Abstract
The inhibitory action of 20 antagonistic Trichoderma isolates against the aflatoxigenic isolate A. 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 colonies and by fungal interactions in dual confrontation tests. A total of 8 out of 20 isolates resulted in a significant growth inhibition of 3-day-old cultures of Af-9, ranging from 13% to 65%. A total of 14 isolates reduced significantly the aflatoxin B1 (AfB1) content of 15-day-old Af-9 cultures; 4 were ineffective, and 2 increased AfB1. Reduction of AfB1 content was up to 84.9% and 71.1% in 7- and 15-day-old cultures, respectively. Since the inhibition of Af-9 growth by metabolites of Trichoderma was not necessarily associated with inhibition of AfB1 production and vice versa, we investigated the 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 mycotoxin content but not Af-9 growth. The expression analyses for the two regulatory genes aflR and aflS, and the structural genes aflA, aflD, aflO and aflQ of the aflatoxin biosynthesis cluster indicated that neither strain was able to downregulate the aflatoxin synthesis, leading to the conclusion that the AfB1 content reduction by these Trichoderma strains was based on other mechanisms, such as enzyme degradation or complexation. Although further studies are envisaged to identify the metabolites involved in the biocontrol of A. flavus and prevention of aflatoxin accumulation, as well as for assessment of the efficacy under controlled and field conditions, Trichoderma spp. qualify as promising agents and possible alternative options to other biocontrol agents already in use.
Highlights
Aflatoxins are a group of potent mycotoxins produced by moulds of the genus Aspergillus in the course of spoilage of agricultural products, stored commodities, feeds and foods
In this study we examined the inhibitory action of 20 antagonistic Trichoderma isolates against an aflatoxigenic strain of A. flavus and their effect on aflatoxin production, with an emphasis on the effect of Trichoderma metabolites and their involvement in the mode of action
In the present research work, we have investigated the potential of 20 Trichoderma isolates belonging to different species for biological control of A. flavus and aflatoxins, with a focus on the effect of metabolites on A. flavus growth, aflatoxin B1 (AfB1) production and expression of genes of aflatoxin biosynthesis
Summary
Aflatoxins are a group of potent mycotoxins produced by moulds of the genus Aspergillus in the course of spoilage of agricultural products, stored commodities, feeds and foods. Among the different forms of aflatoxins, aflatoxins B1 , B2 , G1 and G2 are especially important [1], since they exhibit carcinogenic, mutagenic and hepatotoxic effects [2]. The most potent form is aflatoxin B1 (AfB1 ), which is classified as carcinogenic to humans (group I) by the International Agency for Research on Cancer [3,4]. S strains show less variation in aflatoxin production, are generally higher aflatoxin producers than L strains and can produce aflatoxins G1 and G2 in addition to aflatoxins B1 and B2 [8]. Another important aflatoxigenic species is A. parasiticus, which is able to produce all four of the above aflatoxins. Aspergillus flavus occurs more widely on cereals, oilseeds and dried fruits, including economically important crops, such as peanuts and corn [9–11], while
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