Effects of N treatments on the yield advantage of Bt-SY63 over SY63 (Oryza sativa) and the concentration of Bt protein

It has been widely demonstrated that insect-resistant rice containing various Bt genes can provide an effective control of lepidopteron pests. It is well known, however, that rice plants will suffer more pressure from pests when high nitrogen fertilizer is applied. Therefore, how is the efficacy of Bt transgenic rice against lepidopteron pests in response to N application? In this study, we try to study the effect of nitrogen treatments on the yield advantage of Bt transgenic SY63 (1C*) and SY63 (2A*) [SY63 (1C*) and SY63 (2A*) represent the hybrid variety Shanyou63 contain a Bt gene of cry1C* and cry2A*, respectively.] over its non-Bt Shanyou63 (SY63) and disclose the relationship between N concentration and Bt protein in rice leaves. Field experiment was conducted in 2010 and 2011 at Zhangbang village, Wuxue city (29°51′N 115°33′E), Hubei Province, China from May to October. Treatments were arranged in a split-plot design with three replications, and nitrogen treatments were the main plots and genotypes were the subplots. No pesticides against lepidopteron pests were applied in the whole growth season. It was found that both SY63 (1C*) and SY63 (2A*) exhibited effective resistance to leaffolders, although SY63 (1C*) was more efficient than SY63 (2A*). There were significant correlations between the yield advantages of SY63 (1C*) and SY63 (2A*) over SY63 and their grain yield, respectively. The maximum yield advantages of SY63 (1C*) and SY63 (2A*) over SY63 were both near 20%, however, no significant yield advantages for Bt rice were observed when their grain yield was below 6.5tha⁻¹. There was a significant correlation between N and Bt protein concentrations. Bt protein concentrations at 210kgNha⁻¹ were significantly higher than those at zero N treatment, but there were no significant differences among 90, 150 and 210kgNha⁻¹. In addition, the concentration of Cry2A* was several times higher than that of Cry1C*. Therefore, it is meaningful to incorporate the Bt genes into varieties with high yield potential and adopt appropriate N management practice to ensure high grain yield, so that its insect-resistance advantage could be fulfilled.