Pre-/Post-Harvest Pathogen-Control Strategies for Improving the Quality and Safety of Horticultural Plants

The microbiological safety of horticultural plants (vegetables, fruits, spices, flowers, other edible crops, ornamental plants, etc.) is important for both human health and the product quality of edible and ornamental plants [1]. This Special Issue, entitled “Pathogen Control Strategies for Pre-/Post-harvest Management of Horticultural Plants and the Application of Plant-Derived Substances for Microbial Risk Management”, includes a series of original research and review articles regarding recent progress in the field of horticultural sciences to develop pre-/post-harvest treatment technologies and to identify the risk factors to be controlled by these technologies. Examples include both plant pathogens causing decay and human pathogens causing contamination. Key topics of this collection are as follows: identification and characterization of microorganisms causing post-harvest contamination and decay in plants; decontamination, control, and microbial detection technologies applicable to pre-/post-harvest systems against horticultural pathogens; examination of pathogenic mechanisms; development and application of technologies for product quality (decay control in post-harvest systems, shelf-life extension, maintenance of post-harvest freshness, preservation, etc.); and analysis of the incidence of pathogens from farm, retail establishment, market, and commercial horticulture operations.

Pathogen-control studies include research areas regarding not only the development and/or application of decontamination technologies but also the examination of the occurrence and characterization of plant or human pathogens isolated from horticultural plants [2,3]. Identification and understanding of the distinct characteristics of major pathogens that can cause plant diseases can be regarded as the primary step for the establishment of pre- and/or post-harvest treatment strategies. The review article by Nicoletti et al. [4] summarizes recent findings regarding the ecological interactions of hazelnut with plant pathogenic bacteria based on the disease type (e.g., bacterial blight, bacterial canker) and also highlights the importance of understanding indigenous bacteria associated with hazelnut (e.g., plant growth promoters, endophytes, epiphytes, and root associates). In terms of the strategies designed for the management of bacterial diseases of hazelnut, the restriction of the use of conventional treatment agents (e.g., copper-based products) is suggested as the trigger for the development of alternative treatment technologies, and the advantages/disadvantages of those technologies are comprehensively discussed [4]. The analysis of the prevalence of microorganisms linked to pre-/post-harvest diseases of horticultural commodities and environments can identify critical control points for the prevention of contamination of pathogenic microorganisms [5]. In particular, the diversification of the cultivation environment implies the necessity for the exploration of possible contamination routes prior to the establishment of pathogen-control methods. Deng et al. [6] demonstrate the transfer of the human pathogens Salmonella enterica subsp. enterica ser. Javiana and Listeria monocytogenes from a soil-free cultivation matrix (i.e., hydroponic) to mature microgreens including sunflower and pea shoots [6]. Whereas insect pests are also known as one of the major causes of damage to horticultural plants during cultivation, Hamza et al. [7] examine the biological relationship of leaf miners with their host plants and also evaluated the efficacy of insecticides to establish management strategies.

Advances in the management of hazardous microorganisms in horticultural plants have contributed to the establishment of effective/efficient intervention strategies against microbiological risk factors [8,9]. Since there is a wide diversity for the applicability of decontamination technologies according to each horticultural plant species, the accumulation of scientific findings is crucial for microbial risk assessment/management of raw and/or processed products of horticultural origin. The review article by Shin et al. [10] describes pre- and post-harvest treatments for peach fruit according to the technical principles (i.e., physical, chemical, biological) and especially focuses on the combined use of these technologies, which can induce synergistic effects [10]. Original research articles of this topical collection report chemical and biological pathogen-control technologies applicable as single and/or combined treatments. Pre-/post-harvest treatment of antimicrobial chemicals to prevent infectious diseases and/or the deterioration of various horticultural plants has been widely adopted [11,12]. Saltos-Rezabala et al. [13] suggest a pre-harvest foliar spray of antifungal essential oil (e.g., oils from thyme, lemongrass, tea tree) as an effective alternative method to conventional synthetic chemicals for controlling early blight in tomato plants via the inactivation of pathogens (e.g., Alternaria linariae) and the stimulation of the defense system of infected plants. Xi et al. [14] suggest ginger rhizome extract (GRE) as a natural agent to replace synthetic fungicides and/or bactericides and demonstrate growth inhibition effects against the soil-borne crop pathogen Fusarium solani: morphological characterization of F. solani exposed to GRE and the analysis of the chemical constituents of GRE revealed the key mechanism of antifungal effects [14]. As shown in the research by Sánchez-Hernández et al. [15], the capability of crop pathogen control is generally ensured by the validation of in vivo plant protective effects after the screening of bacteriostatic/bactericidal activities against horticultural crop bacteria [15]. Borotová et al. [16] report that multiple post-harvest treatment effects including antioxidant, antimicrobial, and anti-insect properties can be expected from the application of frankincense essential oil to harvested horticultural plants consumed as food products [16]. In the case of combination treatments, the research by Oliveira-Pinto et al. [17] and Hassan et al. [18] suggest novel chemical–chemical and chemical–biological combinations, respectively. Oliveira-Pinto et al. [17] developed a biocontrol strategy using Satureja montana essential oil nano-formulated with zein nanoparticles against the causative agent of tomato bacterial spot. Hassan et al. [18] report the biological control activity of natural plant extracts (Eucalyptus camaldulensis leaf extract, Citrus sinensis leaf extract, Ficus benghalensis fruit extract) combined with microbial antagonists (Pseudomonas fluorescens, Trichoderma viride) against zucchini fungal pathogens and also demonstrate an increase in the productivity of zucchini plants from not only in vitro experiments, but also greenhouse tests. While cleaning and sanitizing of mechanical harvesters are also expected to act as key determinant factors for the food hygiene of horticultural plants, Holland et al. [19] identified best practices regarding the use of cleaning agents and sanitizers applied to mechanical blueberry harvester surfaces [19].

In conclusion, this Special Issue highlights advances in plant quality and safety control technologies and their application strategies. These findings also contribute to the improvement of our knowledge regarding the determinant factors of changes in fruit quality and safety (e.g., plant metabolisms associated with defense against undesirable environmental stresses including attacks by pathogens). Understanding the current advancements in risk management technologies can give direction to future perspectives on countermeasures to the threats of pre-/post-harvest contamination and diseases caused by pathogens. The contribution of all authors to this topical collection is highly appreciated.