Aflatoxin reduction in corn through field application of competitive fungi

Soil in corn plots was inoculated with nonaflatoxigenic strains of Aspergil lus flavus and A. parasiticus during crop years 1994 to 1997 to determine t he effect of application of the nontoxigenic strains on preharvest aflatoxi n contamination of corn. Corn plots in a separate part of the field were no t inoculated and served as controls. Inoculation resulted in significant in creases in the total A. flavus/parasiticus soil population in treated plots , and that population was dominated by the applied strain of A. parasiticus (NRRL 21369). In the years when weather conditions favored aflatoxin conta mination (1996 and 1997), corn was predominately colonized by A. flavus as opposed to A. parasiticus. In 1996, colonization by wild-type A. flavus was significantly reduced in treated plots compared with control plots, but to tal A. flavus/parasiticus colonization was not different between the two gr oups. A change to a more aggressive strain of A. flavus (NRRL 21882) as par t of the biocontrol inoculum in 1997 resulted in a significantly (P < 0.001 ) higher colonization of corn by the applied strain. Weather conditions did not favor aflatoxin contamination in 1994 and 1995. In 1996, the aflatoxin concentration in corn from treated plots averaged 24.0 ppb, a reduction of 87% compared with the aflatoxin in control plots that averaged 188.4 ppb. In 1997, aflatoxin was reduced by 66% in treated corn (29.8 ppb) compared w ith control corn (87.5 ppb). Together, the data indicated that although the applied strain of A. parasiticus dominated in the soil, the nonaflatoxigen ic strains of A. flavus were more responsible for the observed reductions i n aflatoxin contamination. Inclusion of a nonaflatoxigenic strain of A. par asiticus in a biological control formulation for aflatoxin contamination ma y not be as important for airborne crops, such as corn, as for soilborne cr ops, such as peanuts.