| dc.description.abstract | The bacterium Bacillus thuringiensis presents a high specific activity against insects
due to delta-endotoxin syntheses, codified by cry genes. This study aimed to
evaluate the toxic activity of strains of B. thuringiensis derived from rice fields of Rio
Grande do Sul, as an agent of control of insect pest of rice and corn Spodoptera
frugiperda and Ostrinia nubilalis, in order to select potential strains to control and
identify whether the enzymatic activity of alkaline-phosphatase (ALP) and
aminopeptidase (APN) receptors may play an important role in the resistance of
B. thuringiensis. In this study we used phenotypic tests and PCR techniques to identify
subclasses of gene cry1; proteins profile to observe the composition of the spore-
crystal complex, rep-PCR for the observation of genetic variability, plasmid DNA,
quantification of the enzymes ALP and APN to observe resistance profile of strains
and bioassay capacity against insect pests. Assays for quantification of proteins ALP
and APN showed reduced levels being a potential biomarker for resistance to Cry
toxins. The results of studies of rep-PCR demonstrated a high degree of similarity
between the rice regions, probably associated with ecological speciation. Regarding
the protein profile characterization, the results revealed differences between the
strains, some being similar to those used as standard analysis (Bt thuringiensis
4412, Bt IPS 82 and Bt HD1). In trials of plasmid profile, the strains formed three distinct patterns. In data and toxicity assessed by bioassays against first instar
O. nubilalis larvae, all tested strains showed mortality exceeding 75%, highlighting the Bt strain 1893-15, which caused 95% mortality. In the data of the biological assays conducted against S. frugiperda larvae, the Bt strain 3420-11 stood out showing mortality greater than 88%. | en |
