Abstract
Allelopathic plants and their related phytotoxic chemicals have been explored as alternatives for environmentally friendly weed management. Dregea volubilis (L.f.) Benth. ex Hook.f., a woody vine, is well-known for its uses in various therapeutic treatments, and several bioactive compounds have been isolated from this species. However, to date, no phytotoxic substances from D. volubilis have been reported. Hence, in this research, we aimed to investigate the allelopathic effect of D. volubilis and characterize its phytotoxic substances. Extracts of D. volubilis exhibited significant inhibitory activity against the seedling growth of Italian ryegrass (Lolium multiflorum Lam.) and cress (Lepidium sativum L.). The extracts were purified through several chromatography steps, yielding two phytotoxic substances, and using spectroscopy, their structures were determined as dehydrovomifoliol and loliolide. The compounds inhibited the Italian ryegrass and cress seedlings with the I50 (concentrations needed for 50% inhibition) values ranging from 0.022 to 0.102 mM, for loliolide and 3.24–4.60 mM, for dehydrovomifoliol. These results suggest that both phytotoxic compounds might be responsible for the allelopathy of D. volubilis, and they may be released into the soil through the decomposition of the D. volubilis leaf and probably act as allelopathic active substances. Therefore, the extracts of D. volubilis and its related phytotoxic compounds may be applied as biological agents for controlling weeds.
Highlights
The extensive use of synthetic herbicides negatively affects the environment because of their residual toxicity in the soil and groundwater, and their detrimental effect on human health [1], and lead to major weed species developing herbicide resistance [2,3]
The extract obtained from 10 mg of D. volubilis inhibited the shoot growth of Italian ryegrass and cress by 50.41 and 22.13% of the control shoot growth, respectively, and inhibited the root growth of Italian ryegrass and cress by 19.5 and 15.4% of the control root growth, respectively
The I50 values of the D. volubilis extracts against the growth of the Italian ryegrass and cress varied from 3.21 to 10.15 mg D.W. equivalent extract/mL (Table 1), and the I50 values for the roots of both plants were significantly lower than those of their shoots (p ≤ 0.05)
Summary
The extensive use of synthetic herbicides negatively affects the environment because of their residual toxicity in the soil and groundwater, and their detrimental effect on human health [1], and lead to major weed species developing herbicide resistance [2,3]. To develop eco-friendly agricultural practices, allelopathic plants and their isolated allelochemicals have performed a vital part in weed management [5]. Most allelochemicals are eco-friendly due to their structural organization, short half-life in soils, and synergistic action when released into the environment [9]. Allelochemicals obtained from allelopathic plants possess the potential to be used as either a promising source of biological herbicides or templates for new synthetic herbicide classes [10,11]
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