Acta agriculturae Slovenica, 117/4, 1–12, Ljubljana 2021 doi:10.14720/aas.2021.117.4.1520 Original research article / izvirni znanstveni članek Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species Marjan DYANAT 1, 2 , Farzad ASGARI 1 Received February 15, 2020; accepted October 16, 2021. Delo je prispelo 15. februarja 2020, sprejeto 16. oktobra 2021 1 Department of Agricultural Sciences and Food Industries, Science and Research Branch, Islamic Azad University, Tehran, Iran 2 Corresponding author, e-mail: Ma_dyanat@yahoo.com Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species Abstract: In the present study the bioherbicidal activity of essential oils hydrodistilled from Nepeta glocephalata Rech.f and N. ispahanica Boiss were investigated on four weed spe- cies (barnyard grass (Echinochloa crus-galli (L.) Beauv), redroot pigweed (Amaranthus retroflexus L.), lambsquarters (Chenopo- dium album L.) and canary grass (Phalaris canariensis L.)). A total of 37 components were identified from the essential oils of N. glocephalata and N. ispahanica constituting approximately 98.61 % and 96.1 % of the oils, respectively. In laboratory bio- assay different concentrations (0, 1, 2, 4 and 8 μl ml -1 ) of two Nepeta essential oils on germination, root and shoot length were studied. Results showed by increasing the concentration of oils, all studied traits of the weeds were decreased compared with control. In a glass house bioassay post-emergence appli- cation of Nepeta essential oils (1.25 %, 2.5 %, 5 % and 10 %, v/v) on 3-week-old weed plants caused visible injury (7-days after spray) ranging from chlorosis to necrosis of plant weeds. In foliar application under glasshouse conditions, both Nepeta essential oils reduced the seedling dry mass and concentra- tions of chlorophyll a chlorophyll b. The study concludes that Nepeta essential oils have phytotoxic effects and could be used as bioherbicides but the selectivity of these compounds should be considered also. Key words: Nepeta glocephalata Rech.f.; N. ispahanica Boiss.; bioherbicide; 1, 8-cineole; chlorophyll a; weed seed ger- mination; root length Fitotoksični učinki eteričnih olj iz dveh vrst mačje mete (Ne- peta glocephalata Rech.f. in N. ispahanica Boiss.) na izbrane vrste plevelov Izvleček: V raziskavi je bila preučevana bioherbicidna ak- tivnost vodnih destilatov eteričnih olj iz dveh vrst mačje mete (Nepeta glocephalata Rech.f in N. ispahanica Boiss. ) na štiri ple- velne vrste (navadna kostreba (Echinochloa crus-galli (L.) Be- auv), navadni (srhkodlakavi) ščir (Amaranthus retroflexus L.), bela metlika (Chenopodium album L.) in kanarska čužka (Pha- laris canariensis L.)). Celokupno je bilo v eteričnih oljih obeh vrstah določenih 37 sestavin, ki so predstavljale 98,61 % oziro- ma 96,1 % olja. V laboratorijskem poskusu so bili preučevani učinki različnih koncentracij (0, 1, 2, 4 in 8 μl ml -1 ) eteričnih olj iz obeh vrst mačje mete na kalitev, dolžino korenin in poganj- kov izbranih plevelov. Rezultati so pokazali, da so se vrednosti vseh merjenih parametrov plevelov zmanjševale s povečeva- njem koncentracije eteričnih olj. V poskusu v rastlinjaku so bile preučevane vidne poškodbe uporabe eteričnih olj iz obeh vrst mačje mete (1,25 %, 2,5 %, 5 % and 10 %, v/v) na tri tedne starih sejankah plevelov, sedem dni po škropljenju z eteričnimi olji, ki so se pojavile kot kloroze in nekroze. Pri foliarni uporabi eterič- nih olj obeh vrst mačje mete v rastlinjaku se je zmanjšala suha masa sejank plevelov, zmajšale so se tudi vsebnosti klorofila a in b. Na osnovi raziskave lahko zaključimo, da imajo eterična olja obeh vrst mačje mete fitotoksične učinke in bi lahko bile upo- rabljene kot bioherbicidi vendar je pri tem potrebno upoštevati selektivne učinke njihovih sestavin. Ključne besede: Nepeta glocephalata Rech. f.; N. ispaha- nica Boiss.; bioherbicid; 1, 8-cineol; klorofil a; kalitev semen plevelov; dolžina korenin Acta agriculturae Slovenica, 117/4 – 2021 2 M. DYANAT and F. ASGARI 1 INTRODUCTION Herbicide-resistant weeds and environmental con- cerns have