Antimicrobial activity and induction of systemic resistance in rice by leaf extract of Datura metel against Rhizoctonia solani and Xanthomonas oryzae pv. oryzae

The leaf extracts of Datura metel significantly reduced the in vitro growth of Rhizoctonia solani (RS7, Anastomosis group AG1) and Xanthomonas oryzae pv. oryzae (Xoo). Methanol extract exhibited the best control of the pathogens recording 10-35% more toxicity than aqueous extract. Foliar application of leaf extracts effectively reduced the incidence of sheath blight and bacterial blight diseases of rice under greenhouse condition. Pre-inoculation applications of leaf extract were found better than post-inoculation applications. Induction of systemic resistance as evident from the increased accumulation of pathogenesis related (PR) proteins and other defense related compounds was observed in rice plants following application of leaf extract of D. metel and challenge inoculation with either R. solani or Xoo. The methanol extract of D. metel when subjected to thin layer chromatography (TLC) showed a spot with relative front (Rf) value of 0.705. Well pronounced antibacterial activity against Xoo was demonstrated by the compound eluted from the region corresponding to this spot. The molecular ion peak and the fragmentation peaks of the eluted compound analyzed by mass spectrometry correspond to the already published mass spectrum of daturilin (Siddiqui et al., Phytochemistry 26: 2641-2643, 1987), a withanolide compound from D. metel. (c) 2005 Elsevier Ltd. All rights reserved.