Submitted to: Aflatoxin Workshop
Publication Type: Abstract Only
Publication Acceptance Date: 11/25/2005
Publication Date: 3/6/2006
Citation: Horn, B.W. 2006. Effect of fungal competition on the colonization of wounded peanut seeds by aspergillus section flavi from natural soil populations. Aflatoxin Workshop. Interpretive Summary: none required.
Technical Abstract: The effect of fungal competition on the colonization of wounded peanut seeds by Aspergillus section Flavi species in soil was examined. Viable peanut seeds were wounded and inoculated with cultivated soils differing in composition and density of Aspergillus species, then incubated for 14 d at different temperatures and seed water activities. Maximum percentages of seed colonization by section Flavi species occurred at 22-37 ºC and a seed water activity of 0.92-0.96. Under these conditions, competitive saprotrophic ability of section Flavi was high and approximately 50% of the peanut seeds with a propagule of A. flavus or A. parasiticus at the wound site became colonized. Wounds inoculated with soil were initially colonized by A. terreus (2-4 days), which was then quickly overgrown by section Flavi species and A. niger (> 4 days). Further successional changes in the peanut mycobiota were not observed except for the appearance of Eupenicillium ochrosalmoneum sporulating on the heads of section Flavi species. A significant interactive effect (P < 0.0001) was observed between soil densities of A. flavus and soil densities of other, potentially competing species within section Flavi (A. parasiticus, A. caelatus and A. tamarii). Colonization of seeds by A. flavus decreased as soil densities of competing section Flavi increased. Soil densities of section Flavi species and A. niger showed a similar interactive effect (P < 0.0001). Therefore, competition among Aspergilli is responsible for suppressing seed colonization by individual section Flavi species. Other species in the genera Aspergillus, Penicillium and Fusarium were capable of invading peanut seeds primarily when soils contained low densities of section Flavi species (< 50 CFU/g) or when combinations of temperature and seed water activity were suboptimal for section Flavi.