led researchers to consider using alterna- tive ways to manage weeds (Vyvyan, 2002; Ashraf et al., 2017). Allelopathy is one of these ways (Weston, 1996). Allelopathic compounds can reduce the use of synthetic herbicides and thus reduce environmental pollution and lead to more safe crops (Singh et al., 2002, 2003, 2005a, b). Among the natural plant products, essential oils con- stitute an important group of that provide a characteristic odor to the aromatic plants (Singh et al., 2002). Earlier studies have documented that essential oils and their constituents inhibited seed germination and retard plant growth (Barney et al., 2005; Batish et al., 2006; Ens et al., 2009). The allelopathic activities of some essential oils and their monoterpenes on seeds germination or seed- ling growth at several species have been shown in pre- vious studies (Dudai et al., 1999; Abrahim et al., 2000; Tworkoski, 2002; Singh et al., 2004; Dudai et al., 2004; Armirante et al., 2006; Kordali et al., 2006; Kordali et al., 2007). Allelopathic properties of essential oils from dif- ferent aromatic plants belonging to Lamiaceae, Composi- tae, Myrtaceae, Cupressaceae, Rutaceae and Verbenaceae families have been reported (Dudai et al., 1999; Angelini et al., 2003; Kaur et al., 2010; Amri et al., 2013 ; Verde- guer et al., 2011). Also allelopathic potential of the es- sential oil of many plants from family Lamiaceae such as Salvia apiana Jeps. and Salvia leucophylla Greene (Muller et al., 1964), Satureja hortensis L. and Thymus vulgaris L. (Tworkoski 2002), Rosmarinus officinalis L., Satureja montana L. (Angelini et al., 2003), Lavandula spp. and peppermint (Mentha × piperita ‘Mitcham’) (Campiglia et al., 2007; Mahdavikia and Saharkhiz, 2015), Zataria mul- tiflora Boiss and its different chemotypes (Saharkhiz et al., 2010), Satureja khuzestanica Jamzad, Satureja bach- tiarica Bunge, Satureja rechingeri Jamzad and Satureja spicigera (K.Koch) Boiss. (Taban et al., 2013) have been previously reported. Genus Nepeta is one of the largest genera of the Lamiaceae family that comprises about 300 herbaceous perennial and annual species (Formisano et al., 2011). The greatest diversity and richness of species is found in Southwestern Asia, (especially Iran and Turkey), and the W estern Himalayas. There are seventy-nine species of Ne- peta in Iran and about 39 of them are endemics (Jamzad, 2012). Much research was done on diversity, species rich- ness and chemical properties of Nepeta species. Most Ne- peta species are rich in essential oils. Diverse biological activities of Nepeta oil such as feline attractant, canine attractant, insect repellant, arthropod defense (Tucker and Tucker, 1988, Wagner and wolf, 1977), antibacterial, antifungal and antiviral activities (Tucker and Tucker, 1988) have been reported previously. There are several reports on the chemical composition of the essential oils of the genus Nepeta found in Iran (Sefidkon, 2004, 2005; Sajjadi, 2005; Sonboli et al., 2005; Jamzad, 2012). Allelo- pathic potential of this genus was revealed. Phytotoxicity of Nepeta essential oils has been mainly tested (Kobaisy et al., 2005, Eom et al., 2006, Mancini et al., 2009, Mutlu et al., 2011, Kekec et al., 2012, Bozari et al., 2013, Živković, 2013). Allelopathy of water extracts has been studied by Mutlu and Atici (2009) and Babaahmadi et al. (2013). No bioassays or field experiments had been done to study the allelopathic potential of Nepeta glocephalata Rech.f and N.ispahanica Boiss., Endemic plants of Iran. The aim of the present study was to study the essen- tial oil composition of N. glocephalata and N. ispahanica in order to know if these compositions have phytotoxic effects on germination, seedling growth injury and pho- tosynthesis of barnyard grass (Echinochloa crus-galli (L.) Beauv), a most important weed in rice (Oryza sativa L.), redroot pigweed (Amaranthus retroflexus L.) and lambs- quarters (Chenopodium album L.), annual plants serious- ly influencing summer crops and canary grass (Phalaris canariensis L.), serious weed of wheat (Triticum aestivum L.) fields in Iran. 2 MATERIALS AND METHODS 2.1 PLANT MATERIAL Above ground parts (leaves and flowers/inflores- cences) of N. glocephalata rech.f. were collected from natural sites of Kashan, Esfahan Province, at an altitude of 1600 m and the above ground parts of N. ispahanica Boiss. were collected from north-west of Tehran, at an altitude of 1800 m during the flowering period in July 2015 in Iran. The air-dried of the plant were powdered and hydrodistillated in a Clevenger-type apparatus for 3 h. The essential oils were dried over anhydrous sodium sulphate and stored at 3 °C in a dark before analysis. 2.2 GC AND GC/MS ANALYSES The oils were analyzed by GC and GC/MS. The GC analyses were performed using a Perkin-Elmer (UK) 8500 gas chromatograph equipped with Flame Ioniza- tion Detector (FID) and a DB-5 fused silica column ( 30 m × 0.25 mm, film thickness 0.25 μm .Oven temperature was held at 60 ºC for 3 min and programmed to 275 °C at a rate of 3 °C/min; injector temperature (split: 1: 25) 250 °C; detector temperature, 280 °C; carrier gas, N2 at 12 psi. V arian 3700 chromatography equipped with a CP- Acta agriculturae Slovenica, 117/4 – 2021 3 Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species Sil5CB column (25 m×0.25 mm i.d., film thickness 0.39 μm) combined with a Varian MAT 44S, ionization ener- gy 70ev. The carrier gas was He and injector temperature was 270 ⁰C. Approximately, 0.1 μl of neat oil was injected under split condition (100:1) and the oven temperature was held at 60 ºC for 5min., programmed at 5 ºC min -1 . to 220 C and then holds at this temperature for 20 min. 2.3 IDENTIFICATION OF COMPONENTS The compounds in the oil were identified by com- parison of their retention indices (RI, HP-5) with those reported in the literature as well as by comparing their mass spectra with the Wiley GC–MS Library, Adams Li- brary, Mass Finder 2.1 Library data, and published mass spectra data (McLafferty and Stauffer, 1989; Adams, 2007). 2.4 GERMINATION AND SEEDLING GROWTH BIOASSAY Seeds of two monocotyledon weeds (barnyard grass (Echinochloa crus-galli (L.) Beauv) and canary grass (Phalaris canariensis L.)) and two dicotyledon weeds (redroot pigweed (Amaranthus retroflexus L.) and lamb- squarters (Chenopodium album L.)) were collected from weeds growing in the summer crops. The germination tests were done in petri dishes (9 cm dia) in a germination chamber at 30 °C (day) and 20 °C (night) for barnyard grass, canary grass and redroot pigweed and at 20 °C and 10 °C for canary grass, respectively. For each essential oil, an oil-in-water emulsion was prepared at 1, 2, 4 and 8 μg ml -1 concentrations. Distillated water used as con- trol. Each Petri dish contained 25 weed seeds placed on two layers of filter paper (Whatman® No.5) wetted with 6 ml oil-in-water emulsion. To prevent evaporation, petri dishes were sealed with parafilm (16). After 14 days, all germinated seeds were counted. Seeds showing root emergence (2 mm) were recorded as germinated. After 14 days no seed germinations were observed. The ger- mination percentages were determined. Root and shoot length were measured by scientific ruler. 2.5 GLASS HOUSE STUDIES In another experiments, the effects of Nepeta species oils on 3-week-old weed plants raised under controlled conditions in experimental glass house were studied. Plants of the four weed species were raised from the seeds in plastic pots 12-cm in diameter. Pots were filled with 730 g garden soil (soil: sand: manure: 3:1:1, w/w) and ten seeds of each weed species were sown per pot. Pots were thinned to 5 equal-sized healthy plants per pot at one- week after sowing. Plants were watered every other day. Studied treatments in this experiment were 1.25, 2.5, 5 and 10 % (v/v) solution of essential oil or distilled water (control) at 3-week-old plants. A hand pressure sprayer filled with flooding nozzle was used for spraying at a rate of 400 l ha−1. The weed plants were examined for visible injury levels in terms of percent chlorotic and necrotic areas at 7-days after