Exploring the Characteristics of Atoxigenic Aspergillus flavus Isolates and Their Biocontrol Impact on Soil Fungal Communities

<i>Aspergillus flavus</i> can produce aflatoxins, posing a threat of contamination to peanuts. To mitigate this issue, the use of biocontrol isolates, which do not produce aflatoxins (AF^-), has been considered to reduce aflatoxin levels. In this study, we evaluated five different AF^- isolates belonging to different vegetative compatibility groups, all of which exhibited varying degrees of deletion in aflatoxin biosynthesis gene clusters. One isolate that exhibited poor competitive ability against toxigenic <i>A. flavus</i> was eliminated, and the remaining four isolates were formulated as biocontrol agents and applied to a peanut field in Tai'an, Shandong, as a combination. Three months after application, the soil aflatoxin content was reduced from 0.62 ± 0.01 to 0.19 ± 0.03 μg/kg (inhibition rate: 69.35%). Among filamentous fungi in the soil, the proportion of AF^- isolates increased from 0% to 4.33%. Using SSR-specific primers, the microbial agents were recovered. We discovered that among the four AF^- isolates, CA04 had a lower colonization rate compared to the other three (only 12.00% of the total AF^- population), suggesting that the absence of sclerotia may result in poor reversibility and weaker dispersal ability. We utilized Illumina sequencing to investigate the changes in soil fungal ecology. The results showed a reduction in the population density of harmful fungi, such as <i>Fusarium</i> spp. (66.18%) and <i>Plectosphaerella</i> spp. (79.90%), but an increase in the density of <i>Nothopassalora personata</i>. This is the first study on the dispersal distance and soil fungal community structure following the application of AF^- agents in peanut fields in China.