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. 2023 Mar 26;28(7):2958.
doi: 10.3390/molecules28072958.

Evaluation of Inhibitory Effect and Mechanism of Euphorbia Factor L3 against Phytophthora capsici

Bi Wang  1 , Guodong Zhang  1 , Jingjing Yang  1 , Linwei Li  1 , Pirui Li  1 , Shu Xu  1 , Xu Feng  1 , Yu Chen  1
Affiliations

Evaluation of Inhibitory Effect and Mechanism of Euphorbia Factor L3 against Phytophthora capsici

Bi Wang et al. Molecules. .

Abstract

Phytophthora capsici is a highly destructive phytopathogenic oomycete with a broad host range and is responsible for tremendous losses. Euphorbia factor L3 (EFL3) is a natural plant-derived compound that has been widely studied in medicine and cosmetic applications. In this study, the sensitivity of 105 P. capsici isolates to EFL3 was determined, and the biological activity and physiological effects of EFL3 against P. capsici were investigated. The median effective concentration (EC50) values for EFL3 inhibition mycelial growth and spore germination ranged from 0.66 to 8.94 μg/mL (mean, 2.96 ± 0.91 μg/mL) and 1.63 to 13.16 μg/mL (mean, 5.30 ± 1.64 μg/mL), respectively. EFL3 treatment resulted in cell wall and cell membrane damage of P. capsici, which was revealed by morphological and ultrastructural observations, propidium iodide (PI) and calcofluor white (CFW) staining, and measurements of relative conductivity as well as malondialdehyde (MDA) and glycerol contents. In addition, the contents of phospholipid and cellulose, which are the major components of cell membrane and cell wall, were significantly reduced following EFL3 treatment. Furthermore, EFL3 provided protective as well as curative efficacies against P. capsici on detached tomato leaves and pepper seedlings in vivo. These data show that EFL3 exhibits strong inhibitory activity against P. capsici, thereby suggesting that it could be an effective alternative for controlling P. capsici-induced diseases.

Keywords: Euphorbia factor L3; Phytophthora capsici; action mechanism; baseline sensitivity; botanical fungicide.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Sensitivity distribution of 105 isolates of Phytophthora capsici to Euphorbia factor L3 (EFL3). (A) Chemical structure of EFL3. (B) Sensitivity distribution of EFL3 median effective concentration (EC50) values against P. capsici from mycelial growth assay. (C) Sensitivity distribution of EFL3 EC50 values against P. capsici from spore germination assay.
Figure 2
Figure 2
Optical microscopy observations of the mycelial morphology of P. capsici. Mycelia of P. capsici isolates LT263 and TA54 treated with EFL3 at 0, 5, or 10 μg/mL. The scale bar represents 50 μm.
Figure 3
Figure 3
Transmission electron microscopy observations of the mycelial ultrastructure of P. capsici. Mycelia of P. capsici isolates LT263 and TA54 treated with EFL3 at 0, 5, or 10 μg/mL. The scale bar represents 1 μm.
Figure 4
Figure 4
Effect of EFL3 on the cell membrane permeability of P. capsici. (A,D) Effect of EFL3 on the relative electrical conductivity of P. capsici isolates LT263 and TA54. (B,E) Effect of EFL3 on the malondialdehyde (MDA) content of P. capsici isolates LT263 and TA54. (C,F) Effect of EFL3 on the glycerol content of P. capsici isolates LT263 and TA54. Data are shown as the mean ± standard error (SE), and small letters indicate significant differences across treatments (p < 0.05).
Figure 5
Figure 5
Effect of EFL3 on the cell membrane integrity of P. capsici. The mycelia of P. capsici isolates LT263 and TA54 were stained with propidium iodide (PI) and observed under a fluorescence microscope. The scale bar represents 50 μm.
Figure 6
Figure 6
Effect of EFL3 on the cell wall integrity of P. capsici. The mycelia of P. capsici isolates LT263 and TA54 were stained with calcofluor white (CFW) and observed under a fluorescence microscope. The scale bar represents 50 μm.
Figure 7
Figure 7
Effect of EFL3 on phospholipid and cellulose contents of P. capsici. (A,C) Effect of EFL3 on phospholipid content of P. capsici isolates LT263 and TA54. (B,D) Effect of EFL3 on cellulose content of P. capsici isolates LT263 and TA54. Data are shown as the mean ± standard error (SE), and small letters indicate significant differences across treatments (p < 0.05).
Figure 8
Figure 8
Control activity of EFL3 against P. capsici on detached tomato leaves. (A) Disease symptoms on tomato leaves were photographed after inoculation with a fresh mycelial plug for 4 days. (B) Protective and curative activities of EFL3 against P. capsici isolate LT263. (C) Protective and curative activities of EFL3 against P. capsici isolate TA54. Data are shown as the mean ± standard error (SE), and small letters indicate significant differences across treatments (p < 0.05).
Figure 9
Figure 9
Control activity of EFL3 against P. capsici on pepper seedlings. (A) Disease symptoms on pepper seedlings were photographed after being injected with zoospore suspensions for 10 days. (B) Protective and curative activities of EFL3 against P. capsici isolate LT263. (C) Protective and curative activities of EFL3 against P. capsici isolate TA54. Data are shown as the mean ± standard error (SE), and small letters indicate significant differences across treatments (p < 0.05).
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