Biology Reference
In-Depth Information
et al. 2011) and sequencing of other Brassica
genomes is underway. Consequently, all major
Brassica genomes will be sequenced in the near
future, which will facilitate molecular marker
development, gene mapping, and cloning, as
well as marker-assisted selection in Brassica crop
breeding.
from wild crucifers and from B. napus and B.
juncea with high levels of resistance to scle-
rotinia stem rot. Navabi and colleagues (2010)
detected B-chromosome carrying B. napus lines,
derived from an interspecific cross of B. napus
and B. carinata, with a high level of resistance
to sclerotinia stem rot.
Sclerotinia
Optimization of Testing Methods for
Sclerotinia Stem Rot Resistance
Searching for Resistance to Sclerotinia
Stem Rot
It is critical to develop an adequate testing
method to detect sclerotinia partial resistance.
In previous reports, several testing methods,
such as cotyledon, detached true leaf, and peti-
ole and stem inoculation, have been developed
(Table 16.1). Zhao and colleagues (2004) used a
petiole inoculation technique to test 47 acces-
sions of oilseed B. napus collected from ten
countries and found that most cultivars show-
ing relatively high levels of resistance to scle-
rotinia stem rot were from China. Bradley and
colleagues (2006) tested 19 canola cultivars from
Canada and the United States, using three indoor
inoculation methods - the petiole inoculation
technique (PIT), the detached leaf assay, (DLA),
and the oxalic acid assay (OAA) - and also
screened a few canola cultivars under field con-
ditions. The results showed that the PIT and the
OAA methods significantly differentiated levels
of sclerotinia stem rot resistance, while the dis-
ease incidence of tested cultivars collected under
field conditions over a period of four years was
Sclerotinia stem rot, caused by Sclerotinia scle-
rotiorum (Lib.) de Bary is one of the most devas-
tating diseases of Brassica oilseed crops. Since S.
sclerotiorum is non-host specific, necrotrophic,
and very aggressive, it can cause heavy yield
losses in canola production. Unfortunately, there
is no Brassica species with a high level of resis-
tance to sclerotinia stem rot although there are
some accessions in B. napus , B. oleracea , B.
juncea, and B. carinata that confer partial resis-
tance or field tolerance. For example, Zhao and
colleagues (2004) evaluated resistance to sclero-
tinia stem rot in B. napus, and CK821 showed
a high level of resistance in all tested acces-
sions. Mei and colleagues (2011) did testing of
sclerotinia resistance with 68 accessions from
six Brassica species, and their data showed that
wild species of B. oleracea such as B. insularis
and B. villosa are resistant sources to sclero-
tinia stem rot. Additionally, Garg and colleagues
(2010) identified introgression lines developed
Table 16.1.
Testing methods for sclerotinia resistance in Brassica species*
Inoculation
methods
Inoculation
tissues
Full Description
Inoculum
Scoring methods
References
CT
Cotyledon test
Mycelial
suspension
Cotyledon
Lesion size
Garg et al. 2008
PIT
Petiole inoculation technique
Mycelial agar plug
petiole
Days to wilt
Zhao et al. 2004
DLT
Detached leaf assay
Mycelial agar plug
leaf
Lesion size
Zhao et al. 2003
IPI
Infected petal inoculation
Infected petals
leaf
Lesion size
Yin et al. 2010
MTI
Mycelial toothpick inoculation
Mycelial agar plug
Stem
Lesion length
Zhao et al. 2003
MPI
Mycelial plug inoculation
Mycelial agar plug
Stem
Lesion length
Yin et al. 2010
OAA
Oxalic acid assay
Oxalic acid
Stem
OA concentration
Bradley et al. 2006
*Fungal inoculum is cultured in potato dextrose agar medium (PDA).
 
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