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United States Department of Agriculture

Agricultural Research Service


Location: Foodborne Toxin Detection and Prevention

2010 Annual Report

1a.Objectives (from AD-416)
The overall objective of this project is to apply the Pichia anomala yeast product to pistachio orchards early in the season prior to June 15 to be followed by 'atox' technology. Measure the reduction of recoverable Aspergillus flavus spores in treated plots or use some other appropriate measure of reduced colonization of natural substrates. Will develop commercially viable methods for control of fungal and insect pests which contribute to pre-harvest aflatoxin contamination of tree nuts. The methods are to be environmentally benign and not harmful to humans. To control fungi, there are two main objectives. The first objective for this project is to control mycotoxin-producing fungi using bacteria. The second biocontrol effort is well underway and involves the biological control of A. flavus in tree nut orchards using the saprophytic yeast Pichia anomala. The yeast will also be examined to determine its effectiveness against other fungal pathogens, e.g., Fusarium spp., Penicillium spp. The third objective of this project is also an ongoing research effort. This objective entails development of semiochemical-based low-risk control strategies against key insect pests of tree nuts. Insect feeding damage is associated with the invasion of microbial pathogens and mycotoxin contamination.

1b.Approach (from AD-416)
Develop methods to control insect pests and toxic fungi of tree nuts. Insects include naval orangeworm, codling moth and peach twig borer. Feeding damage by these insects leads to infection by aflatoxigenic aspergilli. Control methods for insects are to be environmentally benign and employ semiochemicals to disrupt insect behavior. Control of toxic fungi focuses on biological control using competitive or antagonistic microorganisms. These microorganisms include either yeasts or bacteria that can be mass-produced and effectively utilized in a variety of pre- or post harvest environments. Replacing 5325-42000-031-00D (2/06).

3.Progress Report
PMR scientists have made significant progress in developing methods that involve insect and microorganism control with regard to the aflatoxin contamination problem. MU scientists identified a number of host-plant volatiles (HPVs) that, as a blend, were as active at attracting navel orangeworm (NOW) females as the current commercially used almond press cake. Moreover, these volatiles also attracted male NOW equivalent to and better than current NOW pheromone bait traps. PMR scientists have made substantial progress in this area by developing a new method for collecting VOCs in situ and using electro-antennagram (EAG) and wind tunnel bioassays to determine which VOCs have bioactivity. This work is being done under a CRADA with a major tree nut stakeholder, Paramount Farms, in California. These VOCs that attractd NOW are now being tested in field studies by our collaborator.

The second approach by the scientists in the project for controlling aflatoxin contamination is use of competitive micro-organisms against the fungus that makes aflatoxin. In this regard, there are two approaches. PMR scientists have discovered a strain of yeast, Pichia anomala, that is a viable biocontrol microorganism against the fungi that make aflatoxin. This yeast shows a great deal of viability in tree nut orchards, has no human pathogenicity, is not phytotoxic, and thus can be sprayed directly onto the tree nut canopy. PMR scientists have optimized the culture medium for the yeast and are able to produce large quantities. The research is being done in collaboration with scientists in the Dept. of Pomology, Univ. of California, Davis. A second biocontrol effort identified a number of natural soil bacteria in tree nut orchards and vineyards that show promise as biological control agents against fungi in soil.

1. Host-plant-volatiles (HPVs) affect navel orangeworm (NOW) behaviors. NOW is the major insect pest of the California tree nut industry requiring a great deal of pesticidal control. Improved and more efficient means of control are needed. One approach would be to develop lures and monitoring methods based on host volatiles that are attractive to these insects. Researchers at the Plant Mycotoxin Research Unit in Albany, California developed new instrumentation for collection of volatile compounds from almond and pistachio orchards. Nearly 200 compounds were identified as candidate attractants of NOW based on laboratory and field methods, with some blends being more active as attractants than current, commercially available lures. Discovery of any effective natural lures for the control of NOW would have a major impact on California agriculture in that this insect destroys millions of dollars of tree nuts annually.

2. Culture medium for mass production of a biocontrol agent of aflatoxin producing fungi. Aflatoxin is a natural cacinogen made by fungi and its contamination of tree nuts is a major economic and food safety issue. Pre-harvest control aflatoxin-producing fungi would greatly assist the industry. Biocontrol using competing microorganism is an economic and safe approach to controlling aflatoxin-producing fungi. Researchers at the Plant Mycotoxin Research Unit in Albany, California have found a method for maintaining the viability of a promising biocontrol agent, Pichia anomala, by developing a routine procedure for analyzing yeast cell viability. This led to development of a stable liquid formulation of P. anomala for application in field plots for the control of aflatoxin-producing fungi.

3. Attracticide developed against codling moth (CM), a major pest of pome fruits and tree nuts. CM is a major insect pest of pome fruits (apples, pears, etc.) and tree nuts and improved control measures that reduce pesticide usage are greatly needed. Researchers at the Plant Mycotoxin Research Unit in Albany, California discovered a novel attract and kill (AK) control tactic against CM larvae using a volatile from pears. This volatile was encapsulated in small beads and co-applied in sprays that included various insecticides. This combination enhanced the effectiveness of insecticidal usage against CM allowing for lower, less costly, and more environmentally safe rates of insecticides to be used for CM control.

Review Publications
Dragull, K.D., Beck, J.J., Merrill, G.B. 2010. Essential oil yield and composition of Pistacia vera "Kerman" fruits, peduncles, and leaves grown in California. Journal of the Science of Food and Agriculture. 90(4):664-668.

Beck, J.J. 2010. Letter to the Editor: Styrene-producing microbes in food-stuff. Journal of Food Science. 75(1):X.

Last Modified: 4/18/2014
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