Association of PCR and feeling bioassays as a large-scale method to screentropical Bacillus thuringiensis isolates for a cry constitution with higher insecticidal effect against Spodoptera frugiperda (Lepidoptera : Noctuidae) larve

Aims: To verify whether the presence of any of the cry1C, 1D, 1E and 1F gen es could be associated with high toxicity against fall armyworm. Methods and Results: A sample of 60 strains from a large collection of trop ical Bacillus thuringiensis (B.t.) isolates was subjected to feeding bioass ays and gene-specific PCR. Positive amplification of cry-specific fragments , so confirmed by sequencing, revealed that cry1C was ubiquitous and. distr ibuted among high and low mortality; classes, cry1D was underrepresented an d showed no clear association to high toxicity, and cry1F was not detected. The presence of cry1E significantly correlated to high levels of insectici dal activity, as estimated by linear regression analysis. Conclusions: The PCR amplification of cry1E-specific fragments alone appear s to be sufficient to identify B.t. strains with high mortality levels agai nst tropical armyworm. Significance and Impact of the Study: The approach presented is promising a s a simple and efficient method for first-tier, marker-assisted screening o f environment-specific B.t. germplasm effective in controlling a single tar get pest.