2010 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.
Many of the research activities are carried out in Agricultural Research Service (ARS) laboratories in Tucson, Arizona. Previous observations of commercial fields applied with the AF36 biocontrol product in Arizona indicate that application of this atoxigenic strain of Aspergillus (A.) flavus which does not produce the potent carcinogen, aflatoxin, to fields can benefit subsequent crops in treated fields and that applications 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 once winter crops were planted. Effects of practices on the proportion of the A. flavus community composed of AF36 are not clear. Initial results suggest that A. flavus communities are significantly affected by spring 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 biocontrols. A component of understanding long-term influences of applications includes completion of a joint effort with Arizona Cotton Research & Protection Council. Soil samples throughout several areas where there has been a history of AF36 use were collected during 2009. Incidence of AF36 is being analyzed to establish the extent of area wide and long-term influences of the AF36 applications in cotton in regions where AF36 continues to be used and in regions where use has been discontinued (i.e., the Mohave Valley). Data is being analyzed to describe both temporal and spatial influences on long-term efficacy. Geostatistics and geographic information systems (GIS) will be employed and emphasis will be on providing a quantitative basis for treatment decisions by the Arizona cotton industry. Data to date suggest that long term influences of the biocontrol applications are dependent upon field, region, and cropping system. 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. Research progress was monitored through weekly meetings with investigators, presentations at professional meetings, and trips to research fields.