Biology Reference
In-Depth Information
blackleg, and clubroot, cause heavy yield losses
worldwide, while some diseases, such as verti-
cillium wilt, light leaf spot, and fusarium wilt are
regional problems in canola production. In addi-
tion, diseases such as clubroot, downy mildew,
bacterial soft rot, and turnip mosaic virus also
causes heavy yield losses in Brassica vegetables.
Development and deployment of resistant cul-
tivars is the most commonly used strategy to
control diseases in crop production. For most dis-
eases of Brassicas, such as clubroot and blackleg,
sources of resistance are identified easily and the
resistance can be successfully transferred from
variety to variety and from species to species.
On the other hand, for other diseases of Bras-
sicas, such as sclerotinia stem rot and bacterial
soft rot, it is very difficult to identify sources with
high levels of resistance so it is very challenging
to develop resistant cultivars for these diseases.
Genetic and genomics research is currently
being conducted for many diseases of Brassicas,
especially clubroot, blackleg, sclerotinia, downy
mildew, and turnip mosaic virus. Molecular
markers such as restriction fragment length
polymorphism (RFLP); simple sequence repeats
(SSR), also known as microsatellite repeats;
inter-simple sequence repeat (ISSR); single
nucleotide polymorphism (SNP): amplified frag-
ment length polymorphism (AFLP); sequence-
related amplified polymorphism (SRAP);
sequence-characterized amplified region
(SCAR); sequence-tagged sites (STS); and
random amplified polymorphic DNA (RAPD)
are used for gene mapping, gene cloning, and
marker-assisted selection in Brassica crops.
In the amphidiploid species
B. napus
,
B.
juncea,
and
B. carinata
, it is necessary to develop
genome-specific molecular markers, since most
polymorphic loci occur in one genome while
their corresponding loci in another genome are
monomorphic. To detect all homozygous and
heterozygous genotypes in breeding lines and
populations, genome-specific primers are nec-
essary in order to amplify the alleles of inter-
est in the genomic DNA. Fortunately, the whole
genome sequence of
B. rapa
is available (Wang
Fig. 16.1.
The U-triangle in Brassica species (U 1935).
For a color version of this figure, please refer to the color
plate.
Therefore, canola oil is in high global demand,
which encourages steadily higher canola produc-
tion.
B. juncea
and
B. rapa
also produce edible
oil, consumed in India, China, and other coun-
tries.
B. oleracea
vegetables, including cabbage,
broccoli, cauliflower, Brussels sprouts, collard
greens, kale, Chinese kale, and kohlrabi are cul-
tivated globally, and similarly
B. rapa
vegetables
such as Pak choi, Chinese cabbage (Napa cab-
bage), and turnip are popular in Asia. Two Bras-
sica species including
B. juncea
and
B. nigra
are
used for condiment mustard production. Con-
sequently, the Brassica genus plays an important
role in the human diet and in the global economy.
Various bacterial, fungal, and viral diseases
pose significant risk to Brassica crop produc-
tion. There are many diseases that affect Bras-
sica species, for example, bacterial soft rot
(
Erwinia carotovora
), bacterial leaf spot (
Pseu-
domonas syringae
), sclerotinia stem rot (
Scle-
rotinia sclerotiorum
), clubroot (
Plasmodiophora
brassicae
), blackleg (
Leptosphaeria maculans
),
fusarium wilt (
Fusarium avenaceum
and
F.
oxysporum
), verticillium wilt (
Verticillium albo-
atrum
), light leaf spot (
Pyrenopeziza brassicae
),
downey mildew (
Peronospora parasitica
), pow-
dery mildew (
Erysiphe polygoni
), and turnip
mosaic virus.
Canola has become one of the most impor-
tant oilseed crops in the world, second only
to soybean. Some as diseases, such sclerotinia,
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