Expression of Cry2Aa, a Bacillus thuringiensis insecticidal protein in transgenic pigeon pea confers resistance to gram pod borer, Helicoverpa armigera

Abstract

Pigeon pea is an important legume infested by a plethora of insect pests amongst which gram pod borer Helicoverpa armigera is very prominent. Imparting resistance to this insect herbivore is of global importance in attaining food security. Expression of insecticidal crystal proteins (ICP) in diverse crops has led to increased resistance to several pests. We report in this paper, expression of Cry2Aa in transgenic pigeon pea and its effectiveness towards H. armigera by employing Agrobacterium-mediated in planta transformation approach. Approximately 0.8% of T1 generation plants were identified as putative transformants based on screening in the presence of 70 ppm kanamycin as the selection agent. Promising events were further recognized in advanced generations based on integration, expression and bioefficacy of the transgenes. Seven T3 lines (11.8% of the selected T1 events) were categorized as superior as these events demonstrated 80–100% mortality of the challenged larvae and improved ability to prevent damage caused by the larvae. The selected transgenic plants accumulated Cry2Aa in the range of 25–80 µg/g FW. The transgenic events developed in the study can be used in pigeon pea improvement programmes for pod borer resistance.

Assessment of Pigeonpea (Cajanus cajan L.) transgenics expressing Bt ICPs, Cry2Aa and Cry1AcF under nethouse containment implicated an effective control against herbivory by Helicoverpa armigera (Hübner)

“…Bacillus thuringiensis ( Bt ) insecticidal proteins (ICPs) that encode a delta endotoxin have proved to be the most suitable and safe alternative to chemical pesticides. The major emphasis of our group has been in the development of transgenics in pigeonpea for mitigation of the pod borer H. armigera using a tissue culture‐independent in planta transformation strategy . Several other research groups have also produced transgenic pigeonpea with the development of diverse Bt genes .…”

“…Diet feed assays have shown that there was severe growth inhibition among the survivor larvae . This prompted scientists to exploit this gene as an alternative to cry1Ac to mitigate pod borer . These two ICPs show potent activity against H. armigera and apparently target different receptors in the insect gut.…”

“…We have developed transformants in pigeonpea independently harboring the above two Bt ICPs, Cry2Aa and Cry1AcF. Based on stringent molecular and bioefficacy studies against deliberate challenging by pod borer, we have identified 11 cry2Aa and 8 cry1AcF events to be promising.…”

“…We have developed transformants in pigeonpea independently harboring the above two Bt ICPs, Cry2Aa and Cry1AcF. Based on stringent molecular and bioefficacy studies against deliberate challenging by pod borer, we have identified 11 cry2Aa and 8 cry1AcF events to be promising. In vitro challenging of these events under detached leaf and pod bioassays by the larvae of H. armigera demonstrated 80–100% larval mortality and reduced leaf damage .…”

“…Based on stringent molecular and bioefficacy studies against deliberate challenging by pod borer, we have identified 11 cry2Aa and 8 cry1AcF events to be promising. In vitro challenging of these events under detached leaf and pod bioassays by the larvae of H. armigera demonstrated 80–100% larval mortality and reduced leaf damage . Furthermore, molecular characterization revealed the transgenic nature of these events.…”