Location: Biological Control of Pests Research
2018 Annual Report
Objectives
The overall objective of this project is the improved biological control of aflatoxin in corn through a more complete ecological understanding of the pathogen and the agroecosystem through applied investigation of biocontrol agent delivery systems.
Over the next 5 years, our research will focus on the following objectives:
Objective 1: Enhance shelf life, survival growth, germination, and host colonization of biocontrol agents for aflatoxin management through formulation improvements.
Objective 2: Refine aerial, foliar and seed treatment application strategies of biocontrol agents for aflatoxin management.
Objective 3: Develop and implement molecular markers for post-release tracking of foliar and seed treatment biocontrol applications.
Objective 4: Determine population size, chemotype and mating type frequency in soil-borne Aspergillus (A.) flavus populations and subsequent infections in corn to improve predictions of aflatoxin risk and enhance biocontrol measures.
Sub-Objective 4a.Correlation of aflatoxin contamination of corn with the population distribution of A. flavus in soil.
Sub-Objective 4b. Correlating A. flavus mating type with corn infection.
Objective 5: Apply novel formulation and application technology to other pathogen biocontrol systems.
Approach
Biological control technology is an effective method for reducing aflatoxin contamination in corn; however, present formulation and application strategies are still rudimentary and fundamental gaps remain in our knowledge of the population structure of Aspergillus (A.) flavus. Improved application technology will be developed aimed at increasing adoption of biocontrol measures by increasing efficacy and convenience of the application systems. Although previous efforts using a water dispersible formulation did not meet industry standards, they provided avenues for further research using bioplastic as a vector for application of biocontrol agents. Corn starch-based bioplastics are naturally-derived, biodegradable, recyclable, inexpensive, and provide nutrition favoring fungal growth after application. Bioplastics are easily prepared by heating commercial bioplastic for 2-3 hours at 80-90°C and applying (i.e., aerial, foliar, and seed treatment) after cooling. Bioplastic vectors promise to provide effective, efficient delivery of biocontrol agents. We also plan to develop and implement molecular markers for post-release monitoring of biological control agents. The resulting data will enable optimizing delivery tools to meet industry standards. Knowledge of local A. flavus population size, chemotype and mating type frequency will also lead to a better understanding of aflatoxin risk and permit more sound decisions of when fields warrant application of commercial biocontrol products. Domestic and international industrial companies have already inquired and invested in the development of this technology for control of various agricultural pests beyond just A. flavus. Optimization of these techniques during the next five years will improve the efficiency and practicality of biocontrol agents used in agriculture.
Progress Report
This project began in March 2017. A copious amount of non-toxigenic strains of Aspergillus (A.) flavus (strains K49 and Afla-Guard) spores were produced. Laboratory evaluations of spores, including viability, germination, concentration, and quality control, were conducted to determine efficacy of the spores. Experiments for conventional corn seed treatments and sprayable formulation of non-toxigenic A. flavus formulated in starch-based material (bioplastic) were conducted in the field and greenhouse. A collection of several thousand geo-referenced isolates of A. flavus has been made and is undergoing phenotypic and genotypic characterization. This collection, covering the Mississippi Delta, includes aflatoxigenic and non-aflatoxigenic isolates from soil and from grain. The complete genome has been sequenced and published for three biocontrol strains to facilitate comparisons with the field isolates. These experiments are proceeding in spite of limited availability of field equipment, personnel, and support needed to accomplish the goals of this objective.
Accomplishments
1. Reductions of aflatoxin in the field. Field evaluations used Aspergillus (A.) flavus (Strains K49 and AG) to determine the efficacy under field conditions to control aflatoxin in pre-harvest corn. Planting the fully-protected seed resulted in an average of 82.5% reduction in aflatoxin levels. The application of the biocontrol agents have been utilized to optimize the application method using seed treatment techniques of a corn-starch based formulation, called “bioplastic.” Results from the present study by ARS scientists at Stoneville, Mississippi, confirm the significance of this novel technical approach for reducing the risk of aflatoxin contamination in corn by using a reduced dose of inoculum (spores) of biocontrol isolates. The impact of this study further strengthens the efficacy of biological aflatoxin using the novel technical approach and will help reduce the preparation costs for biological control pathogens for use by the public and private sector research units including ARS, academia, and industrial grain producers.
2. Toxin role in pathogenicity of soybean charcoal rot disease. Charcoal rot disease is one of the major diseases of soybean that results in the dramatic yield loss and economical value. Research has been conducted by ARS scientists at Stoneville, Mississippi, to understand the infection mechanisms by the charcoal rot disease mold Macrophomina phaseolina. Research results establish that the toxin botryodiplodin and other mycotoxins play a role in the root infection mechanism or process. These results could help uncover more information on the mechanism which lead to breeders discovering variants that do not signal the toxin release needing for the infection mechanism and develop management strategies of the disease by selecting for soybean variety resistance against the toxin. The results from this study will provide useful information to the public and private sector research units including ARS, academia, and industrial grain producers.
Review Publications
Accinelli, C., Abbas, H.K., Little, N., Kotowicz, J.K., Shier, W.T. 2018. Biological control of aflatoxin production in corn using non-aflatoxigenic Aspergillus flavus administered as a bioplastic-based seed coating. Crop Protection Journal. 107:87-92. https://doi:10.1016/j.cropro.2018.02.004.
Weaver, M.A., Scheffler, B.E., Duke, M.V., Ballard, L.L., Abbas, H.K., Grodowitz, M.J. 2017. Genome sequences of three strains of Aspergillus flavus for the biological control of Aflatoxin. American Society for Microbiology, Genome Announcements. 5(44):e01204-e01217x. https://doi:10.1128/genomeA.01204-17.
Accinelli, C., Abbas, H.K., Shier, W. 2018. A bioplastic-based seed coating improves seedling growth and reduces production of coated seed dust. Journal of Crop Improvement. Seed Science Research. Pages 1-13. https://doi:10.1080/15427528.2018.1425792.
Abbas, H.K., Accinelli, C., Shier, W. 2017. Biological control of aflatoxin contamination in U.S. crops and the use of bioplastic formulations of Aspergillus flavus biocontrol strains to optimize application strategies. Journal of Agricultural and Food Chemistry. 65(33):7081-7087. https://doi:10.1021/acs.jafc.7b01452.
