Genotypic variations of yields and nitrogen nutrition efficiencies in Bt transgenic cotton

Seven Bt （Bacillus thuringiensis）transgenic cotton （Gossypium hirsutum L.）cultivars including 33B from USA, domestic inbred cultivars SCRC21, SCRC22, SCRC28, and SCRC29, and domestic hybrids SCRC15 and 25 were grown in Linqing and Dongying, and managed under normal fertilization. Their yields and nitrogen nutrition efficiencies(NNE)were comparatively examined. The results show that the average yields of the 4 domestic inbred cultivars are 12.5%(Linqing)and 28.3%(Dongying)higher than those of 33B, and are about 9.7% lower than those of the hybrids. Total quantity of nitrogen(TQN)for producing 100 kg fiber of the early-developed(ED)cultivars is 13.9% lower than that of the later-developed(LP)cultivars, and the nitrogen nutrition efficiency coefficient(NNEC)of ED is 20.4% higher than that of LP. TQN of the hybrids is 13.9% lower than that of the inbred cultivars, resulting in 16.8% increase in NNEC relative to that of the inbred cultivars. These results suggest that NNE of ED and the hybrids is better than that of LD and the inbred. NNE can be improved by adoption of hybrid or inbred cultivars with early maturity, better yield and high economic index. NNE is closely related to maturity performance. Realization of normal maturity performance with proper agronomic practice is also important for improving NNE.