Submitted to: Journal of Food Additives & Contaminants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2008
Publication Date: 3/23/2009
Citation: Lyn, M.E., Abbas, H.K., Zablotowicz, R.M., Johnson, B.J. 2009. Delivery systems for biological control agents to manage aflatoxin contamination of pre-harvest maize. 2009. Food Additives & Contaminants. Part A(26):381-387. Interpretive Summary: The fungus Asperigillus flavus can attack corn and produce toxic substances. We have been able to take a close relative of the toxic fungus and "infect" corn. The non-toxic relative out-competed the toxic fungus. The rot-toxic relative was combined with incredients to make pellets that dissolved in water and was sprayed on the corn. After time had passed, measurements showed that the corn "infected" with the non-toxic relative was the most common type of fungus on the corn.
Technical Abstract: Aflatoxin is a potent group of toxic compounds produced by the fungi Aspergillus flavus and A. parasiticus. Maize (corn, Zea mays L.) and other crops are prone to aflatoxin contamination, which may cause severe health problems in humans and livestock. The pre-harvest biological control approach of applying a competitive non-toxigenic strain of A. flavus on solid substrates has been successful for certain crops. However, a foliar application to the terminal growth bearing the reproductive structures may be more effective. The objectives were to develop a formulation amenable to conventional agricultural spray systems in the form of a liquid suspension and to evaluate the effectiveness of the formulation at mitigating aflatoxin contamination in field maize. A water dispersible granule (WG) formulation containing a non-toxigenic strain of A. flavus K49 was developed for application. Pinbar inoculation techniques demonstrated a similar final colonization of maize was achieved by formulated and free conidia of K49. A second field study compared K49 colonization on maize and effectiveness in reducing aflatoxin contamination when applied either as a wheat-based solid inoculant to soil or as a direct spray to reproductive structures at the mid-silking growth stage in plots artificially infested with an aflatoxigenic strain of A. flavus F3W4. Aspergillus flavus was recovered from harvested grain, populations of colony forming units (cfu) were determined and single colony isolates were evaluated for aflatoxin production based on cultural techniques. In spray applications of either formulated or unformulated conidia to maize, over 90% of the A. flavus recovered were non-toxigenic whereas in non-treated controls and in plots where soil was inoculated with a mixture of K49 and F3W4, only 50% of A. flavus colonies recovered were non-toxigenic indicating a better establishment of K49 when applied as a spray. Indirect application of K49 as a solid inoculant to soil showed a 65% reduction in mean aflatoxin contamination from 635 µg kg-1, whereas mean aflatoxin concentration was significantly reduced (P<0.05) by ~97% to ~20 µg kg-1 for formulated and unformulated conidial suspensions. These findings suggest that maize aflatoxin levels may be better controlled by direct application of a liquid suspension containing a competitive non-toxigenic strain of A. flavus such as K49. The water dispersible granular formulation is a suitable delivery system capable of maintaining the viability and efficacy of the biological control agent, K49, even after 11 months of storage at 4 degrees C.