1) International Rice Research Institute, P. 0. Box 933, Manila, Philippines
2) Faculty of Agriculture, Kyushu University, Higashi-ku, Fukuoka, 812 Japan
During the inoculation test using Philippine races of bacterial blight, variety Taichung Native 1 (TN1) showed a specific reaction. It is resistant only to race 5 p (PXO112) but is very susceptible to other five races (races 1, 2, 3, 4, and 6). Its reaction was compared with other differential varieties by inoculating with 6 Philippine races (Table 1). The data showed that there was no other differential similar to the reaction pattern of TN 1. Therefore, it appeared that TN 1 has a new gene for resistance to race 5. We carried out analysis to determine the inheritance of resistance to race 5 of TNI.
We crossed TNI with susceptible varieties, Toyonishiki and Milyang 23, and with a Japanese differential variety Te-tep. The F1 plants and the F2 populations were inoculated with four Philippine races (races 1, 2, 4 and 5). In addition, the backcross progeny (IR24/TN1//IR24) was also analyzed.
All F1 plants showed resistance only to race 5. Therefore, the resistance gene of TNI appeared to be dominant.
The F2 populations of Toyonishiki/TN1, Milyang 23/TN1 and TN1/Te-tep
Table 1. The reaction of differential rice varieties to Philippine races of bacterial blight at booting stage ________________________________________________________________ Race 1 Race 2 Race 3 Race 4 Race 5 Race 6 Variety _______ _______ _______ _______ _______ _______ LL RE LL RE LL RE LL RE LL RE LL RE ________________________________________________________________ IR24(+) 25.7 S 35.6 S 32.5 S 31.6 S 22.7 S 36.0 S Milyang 23(+) 15.3 S 26.5 S 28.5 S 31.3 S 24.9 S 43.5 S Toyonishiki(+) 8.3 MS 17.0 S 16.2 S 11.6 S 12.9 S 21.2 S TN1 19.6 S 35.2 S 37.4 S 31.5 S 4.9 R 30.7 S Tetep(Xa-1, Xa-2) 14.5 S 30.7 S 29.1 S 26.5 S 17.0 S 33.1 S Chugoku 45 (Xa-3) 0.4 R 1.9 R 2.2 R 1.3 R 3.5 R 11.5 S Java 14 (Xa-1, Xa-3, Xa-12) 0.6 R 2.3 R 1.4 R 2.9 R 6.9 R 24.4 S IR8 (Xa-11) 17.0 S 25.6 S 28.7 S 14.9 S 13.6 S 19.5 S IR20 (Xa-1, Xa-4) 6.9 R 22.5 S 24.5 S 9.7 MS 3.9 R 18.3 S IR1545-339 (xa-5) 1.2 R 2.6 R 1.1 R 17.9 S 4.4 R 30.0 S DV85(xa-5,Xa-7)0.4 R 0.4 R 0.5 R 6.0 MR 2.0 R 6.5 MR Cas209(Xa-10) 24.2 S 3.5 R 45.3 S 40.0 S 1.7 R 50.4 S BJ1(xa-5,Xa-13)0.6 R 3.8 R 2.8 R 4.7 R 0.6 R 3.7 R PI231129(xa-8) 3.5 R 8.0 R 6.5 R 12.2 MS 5.5 R 4.5 R ________________________________________________________________LL: Average lesion length in cm from 15 inoculated leaves (3 leaves from 5 plants) at 14 days after inoculation.
RE: R = resistant; MR = moderately resistant; MS = moderately susceptible; ans S = susceptible.
Table 2. The reaction of F1 and F2 Populations from the crosses of TN1 with four varieties to four races (Races 1, 2, 4, 5) of bacterial blight
________________________________________________________________ Crosses Reaction of F2 Populations X2 P Reaction of F1 _______________ progenies SSSR SSSS 3:1 ________________________________________________________________ Toyonishiki/TN1 SSSR 185 84 5.56 0.01-0.02 Milyang 23/TN1 SSSR 200 70 0.12 0.7 -0.8 TN1/Tetep SSSR 208 57 1.72 0.1 -0.2 ________________________________________________________________ R=resistant; S=susceptiblewere susceptible to races 1, 2 and 4 but clearly segregated in a ratio of 3 resistant: 1 susceptible for race 5 (Table 2). In the backcross progeny of IR24/TN1//IR24, there were 98 resistant: 97 susceptible plants (a 1 : 1 ratio). These results confirm that the resistance of TN1 to race 5 is governed by a single dominant gene. This kind of reaction pattern to Philippine races has not been found before. As shown in Table 1, Japanese differentials having any of the genes Xa-1, Xa-2, Xa-12 (Xa-kg) and Xa-3 also did not show this kind of reaction pattern.
Following the rules of gene symbolization in rice we have designated the dominant gene for resistance to race 5 in TN1 as Xa-14. In common with Te-tep (Xa-1/Xa-2), TN1 shows resistance to Japanese races IA, IB and II (Ogawa and Yamamoto 1987). Therefore, we plan to study the relationships between Xa-1/ Xa-2 and the new gene. It should be noted that Te-tep does not show resistance to race 5 in the Philippines.
References
Ogawa, T. and T. Yamamoto, 1987. Selection of recurrent parents to develop near-isogenic lines resistant to bacterial leaf blight of rice. JARQ, 21: 65-69.