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enhanced resistance to
Xoo
(Liu et al. 2007).
Two MAPK genes also regulate quantitative
resistance.
MPK5
-suppressing rice plants dis-
play increased resistance to
Xoo
(Xiong and
Yang 2003). MPK12 (BWMK1) positively reg-
ulates rice resistance to
Xoo
(Seo et al. 2011).
Another key component of rice defense signal-
ing, Rac1, which is a small GTPase of Rho type,
functions in basal resistance to
Xoo
as a regulator
of reactive oxygen species and programmed cell
death (Ono et al. 2001).
In addition,
R
-type gene or defeated
R
-type
gene also contribute to quantitative resistance.
Activation of
MRKa
, a member of the
Xa3/Xa26
gene family, displayed partial resistance to
Xoo
(Cao et al. 2007b). A member of the
Xa21
gene family,
Xa21D
that encodes only the LRR
domain of Xa21 protein, confers partial resis-
tance to
Xoo
, and its resistance spectrum is iden-
tical to that of
Xa21
gene (Wang et al. 1998). The
MR
gene
Xa4
, which confers qualitative resis-
tance to Philippines
Xoo
race 1 and 4, can act
as a recessive QTL and mediate partial resis-
tance against new virulent
Xoo
races (Nino-Liu
et al. 2006). The recessive
xa5
mediates qualita-
tive resistance to Philippine race 1, 2, 3, and 5,
but it also has moderately resistance to Philippine
race 4 (Wan and Zheng 2007).
effectively kills
Xoo
or inhibits its multipli-
cation. Although pesticides are efficient in
controlling BB, they can lead to environmental
contamination and pesticide-resistant pathogens.
Biological control is accomplished by using
antagonistic organisms, such as
Bacillus
species,
to protect rice plants. In contrast to chemical con-
trol, biological control is a more environmentally
friendly and cost-effective method.
BreedingforRiceResistancetoBacterialBlight
Although the agronomic practices are useful
in controlling BB, most of these strategies are
labor intensive. Utilization of resistant varieties
with agricultural management practices is a more
effective way to control BB. Conventional breed-
ing is irreplaceable in resistance breeding. It is
achieved by hybridization and phenotypic selec-
tion, in which the experience of breeders plays a
major role. In the past,
MR
genes and resistance
QTLs have been used in rice improvement by
conventional breeding. However, conventional
breeding is painstaking and time-consuming and
may not be applicable for certain types of quan-
titative resistance (Kou and Wang 2010, 2012).
In the last decades, rice genomic research
has generated a wealth of information about
gene function. These advances are now accessi-
ble for rice improvement and have been applied
in MAS and genetic engineering in breeding
programs. MAS can be a “shortcut” in breeding
programs because it reduces the number of gen-
erations that must be developed to have a viable
product that can be released to the farmers; it
also can make conventional breeding more effi-
cient by using genetic markers. This technology
has already proven to be a useful tool for rice
breeding to control BB. Minghui 63(
Xa21
) car-
rying the
MR
gene
Xa21
is the first BB-resistant
rice cultivar developed by MAS in China (Chen
et al. 2000). MAS is also effective for pyramid-
ing more than one
MR
gene in rice improve-
ment. A MAS-developed rice cultivar, Tubigan
7, which has an IR64 background and was intro-
gressed with three
MR
genes (
Xa4
,
xa5
, and
Control of Bacterial Blight
AgronomicPracticesforDiseaseManagement
Different strategies including integrated disease
management combining cultivation methods,
chemical control, and biological control have
been used to combat this disease. Weed hosts,
volunteer seedlings, rice stubble and ratoons,
and infected plants are important sources of
Xoo
inoculums. Thus, utilizing pathogen-free seed,
removing contaminated sources to keep field
clean, and allowing fallow fields to dry are the
control options to suppress inoculums.
Chemical control of
Xoo
in rice fields began
in the 1950s (Ni no-Liu et al. 2006). An ideal
agent for chemical control is a pesticide that
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