Expressional dynamics of cry proteins in first and second generation interspecific bt cotton hybrids and their comparative bioefficacy against pink bollworm, Pectinophora gossypiella (Saund.) and tobacco caterapillar, Spodoptera litura (Fab.)

Variability of Cry toxin expression among the plant parts, and temporal changes in expression during first and second generation Bt cotton hybrids was evaluated through ELISA, and their comparative bioefficay was studied under laboratory conditions at Agricultural Research Station, Dharwad farm, Dharwad during 2009–2010. Higher expression of Cry1Ac in both BG-I (MRC-6918) and BG-II (MRC-7918) hybrids and Cry2Ab in BG-II hybrid was observed at 80 DAS and declined significantly at 140 DAS. Higher expression of Cry1Ac was noticed in leaf canopy (3.55- 0.42 and 3.66 - 0.47 μg/g fresh weight, fwt) in comparison to that in fruiting parts (1.85–0.14 and 1.83 to 0.15). The least expression was observed in boll rind (0.95–0.14 and 0.95–0.15). Similar expressional pattern was observed in Cry2Ab which ranged from 61.66–24.63 μg/g fwt in leaves followed by 49.53- 17.45 μg/g fwt in squares. The least expression of 34.66–9.52 μg/g fwt was observed in boll rind. The bioassay studies revealed that, mortality of pink bollworm and Spodoptera neonates was significantly higher in stacked Bt cotton. The mortality on staked Bt cotton was 95.00 to 66.67 and 100.00 to 76.94 on flowers and tiny bolls respectively, and was significantly higher as compared to 79.72 to 28.06 and 92.22 to 33.61 per cent in single gene Bt cotton. Staked Bt cotton was found to be more effective with higher per cent mortality of Spodoptera (100.00 to 62.50%), as compared to mortality on leaves of single gene Bt cotton with only 35.00 per cent mortality at 60 DAS itself.