Transgenic Corn Rootworm Protection (HERCULEX® XTRA) Improves Maize Nitrogen Uptake and Grain Yield in the Intermated B73 x Mo17 Population.

Feeding from insects such as Western corn rootworm (Diabrotica virgifera virgifera) frequently reduce uptake of water and nutrients such as N, thereby limiting grain yield. Transgenic corn rootworm protection has become widely accepted in maize production systems, yet the indirect benefit of this strategy on N use characteristics is poorly documented. In 2008 and 2009, we evaluated the HERCULEX® XTRA (HXX) trait in hybrids formed from the intermated B73 x Mo17 recombinant inbred line (IBM RIL) population using proprietary near-isogenic testers (with and without HXX). Hybrids possessing the HXX trait were compared to their near-isogenic counterparts at low and high N, and evaluated for N use traits, grain yield, and yield components. The objectives of this study were to i) document the relationship between rootworm protection transgene dependent increases in grain yield and N uptake, and ii) assess the quantitative variation in these responses using near-isogenic hybrids derived from the IBM RIL population.

In hybrids possessing the HXX trait, N uptake (g plant^-1) was increased at low N by 16.7% in 2008 and by 12.2% in 2009. Similarly, N uptake in HXX hybrids was increased at high N by 9.7% and 6.9% in 2008 and 2009, respectively. The difference between plant N contents at low and high N was also greater in HXX hybrids. This increase was nearly 3% in 2008 and approximately 5% in 2009 suggesting that HXX hybrids have greater N fertilizer recovery efficiencies.

Greater N uptake in HXX hybrids translated into grain yield increases at low N of 1.0 and 0.6 Mg ha^-1 in 2008 and 2009, respectively. Similarly, grain yield at high N was increased by 1.3 and 0.3 Mg ha^-1 in 2008 and 2009, respectively.

This study demonstrates that transgenic protection from corn rootworm feeding has benefits in addition to increased grain yield. N uptake was increased in both years at low N suggesting that corn rootworm protection traits such as HERCULEX XTRA are a vital component of germplasm improvement and agronomic strategies for maize production with reduced N inputs. Furthermore, HXX hybrids were more efficient at recovering fertilizer N which is clearly beneficial for improving the sustainability of maize production.