Efficacy of Dimethyl Trisulfide on the Suppression of Ring Rot Disease Caused by Botryosphaeria dothidea and Induction of Defense-Related Genes on Apple Fruits

Abstract

Apple ring rot caused by Botryosphaeria dothidea is prevalent in main apple-producing areas in China, bringing substantial economic losses to the growers. In the present study, we demonstrated the inhibitory effect of dimethyl trisulfide (DT), one of the main activity components identified in Chinese leek (Allium tuberosum) volatile, on the apple ring rot on postharvest fruits. In in vitro experiment, 250 μL/L DT completely suppressed the mycelia growth of B. dothidea. In in vivo experiment, 15.63 μL/L DT showed 97% inhibition against the apple ring rot on postharvest fruit. In addition, the soluble sugar content, vitamin C content, and the soluble sugar/titratable acidity ratio of the DT-treated fruit were significantly higher than those of the control fruit. On this basis, we further explored the preliminary underlying mechanism. Microscopic observation revealed that DT seriously disrupted the normal morphology of B. dothidea. qRT-PCR determination showed the defense-related genes in DT-treated fruit were higher than those in the control fruit by 4.13-296.50 times, which showed that DT inhibited apple ring rot on postharvest fruit by suppressing the growth of B. dothidea, and inducing the defense-related genes in apple fruit. The findings of this study provided an efficient, safe, and environment-friendly alternative to control the apple ring rot on apple fruit.

Keywords: Allium tuberosum; Botryosphaeria dothidea; biocontrol; defensive genes; fruit quality.

FIGURE 1

The mycelial growth of Botryosphaeria dothidea on PDA medium containing various concentrations of dimethyl trisulfide for 5 days. (A) 500 μL/L, (B) 250 μL/L, (C): 125 μL/L, (D) 62.5 μL/L, (E) control.

FIGURE 2

The dimethyl trisulfide inhibition on the mycelia growth of Botryosphaeria dothidea. (A) The colony diameters of Botryosphaeria dothidea treated by the various concentration of dimethyl trisulfide. (B) The inhibition of various concentrations of dimethyl trisulfide against mycelia growth of Botryosphaeria dothidea. (C) The area-under-curve (AUC) of fungal colony diameters treated by various concentrations of dimethyl trisulfide. Different lowercase letters indicate a significant difference between treatments (P < 0.05).

FIGURE 3

The mycelial morphology of Botryosphaeria dothidea. (A) The mycelia of the untreated control. (B–D) The mycelia treated with 500 μL/L dimethyl trisulfide for 24 h.

FIGURE 4

The apple fruit was first inoculated with Botryosphaeria dothidea disk, subsequently treated with dimethyl trisulfide, then cultured at 28°C in the dark for 5 days. Apple fruits with different treatments exhibited varying degrees of disease symptoms. (A) 62.5 μL/L, (B) 31.25 μL/L, (C) 15.63 μL/L, (D) control.

FIGURE 5

The inhibitory effect of dimethyl trisulfide on the apple ring rot on apple fruit. (A) The disease spot diameter on apple fruits treated by various concentrations of dimethyl trisulfide. (B) The inhibition of various concentrations of dimethyl trisulfide against the apple ring rot on fruit. (C) The area-under-curve (AUC) of disease spot diameter on fruit treated by the various concentration of dimethyl trisulfide. Different lowercase letters indicate a significant difference between different treatments (P < 0.05).

FIGURE 6

The apple fruit was first dipped in a Botryosphaeria dothidea culture for 15 min, subsequently exposed to various concentrations of dimethyl trisulfide, then cultured at 28°C in the dark for 4 weeks. Apple fruits with different treatments exhibited varying degrees of disease symptoms. (A) 15.63 μL/L, (B) 31.25 μL/L, (C) 62.5 μL/L, (D) control.

FIGURE 7

The dynamic changes of internal quality indexes including total soluble solid (A), soluble sugar (B), titratable acidity (C), TSS/TA (D), SS/TA (E), and vitamin C (F) in the different treatment fruit.

FIGURE 8

The area-under-curve (AUC) of internal quality indexes including total soluble solid (A), soluble sugar (B), titratable acidity (C), TSS/TA (D), SS/TA (E), and vitamin C (F) the different treatment fruit. *P < 0.05, ^***P < 0.001, ns P > 0.05.

FIGURE 9

The expression analysis of various defense-related genes including phenylalanine ammonia-lyase (A), glucanase_1 (B), glucanase_2 (C), glucanase_3 (D), peroxidase_1 (E), peroxidase_2 (F), polyphenol oxidase (G), catalase (H), endochitinase (I) in the DT-treated fruit. *P < 0.05, ^**P < 0.01, ^***P < 0.001, ns P > 0.05.