Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: March 1, 2004
Publication Date: March 24, 2004
Citation: Janisiewicz, W.J. Mechanisms of biological control of postharvest fruit decays. Meeting Abstract. Abstract #23 for International Workshop on "Development of Biocontrol Agents of Fungal Diseases for Commercial Applications in Food Production Systems", Sevilla, Spain, March 24-27, 2004. Technical Abstract: Microbial ecology has been the driving force during the initial development of biological control of postharvest decays (BCPD) on fruits; however, knowledge of the mechanisms involved in biological control will play an essential role in maximizing the efficacy of these systems in the future. Efficacy may be improved by stimulating expression of biocontrol traits, enriching for the selection of antagonists with specific mechanisms of biological control (MBC), developing antagonist mixtures with different MBC, and manipulating and utilizing genes responsible for biocontrol traits. Attempts to characterize MBC on fruit resulted in reports implicating a variety of mechanisms including antibiosis with volatile and non-volatile compounds, lysis, competition for limiting nutrients and space, hyperparasitism, and the induction of resistance in fruits. Although these mechanisms were often well described, their significance for the individual antagonists is often uncertain, as many antagonists utilize more than one mechanism. Competition for nutrients has been implicated in the majority of these systems. Progress in understanding MBC on fruit has often been hindered by the lack of appropriate methods to investigate these mechanisms. Many methods were adopted from soil and phyllosphere biocontrol systems which often do not take into account the unique nutrient-rich-empty-niche environment of fruit wounds that are invaded by necrotrophic pathogens. Progress in the study of MBC on fruit could be accelerated by developing bacterial and yeast antagonist model systems to test various MBC in fruit systems. The development of transformation systems for bacterial and yeast antagonists has been significantly advanced recently and further progress in describing MBC will depend on the availability of suitable genes for testing. Many of these genes can be identified using plasmid mediated insertional mutagenesis (plasposon) and complementation of the disrupted genes in biocontrol agents. Important information on the activity of particular genes in a given environment can be obtained by fusing environmentally responsive promoters to suitable reporter genes (e.g. gfp). Such bioreporter systems were successfully used to determine the utilization of fructose by a Pseudomonas antagonist, and can be engineered for other sugars and amino acids. The metabolic activity of antagonists can be determined by bioluminescence, and the biomass by fluorescence, using the dual gfp-lux AB marker system. This system has been useful in nutrient competition studies. Recent advances in molecular approaches, coupled with new techniques for studying pathogen germination and growth are powerful tools that can greatly advance our knowledge on MBC and their significance in individual antagonists in fruit systems. The ultimate goal of BCPD to reduce the use of synthetic fungicides may also be realized by engineering new antagonists that are transformed with genes responsible for biocontrol traits in other antagonists. Novel genes from other sources coding for antimicrobial substances may also be used.