1a.Objectives (from AD-416):
Characterize adaptive differences among aflatoxin-producing fungi in their interactions with host plants and utilize on farm sampling to describe interactions between the life cycle of the causal agent and agronomic practices and in so doing define optimal windows for implementation of biological control and other interventions.
1b.Approach (from AD-416):
Genetic groups identified by ongoing ARS programs will be contrasted in field tests and controlled environment laboratory tests for variation in ability to colonize and decay host tissues using newly developed methods. Host samples from farmer fields in key target regions with severe contamination will be analyzed with novel microbiological assays. Coordination of sampling with farmers will test importance of various agronomic practices on the A. flavus life cycle.
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. Aflatoxin contamination of crops is the product of complex interactions of Aspergillus (A.) section Flavi species, and, within species, individuals belonging to different vegetative compatibility groups (VCGs). Members of species vary phenotypically, but members of the same VCG are phenotypically (outside appearance) uniform especially in epidemiologically significant traits, like toxin-producing and competitive ability. The most prevalent species implicated in the most severe aflatoxin contamination events are A. flavus and A. parasiticus. The composition of these communities and the aflatoxin producing abilities of their constituents affects the likelihood and severity of aflatoxin contamination for susceptible crops grown in production areas. Crop-associations have been shown to affect the composition of aflatoxin-producing communities in the Rio Grande Valley of South Texas, where A. parasiticus dominates the aflatoxin-producing community in sugarcane fields and has been detected in the rotation crops. A. parasiticus appears to be moved with sugarcane planting material around the globe. In order to address the potential human involvement in a group of aflatoxin-producing fungi, a global sampling of A. parasiticus was undertaken and isolates were characterized with phylogenetics and population genetics. Microsatellite polymorphisms (variations in specific deoxyribonucleic acid sequences) clustered to define populations that were globally distributed in association with crops and some that were geographically isolated. Phylogenetics (examining genetic relationships and evolution) showed that these populations are likely very old, and that several boundaries to gene flow are leading to divergence within A. parasiticus including crop associations. This work is expected to give insights into how cropping systems select specific aflatoxin-producing fungi and in so doing alter both the structure and the average aflatoxin producing potential of fungal populations. Such information should serve the design of improved aflatoxin management strategies.