Advances in the application of antagonistic yeasts to manage postharvest diseases in fruit

Astract: Postharvest decay of fruits causes significant economic losses. Biological control of postharvest decay of fruits was developed as one of several promising alternatives to chemical fungicides. This paper provides a brief overview of the application of yeasts as postharvest biocontrol agents, which includes information on the sources which yeast antagonists have been isolated from, proposed biological mechanisms, and approaches to improve their efficiency and commercial applications. Yeast species have several attributes that make them suitable for use as biocontrol agents in fruit. Yeasts are tolerant to extreme environmental conditions (e.g., low and high temperatures, desiccation, wide range of relative humidity, low oxygen levels, p H fluctuations and UV radiation) that prevail before and after harvest. Also, yeasts have unique adaptation strategies to the fruit micro-environment (such as high sugar concentration, high osmotic pressure and low p H) . Yeasts can grow rapidly on inexpensive substrates in fermenters. Large quantities of yeasts can be produced. Yeasts have simple nutritional requirements, so they can colonize dry surfaces for long periods of time. This paper also discusses the problems of yeast used in postharvest biocontrol, and suggests new ideas for future research, such as newly developed technologies, genomics, transcriptomics, metabolomics and bioinformatics, which could be used for research on antagonistic yeast in a biocontrol system. Yeast species have been isolated from a variety of sources, including fruit surfaces, the phyllo sphere, soil and sea water, et al. The proposed mechanisms of yeasts that are responsible for their antagonistic activity include competition for nutrients and space, parasitism of the pathogen, secretion of antifungal compounds, induction of host resistance, and biofilmformation. Competition for nutrients and space are considered to be the primary mechanisms. Yeast is able to use limited resources more efficiently than the pathogen. Yeasts have the ability to use specific features facilitating their adherence, colonization and multiplication to successfully colonize on fruit surfaces. This feature is associated with the formation of a biofilm. Yeasts can produce antifungal compounds, such as killer toxins, peptides and antibiotic metabolites. Yeasts have the capability to interact with the host tissue, particularly the wounds, increasing the cicatrization processes. These antagonistics were much more effective when applied before pathogen inoculation. Yeast cells could induce resistance processes in fruit skin. The performance of a biocontrol agent can be seen as the result of complex mutual interactions between all the biotic (organisms) and abiotic (environmental) components of the system. Although these interactions have been the subject of postharvest biocontrol research for many years, our understanding is still very incomplete. When studying mechanisms of action, a systems approach should be employed to investigate the network of interactions. Such an approach, that takes into account all the components of the system, may provide the greatest understanding of biocontrol systems. The exploration into the overall diversity and composition of microbial communities on fruit and how these communities vary across produce types, their function, the factors that influence the composition of the microbiota after harvest and during storage, and the distribution of individual taxa is needed.Information on the dynamics and diversity of microbiota may be useful to developing a new paradigm in postharvest biocontrol that is based on constructing synthetic microbial communities that provide superior control of pathogens. The availability of more cost-efficient, high throughput DNA/RNA and proteomic technologies, along with bioinformatics, have provided new opportunities and tools to obtain deeper insights into the mechanisms and interactions that have already been established. Developments in deep sequencing, transcriptomics, MS-MS proteomics, metagenomics, and comparative and functional genomics can be utilized to determine changes in the physiological status of biocontrol agents, and the effect of environmental stress on its intracellular machinery. Changes in the level of expression of related genes during mass production, formulation and storage, or in response to exposure and contact with host plant tissue after application can now be more readily investigated. Omic techniques (genomic, transcriptomic or proteomic) have been utilized, studies of postharvest biocontrol agents have been sparse and it is expected that greater details about interactions in the entire biocontrol system will be forthcoming. Acceptable and consistent performance under commercial conditions is critical to the success of any biocontrol agent. Economical production of large quantities of yeast in a formulation needs to ensure reasonable shelf life and maintain efficacy during large-scale testing. Industrial fermentation is accomplished under conditions quite different from those in shake culture. The process must be costeffective, using industrial by-products as nutrients and fermentation must be completed within 24-30 h.Downstream processing involves various steps, such as drying, addition of volume materials, adhesives, emulsifiers and adjuvants. All these actions may affect the properties of the selected biocontrol agent. It is essential that a formulated product retains the properties of the initial lab-grown cultures. The formulation must retain its species purity (not be contaminated) and the microbial cells must retain their genetic stability, cell viability, and their attributes as colonizers on fruit surfaces, as