Benzothiadiazole-induced Systemic Acquired Resistance in Rice Against Xanthomonas oryzae pv. oryzae

Suppression of the bacterial leaf blight disease caused by Xanthomonas oryzae pv. oryzae was observed in rice seedlings pretreated with benzothiadiazole (BTH, 0.5 mmol/L), salicylic acid (1 mmol/L), nickelous nitrate (0.5 mmol/L), paclobutrazole (0.3 g/L) or uniconazole (0.04 g/L) 3 days before inoculation with the bacteria, resulting in reduction of lesion length by 14-51%. No significant inhibitory effect of BTH at 1 mmol/L on the growth of X. oryzae pv. oryzae was detected in vitro. The optimum concentration of BTH for resistance induction was found to be at 0.5-1.0 mmol/L. An interval of at least 1 day between BTH induction and challenge inoculation was required for establishment of the induced resistance, among which a 7 day interval gave the highest protection. The BTH induced resistance gave protection from the disease for at least 15 days once induced. Lesion length on the third and the fourth fully expanded leaves was significantly reduced when the lower second leaves were induced by injection with BTH. The development of the BTH induced resistance on the upper leaves required the presence of the lower induced leaves for at least 24 h after treatment with BTH. The results indicate that the BTH induced resistance against the bacterial leaf blight disease was most likely to be a response of systemic acquired resistance.