Allelopathic Potential of Aqueous Plant Extracts Against Seed Germination and Seedling Growth of Weeds

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Abstract
Allelopathy has been described as a negative or positive effect on a specific species of plant caused by a chemical produced by another species of plant. This research analyzed the allelopathic effect of various plant extracts against seed germination and seedling properties of some weed species in two experiments in the autumn of 2021. The impacts of plant extracts, such as peels of pomegranate (Punica granatum), green husk of walnuts (Juglans regia), leaves of eucalyptus (Eucalyptus camaldulensis), galls of Aleppo oak (Quercus infectoria), rhizomes of cogon grass (Imperata cylindrica), and tubers of nutgrass (Cyperus rotundus) plus control on some weed species, like Vaccaria pyramidata, Cynodon dactylon, Sorghum halepense, Trifolium campestre, Portulaca oleracea, Sinapis arvensis, Avena fatua), Hordeum glaucum and Daucus carota were evaluated. The first experiment was conducted in the lab and designed by a factorial-completely randomized design to investigate germination parameters such as final germination percentage (G), mean germination time (MGT), coefficient of the velocity of germination (CVG), and germination rate index (GRI), and another experiment was in a greenhouse and designed in a split-plot pattern, in which the plant extracts were placed in main plots. At the same time, the weed species were distributed in the sub-plots to evaluate the seedling of weeds’ fresh and dry weight and percent of weed inhibition (PWI). The characters’ means (from three replicates) were compared according to Duncan’s multiple range test at the 5% level. The laboratory trial revealed that the green walnut husk was the most successful in reducing all seed germination parameters compared to the control by 13.5, 5.16, and 8.37% for G, MGT, and GRI, respectively. For the greenhouse experiment, the eucalyptus leaves’ extract and pomegranate peels had a higher impact on reducing weed seedlings’ fresh and dry weight and PWI than the control. The most affected species were broad-leaved weeds, while grasses were the least affected. Our results indicated that green walnut husk has a significant role in decreasing seed germination and inhibiting the dry weight of seedlings. Thus, it can be used as a bioherbicide to prevent some weeds from sprouting and growing seedlings.

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