Development and evaluation of lepidopteran insect resistant jute expressing the fused Bt-Cry1Ab/Ac toxin driven by CaMV35S promoter

Abstract

The global demand for jute fibres in industrial and commercial applications makes jute (Corchorus sp.) a popular cash crop. Jute is an ideal eco friendly material for packaging and product manufacturing owing to its long, shiny, non-toxic, biodegradable bast fibres and high yield of cellulosic biomass produced per acre in cultivation. In order to match the increasing global demand for jute fibres, sustainable protection of jute cultivation from insect pests is essential. Lepidopteran pest resistant Bt (Bacillus thuringiensis) jute lines were developed by expressing the fused Bt-cry1Ab/Ac gene, driven by the CaMV35S constitutive promoter in the white jute (C. capsularis) cultiver- JRC321 and named as CBT (CaMV35S Bt). Molecular analyses confirmed the single copy integration of the Bt-cry1Ab/Ac gene in the transgenic CBT lines and 0.25 ng/mg of Bt-Cry1Ab/Ac δ-endotoxin production in the leaf tissue. The study involved evaluation of the insect resistance and the level of Bt-cry1Ab/Ac gene expression in different parts (leaf, stem, seed coat, and root) of the CBT lines in comparison with the previously developed, actin1 promoter driven Bt-cry1Ab/Ac gene containing, ABT lines (actin1 Bt). The CBT and ABT (Bt jute) lines were tested against two major jute pests- hairy caterpillars (Spilarctia obliqua) and indigo caterpillars (Spodoptera exigua). The Abbott’s insect mortality was observed for hairy caterpillars and indigo caterpillars on CBT lines as 90.74 % and 76.37 % respectively and on ABT lines as 97.11 % and 80.74 % respectively. Progeny plants of both the CBT and ABT lines showed similar and significant effects of insect resistance on the test insects under bioassay. Quantification of the expression of Bt-cry1Ab/Ac gene transcripts was similar in the leaves of both CBT and ABT lines but for stems, seed coats, and roots, the expression was found to be higher in ABT lines. This study confirmed that ABT lines were superior and more promising than CBT lines for jute pest management. The progeny plants from both CBT and ABT lines were similar to WT plants in terms of agronomic parameters.