Biocontrol of aflatoxin in corn by inoculation with non-aflatoxigenic Aspergillus flavus isolates

The ability of two non-aflatoxigenic Aspergillus flavus Link isolates (CT3 and K49) to reduce aflatoxin contamination of corn was assessed in a 4-year field study (2001–2004). Soil was treated with six wheat inoculant treatments: aflatoxigenic isolate F3W4; two non-aflatoxigenic isolates (CT3 and K49); two mixtures of CT3 or K49 with F3W4; and an autoclaved wheat control, applied at 20 kg ha−1. In 2001, inoculation with the aflatoxigenic isolate increased corn grain aflatoxin levels by 188% compared to the non-inoculated control, while CT3 and K49 inoculation reduced aflatoxin levels in corn grain by 86 and 60%, respectively. In 2002, the non-toxigenic CT3 and K49 reduced aflatoxin levels by 61 and 76% compared to non-inoculated controls, respectively. In 2001, mixtures of aflatoxigenic and non-aflatoxigenic isolates had little effect on aflatoxin levels, but in 2002, inoculation with mixtures of K49 and CT3 reduced aflatoxin levels 68 and 37% compared to non-inoculated controls, respectively. In 2003 and 2004, a low level of natural aflatoxin contamination was observed (8 ng g−1). However, inoculation with mixtures of K49 + F3W4 and CT3 + F3W4, reduced levels of aflatoxin 65–94% compared to the aflatoxigenic strain alone. Compared to the non-sclerotia producing CT3, strain K49 produces large sclerotia, has more rapid in vitro radial growth, and a greater ability to colonize corn when artificially inoculated, perhaps indicating greater ecological competence. Results indicate that non-aflatoxigenic, indigenous A. flavus isolates, such as strain K49, have potential use for biocontrol of aflatoxin contamination in southern US corn.