A 3-yr field study was conducted to determine the effect of biological control formulations of nontoxigenic strains of Aspergillus flavus and A. parasiticus, peanut cultivars, and fungicides on preharvest aflatoxin contamination of peanuts. Formulation treatments consisted of (a) no biocontrol treatment, (b) the fungi cultured on rice via solid-state fermentation, (c) conidia of the fungi coated onto the surface of rice, and (d) conidia coated onto the surface of wheat (year one) or hulled barley (years two and three). Experiments consisted of factorial combinations of the four formulation treatments, two peanut cultivars (Florunner or Georgia Green), and two fungicide treatments (chlorothalonil or combinations of chlorothalonil and tebuconazole). Florunner and Georgia Green peanuts were each planted in 32 individual plots consisting of six rows 15.2 m in length. Biological control formulations, consisting of a mixture of nontoxigenic strains of A. flavus (NRRL 21882) and A. parasiticus (NRRL 21369), were applied to the same plots in each of the 3 yr at a rate of 56 kg/ha. Foliar applications of fungicides were made as recommended for control of leaf spot, with one treatment being full-season applications of chlorothalonil, and the other being two applications of chlorothalonil followed by four applications of tebuconazole and remaining applications of chlorothalonil. Only in year two of the study was late-season drought sufficient to produce preharvest aflatoxin contamination. All biocontrol formulation treatments produced significant reductions in aflatoxin compared with untreated controls, averaging 81%. There was also a significant cultivar effect on aflatoxin with Georgia Green averaging 119 μg/kg compared with 402 μg/kg for Florunner. No differences were observed between the two fungicide treatments, and there was no interaction among the three factors. Analysis of soil for populations of A. flavus and A. parasiticus throughout the study showed that all formulations, except the conidia-coated wheat in the first year, were effective in delivering competitive levels of the nontoxigenic strains. In the third year, which did not result in significant aflatoxin contamination, analysis of peanuts for fungal colonization showed no significant differences among biocontrol treatments (including control) for total amounts of A. flavus and A. parasiticus in peanuts. However, the incidence of toxigenic isolates in peanuts was significantly reduced by all three biocontrol formulations.
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Keywords: Arachis hypogaea L., Groundnut, Aspergillus flavus, Aspergillus parasiticus, biocontrol, competitive exclusion.
How to Cite:
Dorner, J., (2004) “Combined Effects of Biological Control Formulations, Cultivars, and Fungicides on Preharvest Colonization and Aflatoxin Contamination of Peanuts by Aspergillus Species”, Peanut Science 31(2), p.79-86. doi: https://doi.org/10.3146/pnut.31.2.0004