2002-2004 Specialty Crops Research Program
University of California

Principal Investigators: Carlos Crisostos

Project title: Evaluation of food additives and low-toxicity compounds as alternative chemicals to synthetic fungicides for the control of the main postharvest diseases of California stone fruits.

Stone fruits (peach, nectarine, plum) are major crops in California. Economic losses caused by postharvest diseases are among the most important concerns of the growers. Postharvest fruit decay has typically been controlled by application of synthetic fungicides. However, important problems associated with the massive use of these chemicals, such as the proliferation of resistant strains of the pathogens and concerns about public health and environmental contamination, have increased the need for alternatives, especially in the context of Integrated Pest Management (IPM) practices in California. Furthermore, since the cancellation by the EPA in 1996 of all postharvest uses of iprodione (Rovral 50WP) because of carcinogenic risk associated with high exposure, there is a lack of reliable means to control postharvest decay of stone fruit crops in California.

We propose the evaluation of a wide range of food additives and low-toxicity chemicals as potential alternatives to synthetic fungicides for the control of the most important postharvest pathogens of stone fruits. These compounds leave low or non-detectable residues on the fruit and are allowed for many industrial and agricultural applications by federal and state regulations. Many of them are affirmed as Generally Recognized As Safe (GRAS) by the EPA, or are included in the National List of substances allowed as ingredients in products labeled as organic.

We propose a project with three objectives that involves a sequential screening process. The goal is to set the basis for the commercial implementation of reliable and cost-effective alternative treatment(s) for the control of target postharvest diseases of stone fruit crops in California. In the first year, a first selection of the most effective alternative chemicals will be performed for each host/pathogen pair through in vivo primary screenings (Objective 1). Fruit will be wound inoculated with the pathogen, and a droplet of the sterile chemical solution at the desired concentration will be applied at the same pathogen inoculation site. In the second year, compounds selected under Objective 1 will be assayed in small-scale trials. Short-length dips in aqueous solutions will be performed with artificially inoculated fruit to determine the most effective solution temperature, chemical concentration, and immersion period (Objective 2). Postharvest treatments selected under Objective 2 will be tested during cold storage of the treated fruit (Objective 3). With the economic need to control postharvest fruit decay and the clear urgency to develop safe and reliable alternative methods to synthetic fungicides, we believe that this project can provide considerable long-term benefits to California producers of specialty fruit crops.