Molecular characterization and distribution of Bacillus thuringiensis cry1 genes from Brazilian strains effective against the fall armyworm, Spodoptera frugiperda

A total of 165 Bacillus thuringiensis (Bt) strains that showed larval mortality above 75% were selected from 4459 isolates previously evaluated with respect to Spodoptera frugiperda activity. Molecular characterization was performed based on PCR using specific cry1 primers where 20% did not amplify the expected fragments; 62.4% amplified fragments corresponding to the presence of only one gene, and 15.2%, 1.8% and 0.6% presented a profile of two, three and four different cry1 genes, respectively. SDS-PAGE protein analyses were in accordance with the presence of cry1 genes. The most frequent gene (57.5%) was cry1D, whereas the least frequent genes were cry1Aa/cry1Ad and cry1C (1.2%). However, more than 60% of the evaluated strains had cry1B or cry1E genes. Analyzing cry1 genes and the larval mortality together, the range of activity from the most to least lethal to S. frugiperda was Bt strains with cry1C, cry1B, cry1E, cry1F, cry1A, cry1G and cry1D genes, respectively. The distribution of the strains and cry1 genes varied according to the origin of the sample and the source. DNA sequencing of the PCR products of the cry1C and cry1F genes confirmed their identities.