Phytochemical profiling and allelopathic effect of garlic essential oil on barnyard grass (Echinochloa crusgalli L.)

Abstract

In agriculture, barnyard grass (Echinochloa crusgalli L.) is one of the most harmful weeds in rice fields now. In order to identify active ingredients which had inhibiting effect on barnyard grass (Echinochloa crusgalli L.), we evaluated several possible natural plant essential oils. Essential oils from twelve plant species showed inhibitory activity against barnyard grass seedlings and root length. The garlic essential oil (GEO) had the most significant allelopathic effect (EC50 = 0.0126 g mL-1). Additionally, the enzyme activities of catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) increased during the first 8 hours of treatment at a concentration of 0.1 g mL-1 and then declined. The activities of CAT, SOD and POD increased by 121%, 137% and 110% (0-8h, compared to control), and decreased (8-72h, compared to the maximum value) by 100%, 185% and 183%, respectively. The total chlorophyll content of barnyard grass seedlings decreased by 51% (0-72h) continuously with the same dosage treatment. Twenty constituents of GEO were identified by gas chromatography-mass spectrometry, and the herbicidal activity of two main components (diallyl sulfide and diallyl disulfide) was evaluated. Results showed that both components had herbicidal activity against barnyard grass. GEO had a strong inhibitory effect (~88.34% inhibition) on barnyard grass growth, but safety studies on rice showed it did not have much inhibitory effect on rice seed germination. Allelopathy of GEO provide ideas for the development of new plant-derived herbicides.

Fig 1. Inhibitory effect of plant essential oils on barnyard grass seedlings.

(A) The control effect of twelve essential oils with different concentrations (0, 0.01, 0.03, 0.05, 0.08, 0.1 g mL^-1) on barnyard grass seedlings. a: Garlic essential oil; b: Tangerine peel essential oil; c: Spearmint essential oil; d: Yellow mugwort essential oil; e: Litsea cubeba essential oil; f: Pine needle essential oil; g: Cedar essential oil; h: Lemon grass essential oil; i: Rosemary essential oil; j: Juniper essential oil; k: Geranium essential oil; l: Star anise essential oil. (B) the average growth inhibition rate of 12 plant essential oils on barnyard grass seedlings after 7 days at a concentration of 0.1 g mL^-1. Error bars represent the standard error of the mean. Different small letters above the error bars indicate significant differences at 0.05 (ANOVA). The same letters indicate that there were no significant differences among treatments. (GEO: garlic essential oil, TEO: tangerine peel essential oil, SEO: spearmint essential oil, YEO: yellow wormwood leaf essential oil, LCEO: litsea cubeba essential oil, PEO: pine needle essential oil, CEO: cedar essential oil, LGEO: lemon grass essential oil, REO: rosemary essential oil, JEO: juniper essential oil, GEEO: geranium essential oil, SAEO: star anise essential oil). (C) the root length inhibition rate of 12 plant essential oils on barnyard grass seed after 7 days at a concentration of 0.01 g L^-1. Error bars represent the standard error of the mean. Different small letters above the error bars indicate significant differences at 0.05 (ANOVA). The same letters indicate that there were no significant differences among treatments. (D) the inhibiting effect of GEO on barnyard grass seedlings, the concentrations are 0, 0.001, 0.005, 0.01, 0.03, 0.1 g mL^-1.

Fig 2. Inhibition effect of GEO on rice.

a: seed germination rate; b: inhibition rate of fresh weight at the 1-leaf stage; c: inhibition rate of fresh weight at the 2-leaf stage.

Fig 3. GC-MS chromatogram of the ion peak area of GEO.

Fig 4. Inhibitory effects of two main compounds with different concentrations on barnyard grass.

(A) Diallyl sulfide treatment (0, 0.01, 0.05, 0.1 and 0.3 g mL^-1); (B) Diallyl disulfide treatment (0, 0.001, 0.005, 0.01, 0.1 and 0.3 g mL^-1).

Fig 5. Changes in activities of antioxidant defense enzymes (A-CAT, B-POD, C-SOD) and chlorophyll(D) in barnyard grass seedlings treated with 0.1g mL^-1 GEO.

C_a: chlorophyll a; C_b: chlorophyll b; CT: total chlorophyll.