Role of silymarin induced rice immunity against blast pathogen Magnaporthe oryzae through regulation of resistance genes expression

The effect of silymarin as an active ingredient of milk thistle seed as an systemic acquired resistance (SAR) substance in rice (Oryza sativa L.) against rice blast disease caused by Magnaporthe oryzae was investigated in this study. Silymarin is considered as a medication substance on human drug and has a metabolic and cell-regulating effect and scavenging oxygen radicals reactions. Results showed that, silymarin do not inhibits fungus linear growth in vitro. Significant improvement of resistance under greenhouse conditions with different concentrations 10, 25, 50, 125, 250, 500, 1000 and 2000 mg/L of silymarin was recorded. The most suitable concentration was 500 mg/L. The recorded disease severity was 23.5% when applied five days before inoculation and significantly reduced disease severity under field condition at both experimental seasons. Gene expression for some indicators for salicylic acid (SA) pathway such as OsWRKY45 and OsNPR1, jasmonic acid (JA) pathway such as AOS2, JAMYB and PBZ1 (OsPR10) and ethylene (ET) pathway such as ACO7 was studied. Salicylic acid effect on the pathway related to salicylic acid is evident through both genes (OsWRKY45 and OsNPR1), not jasmonic acid and ethylene pathways, while the effect of silymarin is not clear through the genes studied in all pathways. Finally, the results suggested that silymarin activates SAR at least in part by reinforcing basal plant defense responses on induced defense state.