Document Type : Research Article
Authors
1
Department of Agronomy, Faculty of Agriculture, University of Zabol, Zabol, Iran
2
Department of Plant Production and Genetics Engineering, Faculty of Agriculture, Razi University, Kermanshah, Iran
Abstract
Introduction
Weeds represent a major constraint in agricultural production by competing with crops for essential resources such as light, water, nutrients, and space. In chickpea (Cicer arietinum) cultivation, species like Galium aparine L. (cleavers) and Vicia villosa Roth. (hairy vetch) can cause significant yield losses, estimated between 40% and 87% in the absence of effective weed management strategies. Conventional weed control relies heavily on synthetic herbicides, which provide rapid and effective results but raise environmental and health concerns due to their toxicity, persistence, and bioaccumulation. Allelopathy involves the release of allelochemicals by plants, which inhibit the growth and development of neighboring plants, offering a targeted approach to weed management. Plants such as Gundelia tournefortii (cardoon), Anthemis species (chamomile), and Arachis hypogaea (peanut) produce bioactive compounds, including terpenoids, phenolic acids, and flavonoids, known for their phytotoxic effects on weeds. Previous studies have demonstrated the efficacy of these plant extracts in suppressing weed growth, but their allelopathic effects on Galium aparine and Vicia villosa in chickpea fields remain underexplored. This study aimed to evaluate the phytotoxic and allelopathic potential of chamomile, cardoon, and peanut shell extracts, compared to pelargonic acid and the commercial herbicide Challenge, on these weeds over two growing seasons (2021–2022 and 2022–2023).
Materials and Methods
The experiment was conducted over two consecutive growing seasons (2021–2022 and 2022–2023) in an 80-hectare chickpea field located in Jiranblagh, Serfirouzabad, Kermanshah, Iran (34°12′34″N, 47°5′48″E; 1728 m above sea level). The study area has a Mediterranean climate characterized by long, dry summers and cold winters, with an average annual precipitation of 435 mm. Soil analysis confirmed adequate NPK levels, and 25 kg.ha-1 bentonite sulfur and 1 kg.ha-1 ammonium molybdate were applied for balanced nutrition. Chickpea seeds (cv. Mansour) were sown mechanically at 15 plants.m-². Treatments included chamomile extract (50 g.L), cardoon extract (100 g.L-1), peanut shell extract (100 g.L-1), pelargonic acid (5 L.ha-1), Challenge herbicide (2 L.ha-1), and water control, applied in a factorial randomized complete block design with three replicates. Plant materials were collected from Kermanshah’s Koohsefid mountains (chamomile and cardoon) and Razi University’s agricultural campus (peanut shells). Extracts were prepared using ethanol (1:10 ratio), filtered, and stored at 4°C. Total phenolic content was measured gravimetrically, and antioxidant activity was assessed via the DPPH assay. Weed traits, including growth inhibition, chlorophyll content, stomatal conductance, and chlorophyll fluorescence (Pocket PEA), were measured 48 hours post-treatment. Gas chromatography-mass spectrometry (GC-MS) analyzed chamomile essential oil composition. Data were analyzed using SAS 9.1, with variance homogeneity tested via the F-test, and means compared using the Least Significant Difference (LSD) test at P<0.05.
Results and Discussion
The weed flora of the chickpea field consisted of 27 species, with Galium aparine (92% frequency, 10.6 plants m⁻²) and Vicia villosa (60% frequency) identified as the dominant species. GC–MS analysis of chamomile essential oil revealed 21 constituents, accounting for 82.49% of the total oil composition. The predominant compounds were myrtenyl acetate (20.37%), decanoic acid (9.85%), spathulenol (7.99%), and caryophyllene oxide (5.12%), consistent with previous reports (Nejadhabibvash, 2017). These terpenoids are known for their phytotoxic effects, disrupting photosynthesis and inducing oxidative stress. Growth inhibition of Vicia villosa was most pronounced in the first year with pelargonic acid (70.3%) and cardoon extract (67.13%), while for Galium aparine, cardoon extract (53.33%) and pelargonic acid (52.76%) were most effective in year one, and pelargonic acid (47.03%) and cardoon (46.79%) in year two. Treatments significantly reduced chlorophyll content, with a 69.91% decrease in Galium aparine (pelargonic acid, year two) and 74.28% in Vicia villosa (chamomile, year two) compared to the control. Stomatal conductance was notably reduced by chamomile extract, with a 66.80% decrease in Galium aparine and 51.75% in Vicia villosa in the second year. Chlorophyll fluorescence (Fv/Fm) decreased by 56.63% in Galium aparine and 36.14% in Vicia villosa under chamomile treatment in year two, indicating photosystem II impairment. These effects are attributed to allelochemicals, particularly terpenoids, which inhibit photosynthesis, reduce chlorophyll synthesis, and cause cellular damage.
Conclusion
Chamomile extract exhibited pronounced phytotoxic and allelopathic activity, markedly reducing growth parameters, chlorophyll content, stomatal conductance, and chlorophyll fluorescence in Galium aparine and Vicia villosa, with efficacy surpassing that of the commercial herbicide Challenge. The high proportion of myrtenyl acetate in chamomile essential oil is likely a key contributor to its herbicidal potential. Cardoon extract and pelargonic acid also showed strong weed suppression, while peanut shell extract was less effective. These findings suggest that chamomile extract is a promising eco-friendly bioherbicide for sustainable weed management in chickpea fields. Further studies are recommended to elucidate the mechanisms of action of these allelochemicals and optimize their field application.
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