Competition of Different Aspergillus flavus VCGs in the Culture Medium and Soil

The most effective aflatoxin prevention strategy is limiting populations of toxigenic Aspergillus flavus strains using non-toxigenic strains, as a biological method.

Ten different vegetative compatibility groups (VCGs) of A. flavus strains (5 toxigenic and 5 non-toxigenic) isolated from the fruit and soil of pistachio orchards were used for the purpose of this study. Next, an equal population of spores of each isolate was mixed together and cultured on a coconut agar medium (CAM) and incubated in the dark at 30 °C for 3 days. On the other side, 20 gr of a mixture containing soil, peat, and pistachio powder was inoculated with the same spore mixture in the flask for 10 days. In addition, 10 colonies were selected randomly from each treatment and cultured on the coconut agar medium for three days. Besides, ammonium hydroxide vapor was used as an aflatoxin marker.

Simultaneous inoculation of the isolates in the culture medium showed 4 different types of color spectra after contacting ammonia vapor. Non-toxigenic and toxigenic isolates were predominant in 60 and 20% of the colonies, respectively. Besides, there was an intermediate situation in the remaining 20% of the culture media. The results showed that toxigenic and non-toxigenic populations were equal in 36% of the treatments. In addition, toxigenic and non-toxigenic isolates were dominant in 40 and 24% of the treatments, respectively. Non-toxigenic isolates with a high prevalence seemed to be qualified volunteers for supplementary biocontrol assays.

Non-toxigenic isolates with a high prevalence seemed to be qualified candidates for supplementary biocontrol assays.