Distribution, occurrence of cry genes, and lepidopteran toxicity of native Bacillus thuringiensis isolated from fig tree environments in Aydin Province

Abstract

Bacillus thuringiensis (Bt) has a significant impact on biological pest control because of the insecticidal activity through its parasporal inclusion bodies (crystal proteins). Fig is an economically important plant in Turkey; agricultural pests result in a considerable economic loss in fig quality and cultivation. The aim of this work was to isolate, characterize, and determine the lepidopteran toxicity of Bt obtained from fig groves in Aydin Province. A total of 606 colonies (out of 1167) obtained from 380 samples were identified as Bt based on parasporal crystal formation. The highest Bt index of 0.60 was observed in the Kuyucak region. A total of 288 Bt isolates were characterized in terms of cry gene content by PCR analysis. It was found that the cry1 plus cry2 genotype was the most abundant (40%) in our collection. Bioactivity tests indicated that 6 isolates exhibited high mortalities against Cadra cautella and 3 isolates were found to exhibit high toxicity against Carpophilus hemipterus. Moreover, 13 Bt isolates exhibiting toxic activity against fig pests were further characterized based on specific cry gene content, protein profiles, and PCR-RFLP analysis. Among cry1 genes, the cry1Aa, cry1Ab, cry1Ac, cry1B, cry1C, cry1D, and cry1Ea genes were the most frequent (100%). Protein profiles of isolates toxic to C. cautella were different from those of isolates toxic to C. hemipterus. PCR-RFLP analysis indicated that toxic isolates differed from the reference strain with respect to cry1 type gene. Finally, it was concluded that Bt strains isolated from fig groves showed high level of toxicity against fig pests. These strains can serve as potential biopesticides for the control of C. cautella in the region as well as alternative biopesticides in the case of pesticide resistance in insects.