Assessment of yield advantages of Bt-MH63 with cry1C* or cry2A* genes over MH63 (Oryza sativa L.) under different pest control modes

Transgenic Bacillus thuringiensis (Bt) rice had been successfully cultivated to maintain yield potential of rice under pest invasion. Yield and resistance performance of the transgenic Bt rice are important to be meticulously evaluated under different pest pressures. Field experiments were conducted to investigate field performances of Bt-MH63 with cry1C* or cry2A* genes under four pest control modes: chemical control for all the pests (MPC), no chemical control for the target pests (MNTP), chemical control for the target pests (MTP) and no chemical control for all the pests (MNPC). The results showed that the maximum yield advantages of MH63 (cry1C*) and MH63 (cry2A*) over MH63 were 8.4 and 25.4% (P < 0.05) under MNTP, respectively. The grain yield of MH63 (cry1C*) was lower than that of MH63 under MPC and MTP. Moreover, the grain yield of MH63 (cry2A*) was lower than that of MH63 under MTP only. The correlation analysis revealed that the yield advantages of Bt-MH63 over MH63 were positively correlated with the damage to MH63 (expressed as percentage of white leaves) caused by leaffolders (Cnaphalocrocis medinalis Guenee). Although MH63 (cry1C*) and MH63 (cry2A*) showed great differences in Bt protein contents in their leaves, they had high effective resistances to leaffolders. It can be concluded that Bt-MH63 had obvious yield advantages over MH63 when no pesticides were applied against the target pests. However, yield reductions in Bt-MH63 were existed when pesticides were applied against the target pests.