2007 Annual Report 1a.Objectives (from AD-416) Reduce contamination of pistachios by aflatoxin through control of A. flavus. The control of A. flavus will be attempted through dispersal of an atoxigenic strain, AF36, as a biocompetitor to displace toxigenic strains indigenous to pistachio orchards. 1b.Approach (from AD-416) Apply AF36 to pistachio orchards using infected wheat kernels. Determine survivability of strain over the summer season in an orchard, irrigated by flooding, following an application of the strain the previous season. Apply AF36 to an orchard irrigated using microsprinklers. Identify isolates of A. flavus collected from treated orchards. Documents SCA with UC Davis. Formerly 5325-42000-031-08S (09/04); 5325-42000-032-09S (3/06). 3.Progress Report This report serves to document research conducted under a specific cooperative agreement between ARS and the Kearney Agricultural Center, University of California. Additional details of research can be found in the report for the parent project 5325-42000-035-00D, Molecular and Genetic Approaches to Suppressing Fungal Pathogens and Mycotoxin Contamination. Aflatoxin Control in Pistachios - The goal of this research was to reduce aflatoxin contamination of pistachio nuts grown in California using biocontrol. The biocontrol agent, AF36 (a strain of Aspergillus flavus that cannot produce aflatoxins and is being used currently in commercial cotton fields to reduce aflatoxin contamination), was applied in a research pistachio orchard. The strain AF36 became the dominant A. flavus strain in areas where a single application of this strain had been made to the orchard floor, suggesting that it would be effective at displacing aflatoxin-producing strains in pistachio orchards. Even though the A. flavus strain AF36 had been applied in this orchard, the incidence of decay of the pistachio nuts by A. flavus did not increase. In addition, the strain AF36 survived at high levels in another research pistachio orchard even though it had been more than two years since an application of the strain AF36 had been made. Furthermore, the strain AF36 was determined to occur naturally in commercial pistachio orchards throughout the major pistachio growing regions in California. These results suggest that the use of the biocontrol agent AF36 in commercial pistachio orchards in California should be an effective way to reduce aflatoxin contamination of pistachio nuts. The ADODR monitored the activity of this subordinate project by meeting with the scientists involved at two meetings specified for presentation of the work performed. One meeting was held in October 2006 to go over the results of the prior research period. Another meeting was held in January 2007 to go over the research planned for the upcoming year. The ADODR also communicated with the scientists via email during interim periods.