Plants protect themselves by using internal proteins and other organic substances. Proteins called pathogenesis related (PR) proteins are antifungal and have been found in plants, fungi, bacteria, insects, shell fish, and some other animals. There are believed to be eleven PR proteins. Lectins and protease inhibitors are two of the PR proteins.
The Latin name for the Ayurvedic herb Ashwagandha is Withania somnifera and it contains a glycoprotein (WSG), which prompted this study. WSG has antibiotic activity against bacteria and has antifungal activity by preventing spore formation and preventing hyphal growth. Withania extracts have previously been shown to be effective against Salmonella typhimurium and E. coli.
In this study, a water extract of powdered Ashwagandha root was tested against Aspergillus flavus, which spoils stored crops. WSG is active against Aspergillus flavus, Fusarium oxysporum, F. verticilloides and Civibacter michiganensis subspecies michiganensis.
WSG is an acidic, non-toxic protease inhibitor, which may be why it works to protect plants from fungi, bacteria, and viruses.
CONCLUSION: WSG from Ashwagandha shows potent antifungal and antibacterial activity. The protease inhibitor action of the PR proteins in Ashwagandha may be the reason it works to protect plants. Further studies are needed about the antifungal effect of Withania in humans.