Submitted to: Agronomy Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/10/2002
Publication Date: 1/20/2003
Citation: Bruns, H.A., Abel, C.A. 2003. Nitrogen fertility effects on Bt endotoxin and N concentrations of early growth. Agronomy Journal. 95:207-211. Interpretive Summary: Maize hybrids that contain the Bt gene offer producers a mean of avoiding considerable crop losses due to European and southwestern cornborers as well as other moth larvae. Low nitrogen fertility rates are known to interfere with protein production in plants. The insecticide produced by the Bt gene is a protein, and the amount of it produced may be affected by the amount of nitrogen fertilizer used to grow the crop. This experiment examined the effect varying nitrogen fertility rates had on the concentrations of the Bt protein produced in maize plants during early plant growth. Two maize hybrids with two different types of Bt insecticide (Dekalb 626Bt and Pioneer 33V08) were grown in pots in a greenhouse in 2000 and 2001. Four nitrogen fertilizer rates (0, 100, 200 and 300 lbs per acre) were used. Total plant nitrogen content and Bt concentrations were determined at the 5-leaf growth stage. Both total plant nitrogen and Bt levels increased as nitrogen fertilizer rates increased. Increased levels of available nitrogen probably increase the amount of protein responsible for making the Bt insecticide and thus increases the insecticide levels in the plant. There were no differences between the hybrids in either Bt or nitrogen concentration in the plant and how they responded to the nitrogen fertility treatments.
Technical Abstract: Deficiencies of nitrogen (N) interfere with protein synthesis and growth in general in maize. Transgenic maize hybrids with the Bt gene offer producers a means of controlling certain Lepidopteron insect species. The effect N fertility has on Bt d-endotoxin concentration and how whole plant N concentrations relate to Bt levels of early growth maize has yet to be documented. Two maize hybrids (Pioneer 33V08 with Bt event MON-810 and Dekalb 626Bty with Bt event DBT 418) were grown in pots in a greenhouse in 2000 and 2001 with N fertility rates of 112, 224 and 336 kg ha-1 N as NH4NO 3. Plants were harvested at growth stage V5 and sampled for d-endotoxin and whole plant N concentrations. Whole plant N and d-endotoxin concentrations increased as N fertility levels increased. Greater levels of available N to the plant likely increases the d-endotoxin synthesizing proteins and thus increases the amount of d-endotoxin produced. Research to determine if similar findings would be made in more mature plants is needed. No significant differences among hybrids, plantings or their interactions were noted indicating the two Bt events responded to N fertility in a similar way.