Geographic cline of TN1 variety group, harboring Xa14, based on inoculation tests with Philippine races and Japanese isolates of bacterial blight

Abstract

Among the 23, 591 native rice varieties preserved at the International Rice Research Institute (IRRI), varieties resistant to bacterial blight consist of four major variety groups: Xa3 (Java14 group), Xa4 (TKM6 group), xa5 (DZ192 group), Xa10 (Cas209 group) based on inoculation tests with Philippine races 1 to 4. Additional inoculation with races 5 and 6 had enabled to further detect the SSSSRS reaction, which corresponds to that of Xa14, and a fifth variety group Xa14 (TN1 group) was identified. However, inoculation tests had not been completed for the varieties from Vietnam, Laos and Myanmar. Therefore, varieties showing the SSSS reaction (races 1 to 4) were inoculated with Japanese isolates I to V to determine the whole spectrum of Asian distribution of Xa14. The results indicated that the RRSSR (Japanese isolates I to V) reaction was associated with the presence of Xa14 which was confirmed in these countries. As a whole in Asia, it was suggested that the presence of the single gene Xa14 was frequent in Malaysia and Vietnam. China was considered to form the eastern margin of the distribution, while the coexistence of Xa14 with other BB resistance genes was frequently observed in Indo-China, particularly with the Xa10 belt, followed by Xa4. Single gene presence was considered to comprise a secondary center, while the coexistence with other genes was considered to involve a primary gene center. It is likely that the primary center is located in the Himalayan foothills of Indo-China.