allelopathic potancial of ziziphora clinopodioides on germination indices and initial growth of sinapis arvensis and avena fatua

Introduction: weeds are a serious threat to crop production because they interfere with the crop growth and development and result in significant crop losses. weeds actually cause yield loss higher than any other pest in crop production. as a result, chemical synthetic herbicides have been widely used for weed management. heavy usage of chemical synthetic herbicides, however, has resulted in public concerns over the impact of herbicides on human health and the environment. therefore, unconventional weed control strategies, especially those based on ecological principles, are very much needed in modern agriculture. allelopathy is considered a multi-dimensional phenomenon occurring constantly in natural and anthropogenic ecosystems, by which one organism produces bio-chemicals that influence the growth, survival, development, and reproduction of other organisms (rice, 1984). allelochemicals (chemical compounds) found in different organs of plants (leaves, flowers, stems, roots, buds and even seeds) can greatly slow or stop the germination and growth of weeds (rezvani & dadkhah, 2023). the multiple effects resulting from allelochemicals include effect on cell division, plant hormones production, membrane permeability, mineral uptake, movement of stomata, photosynthesis, respiration, specific enzyme activities and ect. (dadkhah, 2012). materials and methods: in order to study the allelopathic potential of ziziphora clinopodioides on seed germination and seedling growth of sinapis arvensis and avena fatua in laboratory condition, an experiment based on completely randomized design with four replications was carried out. the experimental treatments including distilled water as control, aqueous extract concentrations of z. clinopodioides 10 and 20% (w/v) were used. the aerial parts of z. clinopodioides were collected from rangeland of shirvan city, north khorasan province, iran. the foliar parts were washed with distilled water and dried in the shade at room temperature. then the aerial parts (stem and leaves) were fine powdered (using an electrical mill). twenty g of the powdered organ was placed in a 2 l erlenmeyer flask and 1l deionized water was added. flask was covered with aluminum foil to protect photo decomposition and placed on a rotary shaker (~200 revolutions per min.) for 24 h. the mixtures were filtered through whatman no.1 filter paper using a vacuum pump. the ph and electrical conductivity (ec) of extracts were determined using a digital ph meter and conductivity meter. the ph (from 6.7 to 6.0) and ec (from 2.20 to 2.6 ms/cm) were within the tolerance range of target plants. data were transformed using arcsine prior to statistical analysis if needed. the data for all measured parameters were analysed using the analysis of variance procedure of statistical analysis system (sas), version 9.1. means were compared by duncan’s multiple range test at the 0.01 probability level for all comparisons. results and discussion: the results of experiment showed that the aqueous extracts of z. clinopodioides inhibited the germination and seedlings growth of s.arvensis and a.fatua. the inhibitory effect was concentration-dependent. the low concentration (10%) of aqueous extract of z. clinopodioides inhibited the germination of s.arvensis and a.fatua by 23.3% and 30.4%, respectively. however, the highest concentration (20%) of z. clinopodioides inhibited the germination of s.arvensis and a.fatua by 65.1 and 74.2%, respectively than control (table 1). the seedlings growth of s.arvensis and a.fatua were severely inhibited at the higher concentration (20%) of z. clinopodioides extract. the low (10%) and high (20%) concentrations of z. clinopodioides extract, decreased the seedling length of s.arvensis by 36.1% and 64.1%, and the seedling length of a.fatua by 47.2% and 74.5%, respectively, than control (table 1). however, the root length of s.arvensis decreased by 42.3% and 75.5%, and the root length of a.fatua decreased by 45% and 80.7%, respectively, than control. shoot length of s.arvensis and a.fatua seedlings were also decreased by 31.5% and 38.1% at low concentration (10%) and 58.1% and 69.5% at highest aqueous extract concentration (20%). some researchers reported that allelochemicals inhibits the physiological processes that leads to reduced growth (jefferson & pennacchio 2003). the effects of allelopathy on germination and growth of plants may occur through various mechanisms such as reduced mitotic activity in roots and hypocotyls, suppressed hormone activity, reduced rate of nutrients uptake, reduction in permeability of cell membranes and inhibition of enzyme action (rice, 1984). the stronger inhibitory effects of extract on roots might be due to the direct contact with the extract and its chemicals (dadkhah, 2012). conclusion: the results of this experiment showed that the aqueous extract of z. clinopodioides inhibited the germination and seedlings growth of both weeds due to its phytotoxic effects. however, further studies are necessary to find out the mechanism involved in its specific recognition ability.