Genetic Diversity among Transconjugants of Bacillus thuringiensis Used for Controlling Tomato Borer Tuta absoluta

Abstract

This study aimed to chacterize transconjugants of Bacillus thuringiensis on the basis of genomic DNA patterns, plasmid curing and bioassay of toxicity against tomato borer, Tuta absoluta in the open field. Eight transconjugants generated from four matings were used in this study. The shortening of extrachromosomal genetic material lead to loss of antibiotic resistance genes in some Bt strains and their transconjugants , as well as, loss of chitin hydrolysis as a consequence. In contrast, some Bt transconjugants were not affected by elevated temperature because they are still harboring antibiotic resistance genes and encoded chitinase. The extrachromosomal genome of Serratia was more stable than Bacillus licheniformis which lost Cf resistance gene at elvevated temperature. Bt strains and their transconjugants were genetically different because some bands appeared and or disappeared between them. Two transconjugants out of eight generated additional bands than the other ones which showed a higher toxicity index in relation to the mid-parent and the other transconjugants. Tomato plants treated with bioinsecticide formulations showed significant increase in photosynthetic pigments. Furthermore, some Bt transconjugants significantly increased shoot dry weight compared to the negative and the positive controls. This study indicated that mixing of dissimilar toxin genes in addition to chitinase genes in the same transconjugant led to increase toxicity and delay of resistance in insect pest than single - toxin gene carried by single strain.