Thyme-licorice nanoemulsion for anthracnose management in Capsicum annuum L. and life cycle assessment of its production

Botanicals, rich in bioactive components, have great promise as plant protectants. The current study aims at developing oil-in-water nanoemulsions using thyme oil (TO) alone and in combination with licorice aqueous extract (LAE) and comparing their efficacies against Colletotrichum capsici, the causal agent of anthracnose disease in Capsicum annuum L. The optimized nanoemulsions developed with TO alone (TFO4) and with LAE (TFO4-10LAE) with droplet size (Z-average diameter) of 24.33 ± 0.86 nm and 217.0 ± 5.9 nm, respectively, exhibited promising results pertaining to their stability and shelf life. As evidenced by their two-year shelf life testing, the nanoemulsions were observed to be stable. The TFO4-10LAE, having the bioactive molecules of LAE and TO intact (GC-MS and FT-IR analyses) and inhibiting the production of ergosterol, displayed synergistic and better antifungal activity (Minimum inhibitory concentration, MIC 2.5 mg ml^-1) than TFO4 containing only TO (MIC 4 mg ml^-1). During in-planta assay, TFO4-10LAE applied as a seed-foliar application at MIC significantly reduced the disease severity index (DSI) to 20.37 % over control (62.96 %), along with the improved activity of induced resistance enzymes and plant growth parameters. The life cycle assessment showed that the production of TFO4-10LAE nanoemulsion has a lesser negative impact on the environment than that of chemical pesticides. This work will pave the path for future research and development of pesticide alternatives that are safer, sustainable, and more effective than synthetic ones for crops of industrial importance.