In-season variation in cry1ac expression in various plant parts of different BT cotton hybrids in India

All hybrids of transgenic Bt cotton do not provide the same level of lepidopteran control. Cry1Ac expression levels among Bollgard hybrids have been correlated to survival levels in various Lepidoptera. To determine a critical level of Cry1Ac expression in Bt cotton plants this aspect was studied. The Cry1Ac was quantified from leaves, squares, flowers and bolls of all Bt cotton hybrids fortnightly using standard commercial ELISA kit. There was inseason variation in Cry1Ac expression from 15 to 135 DAE. The Cry1Ac expression was found to be variable among the hybrids and also between different plant parts. The highest Cry1Ac expression was observed in leaves (3.165 to 8.519 ppm) of Tulshi-9 followed by RCH-Alto (2.872 to 7.866 ppm), JK-99 (2.324 to 7.692 ppm), RCH-2 (2.285 to 7.322 ppm), Ankur-651 (2.218 to 5.292 ppm) and Bunny (1.971 to 5.027 ppm). The minimum expression was observed in squares followed by flowers and bolls in all Bt hybrids. A gradual decline was observed from 15 DAE to 135 DAE. Even after 120 days after emergence, also a small amount of Cry1Ac expression was detected.