Challenges and Opportunities for the Commercialization of Postharvest Biocontrol

The past twenty years has seen the field of postharvest biocontrol evolve into a sophisticated science with global research programs worldwide, numerous yearly publications, patented technologies, and the development of new commercial products. The use of these products, however, still remains limited. The practical application of postharvest biocontrol has changed from a very classical view of using one organism to control another organism to a broader, more integrated approach where antagonists are combined with natural products, physical treatments, and used with both a preand postharvest application. These integrated approaches offer the potential of helping to overcome problems related to the performance of postharvest biocontrol agents and are generally used to increase reliability and efficacy. These integrated approaches, however, need to be standardized if they are to be readily adopted by industry. Continued research is needed on many aspects of the science and technology of postharvest biocontrol in order to integrate biocontrol agents into a combined preand postharvest production and handling system. The tools of molecular biology, such as genome sequences, microarrays, and genetic transformation now provide the ability to develop a better understanding of the mode of action of postharvest biocontrol agents as part of a tritrophic interaction between the host, antagonist, and pathogen. From an industrial viewpoint, knowledge regarding the short and long term effects of fermentation and packaging technologies on efficacy is still very rudimentary. These topics are reviewed with the objective of highlighting the barriers that need to be overcome for the widespread commercialization of postharvest bicontrol agents. INTRODUCTION While in the early 1980’s one could find 1-2 publications per year on postharvest biocontrol, now a literature search on the topic will bring up at least a hundred related publications per year, and over a thousand articles over the past twenty years. Additionally, the development of numerous commercial products has been pursued with limited success. Without question, postharvest biocontrol has matured into a significant area of research. While Wilson and Wisniewski (1989) enumerated many of the first principles and concepts defining postharvest biocontrol research, and several reviews have been written over the years (Droby et al., 2000, 2003; El Ghaouth et al., 2004; Janisiewicz and Korsten, 2002; Janisiewicz, 1998; Wilson and Wisniewski, 1994; Palou et al., 2008), perhaps it is time to evaluate the progress that has been made and more importantly try to identify the challenges and ideas that will generate research and product development in the next two decades. The original, primary justification for conducting postharvest biocontrol research was to reduce or replace the use of synthetic chemicals (Wilson and Wisniewski, 1989) because of concerns regarding their potential impact on human health (US National Research Council, 1987), especially children’s health (US National Research Council, 1993), and the environment. The discovery of biotypes of postharvest pathogens that were 1577 Proc. 6 th International Postharvest Symposium Eds.: M. Erkan and U. Aksoy Acta Hort. 877, ISHS 2010 resistant to the major postharvest fungicides, as well as the potential loss of registration for the use of some of fungicides also added to the urgent need for alternative strategies. Despite distinct advantages of conducting biocontrol strategies in postharvest environment, the performance of postharvest biocontrol products is still subject to significant variability which has limited their acceptance (Wisniewski et al., 2001, 2007; Droby and Lechter, 2004). Currently, the use of chemical agents remains the major method of choice by far for managing postharvest rots and the few postharvest biocontrol products that are commercially available have limited use, mostly in niche markets. A survey of the literature also indicates that most researchers are using strains of a surprisingly limited number of yeast or bacterial species and the majority of research has been limited to studying a new strain on a new commodity and/or perhaps against a new disease. This review attempts to highlight the challenges that need to be addressed for postharvest biocontrol to reach its full commercial potential. AN INDUSTRY PERSPECTIVE The most critical criterion for the success of a biocontrol product is whether or not it performs effectively under commercial conditions, providing an acceptable and consistent level of control of the target disease/s. It is essential that a formulated product, despite mass production of large quantities, retain 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, attributes as colonizers on fruit surfaces, as well as other aspects of their mechanism of action. Industrial fermentation is accomplished under conditions quite different from those in shake culture. The process must be cost effective, rely on industrial byproducts as nutrients and fermentation must be completed within 24 to 30h (Hofstein et al., 1994). Downstream processing involves various steps, such as drying, addition of volume materials (inert ingredients), adhesives, emulsifiers and adjuvants. All these actions may adversely affect the properties of the selected biocontrol agent. While aspects of this topic were addressed by Abadias et al. (2000, 2001, 2003), generally speaking, no serious attempts have been made to address the large scale production and formulation technology of biocontrol agents. Results of tests performed under commercial or semi-commercial conditions with formulated biocontrol preparations indicate that inconsistency and variability in the level of disease control is among the most significant barriers preventing widespread implementation of biocontrol technology. In order to improve reliability and efficacy, efforts have been made to enhance efficacy and reliability by various means that include the addition of salts and organic acids, (Droby et al., 1997; Karabulut et al., 2001), glucose analogs (El Ghaouth et al., 2000), food additives (Qin et al., 2006; Droby et al., 2002b; Karabulut et al., 2003) and integration with physical treatments (Zhang et al., 2006, 2008; Porat et al., 2002). Although promising additive and synergistic effects have been obtained, critical information on the interactions between antagonists, complementary treatments, pathogens, and commodities is still lacking. It is more than likely that each commodity-pathogen system has its own unique features and variables, so specific protocols will need to be developed and commercially evaluated. Biological control of postharvest diseases is viewed with caution and skepticism by many in the agricultural community. Unlike the control of tree, field crop or soil-borne diseases, successful commercial control of postharvest diseases of fruit and vegetables must be extremely efficient, in the range of 95-98%. As of today, such levels of control are difficult to achieve on a reliable basis and pose a significant challenge to the postharvest biocontrol industry. FUTURE CHALLENGES More research is needed in many aspects of the science and technology of postharvest biocontrol and in integrating biocontrol agents into combined preand postharvest production and handling systems. For example, combining chemical and