Abstract:The induced resistance of wheat seedling to leaf rust was tested while spraying with BION (benzo (1,2,3) thiadiazole-7-carbothioic acid S-methyl ester, BTH). The results indicated that the optimum concentration of BION was 200 mg/L for the induction of leaf rust resistance on wheat seedling. The induced activity produced at least two days after spraying with BION while inoculated with challenge pathogen, Puccinia triticina, and could last at least for fourteen days once induced. The highest induction effect was obtained on four days later after spraying with BION. The second leaves of wheat seedlings could produce the induced resistance to leaf rust while the first leaves were sprayed with BION, which could be detected at 48 hours post-spraying. The induced resistance with BION was not able to change the infection type of leaf rust in wheat seedling stage, but the number of leaf rust uredia could be significantly reduced on the second leaves. The activities of phenylalanine ammonia lyase (PAL), polyphenoloxidase (PPO) and peroxidase (POD) on the wheat leaves sprayed with BION at the concentration of 200 mg/L were higher than that on the untreated ones. Three peaks of PAL, PPO and POD activities appeared on the second day after treated with BION while inoculated with Puccinia triticina on Zhengzhou 891. The germination of urediniospores could not be inhibited by BION in vitro. So, it is concluded that BION-induced resistance against wheat leaf rust is most likely to be a response of systemic acquired resistance.