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.
Lab tests were performed to evaluate variation among Aspergillus (A.) flavus strains (which can produce the potent carcinogen, aflatoxin) in ability to colonize intact maize kernels and to influence seed germination. Overall, number of seeds becoming infected by A. flavus increased with the time of incubation. Also, longer periods of incubation had higher effects on rate of germination. The work in this project is undertaken by a graduate student pursuing a Masters Degree in Plant Science. In growth chamber experiments, eight isolates of A. flavus were compared in order to assess variability in virulence to maize. Overall, the eight inoculated isolates reduced by 70 percent the rate of seed germination in comparison to controls (kernels inoculated with distilled water). In addition, all isolates were able to internally colonize healthy looking radical (root) tissues of emerging seedlings. Ability to colonize healthy radical tissue and to produce conidia during maize infection varied among the evaluated isolates. Field experiments were performed during the summer of 2009. Isolate ability to move from the crown through stalk tissue was assessed on two-month old plants. Three of the evaluated isolates were able to colonize new plant tissue above the soil line. These isolates were present in the maize stalk two months after inoculation. Isolates also varied in ability to colonize developing stalk tissue. Additional tests comparing isolates of A. flavus during interactions with maize are underway. Results to date suggest isolates of A. flavus vary widely in their interactions with maize. This variation may have significant influence on selection of resistant maize cultivars and on development of biological control strategies for the prevention of aflatoxin contamination of maize. Research progress was monitored through weekly meetings with investigators, presentations during lab meetings, and direct examination of experiments in progress.