Potential of Trichoderma spp. for Biocontrol of Aflatoxin-Producing Aspergillus flavus

The inhibitory action of 20 antagonistic Trichoderma isolates against the aflatoxigenic isolateA. flavus ITEM 9 (Af-9) and their efficacy in reducing aflatoxin formation in vitro were examined.Production of metabolites with inhibitory effect by the Trichoderma isolates was also investigated.Antagonistic effect against Af-9 was assessed by inhibition of radial growth of the coloniesand by fungal interactions in dual confrontation tests. A total of 8 out of 20 isolates resulted in asignificant growth inhibition of 3-day-old cultures of Af-9, ranging from 13% to 65%. A total of 14isolates reduced significantly the aflatoxin B1 (AfB1) content of 15-day-old Af-9 cultures; 4 wereineffective, and 2 increased AfB1. Reduction of AfB1 content was up to 84.9% and 71.1% in 7- and15-day-old cultures, respectively. Since the inhibition of Af-9 growth by metabolites of Trichodermawas not necessarily associated with inhibition of AfB1 production and vice versa, we investigatedthe mechanism of reduction of AfB1 content at the molecular level by examining two strains: one(T60) that reduced both growth and mycotoxin content; and the other (T44) that reduced mycotoxincontent but not Af-9 growth. The expression analyses for the two regulatory genes aflR andaflS, and the structural genes aflA, aflD, aflO and aflQ of the aflatoxin biosynthesis cluster indicatedthat neither strain was able to downregulate the aflatoxin synthesis, leading to the conclusion thatthe AfB1 content reduction by these Trichoderma strains was based on other mechanisms, such asenzyme degradation or complexation. Although further studies are envisaged to identify the metabolitesinvolved in the biocontrol of A. flavus and prevention of aflatoxin accumulation, as well asfor assessment of the efficacy under controlled and field conditions, Trichoderma spp. qualify aspromising agents and possible alternative options to other biocontrol agents already in use.