Thapsia garganica allelopathic potentialities explored for lettuce growth enhancement and associated weed control

Thapsia garganica phytotoxicity was studied on Lactuca saliva L. and associated weeds, by pulverization of its aqueous extracts (at 10, 20, and 30 %), in pot experiments. To comprehend its mode of action on lettuce, seedlings were grown hydroponically in Hoagland nutrient solution for two months, then the T. garganica leaves aqueous extract was added to the medium for three days. After the harvest, a number of physiological and biochemical parameters had been determined. The antioxidant activity for DPPH (2,2-diphenyl-1-picrylhydrazyl radical) and FRAP (Ferric reducing antioxidant power), and secondary metabolite production were assessed by employing QUENCHER approach. The pulverization treatment was beneficial for lettuce growth, whose length of different organs has been improved at all concentrations. However, it has been very harmful to weeds and in a more important way to monocotyledons, which were totally burned at 30 %, compared to dicotyledons weeds. To allelopathic stress, lettuce developed a defense strategy manifested by a decrease of electrolyte leakage and malondialdehyde content (MDA), an increase in proline content and in polyphenols, flavonoids, flavanols, proanthocyanidins, condensed tannins and carotenoids production. Similarly, a stimulation of the antioxidant activity was recorded, by increasing DPPH free radical-scavenging activity and ferric reducing antioxidant power. For lyase type enzymes (the phenylalanine ammonia-lyase (PAL) and the tyrosine ammonia-lyase (TAL)) activities, an improvement of 25.00 % for the PAL and 38.00 % for the TAL were registered in roots and leaves, respectively. Chlorophyll contents were similarly affected, however the respiration decreased. T. garganica is a species rich in allelochemicals compounds, according to its allelopathic potential. The possibility of using its aqueous extract by spraying shows that it could be an ecofriendly approach to exploit its valuable allelochemicals.