International Rice Research Institute P. 0. Box 933, Manila, Philippines
Rice varieties were classified into three major groups based on their reaction to four Philippine races of Xanthomonas campestris pv. oryzae (Ogawa et al. 1986). Varieties of Java 14 group are resistant to four Philippine races of bacterial blight at booting stage and have a single dominant gene Xa-3 for resistance. Varieties of TKM6 group are resistant to race 1, moderately resistant to race 4, but are susceptible to races 2 and 3. They have a single dominant gene Xa-4 for resistance. Varieties of DZ 192 group are resistant to races 1, 2 and 3 and are moderately resistant to race 4. They are resistant at seedling stage and have a recessive gene xa-5 for resistance.
We have identified another group of varieties which show stable resistance to races 1, 2, 3, 4 and to race 6 (PXO 99) which was found recently in the Philippines. Varieties BJ1, AC19-1-1, Aus 274, Chinsurah Boro II and Kalimakri 77-5 belong to this group. We have designated these as belonging to BJ1 group. These varieties were crossed with a susceptible variety, IR24, and a resistant variety IR1545- 339. The F1 and F2 progenies of these crosses were analyzed by inoculating them with races 1 (PXO 61), 2 (PXO 86), 4 (PXO 71) and 6 (PXO 99).
The F1 plants of the crosses of these varieties with IR24 were susceptible to all the four races. However, the F1 plants of the crosses with IR1545-339 were resistant to races 1 and 2, moderately resistant to race 4, but susceptible to race 6. Thus the reaction of the F1 plants was similar to the reaction of IR1545-339 (Table 1). These results show that varieties of BJ1 group have the recessive gene xa-5 for resistance.
The F2 plants from the crosses of IR24 with BJ1 group varieties could be classified into four groups based on the reaction pattern to four races (Table 2). Plants of group 1 were susceptible to all 4 races. Plants of group 2 showed a reaction pattern similar to that of IR1545-339. The reaction of the plants of group 3 was similar to the reaction of resistant parents (e.g., BJ1 group). The fourth group of plants showed resistance to race 6 only.
The F2 plants from the crosses of IR1545-339 with BJ1 group varieties did
Table 1.The reaction of parents and F1 plants to four Philippine
races (1, 2, 4 and 6) of bacterial blight at booting stage
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Race 1 Race 2 Race 4 Race 6
Variety or _____________ ____________ ____________ ____________
Cross Lesion Reac- Lesion Reac- Lesion Reac- Lesion Reac-
Length1 tion2 Length tion Length tion Length tion
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IR24 17.1 S 13.4 S 13.7 S 15.5 S
IR1545-339 1.5 R 1.9 R 7.8 MS 19.3 S
BJ1 1.1 R 1.2 R 1.2 R 2.6 R
AC19-1-1 0.7 R 0.6 R 0.5 R 1.5 R
Chinsura
Boro II 1.6 R 1.7 R 1.3 R 2.3 R
Aus 274 1.7 R 3.2 R 2.0 R 2.5 R
Kalimakri
77-5 1.6 R 1.5 R 1.2 R 1.4 R
IR1545-339/
BJ1 1.3 R 2.8 R 9.3 MS 15.4 S
IR1545-339/
Aus 274 2.1 R 3.3 R 11.2 MS 18.8 S
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1 Average lesion length in cm in 15 inoculated leaves (3 leaves from 5
plants) at 18 days after inoculation.2 R = resistant; MS = moderately susceptible; and S = susceptible.
Table 2. The reaction of F1 and F2 populations from the crosses of IR24 and BJ1 group varieties to four races of bacterial blight (races 1, 2, 4 and 6) at booting stages
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Reaction Reaction of F2 populations X2 P
Cross of F1 ___________________ (9:3:3:1)
plants SSSS RRMS SSSR RRRR
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IR24/BJ1 SSSS 164 27 29 31 34.2 <.OO1
IR24/AC19-1-1 SSSS 117 35 37 16 1.2 0.7-0.8
IR24/Chinsurah
Boro 11 SSSS 173 43 30 23 14.7 <.001
IR24/Aus 274 SSSS 171 40 47 11 6.9 0.05-0.1
IR24/Kalimakri
77-5 SSSS 155 39 55 21 4.1 0.2 -0.3
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R=resistant;M=moderately resistant;and S=susceptible.
Table 3. The reaction of F1 and F2 populations from the crosses of IR1545-339
with BJ1 group varieties to four races of bacterial blight (races 1, 2, 4 and
6) at booting stage
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Reaction Reaction of F2 X2 P
Cross of F1 populations (1:3)
progenies __________________
RRRR RRMS
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IR1545-339/BJ1 RRMS 78 184 3.2 0.05-0.1
IR1545-339/
AC19-1-1 RRMS 67 192 0.1 0.7-0.8
IR1545-339/Chin-
surah Boro II RRMS 69 184 0.7 0.3-0.5
IR1 545-339/Aus
274 RRMS 70 200 1.1 0.7-0.8
JR1543-339/Kali-
makri 77-5 RRMS 81 187 3.9 0.02-0.05
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not segregate for susceptibility to races 1 or 2, but segregated in a ratio
of 1 resistant: 3 susceptible for race 6 (Table 3). No clear-cut
segregation for resistance to race 4 was obtained and most of the F2 plants
showed moderately resistant reaction.These results indicate that the five varieties of BJ1 group have two recessive genes. One of them is xa-5 and the other is a new recessive gene. This new gene convey resistance to race 6. From the cross of IR24 and BJ1 we have obtained lines which are homozygous for the new gene. Following the rules of gene symbolization in rice, we have designated this new recessive gene as xa-13, The F2 data indicate that xa-5 and xa-13 are linked. The linkage intensity is being studied. Moreover, xa-5 and xa-13 have complementary effect in imparting resistance to race 4, This aspect is also being investigted.
Reference
Ogawa, T., G. A. Busto, T. Yamamoto, G. S. Khush and T. W. Mew, 1986. Group of rice varieties based on the reaction to four Philippine races of Xanthomonas campestris pv. oryzae. RGN 3: 84-86.