Compatibility of different entomopathogenic fungi isolates with synthetic antioxidants to control insect vectors of aflatoxigenic fungi in stored maize

BARRA, P.; NESCI A; ETCHEVERRY, M

Mendoza

Conferencia; MYCORED ARGENTINA ISM 2011 Conference, Strategies to reduce the impact of mycotoxins in Latin Amrica in a global context; 2011

MYCORED ARGENTINA

In Argentina maize can be colonized by Aspergillus section Flavi at harvest and storage. Some species of these fungi produce aflatoxins, being aflatoxin B1 clasificated as 1 A carcinogen by the IARC. Stored grain insects cause significant damage to stored maize and contribute to the dispersal of Aspergillus spores. Synthetic phenolic compounds have bioactivity against Aspergillus and also insecticidal activity. Some fungi are natural enemies of insects and have been investigated for their potential as biological control agents. We have isolated and identified entomopathogenic fungi of maize agroecosystem. Therefore, the combined use of different methods as the use of biological control agents of insect vectors of aflatoxigenic fungi, plus the use of synthetic chemicals in sublethal doses, could contribute to the reduction of aflatoxin contamination in stored maize. The purpose of this study was to determine the compatibility of 15 entomopathogenic fungal isolates with the synthetic antioxidants 2(3)-tert-butyl-4 hydroxyanisole (BHA) and 2,6-di tert-butyl-p-cresol (BHT) at concentrations of 1, 2, 3, 4, 5, 7 and 10 mM. Studies were carried out in vitro, in 3 % maize meal extract agar (MMEA) over the aw range 0.99-0.95. The appropriate amount of antioxidants was added to sterilize MMEA. Fungi were grown on PDA (potato dextrose agar) for 7 days at 25°C to obtain heavily sporulating cultures. Each plate of MMEA was inoculated with 100 µl of a spore suspension of 107 spores/ml of the fungal isolated. Petri plates of the same aw values were sealed in polyethylene bags, and incubated for 25 days at 25°C. The maximum concentration at which the isolates were able to grow was determined, and the fungal count as CFU/ml was determined at this concentration. Entomopathogenic fungi count was determined by using 3 replicates for each experiment repeated 3 times. The results showed that all isolates were able to grow at 1 mM of BHA. At this concentration all isolates showed a similar count to control treatment at all water activities assayed. Similar results were found with the antioxidant BHT. Therefore, we continue evaluating the possibility of use these entomopathogenic fungi with the antioxidants BHA and BHT as a potential combined strategy.