spray (DAS). Fresh leaves of all weed species (100 mg fresh leaf samples) were homogenized in 80 % aqueous acetone (5 ml). The homogenate was fil- tered through Whatman filter paper no. 1. The final vol- ume was adjusted to 5 ml by acetone (80 %). Chlorophyll a and chlorophyll b contents were determined spectro- photometrically using Unico 1200-Spectrophotometer at 663 nm for chlorophyll a and 647 nm for chlorophyll b. Calculations were completed using Lichtenthaler’s equa- tion (Lichtenthaler, 1987) and expressed as mg g -1 dry mass. Also dry mass of plant were measured after were oven-drying at 750 ⁰C for 48 h. 2.6 STATISTICAL ANALYSIS All the experiments were repeated and the present- ed data are average of the two experiments. The experi- mental design used for both experiments was completely randomized in a 5 x 2 factorial scheme (5 concentrations × 2 Nepeta essential oils), with four replications. ANO- VA was used to test for significant differences between the means of each Nepeta species and each essential oil concentration. For all statistical analysis, the SAS ver 9.1 program was used. The means were compared by Tukey’s HSD post hoc test (p < 0.05). 3 RESULTS 3.1 CHEMICAL COMPOSITIONS OF THE EXAM- INED ESSENTIAL The chemical compositions of the two Nepeta es- sential oils compounds were listed in Table 1. Total of 35 compounds were identified in N. ispahanica and N. glocephalata essential oils by GC/MS analysis. Eight- een components were identified, representing more than 96.1  % of the total oil components of N. ispa- hanica essential oil detected. The major components of N. ispahanica oil were 1,8-cineole (66.4 %), β-pinene (10.7  %) and α-pinene (3.1  %). Twenty-nine com- pounds reached 98.6 % of the total N. glocephalata es- Acta agriculturae Slovenica, 117/4 – 2021 4 M. DYANAT and F. ASGARI sential oils. The main components of N. glocephalata oil were 1,8-cineole (34.1 %), β-pinene (21.5 %), α-pinene (8.1  %) sabinene (7.8  %), (Z)-β-ocimene (7.6  %) and (E)-β-ocimene (6.9 %). Other components were pre- sent in amounts less than 3 %. No Compound IR % N. ispahanica N. glocephalata 1 α-Thujene 935 - 0.8 2 α-Pinene 940 3.1 8.1 3 Camphene 954 - 0.2 4 Sabinene 981 1.9 6.6 5 β-Pinene 986 10.7 21.5 6 Myrcene 998 - 1.7 7 δ-3-Carene 1011 - 0.5 8 α-Terpinene 1024 - 0.2 9 p-Cymene 1034 - 0.8 10 1,8-Cineole 1041 66.4 34.1 11 (Z)-β-Ocimene 1046 - 7.1 12 (E)-β-Ocimene 1056 - 6.5 13 γ-Terpinene 1066 - 0.3 14 trans-Sabinene-hydrate 1075 0.4 0.8 15 cis-Sabinene hydrate 1088 0.4 - 16 Tepinolene 1095 - 0.3 17 Linalool 1107 - 0.4 18 trans-Pinocarveole 1129 1.1 - 19 cis-p-menth-2-en-1-ol 1131 - 0.2 20 Verbenol 1134 0.6 - 21 Allo-ocimene 1137 - 0.2 22 trans-Sabinole 1149 - 0.5 23 Pinovarvone 1172 0.9 0.2 24 Myrtenal 1175 1.0 - 25 δ-Terpineole 1177 1.1 0.5 26 Myrtenol 1184 1.0 - 27 Terpinen-4-ol 1187 1.0 1.8 28 Cryptone 1196 - 0.2 29 α-Terpineole 1200 2.0 2.9 30 Myrthanol 1207 - 0.5 31 4aα,7α,7aα-Nepetalactone 1422 0.1 - 32 β-caryophyllene 1434 0.2 0.1 33 Germacrene D 1496 - 1.2 34 Bicyclogermacrene 1512 - 0.3 35 4aβ,7α,7aα-Nepetalactone 1575 2.1 - 36 β-caryophyllene oxide 1585 2.1 - 37 Spathulenole 1595 - 0.1 Total - 96.1 98.6 Table 1: Percentage composition of the essential oils of Nepeta species Retention Indices (The retention indices were determined on CPSil5CB column) Acta agriculturae Slovenica, 117/4 – 2021 5 Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species and N. glocephalata essential oils, respectively. The re- gression lines between seed germination and essential oil concentrations confirm the different susceptibility of weed species (Fig. 1). There were significant differences among control and all concentrations, and between two Nepeta species essential oils for each weed species. The regression analysis between oil concentrations and root length showed that increasing concentration of essential oil increased the inhibitory effects on weed root length till a lethal dose (Fig. 2). When the root length of redroot pigweed and lambsqaurters was completely inhibited by essential oils of