Effects of silicon application on resistance against bacterial blight and antioxidant defense activities of rice leaves

【Objectives】 Bacterial blight of rice is a bacterial wilt disease in the world, which is one of the important biological factors limiting rice yield. By inoculating Xoo into leaves of field-grown rice, we investigated the effect of silicon on concentration of malondialdehyde and activities of antioxidant defense enzymes in rice leaves and the underlying mechanism of Xoo resistance to provide theoretical basis for safe and effective prevention and control measures for the disease. 【Methods】 A field experiment was conducted in Qinhuangdao, Hebei province in 2013. Rice was grown with no Si (-Si), sodium silicate at 70 kg/hm2 (Si1, SiO2) and calcium silicon fertilizer at 70 kg/hm2 (Si2, SiO2) at two nitrogen levels, i.e. 180 kg/hm2 (N180, normal N) and 450 kg/hm2 (N450, high N). The rice variety used was a japonica (Oryza sativa cv. Tang No.2). Five to six of the uppermost fully expanded leaves of each rice plant at the booting stage were inoculated by using leaf clipping method, in which the leaf blade was cut with a pair of scissors pre-dipped in the bacterial suspension. The effect of silicon on rice disease index was examined 30 days after inoculation, and the effect of silicon on the concentration of malondialdehyde and the activities of superoxide dismutase (SOD), catalase (CAT) and ascorbic acid peroxidase (APX) in rice leaves was analyzed at 1, 3, 5, 7 and 10 days after inoculation. 【Results】 After inoculation with leaf blight pathogen, under the normal N level, on the average disease index of Si-treated plants was 17.8% lower than that of Si-untreated plants (P0.05), while under the high N level, the disease index of calcium silicate-treated plants was 15.1% lower than that of Si-untreated plants (P0.05), and the index of sodium silicate-treated plants was statistically insignificant. The concentration of malondialdehyde (MDA) in silicon-treated plants was lower than that in silicon-untreated plants 7 days after inoculation under the normal nitrogen level (P0.05), and so was it at 3 and 7 days after inoculation under the high nitrogen level. The activity of super oxide dismutase (SOD) in silicon-treated plants was significantly higher than that in silicon-untreated plants 7 days after inoculation under the normal N level, and so was it 1 and 5 days after inoculation under the high N level. The SOD activity was significantly higher in calcium silicate-treated plants than in sodium silicate-treated plants 1 day after inoculation. The activity of catalase (CAT) in the Si-treated plants was higher than that in the Si-untreated plants, though the difference was not statistically significant. The activity of ascobic peroxidase (APX) in the Si-treated plants was significantly higher than that in the Si-untreated plants 1, 7, and 10 days after inoculation under the high N level.【Conclusions】 Addition of silicon fertilizer can enhance the activities of SOD, CAT and APX and reduce the concentration of MDA of rice leaves in the field condition, thus effectively eliminating reactive oxygen species and improving resistance against bacterial blight. Under the high N level, calcium silicate is more effective in increasing resistance against bacterial blight than sodium silicate.