Screening of Tunisian plant extracts for herbicidal activity and formulation of a bioherbicide based on Cynara cardunculus

Abstract

The need to reduce the use of chemical pesticides currently fosters great interest in eco-friendly biological control agents. In addition, the isolation of plant allelopathic substances and the evaluation of their phytotoxic effects can lead to the discovery of new natural herbicides. In this context, our study aimed to assess the herbicidal activity of ten crude extracts obtained from aerial parts of Tunisian spontaneous plants against Trifolium incarnatum, Silybum marianum and Phalaris minor. It confirmed that the Cynara cardunculus methanolic extract best inhibited weed germination and seedling growth, and caused necrosis or chlorosis. Following a bioassay-guided fractionation, five main phenolic compounds, (1) syringic acid, (2) p-coumaric acid, (3) myricitrin, (4) quercetin and (5) naringenin were identified in the most active crude methanolic extract. Then, only 3 of the flavonoids contained in the most active fraction were tested on Trifolium incarnatum. The 3 compounds had a significant phytotoxic effect and therefore could be employed in a new composition of botanical herbicides to control crop weeds. Besides, a novel herbicide composition was designed to improve the post-emergence activity of the methanolic extract. The formulation containing the C. cardunculus crude methanolic extract showed the same herbicidal activity as the standard industrial bioherbicide containing pelargonic acid. These results make C. cardunculus a suitable source of natural compounds potentially usable as natural herbicides.

Plant extracts - importance in sustainable agriculture

“…Water extracts have many advantages such as are eco-friendly, easily degradable, are not persistent in the soil, and are not toxic to animals and humans (Li and Zhihui, 2009). In some cases, organic solvents such as ethanol and methanol are used to obtain plant extracts (Basra and Lovatt, 2016;Kole et al, 2016;Green et al, 2017;Zuleta-Castro et al, 2017;Desoky et al, 2018aDesoky et al, , 2018bJang and Kuk, 2019;Kaab et al, 2020). Ethanol is applied for the extraction of botanical active substances because is characterised by low toxicity and is approved by the food industry (Zuleta-Castro et al, 2017).…”

“…These formulations are composed for example from the extract, water, castor oil, and surfactant -Tween 80 (polyethylene glycol sorbitan monooleate) (Zuleta-Castro et al, 2017). In the case of methanolic extract, which was applied as a bioherbicide, the plant extract was mixed with vegetable oil of hazelnut, ethoxylated castor oil, surfactant -Tween 20 (polyethylene glycol sorbitan monolaurate), adjuvant UEP-100, ethanol, and water (Kaab et al, 2020). In the work of Kole et al (2016), methanolic leaf extracts were mixed with surfactants -Na-alkaline sulfonate or K-alkaline sulfonate.…”

“…In the work of Kole et al (2016), methanolic leaf extracts were mixed with surfactants -Na-alkaline sulfonate or K-alkaline sulfonate. Prepared formulations contain amphiphilic substances to mix the hydrophilic extract with the hydrophobic vegetable oil (Kaab et al, 2020). Mixing the plant extract with vegetable oil aims to facilitate the effective and complete penetration of the spray solution with active compounds by epidermal waxes (Kaab et al, 2020).…”

“…For example, methanol extract from teak (Tectona grandis) contains phenolic acids (benzoic, caffeic, gallic, salicylic, tannic, and vanillic acid), which are the major allelochemicals responsible for the inhibition of plants (weeds) germination (Kole et al, 2016). Also, Kaab et al (2020) found that methanolic extract from cardoon (Cynara cardunculus) has in its composition phenolic compounds, such as myricitrin, naringenin, quercetin, p-coumaric acid and syringic acid, which inhibited the germination of weeds, seedling growth and caused chlorosis or necrosis. Another natural weed inhibitor can be sorghum extract, which provides soluble allelochemicals being phytotoxic to certain weeds (Cheema and Khaliq, 2000).…”

“…weeds (Mekky et al, 2019) as well as Angallis arvensis, C. rotundus, and Cynodon dactylon (Khare et al, 2019). It was shown that teak (Tectona grandis) extracts can lower the population of junglerice (Echinochloa colona) and common barnyardgrass (Echinochloa crus-galli) (Kole et al, 2016), while cardoon (Cynara cardunculus) products can inhibit the development of Crimson clover (Trifolium incarnatum) (Kaab et al, 2020). Based on the findings of research studies, it can be seen that essential oils exhibit herbicidal activity against different weed species and therefore could be considered for the development of natural multi-targeted herbicides.…”