N. ispahanica at 4 μg ml -1 , the root length was reduced respectively to 70 % for barnyard grass and to 73 % for canary grass, which explain that monocots weeds were more resistant than dicots. No significant differences among control and all concentrations, and between two Nepeta essential oils observed for shoot length of barnyard grass and canary grass. The shoot re- duction of barnyard grass compared with control was the 29 % and 28 % with N. glocephalata and N. ispahanica essential oils at the highest concentration, respectively. Canary grass showed a reduction of the 28 % with N. glo- cephalata and 25 % with N. ispahanica essential oils at the same concentration. Shoot length of redroot pigweed and lambsqaurters reached to zero at 4 and 8 μg ml -1 of N. ispahanica at 8 μg ml -1 of N. glocephalata. 3.2 GERMINATION AND SEEEDLING GROWTH BIOASSAY The effect of Nepeta species essential oils against seed germination, root length and shoot length of barnyard grass, canary grass, redroot pigweed and lambsquarters is shown in Figs. 1–3. Significant differences were found among control and all concentrations of Nepeta species essential oil tested. The essential oils of two Nepeta species reduced the germination of all studied weeds. Further- more the difference between the control and the lowest concentration was significant for all weed species. At 1 μg ml -1 of N. ispahanica germination reduction compare to control was 25 %, 11 % and 44 % and 49 % for barnyard grass, canary grass, redroot pigweed and lambsqaurters, respectively. Also germination reduction of barnyard grass, canary grass, redroot pigweed and lambsqaurters was 21.5 %, 8 % and 29 % and 44.75 % at 1 μg ml -1 of N. glocephalata, respectively (Fig. 1). Redroot pigweed and lambsquarters were most sensitive to N. ispahanica es- sential oil, their germination was completely inhibited by it at concentration 4 μg ml -1 . At highest concentration 8 μg ml -1 germination percentages were 6.5 % and 10.20 % for canary grass by N. ispahanica and N. glocepha- lata, respectively. Barnyard grass seeds germinated 3 % and 11.75 % at highest concentration of N. ispahanica Figure 1: Effect of N. ispahanica and N. glocephalata essential oils on (a) barnyard grass, canary grass (b) redroot pigweed (c) and lambsqaurters (d) germination measured after 2 weeks. Vertical bars along each data point represent the standard error Acta agriculturae Slovenica, 117/4 – 2021 6 M. DYANAT and F. ASGARI Figure 2: Effect of N. ispahanica and N. glocephalata essential oils on (a) barnyard grass, canary grass (b) redroot pigweed (c) and lambsqaurters (d) root length measured after 2weeks. Vertical bars along each data point represent the standard error Figure 3: Effect of N. ispahanica and N. glocephalata essential oils on (a) barnyard grass, canary grass (b) redroot pigweed (c) and lambsqaurters (d) shoot length measured after 2 weeks. Vertical bars along each data point represent the standard error Acta agriculturae Slovenica, 117/4 – 2021 7 Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species 3.3 GLASS HOUSE STUDIES For more investigation of herbicidal activity of Nepeta essential oils, an experiment was done on 3-week- old weeds. The mature plants of test weeds were dam- aged upon spray of Nepeta essential oils and showed vis- ible injury ranging from chlorosis to necrosis of plants. In general, the visible injury symptoms observed 7 days after spraying increased with increasing concentrations of both Nepeta essential oils (Table 2). At the lowest con- centration 1.25 % of both Nepeta essential oils, all the test weeds showed sign of injury. At the highest concen- tration (10 v/v) visible injury by N. ispahanica essential oil were 44 % 45.5 % 59.25 % and 51.62 % for barnyard grass, canary grass, redroot pigweed and lambsquarters, respectively. While visible injury of barnyard grass, ca- nary grass, redroot pigweed and lambsquarters caused by N. glocephalata essential oil were 39 % 36.62 % 44 % and 41.5 %, respectively at 7 days after spraying that did not have significant