**2. Opportunities and barriers for biopesticides on post-harvest potatoes**

Market success is most likely to occur if the biological control agent is developed to combat pest problems which have no chemical pesticide solution or which exist in situations where chemical applications are prohibited. For example, in the U.S., organic farming is the fastest growing sector of agriculture. Higher commodity prices for these products and regulations restricting the use of chemical pesticides improve the chances for successful commercialization of natural biological tools in these markets (Behle et al., 1999). Once effectiveness is established in this sector of production, the transition to other sectors could follow.

Currently, a major incentive favoring the development of biopesticides is the ease of federal registration in the United States. The Environmental Protection Agency (EPA) has established a Biopesticide Pollution and Prevention Division (BPPD) to manage accelerated registration of biopesticides. In the mid 1990's, the average duration for registration of a biopesticide was 12 months compared with 36 months for all new chemical pesticide registrations (Medugno et al., 1997), and the cost of registration of a chemical was often more than eight times that of a biological (Woodhead et al., 1990). However, despite regulatory incentives, relatively few biological control agents have reached the market place, often due to one or more of the following pitfalls: (a) poor choice of pathosystem for biological control; (b) relatively few candidate microorganisms available for testing; (c) microbes are selected based on the results of an assay that does not replicate field conditions; and (d) the amenability of microbes to commercial development is excluded as a selection criterion.

#### **3. Fusarium dry rot — An appropriate pathosystem for biological control**

Characteristics of a pest problem, or "pathosystem," suitable to a biological control approach include: exploitable weakness(es), existence in an environment favorable to

This article will focus on the control of post-harvest fungal pathogens, which present unique opportunities but also challenges. Though accurately determining the extent of losses is difficult and few reports are available, it has been estimated that post-harvest decay accounts for an approximate 25% loss of fresh commodities (USDA, 1965). Biological control using microbial antagonists can be an appropriate tool for managing post-harvest disease problems, especially in crops which are stored under controlled temperatures and high relative humidities. Such controlled storage environments represent a luxury not found when attempting to introduce microbial biological control agents into the comparatively harsh, variable environments found at the infection courts of fungal pathogens of field-grown plants. In recent years, a considerable research attention has focused on biologically controlling rots of fruits post harvest (Janisiewicz, 1988, 1991, 2002). In this chapter, research examples will be reviewed to illustrate the challenges and strategies of developing processes to manufacture and deliver biological agents for post-harvest potato disease control. Concepts to be covered will include the following: market opportunities, choosing pathosystems for biological control, enrichment techniques to enhance new strain discovery, strategies for ranking strains for commercial suitability, mode of action, production considerations, market-broadening functionality, co-cultivation of strains as the next generation biocontrol product, highthroughput screen concept for optimizing biocontrol agent performance from production to

delivery, remaining knowledge gaps, and future investigations.

in this sector of production, the transition to other sectors could follow.

commercial development is excluded as a selection criterion.

**2. Opportunities and barriers for biopesticides on post-harvest potatoes** 

Market success is most likely to occur if the biological control agent is developed to combat pest problems which have no chemical pesticide solution or which exist in situations where chemical applications are prohibited. For example, in the U.S., organic farming is the fastest growing sector of agriculture. Higher commodity prices for these products and regulations restricting the use of chemical pesticides improve the chances for successful commercialization of natural biological tools in these markets (Behle et al., 1999). Once effectiveness is established

Currently, a major incentive favoring the development of biopesticides is the ease of federal registration in the United States. The Environmental Protection Agency (EPA) has established a Biopesticide Pollution and Prevention Division (BPPD) to manage accelerated registration of biopesticides. In the mid 1990's, the average duration for registration of a biopesticide was 12 months compared with 36 months for all new chemical pesticide registrations (Medugno et al., 1997), and the cost of registration of a chemical was often more than eight times that of a biological (Woodhead et al., 1990). However, despite regulatory incentives, relatively few biological control agents have reached the market place, often due to one or more of the following pitfalls: (a) poor choice of pathosystem for biological control; (b) relatively few candidate microorganisms available for testing; (c) microbes are selected based on the results of an assay that does not replicate field conditions; and (d) the amenability of microbes to

**3. Fusarium dry rot — An appropriate pathosystem for biological control** 

Characteristics of a pest problem, or "pathosystem," suitable to a biological control approach include: exploitable weakness(es), existence in an environment favorable to introduced antagonists, availability of few or no control options, and causative of significant economic loss to agriculture. Our experience on discovery and development of biological control agents first began with the need to find an alternative to thiabendazole (TBZ) for the biological control of Fusarium dry rot, an important post-harvest disease of potatoes. Dry rot is caused primarily by *Gibberella pulicaris* (Fr.:Fr.) Sacc. (anamorph: *Fusarium sambucinum* Fuckel) (Boyd, 1972). The fungus is a serious pathogen in potato tuber storages and can produce trichothecene toxins (Desjardins & Plattner, 1989) implicated in mycotoxicosis of humans and animals. Yield losses attributed to dry rot in storage range from 6 to 25% with up to 60% of tubers affected in some cases (Secor & Salas, 2001). Measures for controlling this disease in storage are limited. Resistance to TBZ, the only chemical registered for postharvest use on tubers for human consumption, is now widespread among strains of *G. pulicaris* (Desjardins et al., 1993; Hanson et al., 1996; Kawchuk et al., 1994; Secor et al., 1994). High levels of resistance to Fusarium dry rot in potato cultivars and breeders' selections are not apparent (Pawlak et al., 1987) and all commonly grown potato cultivars are susceptible (Reiners & Petzoldt, 2004). Therefore, the potential for damage is high enough to justify the economic risk of developing a biological control agent for prevention of dry rot disease losses. A major weakness of the etiology of this pathogen is that it requires a wound in order to infect, and tubers are able to heal wounds in less than 2 weeks in storage. Additionally, the pathogen operates in an environment that is favorable to introduced antagonists in that tuber storage temperatures are uniform and relative humidities are high (>90%), a feature true for many post-harvest pathosystems.
