Hormetic response of blackgram (Vigna mungo) seeds treated with organic extract of seaweeds

Seaweed extract has gained popularity in agriculture due to global trend of promoting sustainable agricultural development. Seaweed contains phytohormones such as IAA and gibberellin and minerals that induce seeds germination. While conventional extraction of seaweeds has been carried out with different organic solvents such as ethanol and methanol, the present study uses natural and commonly available organic liquids i.e., water, vinegar, fermented buttermilk, and cow urine as extracting agents to make them suitable for regenerative agriculture. The organic solvents used in this study have a known nutritional composition and facilitate the enhancement of plant defense systems. Three seaweed species, Caulerpa racemosa , Gracilaria edulis , and Sargassum wightii , were extracted with different solvents at various concentrations and compared. The mineral analysis and FTIR characterization of different seaweeds and their extracts showed variation in composition and functional groups. Seaweed species, however, showed no variation in seed germination. Fermented buttermilk and water extract improved the germination properties of blackgram between 0.1–5% concentrations and led to higher increase in shoot and root length and biomass yield. The hormetic response by blackgram to the seaweed extract was observed starting at an average of 2% concentration with toxicity at 5% concentration and above for water and fermented buttermilk extract. However, vinegar and cow urine extracted seaweed showed toxicity symptoms even at lower concentrations (0.1%) inhibiting germination. Therefore, water and buttermilk extract may be recommended at 0.5–1% for enhanced germination.