2012 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.
Research activities for the current project are carried out in Agricultural Research Service (ARS) laboratories on the campus of the University of Arizona, Tucson, AZ, and on commercial agricultural fields. Application of the strain AF36 of Aspergillus (A.) flavus, which does not produce the potent carcinogen aflatoxin (atoxigenic), has been successful in commercial cotton fields in Arizona. Previous observations of commercial applications of the AF36 biocontrol product in Arizona indicate that application to fields can benefit subsequent crops in treated areas and that applications might have beneficial influences for several years. However, factors that influence this atoxigenic strain's persistence are not well documented. Determining influences of cropping practices and rotation on persistence of AF36 in desert production areas of Arizona is one of the objectives of the present project. Quantities of A. flavus in fields treated with the AF36 biocontrol were highest immediately after harvest, declining significantly after four months, once winter crops were planted. The biocontrol further declined thereafter and maintaining low levels until new applications were done. Time after the 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 months, while the percentage of the highly toxigenic S strain of the fungus significantly increased in the same period. The population structure of the fungus in applied fields is differentially affected in different areas. The biocontrol population decreased faster in the Yuma, AZ, area with levels below 35% after one year from application compared to levels over 55% in the Mohawk, AZ, area. These two areas differ in several characteristics including soil type and chemistry, and crop rotations. Effects of practices on the proportion of the A. flavus community composed of AF36 are not clear. Results suggest that A. flavus communities are significantly affected by winter and summer crops. 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 biocontrol agents. A component of understanding long-term influences of applications includes completion of a second joint effort between the University of Arizona, ARS, and the Arizona Cotton Research & Protection Council. Soil samples throughout several areas where there has been a history of AF36 use were collected during 2009, 2010 and 2011 to establish the extent of area wide and long-term influences of the AF36 applications in cotton. Data is being analyzed to describe both temporal and spatial influences on long-term efficacy. Geostatistics and geographic information systems (GIS) are being employed to provide quantitative basis for treatment decisions by the Arizona cotton industry. Data from 2011 confirm results from previous years suggesting that long-term influences of the biocontrol applications are dependent upon field, region, and cropping system. Percentage of the applied biocontrol in the soil of treated fields one year after application was not significantly different from the percentage occurring in the crop. However, this percentage decreased significantly after two years. This indicates that biocontrol applications might be beneficial to subsequent crops, but only to the next year’s crop, and applications are required at least every other year. 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.