well as other aspects of their mechanisms of action.Postharvest decay of fruits causes significant economic losses. Biological control of postharvest decay of fruits was developed as one of several promising alternatives to chemical fungicides. This paper provides a brief overview of the application of yeasts as postharvest biocontrol agents, which includes information on the sources which yeast antagonists have been isolated from, proposed biological mechanisms, and approaches to improve their efficiency and commercial applications. Yeast species have several attributes that make them suitable for use as biocontrol agents in fruit. Yeasts are tolerant to extreme environmental conditions (e.g., low and high temperatures, desiccation, wide range of relative humidity, low oxygen levels, p H fluctuations and UV radiation) that prevail before and after harvest. Also, yeasts have unique adaptation strategies to the fruit micro-environment (such as high sugar concentration, high osmotic pressure and low p H) . Yeasts can grow rapidly on inexpensive substrates in fermenters. Large quantities of yeasts can be produced. Yeasts have simple nutritional requirements, so they can colonize dry surfaces for long periods of time. This paper also discusses the problems of yeast used in postharvest biocontrol, and suggests new ideas for future research, such as newly developed technologies, genomics, transcriptomics, metabolomics and bioinformatics, which could be used for research on antagonistic yeast in a biocontrol system. Yeast species have been isolated from a variety of sources, including fruit surfaces, the phyllo sphere, soil and sea water, et al. The proposed mechanisms of yeasts that are responsible for their antagonistic activity include competition for nutrients and space, parasitism of the pathogen, secretion of antifungal compounds, induction of host resistance, and biofilmformation. Competition for nutrients and space are considered to be the primary mechanisms. Yeast is able to use limited resources more efficiently than the pathogen. Yeasts have the ability to use specific features facilitating their adherence, colonization and multiplication to successfully colonize on fruit surfaces. This feature is associated with the formation of a biofilm. Yeasts can produce antifungal compounds, such as killer toxins, peptides and antibiotic metabolites. Yeasts have the capability to interact with the host tissue, particularly the wounds, increasing the cicatrization processes. These antagonistics were much more effective when applied before pathogen inoculation. Yeast cells could induce resistance processes in fruit skin. The performance of a biocontrol agent can be seen as the result of complex mutual interactions between all the biotic (organisms) and abiotic (environmental) components of the system. Although these interactions have been the subject of postharvest biocontrol research for many years, our understanding is still very incomplete. When studying mechanisms of action, a systems approach should be employed to investigate the network of interactions. Such an approach, that takes into account all the components of the system, may provide the greatest understanding of biocontrol systems. The exploration into the overall diversity and composition of microbial communities on fruit and how these communities vary across produce types, their function, the factors that influence the composition of the microbiota after harvest and during storage, and the distribution of individual taxa is needed.Information on the dynamics and diversity of microbiota may be useful to developing a new paradigm in postharvest biocontrol that is based on constructing synthetic microbial communities that provide superior control of pathogens. The availability of more cost-efficient, high throughput DNA/RNA and proteomic technologies, along with bioinformatics, have provided new opportunities and tools to obtain deeper insights into the mechanisms and interactions that have already been established. Developments in deep sequencing, transcriptomics, MS-MS proteomics, metagenomics, and comparative and functional genomics can be utilized to determine changes in the physiological status of biocontrol agents, and the effect of environmental stress on its intracellular machinery. Changes in the level of expression of related genes during mass production, formulation and storage, or in response to exposure and contact with host plant tissue after application can now be more readily investigated. Omic techniques (genomic, transcriptomic or proteomic) have been utilized, studies of postharvest biocontrol agents have been sparse and it is expected that greater details about interactions in the entire biocontrol system will be forthcoming. Acceptable and consistent performance under commercial conditions is critical to the success of any biocontrol agent. Economical production of large quantities of yeast in a formulation needs to ensure reasonable shelf life and maintain efficacy during large-scale testing. Industrial fermentation is accomplished under conditions quite different from those in shake culture. The process must be costeffective, using industrial by-products as nutrients and fermentation must be completed within 24-30 h.Downstream processing involves various steps, such as drying, addition of volume materials, adhesives, emulsifiers and adjuvants. All these actions may affect the properties of the selected biocontrol agent. It is essential that a formulated product retains the properties of the initial lab-grown cultures. The formulation must retain its species purity (not be contaminated) and the microbial cells must retain their genetic stability, cell viability, and their attributes as colonizers on fruit surfaces, as well as other aspects of their mechanisms of action.