Seleção e caracterização molecular de cepas de Bacillus thuringiensis eficientes contra lagarta falsa-medideira (Chrysodeixis includens)

Abstract

Soybean looper (Chrysodeixis includens) are important defoliating insects responsible for significant losses in productivity mainly in soybean crops in Brazil. Among the most used sustainable control methods for the suppression of pests in agriculture are the bio-insecticides and transgenic plants containing proteins produced by Bacillus thuringiensis. In order to provide new components for the control of the soybean lopper, this study aimed to select strains of B. thuringiensis toxic to these species and to characterize them molecularly. Fifty strains belonging to the Bank of Microorganisms of Embrapa Milho e Sorgo were used to perform selective bioassays, detection of the presence of genes cry1, cry2 and cry9, β-exotoxin detection assays, in addition to analysis of the plasmid profiles and to patterns of protein total and active of the efficient strains. From the tests, four strains were selected (3820, 531, 547 and 566) and these have been considered promising for the control of C. includens. All of them showed 100% mortality for these species, and through molecular evaluations was observed the presence of cry genes, megaplasmids and two main protein bands produced by the strains. In addition, two of the strains selected for soybean looper (3820 and 566) also presented toxicity to other three lepidopteran species of agricultural importance of the genus Spodoptera. These results demonstrate the high potential of these strains for use in the formulation of products containing Bt for agriculture.