Evaluation du pouvoir herbicide des extraits aqueux de trois plantes spontanées récoltées au Sahara

Abstract

In the context of valorization of natural resources, by the search for new compounds of plant origin and the evaluation of the allelopathic and bioherbicide activity of the leaf extracts of three spontaneous plants, namely Haloxylon scoparium Pomel, Euphorbia guyoniana Boiss. & Reut. and Euphorbia retusa Forsk. harvested in the north-eastern region of Algerian Sahara on a few weeds related to cereal crops: Bromus rubens L., Phalaris minor Retz., Plantago lagopus L., Ammi visnaga L. (LAM) and Triticum durum Desf. The evaluation of the activity of the plant extracts was made by the method of reflux extraction, which allowed us to determine the extraction yields of the different extracts. The extraction yield is of the order of 20.64% for Haloxylon scoparium, followed by the extract of Euphorbia guyoniana with an extraction yield of 17.80%. While the extract of Euphorbia retusa has the lowest yield with 15.45%. Phytochemical screening of leaf extracts of three species shows a remarkable richness in active substances; including alkaloids, flavonoids, steroids, sterols and triterpenes, coumarin, saponosides, free quinone, cyanidin, tannins and reducing compounds are presented in more or less important quantities in all extracts. There is a total absence of reducing compounds in Haloxylon scoparium extract, Alkaloid and coumarin in Euphorbia guyoniana and saponoside in Euphorbia retusa. We also detected the presence of anthocyanin in Euphorbia guyoniana and glycoside in Euphoria retusa. Dosage of total polyphenols and total flavonoids of leaf extracts, shows that the highest levels of polyphenols are found in the extract of Euphorbia guyoniana (2423.80 1.56 mg EAG/100g), while the other plants are less rich in polyphenols, Haloxylon scoparium (588.33 1.87 mg EAG/100g) and Euphorbia retusa (573.8 1.65 mg EAG/100g). Total flavonoids are concentrated mainly in Haloxylon scoparium extract (95.45 1.21 mg EQ/g), and very low in Euphorbia guyoniana extracts (34.88 0.83 mg EQ/100g) and Euphorbia retusa (24.92 0.91 mg EQ/100g). The analysis carried out by LC-MS-MS on plant extracts, allowed us to show the richness of the leaves of these desert species in phenolic compounds and to determine their chemical composition. A wide range of various phenolic compounds have been identified, namely: folic acid, maleic acid, caffeic acid, ascorbic acid and gallic acid, quercetin, rutin, naringenine, myricetin, vanillin, hydroxy-4-coumarin, beta-carotene, BHA and BHT. The evaluation of allelopathic power by two experimental models revealed the bioherbicide capabilities in all extracts. The results obtained are promising, which all extracts significantly inhibit the germination of weed species. However, no extract significantly affected the germination of wheat seeds. The inhibition rates recorded for the different batches of pots treated with plant extracts are relatively lower compared to the results obtained for batches of petri dishes. Germination kinetics and vigor index of weed and cultivated species treated with plant extracts were slower than reported for negative control lots. While according to the calculated values EC50% and EC90%, leaf extracts were found to be more harmful to weed species (Bromus rubens, Phalaris minor, Plantago lagopus, Ammi visnaga) than the cultivated species (Triticum durum). The growth inhibition values of the aerial and root part and the Fisher test results affirm the strong bioherbicide power of the extracts of three plants studied including those of Haloxylon scoparium, where its toxicity at the highest concentration is comparable to that of the herbicide (positive control). On the other hand, the simulator effect at the level of the lots treated by the low concentrations, which is manifested by the elongation or increase of the weight of the aerial and root part compared to the seedlings of the negative control lot.