Transgenic maize inbred lines expressing high levels of Bacillus thuringiensis vegetative insecticidal protein (Vip3Aa86) offer effective control of maize stem borer (Chilo partellus)

Abstract

The increasing incidence of field-evolved resistance in Lepidoptera (bollworms) insects towards Bt δ-endotoxins necessitates the need for an alternate strategy to prolong crop resistance. We have investigated the efficacy of Bacillus thuringiensis (Bt) derived toxin, the Vegetative Insecticidal protein Vip3Aa86 to manage maize stem borer in transgenic maize lines. Vip3A proteins do not share any midgut receptors or mechanism of action with any Cry insecticidal proteins and therefore are expected to possess toxicity even in the Bt resistant insects. The transgenic maize inbred lines generated through Agrobacterium mediated transformation expressing a codon optimized, synthetic vip3Aa86 gene under the influence of the Poly ubiquitin promoter. The T0 progenitor plants were screened initially through GFP reporter gene expression and transgene insertion by specific amplifications that identified four vip3Aa86 transgenic maize lines. Highest vip3Aa86 transcript abundance was observed in the V1 transgenic line while lowest was observed in the VA8 transgenic maize line when subjected to relative mRNA expression analysis. The concentration of Vip3Aa86 protein in T1 transgenic maize lines ranged from 0.94 to 2.24 μg g−1 leaf fresh weight. The percentage mortality of Chilo partellus was 76.6%, 56.7%, 40% and 53.3% respectively when fed on V1, V10, V12 and VA8 transgenic maize lines of T1 plants, for a period of 72 h in comparison to a control, non-transgenic maize sample. The study concluded that vip3Aa86 insecticidal gene holds great potential against maize stem borer and can be used in gene-pyramiding with Bt crops to prolong the crop resistance.