Protease Inhibitors in Wild Relatives of Pigeonpea against the Cotton Bollworm/Legume Pod Borer, Helicoverpa armigera

Cotton bollworm/legume pod borer, Helicoverpa armigera is one of the most damaging pests worldwide. Because of the difficulties associated with chemical control of this pest, emphasis has been placed on developing transgenic plants with resistance to H. armigera. Since toxin genes from the bacterium, Bacillus thuringiensis (Bt) have been deployed on a large scale, there is need to scout for alternate genes which could be deployed alone or in combination with the Bt genes for pest management. Therefore, we evaluated the wild relatives of pigeonpea, which have shown high levels of resistance to this pest, for the protease inhibitors (PIs) under in vivo and in vitro inhibitions. Accessions belonging to Cajanus albicans, C. cajanifolius, C. sericeus, Flemingia bracteata, and Rhynchosia bracteata showed complete inhibition of H. armigera gut proteinases (HaGPs). Some of the C. scarabaeoides accessions (ICPW 116, 152, 278 and 280) exhibited partial inhibition at low concentrations of the PIs. All accessions of wild relatives of pigeonpea showed high to moderate level of inhibition at pH 7.8. Cultivated pigeonpea, ICPL 87 exhibited monomorphism in terms of trypsin inhibitor (TI) and chymotrypsin inhibitor (CTI) isoforms, contrary to the diverse inhibitory profiles of wild pigeonpeas. Cajanus albicans, C. platycarpus, C. scarabaeoides, and R. bracteata showed more number of TI and CTI bands than the cultivated pigeonpea. Protease inhibitor isoforms of wild relatives of pigeonpea showed significant variation in number, band pattern, and protein specificities towards trypsin, chymotrypsin, and H. armigera gut proteinases (HaGPs) as compared to the cultivated pigeonpea. The PIs from the wild relatives of pigeonpea showed considerable potential against the HaGPs, and could be considered as potential candidates for use in genetic transformation of crops for pest management, including H. armigera.