difference each other’s (Table 2). Increasing Nepeta essential oils concentration de- creased dry mass of all weed species. The inhibition rates of barnyard grass dry mass ranged from 24.89 % to 75.21 %, and from 16.75 to 61.17 % in N. ispahanica and N. glocephalata, respectively. In canary grass the in- hibition rates of dry mass, ranged from 22.49 to 63.26 %, and from 13.95 to 56.56 % at concentrations for N. ispa- hanica and N. glocephalata, respectively. Essential oil of N. ispahanica caused dry mass inhibition of redroot pigweed from 37.5 % to 90 % while N. glocephalata re- duced it from 23.75 % to 81.5 %. The inhibition rates of lambsquarters dry mass ranged from 19.75 % to 86 %, and from 14.75 to 76 % in N. ispahanica and N. glocepha- lata, respectively. There was a significant difference in the inhibition of dry mass among concentrations and the the highest inhibition of dry mass caused by N. ispahanica at concentration of 10 v/v that was significantly different from other treatments. Increasing essential oil concentration decreased chlorophyll a and chlorophyll b at all studied weeds. For example contents of chlorophyll a in barnyard grass were reduced 12.77 %, 25.40 %, 44.38 % and 49.62 % by N. ispahanica at concentrations of 1.25 %, 2.5 %, 5 % and 10 % v/v, respectively. N. glocephalata concentrations of 1.25 %, 2.5 %, 5 % and 10 % inhibited contents chloro- phyll a in barnyard grass, 11.65 %, 15.56 %, 29.1 % and 43.56 %, respectively that the difference between the con- centrations of 1.25 v/v and 2.5 v/v was not significant. The highest inhibition of chlorophyll a in canary grass was caused by N. ispahanica at concentration of 10 v/v which was not significantly different from N. glocepha- lata. In redroot pigweed, N. ispahanica at the concentra- tion of 1.25 v/v decreased chlorophyll a by 22.05 % and decreased further by increasing concentration. In lambs- quarters, no significant difference was observed between N. ispahanica and N. glocephalata at a concentration of 2.5 v/v (Table 4). N. ispahanica essential oil inhibited chlorophyll b of barnyard grass by 11.30 %, 21.59 %, 29.13 % and 36.79 % at concentrations of 1.25 %, 2.5 %, 5 % and 10 %, respectively. At concentrations of 1.25 %, 2.5 %, 5 % and 10 % N. glocephalata essential oil reduced chlorophyll b by 7.86 %, 12.09 %, 22.21 % and 33.35 %, respectively in barnyard grass. The highest of inhibition of chloro- phyll b in canary grass and redroot pigweed was caused by N. ispahanica at a concentration of 10 v/v which was not significantly different from N. glocephalata in redroot pigweed. In lambsqarters, there was no significant differ- ence between N. ispahanica and N. glocephalata at a con- centration of 1.25 v/v, but at the highest concentration, a significant difference was observed between these two species (Table 5). In this studies chlorophyll a decreased more than chlorophyll b in all species weeds (Tables 4 and 5). 4 DISCUSSION Many researchers reported the presence of nepeta- lactones in several Nepeta species in relatively high con- centrations (Sefidkon and Shaabani, 2004; Rustaiyan et al., 2000, Rustaiyan and Nadji, 1999, Sajjadi and Khatam- saz, 2000) but no nepetalactones were detected in N. glo- cephalata essential oil. 1, 8-cineole, which was the first major component of the studied oils, has been reported in the oil of some Nepeta species from Iran (Rustaiyan et al., 2000; Rustaiyan and Nadji, 1999; Sajjadi and Khatam- saz, 2000). 