Incidence of the atoxigenic Aspergillus flavus strain AF36 in pistachio and fig orchards in California

Aflatoxin, produced by the fungi Aspergillus flavus and A. parasiticus, can contaminate many crops including almonds, figs, pistachios, and walnuts in California. Certain strains of A. flavus are unable to produce aflatoxins. One such atoxigenic strain, AF36, has been used successfully as a biocontrol agent to substantially reduce aflatoxin contamination in commercial cotton fields in Arizona and Texas. The objective of the current study was to determine the natural occurrence of AF36 and other atoxigenic strains in commercial orchards in California using vegetative compatibility analyses. Out of 431 A. flavus isolates from commercial pistachio orchards, 6.3%, 2.1%, and 1.6% belonged to atoxigenic strains AF36, A564, and A815, respectively. In addition, out of 97 isolates from fig orchards, 6.2%, 1.0%, and 1.0% belonged to strains AF36, A564, and A815, respectively. So far. AF36 has been detected in commercial pistachio orchards in five counties, which contain approximately 89% of the bearing acreage in California. In conclusion, the atoxigenic strain AF36 occurs naturally in pistachio and fig commercial orchards in California and is widespread throughout the major pistachio growing areas.