Biology Reference
In-Depth Information
napus
canola cultivars were tested and only a few
lines showed low levels of resistance in Quebec,
Canada (Vigier et al. 1989).
In
B. oleracea
, Portuguese cole landraces
were screened for clubroot resistance, and among
44 accessions, two cabbage cultivars and one
kale showed the highest clubroot resistance
under field conditions (Dias et al. 1993). More-
over, of 71 accessions of
B. oleracea
evaluated
using indoor testing, several cabbage, broccoli,
and kale that had high levels of clubroot resis-
tance were identified (Voorrip and Visser 1993).
Similarly, Manzanares-Dauleux and colleagues
(2000b) tested 240 kale, 38 cabbage, and 126
winter cauliflower from the
B. oleracea
French
landrace gene pool. Among these 404 acces-
sions, two kale lines were identified with high
levels of clubroot resistance that, it was sug-
gested, could be valuable sources for breeding
clubroot-resistant Brassica vegetables such as
broccoli and cauliflower. In yet another report,
clubroot resistance in 48
B. oleracea
accessions
together with a few
B. rapa
and
B. napus
acces-
sions were tested, in which one
B. rapa
turnip
and one
B. napus
displayed the highest levels
of resistance (Carlsson et al. 2004). Clubroot
resistance in
B. oleracea
is commonly identified.
Some accessions of kale, cabbage, broccoli, and
Brussels sprouts have displayed resistance to clu-
broot disease, whereas most of these sources of
resistance have a relatively lower level of club-
root resistance than that possessed by European
fodder turnips.
In
B. rapa
, most accessions, especially con-
ventional Chinese cabbage cultivars, are highly
susceptible to
P. brassicae
. Fortunately, as
described previously, European fodder turnips
(
B. rapa ssp rapifera
) are strongly resis-
tant to clubroot disease (Crute et al. 1983).
The European fodder turnip resistance sources
have been used successfully to introduce resis-
tance genes into Chinese cabbage in order
to develop clubroot-resistant hybrid cultivars.
These clubroot-resistant hybrid cultivars were
first developed and extensively used to control
clubroot disease in Chinese cabbage production
in Japan. Currently, Chinese cabbage cultivars
with the turnip resistance genes are commonly
used to control clubroot disease in Asian coun-
tries such as Japan, South Korea, and China.
Genetic Analysis of Clubroot
Resistance
Understanding the genetic basis of resistance to
P. brassicae
in Brassica species is vital, and
dozens of reports on the genetics of clubroot-
resistance are available in
B. oleracea
,
B. rapa
,
B. napus,
and other Brassica species (Chiang
and Crete 1970; Crute et al. 1980; Voorrips and
Visser 1993; Voorrips et al. 1997). Early genetic
studies on clubroot resistance were done mainly
in
B. oleracea
(Chiang and Crete 1970; Crute
et al. 1980). Since the resistance in
B. oler-
acea
varies with regards to the materials used,
a multiple-gene model for resistance genes was
commonly reported. In contrast, turnip resis-
tance is strong and dominant, with a single
gene or a few major genes commonly detected
and reported in segregating populations. Voor-
rips and Visser (1993) found that the hybrids of
highly resistant cabbage and kale, and highly sus-
ceptible cabbage were totally susceptible; sug-
gesting that the clubroot resistance in these cab-
bage and kale lines was controlled by recessive
genes. In a diallel analysis of clubroot resis-
tance among several cabbage cultivars, additive
effects were found to be stronger than dominant
effects (Chiang and Crete 1976). In contrast, six
kale lines were used to make crosses in a dial-
lel mating design and analysis of the clubroot-
resistance data showed that incomplete dominant
effects were more important than additive effects
(Laurens and Thomas 1993).
Genetic analysis is generally used to detect
resistance gene loci based on the segrega-
tion of the clubroot-resistance phenotype. Using
two clubroot-resistant accessions of
B. napus
rutabaga, a single major dominant gene locus
was detected in both rutabaga accessions,
whereas another dominant resistance gene locus
was identified in one of these two rutabaga
Search WWH ::
Custom Search