Antifungal activity of volatile organic compounds produced by Pseudomonas fluorescens ZX and potential biocontrol of blue mold decay on postharvest citrus
Introduction
Citrus is one of the most popular fruits throughout the world due to their delicious taste, fragrant flavor, nutritive value and relatively low price (Li et al., 2010). However, citrus fruits are highly perishable and easy to suffer a wide variety of postharvest fungal diseases caused by Penicillium digitatum, Penicillium italicum, Colletotrichum gloeosporioides, Geotrichum citri-aurantii, Alternaria citri, etc (Araújo et al., 2019; Ferraz, da Cunha, da Silva, & Kupper, 2016; Li et al., 2010; Mercier & Smilanick, 2005; Vilanova et al., 2014). Particularly, green mold, caused by P. digitatum, and blue mold, caused by P. italicum, are the most devastating postharvest diseases affecting citrus fruits, significantly reducing fruit value, and shelf-life and inflicting severe economic losses (Talibi, Boubaker, Boudyach, & Ait Ben Aoumar, 2014). Blue mold is particularly pernicious due to its worldwide prevalence, especially in oranges, and its exceptionally rapid spread among packed cartons of oranges stored at low temperatures (Chalutz & Wilson, 1990; Demirci, 2011).
For a long time, traditional physical methods, including transient heat treatment, refrigerated atmosphere storage, modified atmosphere, ionizing radiation, etc., have been applied for the control of postharvest decay, while none of these provided complete control (Hong, Lee, & Kim, 2007; Padova, Kahan, & Barkai-Golan, 1969; Talibi, Boubaker, Boudyach, & Ait Ben Aoumar, 2014). On the other hand, chemical fungicides, such as imazalil, prochloraz, and carbendazim have been offered some degree of control over postharvest diseases, however their efficacy has been diminished in recent years due to the emergence of pathogen resistance (Sánchez-Torres & Tuset, 2011). Worse yet, in order to achieve a sufficient effect for disease control, much more synthetic fungicides are usually required, which can be harmful to non-targeted microorganisms, food safety and human health (Conner, McAndrew, Kiehn, Chapman, & Froese, 2004; Martins et al., 2019). Therefore, it is of great importance to find alternative methods for controlling postharvest decay in a nontoxic and eco-friendly way.
Recently, the use of biological control agents (BCAs) to inhibit pathogens has attracted more attention. BCAs can display diverse modes of action, making pathogen resistance unlikely (Wallace, Hirkala, & Nelson, 2018a). Thus, BCAs are considered an effective, safe, and environmentally friendly approach against phytopathogens (Dukare et al., 2018; Lugtenberg, Rozen, & Kamilov, 2017; Talibi, Boubaker, Boudyach, & Ait Ben Aoumar, 2014; Wallace et al., 2018a). It is generally believed that BCAs exhibit various biocontrol mechanisms, including parasitism (Dukare et al., 2018; Sahu, Singh, Shankar, & Pradha, 2018; Wallace, Hirkala, & Nelson, 2017; 2018a; 2018b), competition for limiting nutrients and niches (Lugtenberg, Rozen, & Kamilov, 2017; Wallace et al., 2017; Wang et al., 2019; 2020) and induced resistance (Dukare et al., 2018; Patel et al., 2015; Zhao et al., 2018). In addition, antimicrobial substances are also found such as phenazine-1-carboxylicacid, 2,4-diacetylphloroglucinol, pyoluteorin, pyrrolnitrin, siderophore, chitinase and β-1,3-glucanase from BCAs (Arseneault, Goyer, & Filion, 2016; Dukare et al., 2018; Prabhukarthikeyan, Keerthana, & Raguchander, 2018; Suganthi, Senthilkumar, Arvinth, & Chandrashekara, 2017; Wallace et al., 2017). Compared with diffusible antimicrobial substances, investigations related with volatile organic compounds (VOCs) produced by BCAs on disease suppression have gained popularity, as they are biodegradable (Qin, Xiao, Cheng, Zhou, & Si, 2017). Moreover, bio-fumigation with VOCs produced by microorganisms circumvents direct contact between fruit and antagonist, and therefore does not leave toxic residues on the fruit surface (Mercier & Smilanick, 2005; Toffano, Fialho, & Pascholati, 2017). Some of the reported examples include VOCs produced by Streptomyces globisporus JK-1 against P. italicum on postharvest Citrus microcarpa (Li et al., 2010); by Bacillus subtilis CF-3 against C. gloeosporioides on litchi fruits (Zhao et al., 2019); and by Aureobasidium pullulans L1 and L8 for biocontrol of brown rot caused by Monilinia spp. on stone fruits (Di Francesco, Di Foggia, & Baraldi, 2020).
