Durantol - a phytosterol antifungal contributor from Duranta repens Linn. For organic Management of Sorghum Downy Mildew

Abstract

Downy mildew of sorghum (DMS) has serious implications agronomically worldwide and to-date the search for a potent fungicide is a high priority and necessity. Phytochemicals have proven to be effective against various plant pathogens with minimal or no side effects. Duranta repens aqueous extract exhibited a promising potential as an organic fungicide for management of sorghum downy mildew (Peronosclerospora sorghi) in greenhouse conditions, at low concentration of 5 %. Activity guided bio-prospecting lead to the isolation of active principle which could control the DMS at as low as 0.1 % concentration. Spectral studies identified the bioactive contributor as a phytosterol namely 16-Hydroxy-8,10,13-trimethyl-1,2,8,10,12,13,14,15-octahydro cyclopenta [a] phenanthren-3-one, designated as Durantol. The results of microscopy exhibited the inhibition of conidial germ-tube growth by formation of bulb-like swellings at the tip, suggesting the mechanism of action of Durantol was via hampering the membrane integrity of the pathogen. Further, the same was virtually predicted using molecular docking for structure-activity relationship (SAR) against four best known membrane receptors namely 1-UDP-glycosyltransferases (UGT), cytochromes P450 (P450), oxidosqualene cyclase (OSC) and serine carboxypeptidase-like acyltransferase (SCPL), proposing that glycosylation onto the membrane would be a reason for inhibition and which is evident from atomic contact energy (ACE) values. The results of the study indicate that, organic management of airborne inoculum of downy mildew of sorghum is feasible and preferable, as compared to the use of chemical fungicides, considering human and environmental health concerns.