Induction of systemic resistance in pearl millet (Pennisetum glaucum) against downy mildew (Sclerospora graminicola) by Datura metel extract

A leaf extract of Datura metel protected pearl millet plants against downy mildew disease caused by Sclerospora graminicola. Of the different concentrations tested, the highest seed germination and seedling vigor was recorded when seeds were treated with a 2% extract for 3 h. When tested for induction of resistance against downy mildew disease, seed treatment with D. metel extract resulted in 79 and 67% protection under greenhouse and field conditions respectively. The resistance offered by D. metel extract was demonstrated to be systemic acquired resistance (SAR) and was active at both early and later stages of plant growth. An association between induction of resistance and salicylic acid (SA) content was drawn by quantifying the enhanced level of endogenous salicylic acid in root (4-fold) and shoot (10-fold) portions of induced seedlings. The highest levels of salicylic acid were observed in roots and shoots of highly resistant (HR) and SAR seedlings 3 and 6 h after inoculation respectively. The defense related enzymes, peroxidase, β-1,3-glucanase and chitinase, showed 1.5–2.6-fold increased activity in SAR seedlings. In addition to disease protection, plants with induced resistance showed 1.2–1.3-fold increased growth, in biomass, number of earheads and grain yield. Taken together, our results strongly suggest that seed treatment with D. metel extract provides protection against the downy mildew pathogen.