Inhibitory activities of essential oils from Syzygium aromaticum on emergence of Echinochloa crus-galli

Echinochloa crus-galli is a serious weed species in rice paddies. To obtain a new potential bioherbicide, we evaluated the inhibitory activities of 13 essential oils and their active substances against E. crus-galli . Essential oil from Syzygium aromaticum (L.) Merr. & L. M. Perry (SAEO) exhibited the highest herbicidal activity (EC 50 = 3.87 mg mL -1 ) among the 13 essential oils evaluated. The SAEO was isolated at six different temperatures by vacuum fractional distillation, including 164 ℃, 165 ℃ (SAEO − 165), 169 ℃, 170 ℃ 175 ℃ and 180 ℃. The SAEO − 165 had the highest inhibitory rate against E. crus-galli . Gas chromatography-mass spectrometry and high phase liquid chromatography identified Eugenol (EC 50 = 4.07 mg mL -1 ), α-caryophyllene (EC 50 = 17.34 mg mL -1 ) and β-caryophyllene (EC 50 = 96.66 mg mL -1 ) as the three compounds in SAEO. Results from a safety bioassay showed that the tolerance of rice seedling (~ 20% inhibition) was higher than that of E. crus-galli (~ 70% inhibition) under SAEO stress. Additionally, defense enzymes in E. crus-galli and rice seedling showed decreased activities, but only CAT levels were affected under SAEO treatment. Our results indicate that SAEO has a potential for development into a new selective bio-herbicide. They also provide an example of a sustainable management strategy for E. crus-galli in rice paddies.