1, 8-Cineole was also reported previously to be the main compound of N. ispahanica oil (Sefidkon et al., 2005). β-pinene has also been found in the oils of some Nepeta species (Thappa et al., 2001; Baser et al., 2000; Rustaiyan et al., 2000; Rustaiyan and Nadji, 1999; Sefid- kon et al., 2002) but the concentrations of it found in this study was the most in comparison with previous studies. β-pinene and α-pinene are typical in most Nepeta species (Gkinis et al., 2003; Thappa et al., 2001, Baser et al., 2000; Rustaiyan and Nadji, 1999; Sefidkon et al., 2002). The herbicidal activity of both Nepeta essential oils were due to the high percentage of 1,8-Cineole. This is in agreement with Zunino and Zygadlo (2004) who re- ported that monoterpenes such as 1,8- cineole, thymol, geraniol and camphor have been reported to inhibit root growth in maize (Zea mays L.). In a study with 27 monoterpenes, against seed germination and primary root growth of radish (Raphanus sativus L.) and garden cress (Lepidium sativum L.), only 1, 8-cineole, inhibited Acta agriculturae Slovenica, 117/4 – 2021 8 M. DYANAT and F. ASGARI Concentration (v/v) Barnyard grass Canary grass Redroot pigweed Lambsquarters N. ispahanica N. glocephalata N. ispahanica N. glocephalata N. ispahanica N. glocephalata N. ispahanica N. glocephalata 1.25 19 ± 1.63 d 13.75 ± 1.89 e 17.87 ± 2.01 d 10.97 ± 0.41 e 21.5 ± 3.76 e 11.125 ± 1.10 f 20.25 ± 2.28 d 12.43 ± 0.47 e 2.5 32 ± 2.16 c 19.5 ± 0.57 d 28.01 ± 1.31 c 20.01 ± 1.07 d 31.5 ± 1.08 cd 25.875 ± 2.78 de 31.75 ± 1.48 c 22.68 ± 1.21 d 5 40.75 ± 0.9 ab 29.25 ± 0.95 c 37.28 ± 0.4 b 29.01 ± 0.81 c 43.75 ± 1.04 b 36.5 ± 1.22 c 42.25 ± 0.45 b 32.87 ± 0.93 c 10 44 ± 3.36 a 39 ± 1.82 b 45.55 ± 2.65 a 36.6 ± 2.47 b 59.25 ± 6.7 a 44 ± 2.61 b 51.62 ± 3.01 a 41.5 ± 0.54 b Table 2: Effects of Nepeta essential oils on visible injury of barnyard grass, canary grass, redroot pigweed and lambsquarters at 7 days after spraying Values are means ±standard error of four replicates. Within each species, different letters indicate that means are different at the 95 % level of probability (Tukey’s HSD post hoc test)s Concentration (v/v) Barnyard grass Canary grass Redroot pigweed Lambsquarters N.ispahanica N.glocephalata N. ispahanica N.glocephalata N.ispahanica N.glocephalata N.ispahanica N.glocephalata 1.25 24.89 ± 1.67 g 16.74 ± 0.56 h 22.49 ± 4.53 f 13.95 ± 2.18 g 37.5 ± 1.73 f 23.75 ± 2.21 g 19.75 ± 2.5 f 14.75 ± 2.21 f 2.5 39.55 ± 1.84 e 28.58 ± 0.96 f 32.55 ± 2.23 d 22.15 ± 0.80 e 53 ± 2.16 e 39.25 ± 0.95 f 41 ± 2.58 d 29.5 ± 2.64 e 5 69.13 ± 1.70 c 51.74 ± 1.84 d 52.60 ± 7.06 b 43.95 ± 3.30 c 77.5 ± 2.08 c 63 ± 2.44 d 61.5 ± 3 c 59 ± 4.6 c 10 75.21 ± 0.61 a 67.17 ± 0.24 b 63.26 ± 4.52 a 56.56 ± 2.8 ab 90 ±01 a 81.5 ± 1.29 b 86 ± 1.41 a 76 ± 1.82 b Table 3: Effects of Nepeta essential oils on dry weights inhibition % of barnyard grass, canary grass, redroot pigweed and lambsquarters at 7 days after spraying Values are means ±standard error of four replicates. Within each species, different letters indicate that means are different at the 95 % level of probability (Tukey’s HSD post hoc test) Concentration (v/v) Barnyard grass Canary grass Redroot pigweed Lambsquarters N. ispahanica N.glocephalata N. ispahanica N. glocephalata N. ispahanica N. glocephalata N. ispahanica N.glocephalata 1.25 12.77 ± 6.79c 11.65 ± 0.55c 13.80 ± 3g 8.71 ± 1.36g 22.05 ± 1.02d 14.47 ± 1.45f 20.27 ± 5.85cd 11.65 ± 0.51e 2.5 25.40 ± 1.31b 15.56 ± 3.57c 31.59 ± 5.92ef 19.09 ± 2.43e 37.80 ± 1.97d 26.47 ± 5.13e 32.90 ± 5.74 c 27.56 ± 0.69 c 5 44.38 ± 5.0a 29.1 ± 5.74b 39.13 ± 4.41bc 32.21 ± 1.33cd 52.47 ± 2.17b 44.69 ± 3.78c 54.38 ± 5.72 a 41.6 ± 4.53 b 10 49.62 ± 2.5a 43.56 ± 2.43a 46.79 ± 3.57a 41.60 ± 1.77ab 59.32 ± 1.0a 53.07 ± 1.85b 59.62 ± 2.54 a 54.81 ± 0.56 a Table 4: Effects of Nepeta essential oils on Chlorophyll a inhibition% of barnyard grass, canary grass, redroot pigweed and lambsquarters at 7 days after sprayingg Values are means ±standard error of four replicates. Within each species, different letters indicate that means are different at the 95 % level of probability (Tukey’s HSD post hoc test) Concentration (v/v) Barnyard grass Canary grass Redroot pigweed Lambsquarters N. ispahanica N.glocephalata N. ispahanica N. locephalata N. ispahanica N. glocephalata N.ispahanica N.glocephalata 1.25 11.30 ± 2.20c 7.86 ± 2.12cd 17 ± 2.37d 8.937 ± 1.46e 19.54 ± 3.42ef 15.11 ± 4.87f 15.43 ± 1.25d 11.04 ± 1.20e 2.5 21.59 ± 5.93b 12.09 ± 5.99c 28.75 ± 1.49c 20.68 ± 1.91d 29.63 ± 2.71cd 23.52 ± 2.52de 25.80 ± 1.38c 18.91 ± 3.19d 5 29.13 ± 4.41ab 22.21 ± 1.34b 39.25 ± 0.46ab 25.87 ± 2.13c 38.27 ± 2.99ab 33.18 ± 1.11bc 32.90 ± 1.73b 26.21 ± 