Chitosan is an effective inhibitor against potato dry rot caused by Fusarium oxysporum

https://doi.org/10.1016/j.pmpp.2021.101601Get rights and content

Highlights

  • Chitosan can inhibit the growth and spore germination of Fusarium oxysporum.

  • Chitosan affects the pathogenicity of F. oxysporum on potato.

  • Chitosan improves the susceptibility of F. oxysporum to environmental stresses.

  • Chitosan enhances the potato resistance against F. oxysporum.

  • The transcriptome analysis reveals the underlying molecular mechanism.

Abstract

Fusarium dry rot was one of the most serious diseases of potato during storage. Biological control based on the use of natural bioactive compounds to suppress tuber diseases offer an attractive alternative. As a biopolymer, chitosan had broad-spectrum antimicrobial activity against various phytopathogens and could induce plant resistance to pathogens. Previous observations showed that chitosan displayed effective inhibition on potato dry rot caused by Fusarium sambucinum, Fusarium sulphureum, etc., however, little is known whether chitosan can suppress potato dry rot caused by Fusarium oxysporum. In this study, the mycelial growth and spore germination of F. oxysporum were significantly inhibited by chitosan, and the pathogenicity of F. oxysporum was reduced after treated by chitosan. Moreover, chitosan could enhance the susceptibility of F. oxysporum to environmental stresses and improve the potato resistance against F. oxysporum. The transcriptome analysis of F. oxysporum with or without chitosan indicated that total 4955 differentially expressed genes (DEGs) were identified, of which 2839 were up-regulated and 2116 were down-regulated. KEGG pathway and GO term analysis showed DEGs were mostly related to protein metabolism, stress tolerance and cell structure. These findings suggested chitosan might be a promising natural fungicide for the potato dry rot caused by F. oxysporum.

Introduction

Fusarium dry rot was a common and important disease of postharvest potato tubers, which has been found in many potato production areas [[1], [2], [3]]. The yield reduction caused by potato dry rot in storage period can reach 6%~25%, and 60% in serious cases, which leads to a significant decrease in the rate of commercial potato [4]. At present, 17 species and 5 variants of Fusarium spp. had been identified and isolated in China, among which Fusarium oxysporum and Fusarium avenaceum were the main pathogens of dry rot [5]. Currently, chemical fungicides were still the main strategy used for preventing and controlling dry rot, and these fungicides: thiabendazole (TBZ), 2-aminobutane (2-AB), imazalil, flusilazole, difenoconazole were proven to have good function for it [6,7]. However, the inappropriate, long-term and excessive usage of chemical fungicides had caused many problems, such as considerable residues of agricultural products, environmental contamination and pathogen resistance. Therefore, it is urgently required to develop some alternatives to reduce the usage of chemical fungicides-based methods which offer environmental sustainability and less toxicity for human health.

Chitosan (poly-β-(1 → 4)N-acetyl-d-glucosamine), a natural macromolecule polysaccharide derived by deacetylation of chitin [8], could be obtained from the outer shell of crustaceans (shrimp, krill, crab and crayfish) and also produced by some fungi (Penicillium notatum, Aspergillus niger, and Mucor rouxii, etc.) [[9], [10], [11]]. Because of its nontoxicity, biocompatibility and biodegradability, it is widely used in medicine [12], food [[13], [14], [15]], agriculture and chemical industry [16]. It was reported that chitosan exhibited the good broad-spectrum antimicrobial activity against various pathogens, like fungi (Agpergillus flavus, Phytophthora capsici, Penicillium digitatum, etc.), bacteria (Xanthomonas axonopodis pv. Glycines, Staphylococcus aureus, Pseudomonas aeruginosa, etc.), and viruses (Newcastle virus, AcMNPV, BmNPV, etc.) [[17], [18], [19], [20], [21], [22], [23], [24]]. The antimicrobial mechanisms of chitosan included electrostatic interactions and metal chelation for plasma membrane damage or alteration of cell surface morphology, resulting in leakage of intracellular material; interaction with DNA/RNA from degradation products of chitosan into cells; and forming a film onto the microbial surfaces to prevent the exchange of matters and gas [25]. Chitosan and its derivatives have been reported to be very effective effect on preventing and controlling various postharvest diseases of horticultural commodities, such as fungal diseases of citrus [26,27], bell pepper anthracnose [28], strawberry gray mold [29], blackberry soft mold [30], kiwifruit soft rot [31], and so on. The fungicidal performance of chitosan included mycelial swelling, excessive branching, abnormal shapes, spore germination reduction, structural alterations and molecular disorganization of fungal cells [[32], [33], [34]]. In addition, chitosan also can induce a plant defense response against phytopathogens through increasing the phenolic compounds, improving the activity of antioxidant enzymes and activating some pathogenesis-related genes, etc. [[35], [36], [37], [38]]. Previous researches also showed chitosan could prevent and control potato dry rot caused by Fusarium sambucinum, Fusarium sulphureum, Fusarium culmorum and Fusarium solani [[38], [39], [40], [41], [42]], while there was little information about whether chitosan can prevent and control potato dry rot caused by F. oxysporum or not. The main objectives of this work were to investigate the direct effects of chitosan on F. oxysporum; reveal the underlying molecular mechanisms of chitosan against F. oxysporum through transcriptome analysis; and determine the induction resistance of chitosan to dry rot in potato tubers caused by F. oxysporum.

Section snippets

F. oxysporum strain, media, and culture conditions

Pathogenic F. oxysporum 4 (FO-4) was isolated from potato tubers in a potato storehouse in Wulong district, Chongqing City, China and now it was kept in the botanical laboratory in Chongqing University, China. According to the previous report [43], F. oxysporum was cultured on potato dextrose agar (PDA) medium at 28 °C in the dark. Chitosan (100 kDa, deacetylation degree ≥ 90%) was purchased from Solarbio (Beijing, China).

Effects of chitosan on mycelial growth and morphology of F. oxysporum

Chitosan was dissolved in 1% acetic acid solution to form 10 mg/mL mother

The growth of F. oxysporum can be significantly inhibited by chitosan

In vitro, F. oxysporum strain was inoculated in the PDA medium with different concentration of chitosan. The results showed that chitosan had a dose-dependent inhibitory effect on F. oxysporum when the chitosan concentration was less than 0.4 g/L (Fig. 1A–C), while the inhibition effect reached plateau at the chitosan concentrations higher than 0.4 g/L. The 50% inhibiting concentration (IC50) of chitosan against F. oxysporum calculated from daily diameter data was 0.215 g/L by IBM SPSS

Conclusions

In this study, the vitro experiments demonstrated that exogenous chitosan can significantly inhibit the mycelial growth and spore germination of F. oxysporum, one of the main pathogen of potato dry rot. Based on the analysis of transcriptome sequencing results, we found that chitosan can increase the protein degradation of F. oxysporum, which could influence the growth of F. oxysporum. Under the stress conditions, chitosan can further inhibit the growth of FO-4 a lot, which indicated that

Author statement

Conceptualization, J.R., J.T. and P.D.; formal analysis, J.R. and XQ.H.; investigation, J.R., J.T. and XQ.H.; data curation, J.R., J.T. and PH.L.; writing—original draft preparation, J.R. and P.D.; writing—review and editing, PH.L. and MZ.R.; funding acquisition, P.D. and MZ.R. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by National Key R&D Program of China (2018YFD0200808 and 2016YFD0100306), Chongqing Natural Science Foundation (cstc2019jcyj-msxmX0127) and Chongqing Primary and Middle School Innovation Talent Training Project (CY180137).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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