Resumo

F. verticillioides is most commonly associated with maize worldwide and produces high levels of fumonisins, one of the most important mycotoxins. Previous studies have demonstrated that cry 1Ab protein from Bacillus thuringiensis sbsp. kurstaki could be suitable for Fusarium toxins management due to the control of crop insect injuries. The aim of this study was to assess the impact of cry 1Ab protein expressed in the 30F35YG (YieldGard) corn hybrid on FUM gene expression and on fumonisin production by F. verticillioides ICB 13BA (GU 989110/NCBI accession number). We also evaluated the influence of B. thuringiensis sbsp. kurstaki spores and cry 1Ab crystals on the F. verticillioides growth. In order to eliminate the original microbiota, Bt corn samples and its respective non-Bt isogenic were previously irradiated with 20 kGy. Plates were inoculated with 5 x 108 F. verticillioides spores/mL and incubated at 25 °C and relative humidity of 97.5%. After 10, 20 and 30 days, samples were analysed regarding FB₁ contamination and expression of 14 FUM genes. The statistical analyses were performed using the softwares R 2.9, Gamlss package and SAS 9.1. An initial fungal inoculum of 5 x 10⁸ spores/mL was cultured with 10 μg/mL of bacterial spores and crystals. F. verticillioides biomass was estimated by dry weight of mycelia during 1, 3 and 5 days . The results showed reduced fumonisin B₁ contamination on 30F35 YG in comparison to its isogenic non-Bt corn during the periods of the analyses (p= 0.0095, Weibull distribution). There was no correlation between FUM gene cluster and fumonisin production according to Pearson’s correlation test (except for FUM19, p<0.005), nevertheless, FUM genes were less expressed on 30F35 YG as revealed by Mann-Whitney test (p<0.04). The biomass of the test species was inhibited by B. thuringiensis sbsp. kurstaki spores and crystals in Potato Dextrose Agar broth.