TOXIGENIC AND NONTOXIGENIC ASPERGILLUS FLAVUS ISOLATES IN MAIZE FIELDS TREATED WITH THE BIOLOGICAL PRODUCT AF-X1: SOIL AND GRAIN COLONIZATION

Aflatoxins contamination of maize, used for both human and animal consumption, is a serious constraint for economical crop production. Different strategies have been developed to manage aflatoxins in crops and among them biological control has shown great promise. This strategy is based on the application of nontoxigenic strains in maize fields to competitively exclude naturally toxigenic strains in the same niche and compete for crop substrates. Field trials were conducted in two different Tuscany locations using maize hybrids of maturity class FAO 400 and 600. Geo-referenced plots (1 ha) were treated or not treated with the biological product AF-X1 (25 kg ha−1). Data were collected from five sites of each plot along two corner-to-corner diagonals (X shaped). Aspergillus section Flavi populations were enumerated and isolated from soils using a modified AFPA medium and were plated on YES medium to assess aflatoxin production by the ammonia vapour method. One-hundred maize kernels from each experimental plot were surface sterilized and plated on PDA amended with streptomycin. All the Aspergillus spp. developed colonies were transferred on AFPA, CZ and YES media in order to determine toxigenic and nontoxigenic A. flavus isolates. Soil propagule density of toxigenic isolates was higher in untreated than in AF-X1 treated plots. A. flavus was isolated from about 80% of all kernels tested, regardless of treatment. Greater than 99% of A. flavus isolates recovered from treated plots were nontoxigenic and significant values of toxigenic isolates were observed in untreated plots.