Recent decades have witnessed global research insights into the antibacterial and antifungal activities of Pseudomonas fluorescens, a strongly colonizing, mesophilic, heterotrophic, gram-negative rod-shaped bacterium with polar flagella (Sahu, Singh, Shankar, & Pradha, 2018). VOCs-producing P. fluorescens have also shown promise in previous work. Wallace et al. (2017) reported that VOCs produced by P. fluorescens 1–112, 2–28 and 4–6 could completely inhibit spore germination of Penicillium expansum. Proteomics analysis conducted by Raza et al. (2016) indicated that VOCs emitted by P. fluorescens WR-1 inhibited protein metabolism of Ralstonia solanacearum to significantly reduce its virulence. Additionally, the VOCs produced by P. fluorescens UM showed strong antagonism against Botrytis cinerea during confrontation assays. They also significantly increased Medicago truncatula biomass and chlorophyll content (Hernandez-Leon et al., 2015).
P. fluorescens ZX has been proposed as a BCA to control postharvest decay in grape caused by B. cinerea (Jiang et al., 2019), or in citrus caused by P. italicum and P. digitatum (Wang et al., 2019; 2020). Investigations carried out by Wang et al. (2019; 2020) provided experimental evidence that VOCs produced by P. fluorescens ZX played significant roles in inhibition of fungal growth. These VOCs were isolated and identified by using headspace solid phase microextraction (SPME) and gas chromatography with mass spectrometric detection (GC-MS), and respectively, 20 and 16 types of VOCs were identified from nutrient broth agar (NA) culture and nutrient broth (NB) culture where P. fluorescens ZX grew (Wang et al., 2020). However, it remains unclear which precise VOC of P. fluorescens ZX are responsible for fungicidal effects against P. italicum.
Therefore, based on the results of our earlier work, the present study aimed to evaluate the bio-fumigation action of P. fluorescens ZX VOCs on citrus fruits, and to investigate the roles of individual VOC components in controlling the development of blue mold on postharvest citrus fruits. The insights provided by this work could provide an effective basis to develop biopreservation agents to efficiently control P. italicum and, thus, to broaden biological protection pathways of postharvest fruits.
Section snippets
Fruit
Freshly hand-harvested, mature and healthy Newhall navel orange fruits (Citrus sinensis Osbeck) were obtained from a local orchard. Citrus fruits used in this study did not received any pre-harvest fungicide treatment. Fruits with similar shape, color and size were selected and randomly divided into groups (27 fruits per group) for the experiments. Before each trial, fruits were washed with tap water, and surface-sterilized with 75% ethanol, followed by air drying at room temperature. After
In vitro antifungal activity of VOCs produced by P. fluorescens ZX
The experimentally determined in vitro antifungal activities of VOCs produced by P. fluorescens ZX are presented in Fig. 1. The fungus P. italicum showed significant (P < 0.05) inhibition of mycelial and CFU growth in presence of VOCs incubation. Moreover, the initial concentration of bacterial inoculation exerted a significant (P < 0.05) effect on inhibition rate, with VOC-induced inhibition strengthened under bacterial suspensions applied to give higher initial inoculation. When the bacterial
Discussion
Extensive study has been conducted on various modes of action related to inhibition of plant pathogenic fungi by BCAs. However, only recently have researchers recognized the important role of antifungal VOCs (Toffano et al., 2017). Previously, VOCs synthetized by P. fluorescens have been studied against some plant soil-borne diseases (Hernandez-Leon et al., 2015; Raza et al., 2016) and apple postharvest pathogens (Wallace et al., 2017; 2018a; 2018b), which yielded satisfactory results. In
Conclusions
This study demonstrated that P. fluorescens ZX-produced VOCs—specifically their pure constituent components of acetic acid, butyric acid, isobutyric acid, 2-MBA, 3-BMA, and especially DMDS and DMTS—were effective for controlling P. italicum, the pathogen that causes blue mold on postharvest citrus fruits. The active compounds identified in this work are promising as widely deployable agents for the biocontrol of blue mold. In addition, we demonstrated that the antifungal activity of VOCs
CRediT authorship contribution statement
Zhirong Wang: Conceptualization, Investigation, Data curation, Formal analysis, Resources, Methodology, Software, Writing - original draft, Writing - review & editing, Supervision. Tao Zhong: Investigation, Data curation, Formal analysis, Software, Writing - original draft. Kewei Chen: Data curation, Writing - original draft, Writing - review & editing. Muying Du: Resources, Writing - original draft, Funding acquisition. Guangjing Chen: Investigation, Data curation. Xuhui Chen: Investigation,
Declaration of competing interest
The authors declare that they have no conflicts of interest.
