels of resistance to
sclerotinia stem rot, some accessions such as
Chinese canola cultivars display partial resis-
tance or field tolerance, and these may facilitate
the development of canola hybrid cultivars with
an effective level of resistance to sclerotinia stem
rot. Indeed, most breeding organizations world-
wide have this goal in their breeding programs.
Clubroot is so devastating that clubroot resis-
tance becomes a prerequisite trait for releasing
new cultivars in the regions of the world where
the soil-borne clubroot pathogen prevails. For-
tunately, excellent sources with high levels of
resistance to P. brassicae have been identified in
several Brassica species, and gene mapping of
dominant resistance genes in B. rapa have been
performed and gene cloning is underway. Black-
leg is another important disease in canola and
extensive research of pathogenicity, mapping
of major dominant resistance genes, and intro-
gression of resistance genes from allied species
into B. napus canola has been accomplished. In
fact, this disease has been controlled effectively
and efficiently in most canola-production areas
in the world. Moreover, cloning of a blackleg-
resistance gene has been successfully done and
more blackleg-resistance genes will be cloned
in the near future, which will provide a solid

References

Ansan-Melayah, D., Balesdent, M.H., Buee, M., and
Rouxel, T. 1995. Genetic characterization of AvrLm1 ,
the first avirulence gene of Leptosphaeria maculans . Phy-
topathology 85:1525-1529.
Ansan-Melayah, D., Balesdent, M.H., Delourme, R., Pilet,
M.L., Tanguy, X. et al. 1998. Genes for race specific
resistance against blackleg disease in Brassica napus L.
Plant Breeding 117:373-378.
Ayers, G.W., and Lelacheur, K.E. 1972. Genetics of resis-
tance in rutabaga to races of Plasmodiophora brassicae .
Canadian Journal of Plant Science 52:897-900.
Badawy, H.M.A., Hoppe, H.H., and Koch, E. 1991. Differ-
ential reactions between the genus Brassica and aggres-
sive single spore isolates of Leptosphaeria maculans .
Journal of Phytopathology 131:109-119.
Balesdent, M. H., Attard, A., Ansan-Melayah, D.,
Delourme, R., Renard, M., and Rouxel, T. 2001. Genetic
control and host range of avirulence toward Brassica
napus cultivars Quinta and Jet Neuf in Leptosphaeria
maculans . Phytopathology 91:70-76.
Balesdent, M.H., Louvard, K., Pinochet, X., and Rouxel
T. 2006. A large-scale survey of races of Leptosphaeria
maculans occurring on oilseed rape in France. European
Journal of Plant Pathology 114:53-65.
Bancroft, I., Morgan, C., Fraser, F., Higgins, J., Wells, R.,
Clissold, L., Baker, D., Long, Y., Meng, J., Wang, X.,
Liu, S., Trick, M. 2011. Dissecting the genome of the
polyploid crop oilseed rape by transcriptome sequencing.
Nature Biotechnology 29:762-768.
Bradley, C.A., Henson, R.A., Porter, P.M., del Rio, L.E.,
and Khot, S.D. 2006. Response of canola cultivars Scle-
rotinia sclerotiorum in controlled and field environments.
Plant Disease 90:215-219.