Grain yield and nitrogen use efficiency responses to N application in Bt (Cry1Ab/Ac) transgenic two-line hybrid rice

•Bacillus thuringiensis (Bt) transgenic two-line hybrid rice (THR) varieties were assessed under field conditions.•Bt-THR varieties demonstrated comparable yield performance comparing to the non-Bt super-high-yielding THR.•Insertion of Bt-gene into the THR varieties did not change the N uptake and NUE related trait comparing to the non-Bt control.•Screening Bt-THR varieties might represent a feasible approach to synergistically improve grain yield and pest resistance without disrupting N nutrition. Transgenic crops with Bacillus thuringiensis (Bt) have been reported to be effective in controlling pests, and some Bt transgenic lines have been used to develop hybrid crop varieties including three-line and two-line hybrid rice (THR). However, it is unclear whether the insertion of an external Bt gene affects nitrogen uptake and N use efficiency (NUE) along with the grain yield of Bt-THR. Thus, field experiments were conducted in two adjacent fields located at Zhangbang village, Hubei province, China from May to October in 2011 and 2012. Treatments were arranged using a split-plot design with four replications. The main plots were N treatments with three rates (90, 135, 180kgha−1) in 2011 and four rates (0, 90, 135, 180kgha−1) in 2012. Four different tested varieties were grown in the subplots. The three Bt-THR examined were Guangliangyou-19 (GLY-19), Chuanyou-4198 (CY-4198), and Zheyou-3 (ZY-3), and the non-Bt control was Yangliangyou-6 (YLY-6) which was used as the check for the national variety traits in China at present. Pests (including Bt target pests, diseases and weeds) were strictly controlled to avoid yield loss. No significant differences were observed in the grain yield between GLY-19, ZY-3 and YLY-6 at each N application for both years. However, the grain yield in response to different N rates varied among different Bt-THR varieties and the control. CY-4198 showed a sensitive N response trait, which produced a maximum grain yield at 90kgNha−1, and further increases in N rates caused a yield decline. The other Bt-THR varieties demonstrated insensitive N responses similar to the control, where the maximum grain yield was at 135kgNha−1 and showed no significant yield decline when applied at 180kgNha−1 in both years. Among the three Bt-THR varieties, GYL-19 and ZY-3 demonstrated a similar N uptake ability, agronomic nitrogen use efficiency, N harvest index, N translocation efficiency, and recovery efficiency compared to the control, whereas those for