Project Number: 2030-42000-039-000-D
Project Type: In-House Appropriated
Start Date: Feb 6, 2016
End Date: Jan 18, 2021
The long-term objective of this project is to reduce, inhibit, or eliminate toxigenic and pathogenic microbes (i.e., mycotoxigenic fungi or pathogenic bacteria) by utilizing intervention techniques such as biological control. Specifically, during the next five years we will focus on the following interrelated objectives. Objective 1: Develop and implement control measures to reduce, eliminate, or detect contamination of toxin producing fungi of tree nuts, for example the use of host plant- or fungal-derived semiochemicals to attract or control insect pests, or use of sterile insect techniques to decrease insect pest populations. • Sub-objective 1A: Use of host plant- or microbe-derived volatile semiochemicals to attract or control insect pests. • Sub-objective 1B: Use of sterile insect techniques to decrease insect pest populations. Objective 2: Elucidate principles of microbial ecology and develop biological control measures to inhibit pathogenic and toxigenic microorganisms, particularly fungi, and can include research on the isolation and development of new biocontrol agents and formulations to control or prevent toxigenic microbes, or survey, identify, and determine ecology of microbial populations for control strategies such as competitive microorganisms. • Sub-objective 2A: Isolate biocontrol agents that prevent pathogenic/toxigenic microbes from colonizing crops. • Sub-objective 2B: Risk analysis of waste used as fertilizers for pathogen/toxigen contamination. • Sub-objective 2C: Develop new biocontrol agents and formulations to control toxigenic fungi, and to survey and characterize populations of Aspergilli. • Sub-objective 2D: Determine ecology of black-spored toxigenic Aspergilli and develop control strategies using competitive microorganisms. Objective 3: Discover natural chemical compounds that enhance the efficacy of established microbe intervention strategies, for instance augment the activity of antimicrobial agents/treatments against pathogens via target-based application of natural chemosensitizing agents.
1A. Tree nuts emit chemicals that attract insect pests that can be used as bait for insect traps. We will analyze volatiles from nuts by GC-MS and test them for pest attraction in electrophysiological and behavioral bioassays. If we are unable to identify volatiles from nuts we will explore volatiles from other biotic and abiotic matrices. 1B. Sterile insect technique can be applied to navel orange worms (NOW) inside discarded nuts on the orchard floor using an X-ray device towed behind a tractor. We will determine the X-ray dose required for sterilization of NOW and adjust this dosage to sterilize NOW inside tree nuts and develop a tractor towed device for field sterilization. If X-ray exposure does not produce sterile NOW other forms of radiation will be used. 2A. Bacteria with agonistic properties to pathogens are present on almond drupes and if applied in large numbers would prevent pathogen contamination. We will isolate bacteria from almonds and test their ability to inhibit pathogen growth in vitro. The bacteria that inhibit pathogen growth in vitro will be examined for the ability to inhibit growth on almonds, then in field trials. If we are not able to identify bacteria that inhibit pathogen growth on almonds we will use other crops. 2B. Applying composted manure to orchards does not represent a food safety threat. We will examine the microbial community structure of soil and fruit before and after the application of manure. We will repeat the analysis for 3 years to determine the effects of manure application. 2C. Atoxigenic Aspergillus flavus strains with deletions in the aflatoxin and CPA genes can be used as biological control agents for toxigenic A. flavus. We will identify atoxigenic A. flavus isolates by PCR and confirm by chemical analysis. We will examine their use as biocontrol agents via growth inhibition assays. Atoxigenic strains that displace the toxigenic strains will be impregnated into biochar and analyzed for as biocontrol agents in green house experiments. If the biochar is not suitable we will examine other matricies such as plastic granula. 2D. Ratios of toxigenic to non-toxigenic Aspergillus sp. fluctuate during the growing season; application of competitive fungal or bacterial strains will reduce mycotoxins in grapes/raisins. Grape/raisin samples will be taken at regular intervals in the growing season and analyzed to determine the ideal time to apply biocontrol agents against toxigenic Aspergillus. At these time points we will isolate bacteria and nontoxigenic Aspergillus sp. from raisin and soil samples and assay their ability to inhibit the growth of Aspergillus sp. If no non-toxigenic strains are not found other sources will be investigated. 3. Natural compounds and derivatives can control the growth of fungal pathogens and the production of toxins. Natural compounds will be tested for the disruption of cell wall integrity and the antioxidant pathway in fungi via genetic and physiologic analysis. We will determine the mode of action of these compounds via microarrays and other genetic tests. If we are unable to identify these compounds we will analyze other chemicals such as benzo derivatives