lation causing bacterial blight of rice in Punjab (India)
R.K. Goel, L. KAUR and R.G. SAINI
Department of Genetics, Punjab Agricultural University, Ludhiana
141004, Punjab, India
Bacterial blight (BB) caused by Xanthomonas oryzae pv oryzae
(X.o.o.) is a major biotic constraint in the irrigated rice belt comprising
Punjab and the adjoining north-western states of India. We studied effectiveness
of different Xa genes conferring BB resistance against the population of
the bacterium prevalent in farmer’s fields at different locations in Punjab
during 1996 and 1997 Kharzf (summer) seasons.
About 50 leaf segments (2 mm long) form each thoroughly washed
leaf sample derived from a rice plant naturally infected with X.o.o. were
agitated in 10 ml sterilized distilled water for 15 minutes. The resulting
suspension of bacterial ooze (109 cfu/ml) was inoculated using the “leaf
clipping method” on groups of rice lines serving as a “differential set”
at maximum tillering to booting stage. Leaf area necrotized on five fully
expanded leaves of 10 plants of each rice line on 0-9 scale following Standard
Evaluation System for Rice (1988). Plants were grown in earthen pots in
the greenhouse.
Each differential set comprised - (a) near-isogenic lines
(NILs) in the background of
1R24 namely IR-BB1, IR-BB3, IR-BB4, IR-BB5, IR-BB7, IR-BB8,
IR-BB1O, IR-BB11, IR-BB13, IR-BB14 and IR-BB21, carrying known resistance
genes Xal, Xa3, Xa4, xa5, Xa7, xa8, Xa1O, Xa11, xa13, Xa14 and Xa21 for
resistance to BB, respectively (Ogawa, 1993); and (b) some international
differential rice cultivars with known Xa genes (Ogawa, 1993), namely Kogyoku
(Xa1 + Xa12), Tetep (Xa2 + Xa16), BJ1 (xa5 + xa13), IR24 (Xa18) and DV85
(Xa7). Taichung (Native) 1, or TN! a cultivar carrying Xa14 but highly
susceptible to most BB races (Ogawa, 1993) was also included in each differential
set to serve as a check.
Out of 17 rice genotypes evaluated in this study, IR-BB1,
IR-BB3, IR-BB1O, IRBB11, IR-BB14, IR24 and TN! were susceptible (S) or
moderately susceptible (MS) whereas IR-BB8, DV85 and BJ1 were resistant
(R) or moderately resistant (MR) to all the isolates of X.o.o. analyzed
(Table 1).
On the basis of differential reaction (R/MR or SIMS) on
IR-BB4, IR-BB5, IR-BB7, IR-BB21, Tetep and Kogyoku, the X.o.o. populations
analyzed here could be classified into 8 pathotypes with varying frequencies
(Table 1). The reaction of cultivar DV85 which is reported to carry Xa7
(Ogawa, 1993) was entirely different from that of nearisogenic line IR-BB7,
having the same gene. BJ1 and DV85 were resistant to all the pathotypes
of X.o.o. encountered in the present study. It is obvious DV85 has another
gene for resistance to BB besides Xa7.
Resistance gene Xa21 is reported (Ikeda et a!. 1992, Mazzola
et a!. 1994) to confer resistance against all the pathotypes of X.o.o.
prevalent in the Philippines and India at post-seedling growth stages.
However, this gene was ineffective against several isolates of the pathogen
evaluated in this study (Table 1). According to Song et a!. (1995) Xa21
locus consists of a small multigene family. The ineffectiveness of Xa21
against some pathotypes of X.o.o., as recorded here, may possibly be due
to the failure of some members of this family to recognize specific pathogen
ligands and subsequent activation of an intracellular defense response
as suggested by Wang et al. (1996).
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(India) during 1996 and 1997
* Ogawaet eI(1993)
**Reaction based on Standard Evaluation System for Rice
(1988). R= Mean BB score <3.4. MR =3.5-5.4, MS = 5.5-7.4, S>7.5 on 0-9
scale
Acknowledgements
Supply of seeds of the near-isogenic rice lines through
the courtesy of Prof. D.S. Brar, Division of Plant Breeding, Genetics and
Biochemistry, IRRI, Manila, Philippines is gratefully acknowledged.
longistaminata. Jpn. J. Breed. 40 (Suppl. 1): 280-287.
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