0.48c 10 36.79 ± 3.58a 33.35 ± 2.88a 42.12 ± 2.21a 37 ± 3.36b 45.11 ± 4.2a 40 ± 2.37ab 40.50 ± 2.60a 37.34 ± 2.35a Table 5: Effects of Nepeta essential oils on Chlorophyll b inhibition % of barnyard grass, canary grass, redroot pigweed and lambsquarters at 7 days after spraying Values are means ±standard error of four replicates. Within each species, different letters indicate that means are different at the 95 % level of probability (Tukey’s HSD post hoc test) Acta agriculturae Slovenica, 117/4 – 2021 9 Phytotoxic effects of essential oils from Nepeta glocephalata Rech.f. and N. ispahanica Boiss. on selected weed species their root elongation at the lowest concentrations (10 −5 M, 10 −6 M) applied (De Martino et al., 2010). Romagni et al. (2000) have shown that 1, 8-cineole, and its natural analogue 1, 4-cineole, both suppress the growth of sev- eral weeds. 1, 8-cineole inhibits the germination, speed of germination, seedling growth, chlorophyll content and respiratory activity of Ageratum conyzoides L. 1753 not Hieron. 1895 nor Sieber ex Steud. 1840. Singh et al. (2002) and De Feo et al. (2002) have investigated the herbicidal activity of 10 volatiles compounds from Ruta graveolens L. essential oils and showed that 1,8-cineole significantly inhibits the germination and radical elonga- tion of radish. The effects of the allelochemicals in studied traits directly dependent on the concentration and Nepeta spe- cies. The germination and root length decreased with increasing concentrations of essential oils. These results are in agreement with that of Ibáñez and Blázquez (2017) who reported that there are significant effects in shoot and/or shoot + root length of weeds depending on the weed and dose. N. ispahanica oil exerted the more in- hibitory effect than N. glocephalata for all weed species. It can be due to higher concentration of 1,8-cineole in N. ispahanica. While the inhibition is not similar between the Nepeta species oils, weed species differed in their response to the toxic effect of each oil. It was reported that the degree of allelopathic interference can even vary within species (Li et al. 2009). My observations in glass house indicated that both Nepeta oils can act as contact herbicides. These observa- tions are in agreement with previous studies showing that volatile oils and even their monoterpenes exhibit herbicidal activity (Tworkoski, 2002; Singh et al., 2005, 2006). Batish et al. (2004, 2007) concluded that the 5 % essential oil from E. citriodora caused 50–80 % visible in- jury in A. viridis, P. minor and E. crus-galli. In addition Poonpaiboonpipat et al. (2013) reported that the essen- tial oil lemon grass (Cymbopogon citratus (DC ex Nees) Stopf) applied on barnyardgrass in greenhouse caused leaf wilting. The reduction in seedling dry mass, chloro- phyll a and chlorophyll b content observed in my study is in agreement with previous reports indicating that the monoterpenes had a potential to reduce chlorophyll con- tent (Chowhan et al. 2011; Kaur et al. 2010; Gouda et al., 2016). It may be due to inhibition of biosynthesis of chlo- rophyll and/or degradation of chlorophyll. 5 CONCLUSION From the present study, it could be concluded that Nepeta essential oils strongly inhibited the germination and root length of all weeds. Dicot weeds (lambsquarters and redroot pigweed) were significantly more sensitive than monocot weeds (barnyard grass and canary grass). Indeed, at the dose of 4 μg ml -1 , germination of lamb- squarters and redroot pigweed was totally inhibited by N. ispahanica essential oil. Further studies are required to investigate the herbicidal potential of Nepeta essential oils under field conditions and determine the effects on crop species and other weed species. This study is con- sidered the first study regarding of herbicidal effects of N. glocephalata and N. ispahanica but the selectivity of these compounds should be considered. 6 REFERENCES Abrahim, D., Braguini, W.L., Kelmer-Bracht, A.M. and Ishii- Iwamoto, E.L. (2000). 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