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United States Department of Agriculture

Agricultural Research Service

Research Project: FACTORS INFLUENCING COMPETITIVENESS OF THE ATOXIGENIC STRAIN A. FLAVUS AF36 WITH THE HIGHLY TOXIGENIC S STRAIN IN COTTON CROPPING SYSTEMS
2011 Annual Report


1a.Objectives (from AD-416)
Extend development of atoxigenic strain technology and characterization of the epidemiology of cottonseed contamination. Improve atoxigenic strain formulations and recommendations for on-farm use of atoxigenic strains. Identify factors influencing over-wintering of atoxigenic strains and agronomic practices that optimize atoxigenic strain performance including sporulation, dispersal, crop colonization, and over-wintering. Increase understanding of the biology and epidemiology of the highly toxigenic S strain.


1b.Approach (from AD-416)
Models will be developed that predict aflatoxin contamination of cotton and S strain incidence in agricultural fields from environmental and agronomic parameters. To identify factors favoring S strain development in commercial fields, communities will be monitored in several regions with varying initial incidences of the S strain. Factors identified as favoring the S strain will be tested in vitro. Incidence, distribution, and behavior of S strain sclerotia will be evaluated in commercial fields to assess roles and S strain life cycles. Dynamics of fungal community compositions as related to atoxigenic strains and the S strain will be monitored during diverse crop rotations in Arizona, including production of winter and spring produce prior to cotton or corn. Sorghum grain will be incorporated into advanced formulations and evaluated in commercial fields as a potential less expensive, more efficacious alternative to wheat.


3.Progress Report

The research activities of the present project are carried out mostly in Agricultural Research Service (ARS) laboratories at the University of Arizona in Tucson and in commercial agricultural fields. The application of atoxigenic strains of Aspergillus (A.) flavus (which does not produce the potent carcinogen, aflatoxin) has been successful in commercial cotton fields in Arizona. Previous observations of commercial applications of the AF36 biocontrol product in Arizona indicate that application of fields can benefit subsequent crops in treated fields and that applications might have beneficial influences for several years. Factors that influence atoxigenic strain persistence are not well documented. Quantities of A. flavus in fields treated with the AF36 biocontrol were highest immediately after harvest, declining significantly once winter crops were planted. Time lapsed since application of the biocontrol significantly affected the population structure of A. flavus in applied fields. The percentage of the applied AF36 biocontrol decreased significantly after 15 month, while the percentage of the highly toxigenic S strain significantly increased in the same period. Analysis of fungal communities in soils of treated fields suggest, agronomic practices influence both the quantity and quality of A. flavus resident in fields and that practices might be optimized to maximize long-term displacement of aflatoxin producers by atoxigenic biocontrols. Geostatistics and geographic information systems (GIS) are being employed to provide quantitative basis for treatment decisions by the Arizona cotton industry. Data suggest that long term influences of the biocontrol applications are dependent upon field, region, and cropping system. The percentage of the applied biocontrol in the soil of treated fields after one year from application is not significantly different from the percentage occurring in the crop; however, it decreased significantly after two years. The goal of understanding agronomic influences on fungal community composition and retention of atoxigenic strains will be incorporated into future projects with the goal of developing general rules for predicting how strains will behave in cropping systems and cropping recommendations for encouraging fungal communities with reduced aflatoxin-producing potential. Progress is monitored through weekly meetings, performing experiments together, through consultations during analysis of results, presentations at professional meetings and shared trips to research fields.


Last Modified: 10/23/2014
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