Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract only
Publication Acceptance Date: 4/1/2002
Publication Date: 3/1/2003
Citation: Dorner, J.W. 2003. Combined effects of biological control formulations, cultivars, and fungicides on preharvest aflatoxin contamination of peanuts. American Peanut Research and Education Society Abstracts. Interpretive Summary: none required.
Technical Abstract: A three-year 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: (1) no biocontrol treatment; (2) the fungi cultured on rice via solid state fermentation; (3) conidia of the fungi coated onto the surface of rice; (4) and 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 [Bravo] or combinations of chlorothalonil and tebuconazole [Folicur]). 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 three years at a rate of 56 kg/ha (50 lb/acre). Foliar applications of fungicides were made as recommended for control of leafspot with one treatment being full season applications of chlorothalonil and the other being two applications of chlorothalonil followed by four applications of tebuconazole and a final application of chlorothalonil. Only in year two of the study was late-season drought sufficient to produce preharvest aflatoxin contamination. Aflatoxin in Georgia Green peanuts with no biocontrol treatment averaged 242 ppb, which was significantly (P < 0.01) lower than that in Florunner (1101 ppb). All three biocontrol formulations produced significant reductions in aflatoxin averaging 81.4%. There was no interaction between cultivar and biocontrol treatment, and no differences were observed between the two fungicide treatments. 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 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 strains in peanuts was significantly reduced by all three biocontrol formulations.