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1) International Rice Research Institute, P. O. Box 933, Manila, Philippines
2) National Agriculture Research Center, Tsukuba, Japan
3) Taisei Biological Research Institute, Chiba, Japan
To widen the genetic base for resistance to bacterial blight (BB), a large number of rice varieties from many Asian countries have been tested for BB resistance since 1986. More than 20,000 varieties have been screened for BB resistance using Philippine races. The tests for resistance were carried out by clipping method (Kauffman et al., 1973) at seedling stage and then at booting stage. Based on reaction patterns to the four or six BB races used, resistant varieties were broadly classified into five main varietal groups some of which have subgroups. Isozyme analysis of BB resistant varieties was also carried out using the methods described by Glaszmann (1987). Each varietal group based on the reaction patterns to BB races belonged to specific isozyme group(s) (Table 1).
About 50 randomly selected varieties from some of the varietal groups were tested for allelism with the appropriate BB resistant gene. High allelic relationships confirmed the use of reaction patterns in estimating BB resistance genes in rice varieties. Table 2 shows the distribution of BB resistance genes of rice in Asian countries. The varieties belonging to Jave 14 group are distributed in almost all of the Asian countries but the percentages vary from country to country from a high 17.2% for Indonesia to a low of 0.3% for India. The varieties with Xa-4 were found in almost all Asian countries. The distribution of xa-5 gene showed area specificity. In Bangladesh and Nepal, the percentage of varieties with xa-5 was 25.9% and 13.3% respectively, but in other countries such as Thailand and Indonesia the percentage was less than 1.0%. Only a few varieties with Xa-10 and Xa-14 were found.
Table 1. Classification of bacterial blight resistant varieties based on reaction and zymogram patterns
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Varietial1 Reaction to 6 Ecotype Isozyme2
Philippine races
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Java 14 (Xa-3) RRRRRS Japonica V, VI
Javanica
TKM6 (Xa-4) RSSMRS Indica I
DZ 192 (xa-5) RRRMRS Aus, Boro II
Cas 209 (Xa-10) SRSSRS Indica I
TN 1 (Xa-14) SSSSRS Indica I
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1Varietal groups according to the presence of a resistance gene
2Isozyme groups according to the classification of Glaszmann (1987).
Table 2. Distribution of BB resistance genes of rice in Asian countries.
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Varieties Percentage of each group
Country of Origin tested ===================================
(no.) Java 14 TKM 6 DZ 192 Cas 209 TN 1
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East Asia
China 3711 4.23 0.73 0.51 0.03 1.83
Korea 878 3.68 1.71 - - -
Taiwan 900 11.78 4.11 - - 1.00
Southeast Asia
Burma 1473 2.04 2.51 0.61 2.99 -
Cambodia 695 - 6.91 4.46 2.30 -
Indonesia 1387 17.23 3.32 0.36 0.14 0.29
Laos 1136 5.28 2.99 0.52 0.08 -
Malaysia 2142 1.17 0.47 0.79 0.05 2.66
Philippines 2634 4.40 1.06 - 0.19 0.15
Thailand 1100 1.64 2.45 0.27 0.18 1.18
Vietnam 1130 7.70 3.89 4.51 4.51 -
South Asia
Bangladesh 1647 4.68 4.37 25.93 2.06 0.12
India 1289 0.31 6.28 7.21 4.03 0.31
Nepal 1110 1.44 3.78 13.33 1.26 -
Pakistan 926 - 3.89 6.26 0.22 -
Sri Lanka 1151 0.52 7.30 0.52 0.35 0.43
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ReferencesGlaszmann, J. C. 1987. A simplified method to classify rice varieties with isozymes. Int. Rice Res. Newsletter 12(3): 5-7.
Kauffman, H. E., A.P.K. Reddy, S.P.Y. Hsieh, and S. P. Merca, 1973. An improved technique for evaluating resistance of rice varieties to Xanthomanas oryzae. Plant Disease Reporter 57(6): 537-541.
