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 was performed in laboratories at the University of Arizona in Tucson and in commercial agricultural fields. Field soils were sampled in the Rio Grande Valley (RGV) of Texas to investigate crop rotation effects on the soil community of aflatoxin-producing fungi. The work was performed by a student pursuing a Ph.D. in plant pathology. Soils were selected from sugarcane fields which have increased frequency of isolation of Aspergillus (A.) parasiticus isolates when compared to maize field soils which favor A. flavus. Maize and sugarcane are common rotation crops in RGV. The community of aflatoxin-producing fungi present in the environment where a susceptible crop is grown correlates to the aflatoxin-contamination risk for that crop. In the lab, soils were planted to maize, cotton, sorghum and sugarcane using plant pieces and seedlings, and the soil fungal community was monitored biweekly over two months by dilution plating. Maize and cotton treatments affected a change in the soil community to become one dominated by A. flavus with colony forming units (CFU) orders of magnitude greater than those of A. parasiticus. Soils planted with sugarcane seed, sugarcane nodes and sorghum maintained communities that were statistically similar to the control soil, with A. parasiticus CFU dominant in the Aspergillus section Flavi community. Maize seedlings were found to carry tens of thousands of A. flavus propagules. Dead, sterile maize roots were capable of causing a shift in the aflatoxin-producing fungal community in the soil similar to that observed when maize seedlings were planted to sugarcane soil without sterilization. The results of these experiments suggest communities of aflatoxin-producing fungi are altered by plant tissues that ramify the soil and select for more competitive host adapted members of the Aspergillus section Flavi community. Progress was monitored with bi-weekly meetings with the graduate student performing the work and through collaborative interpretation of the data.