Allelopathic and antimicrobial evaluation of two Indian weeds- Heliotropium indicum L. and Synedrella nodiflora (L.) Gaertn with phytochemical studies

In the last two decades, antibiotic resistance has become a severe problem worldwide. Herbal antimicrobials have enormous potential as they can serve purpose with lesser side effects than synthetic antimicrobials. Weeds release different allelochemicals which can act as antimicrobials or herbicides. Leaves of two important Indian weeds viz. Heliotropium indicum L. (Boraginaceae) and Synedrella nodiflora (L.) Gaertn. (Asteraceae) were taken in this allelopathic and antimicrobial study.  Seed germination is considered to be the most significant stage especially under stress conditions and thus acts as an excellent model bioassay technique. Aqueous and ethanolic leaves extract of both plants progressively affected germination parameters of tested plants. But it affected seeds of Lactuca sativa more than those of Vigna mungo.  Lactuca sativa Germination % declined to 40%-52% in case of ethanolic extract of these weeds. Ethanolic extracts are more effective in inhibiting germination in both indicator plants. The weed extracts were very effective against Escherichia coli, Staphylococcus aureus and fungus Aspergillus niger. Salmonella enterica is the most resistant strain tested against these extracts. Heliotropium indicum L. was found to have tannin, alkaloid, and saponin and glycoside in both types of extracts. Synedrella nodiflora L. contain phenols, alkaloids and flavonoids in both aqueous and ethanolic extracts. Terpenoids and tannin were found in ethanolic extract of Synedrella nodiflora. The present study concludes that both plants contain herbicidal and antimicrobial constituents. Further studies regarding the isolation and identification of these antimicrobial and herbicidal constituents are necessary.