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. 2022 Dec 8:13:1069517.
doi: 10.3389/fmicb.2022.1069517. eCollection 2022.

Endophytic bacterium Pseudomonas protegens suppresses mycelial growth of Botryosphaeria dothidea and decreases its pathogenicity to postharvest fruits

Yonghong Huang  1   2   3   4 , Junping Liu  1   2   3   4 , Jinghui Li  1   2   3   4 , Xiaoying Shan  1   2   3   4 , Yanxin Duan  1   2   3   4
Affiliations

Endophytic bacterium Pseudomonas protegens suppresses mycelial growth of Botryosphaeria dothidea and decreases its pathogenicity to postharvest fruits

Yonghong Huang et al. Front Microbiol. .

Abstract

Apple (Malus domestica Borkh.), one of the most economically important fruits widely consumed worldwide, has been suffering from apple ring rot caused by Botryosphaeria dothidea, which dramatically affects its quality and yield. In the present study, we demonstrated that Pseudomonas protegens, isolated from Chinese leek (Allium tuberosum), significantly suppressed the mycelial growth and propagation of B. dothidea, respectively, further displayed a considerably inhibitory effect on the apple ring rot of postharvest fruits. In addition, P. protegens significantly improved the total soluble solid/titrable acidity (TSS/TA) ratio and soluble sugar/titrable acidity (SS/TA) ratio and drastically maintained the fruit firmness. Further analysis manifested that P. protegens substantially induced the defense-related genes such as MdGLU, MdPAL, MdPOD, MdCAL, and transcription factors related to the resistance to B. dothidea, including MdWRKY15, MdPUB29, MdMyb73, and MdERF11 in apple fruits. Meanwhile, P. protegens considerably restrained the expressions of the pathogenicity-related genes in B. dothidea, including the BdCYP450, BdADH, BdGHY, BdATS, Bdα/β-HY, and BdSTR. By inference, P. protegens inhibited the apple ring rot on postharvest fruits by activating the defense system of apple fruit and repressing the pathogenic factor of B. dothidea. The study provided a theoretical basis and a potential alternative to manage the apple ring rot on postharvest fruits.

Keywords: apple ring rot; biological control; defense-related genes; fruit quality; pathogenicity-related genes.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

Figure 1
Figure 1
The suppression of Pseudomonas protegens on the mycelia growth of Botryosphaeria dothidea on the PDA medium. The untreated control mycelia (A) and the P. protegens-treated mycelia (B) that were incubated on the PDA medium for 3 days. The comparison of the colony diameter of the different treatments (C). P. protegens significantly inhibited the mycelial growth of the fungus B. dothidea (D). Compared to the control (E), the P. protegens severely damaged the mycelial morphology of B. dothidea (F). Lowercase letters indicate a significant difference between treatments (p < 0.05).
Figure 2
Figure 2
The suppression of P. protegens on the mycelia growth of B. dothidea in the PDB medium. The mycelia incubated with shaking in the PDB medium supplemented with 20% (A), 10% (B), and 5% (C) of P. protegens and the control mycelia (D) for 2 days. (E) The weight of mycelia from different treatments (E). The inhibition of various concentrations of P. protegens to the fungus B. dothidea (F). Lowercase letters indicate a significant difference between treatments (p < 0.05).
Figure 3
Figure 3
The inhibitory effect of P. protegens on apple ring rot on postharvest fruits (Experiment 1). The disease symptom on the P. protegens-treated fruits (A) and the untreated control fruits (B) 3 days later. The disease spot diameter of the P. protegens-treated fruits was significantly smaller than the untreated control (C), demonstrating that P. protegens had potent inhibition on the ring rot disease on postharvest apple fruits (D). Lowercase letters indicate a significant difference between treatments (p < 0.05).
Figure 4
Figure 4
The inhibitory effect of P. protegens on apple ring on postharvest fruit (Experiment 2). The mycelial cluster number on P. protegens-treated fruits was significantly smaller than the control on the first, third, and fifth day (A). In addition, the disease spots on the P. protegens-treated fruits (B) were smaller than that on the control fruits on the seventh day (C), and the number of the disease spots on the P. protegens-treated fruits was also significantly lower than the control (D). *p  <  0.05, **p   <  0.01.
Figure 5
Figure 5
The fruit quality indexes of the apple fruits of the four treatments. Nine days later, the fruit quality indexes, including total soluble solid (TSS) (A), titratable acidity (TA) (B), soluble sugar (SS) (C), total soluble solid/titrable acidity (TSS/TA) (D), and soluble sugar/titrable acidity (SS/TA) (E), vitamin C (VC) (F), and firmness (G), were different among the four treatment. *p < 0.05, ****p < 0.0001, ns p > 0.05.
Figure 6
Figure 6
The relative expressions of various defense-related genes and the transcription factors, including MdGLU (A), MdCATe (B), MdPOD (C), MdPAL (D), MdPUB29 (E), MdWRKY15 (F), MdERF11 (G) and MdMYB73 (H) in various treated apple fruits. *p < 0.05, **< 0.01, ***p < 0.001, ****p < 0.0001, ns p > 0.05.
Figure 7
Figure 7
The relative expressions of various pathogenicity-related genes, including BdCYP450 (A), BdADH (B), BdGHY (C), BdATS (D), Bdα/β-HY (E), and BdSTR (F) in P. protegens-treated and the control B. dothidea. *p < 0.05, **p < 0.01, ****p < 0.0001.
Figure 8
Figure 8
The model of P. protegens inhibiting the apple ring rot on fruit caused by B. dothidea.
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