Acknowledgements
We gratefully acknowledged the Chinese-Hungarian Intergovernmental Scientific and Technological Industrial R + D Program (National Key R&D Program of China, project number in China is 2016YFE0130600; in Hungary is TET_16_CN-1-2016-0004) and A Project Funded by Ministry of Science and Technology of China (No. G20190022022) for supplying the testing materials and related services.
References (48)
- et al.
Aureobasidium pullulans volatile organic compounds as alternative postharvest method to control brown rot of stone fruits
Food Microbiology
(2020) - et al.
Biocontrol ability and putative mode of action of yeasts against Geotrichum citri-aurantii in citrus fruit
Microbiological Research
(2016) - et al.
Antifungal effect of volatile organic compounds produced by Bacillus amyloliquefaciens CPA-8 against fruit pathogen decays of cherry
Food Microbiology
(2017) - et al.
Characterization of the antifungal and plant growth-promoting effects of diffusible and volatile organic compounds produced by Pseudomonas fluorescens strains
Biological Control
(2015) - et al.
Effects of hot water treatment on the storage stability of satsuma Mandarin as a postharvest decay control
Postharvest Biology and Technology
(2007) - et al.
Fumigant activity of volatiles of Streptomyces globisporus JK-1 against Penicillium italicum on Citrus microcarpa
Postharvest Biology and Technology
(2010) - et al.
Microbial volatiles organic compounds control anthracnose (Colletotrichum lindemuthianum) in common bean (Phaseolus vulgaris L.)
Biological Control
(2019) - et al.
Control of green mold and sour rot of stored lemon by biofumigation with Muscodor albus
Biological Control
(2005) - et al.
Efficacy of dimethyl disulfide (DMDS) for the control of chrysanthemum Verticillium wilt in Italy
Crop Protection
(2017) - et al.
Antibiotic-producing Pseudomonas fluorescens mediates rhizome rot disease resistance and promotes plant growth in turmeric plants
Microbiological Research
(2018)
Hanseniaspora uvarum prolongs shelf life of strawberry via volatile production
Food Microbiology
Volatile organic compounds produced by Pseudomonas fluorescens WR-1 restrict the growth and virulence traits of Ralstonia solanacearum
Microbiological Research
Molecular insights into fungicide resistance in sensitive and resistant Penicillium digitatum strains infecting citrus
Postharvest Biology and Technology
Potential of fumigation of orange fruits with volatile organic compounds produced by Saccharomyces cerevisiae to control citrus black spot disease at postharvest
Biological Control
Acidification of apple and orange hosts by Penicillium digitatum and Penicillium expansum
International Journal of Food Microbiology
Postharvest biological control of blue mold of apple by Pseudomonas fluorescens during commercial storage and potential modes of action
Postharvest Biology and Technology
Mechanisms of action of three isolates of Pseudomonas fluorescens active against postharvest grey mold decay of apple during commercial storage
Biological Control
Effect of volatile substances of Streptomyces platensis F-1 on control of plant fungal diseases
Biological Control
Isolation and identification of bacteria from rhizosphere soil and their effect on plant growth promotion and root-knot nematode disease
Biological Control
Identification of volatile organic compounds for the biocontrol of postharvest litchi fruit pathogen Peronophythora litchi
Postharvest Biology and Technology
Volatiles released by endophytic Pseudomonas fluorescens promoting the growth and volatile oil accumulation in Atractylodes lancea
Plant Physiology and Biochemistry
Possible contributions of volatile-producing bacteria to soil fungistasis
Soil Biology and Biochemistry
Determination of tryptoquialanines A and C produced by Penicillium digitatum in oranges: Are we safe?
Food Chemistry
Biocontrol of potato common scab is associated with high Pseudomonas fluorescens LBUM223 populations and phenazine-1-carboxylic acid biosynthetic transcript accumulation in the potato geocaulosphere
Phytopathology
Cited by (65)
Mechanisms of Meyerozyma caribbica isolated from Tibetan soil to inhibit Aspergillus ochraceus on grapes
2024, Postharvest Biology and Technology