Journal of Taiwan Agricultural Research

Author:Lih-Jiuan Hsieh, Yih-Chang Chang and Ting-Fang Hsieh*

Abstract:

    The objectives of this study were to evaluate the susceptibility of Taichung sen 10 rice cultivar to the isolates of Xanthomonas oryzae pv. oryzae, the causal agent of bacterial leaf blight of rice, at the seedling, tillering and booting stages. The rice plants were inoculated with bacterial suspension by root-dipping and leaf-clipping methods at the seedling stage, with leaf-clipping and spraying methods at the tillering and booting stages. Totally five isolates of X. oryzae pv. oryzae were used for inoculation, of which 2 isolates were isolated from plants with leaf blight symptoms and 3 isolates from plants with pale-yellow-leaf symptoms. The experiments were conducted in two continuant crops of 2002 at the experimental field of Taiwan Agricultural Research Institute. Results showed that the seedlings inoculated by the root-dipping method before transplanting in both crops appeared kresek symptoms (death of whole seedlings), except seedlings inoculated with XM 30 isolate in the 2nd crop. Meanwhile, the seedlings inoculated by leaf-clipping method showed leaf blight symptoms in both crops. However, all bacterial isolates didn’t induce pale-yellow-leaf symptoms of inoculated rice plants by both inoculation methods. Disease survey was done at the heading stage after inoculation at the three different growth stages of rice in two crops. Leaf blight symptom was not observed when seedlings inoculated by both methods before transplanting. However, leaf-blight symptoms were observed on the inoculated plants when inoculations were conducted at tillering and booting stages by both methods and in both two crops. Meanwhile, all of the 3 pale-yellow-leaf isolates induced pale-yellow-leaf symptoms on inoculated rice plants at the heading stage when inoculations were done at transplanting and tillering stages by both methods in both crops, except inoculation at the seedling stage by leaf-clipping method in the first crop. In addition, the pale-yellow-leaf symptoms were not found on rice plants inoculated at the booting stage by both methods. Besides, none of the leaf-blight isolates caused pale-yellow-leaf symptoms by all tested methods at all growth stages. These results indicated that the virulence of different types of pathova of the bacterium was different, and symptoms of pale-yellow-leaf were only induced by infection at the earlier stages, such as at the seedling and tillering stages. Both kresek and pale-yellow-leaf symptoms were due to the systemic infection with bacterial pathogen. The kresek symptoms were observed at the seedling stage, whereas the pale-yellow-leaf symptoms on mature plants. In addition, both kresek and pale-yellow-leaf symptoms occurred under lower temperature at the first crop in Taiwan. This indicated that high temperature was not the necessary for induction of these two types of disease symptoms on rice plants.

Key words:Rice, Growth stages, Bacterial leaf blight of rice, Pale-yellow-leaf symptom, Kresek symptom, Temperature determination

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