Interference and Mechanism of Dill Seed Essential Oil and Contribution of Carvone and Limonene in Preventing Sclerotinia Rot of Rapeseed

Abstract

This study aimed to evaluate the inhibitory effects of dill (Anethum graveolens L.) seed essential oil against Sclerotinia sclerotiorum and its mechanism of action. The antifungal activities of the two main constituents, namely carvone and limonene, were also measured. Mycelial growth and sclerotial germination were thoroughly inhibited by dill seed essential oil at the 1.00 μL/mL under contact condition and 0.125μL/mL air under vapor condition. Carvone also contributed more than limonene in inhibiting the growth of S. sclerotiorum. Carvone and limonene synergistically inhibited the growth of the fungus. In vivo experiments, the essential oil remarkably suppressed S. sclerotiorum, and considerable morphological alterations were observed in the hyphae and sclerotia. Inhibition of ergosterol synthesis, malate dehydrogenase, succinate dehydrogenase activities, and external medium acidification were investigated to elucidate the antifungal mechanism of the essential oil. The seed essential oil of A. graveolens can be extensively used in agriculture for preventing the oilseed crops fungal disease.

Fig 1. Effects of the samples at contact phase on colony diameter (cm) growth of S. sclerotiorum.

(A) The oil, (B) mixture of carvone and limonene, (C) limonene, (D) carvone. Values are means (n = 3) ± standard deviations.

Fig 2. Effects of the samples at vapor phase on colony diameter (cm) growth of S. sclerotiorum.

(A) The oil, (B) mixture of carvone and limonene, (C) limonene, (D) carvone. Values are means (n = 3) ± standard deviations.

Fig 3. Effects of the samples at contact phase on sclerotial germination of S. sclerotiorum.

(A) The oil, (B) mixture of carvone and limonene, (C) limonene, (D) carvone. Significant differences (p < 0.05) between means are indicated by the letters above histogram bars. Values are means (n = 3) ± standard deviations.

Fig 4. Effects of the samples at vapor phase on sclerotial germination of S. sclerotiorum.

(A) The oil, (B) mixture of carvone and limonene, (C) limonene, (D) carvone. Significant differences (p <0.05) between means are indicated by the letters above histogram bars. Values are means (n = 3) ± standard deviations.

Fig 5. Efficacy of the oil against S. sclerotiorum in potted plants.

(A) Control; (B)–(E) Treated with the oil (1.25, 2.50, 5.00, and 10.00 μL/mL); (F) Treated with carbendazol (1.00 mg/mL).

Fig 6. Scanning electron microscopy illustrated effects of the oil on microstructure surface of S. sclerotiorum.

Control (A, B, E, and F). Effects of essential oil on hyphal morphology (C and D). Effects of essential oil on surfaces of sclerotia and rind globular cells inside the sclerotium (G and H).

Fig 7. Some possible mechanisms of the oil against S. sclerotiorum.

(A) UV spectrophotometric sterol profiles of S. sclerotiorum treated with the oil in comparison with those of the untreated control. (B) Effect of the oil on activity of malate dehydrogenase. (C) Effect of the oil on activity of succinate dehydrogenase. (D) Inhibitory effect of the oil on glucose-dependent acidification of medium in S. sclerotiorum. Significant differences (p < 0.05) between means are indicated by the letters above histogram bars. Values are means (n = 3) ± standard deviations.