NitroGenes: Improving Corn Yield With Fewer N Inputs

Stephen Moose Assistant Professor of Maize Functional Genomics Department of Crop Sciences (217) 244-6308; smoose@illinois.edu

Fred Below Professor of Crop Physiology Department of Crop Sciences (217) 333-9745; fbelow@illinois.edu

High rates of nitrogen (N) fertilizer are used in Illinois corn production to maximize grain yield. The rising costs of N fertilizer and concerns about the impacts of N runoff on water quality demonstrate a significant need to develop maize hybrids that maintain high yields with lower rates of applied N. Currently, little is known about the genes that control nitrogen use efficiency (NUE) in corn. We have combined our laboratories' strengths in the field measurement of NUE (Below) and maize genetics (Moose) to study "NitroGenes," genes that can be used to improve NUE through breeding and biotechnology approaches.

Nitrogen use efficiency is the ratio of grain yield to N supplied (both from the soil and N fertilizer). The two principal components of NUE are N uptake efficiency, which is the percentage of fertilizer-applied N found in the plant at maturity, and utilization efficiency, the ratio of grain yield to plant N. Today’s commercial hybrids have been optimized for yield and NUE at high rates of applied N and therefore primarily have been selected for only one component of NUE: N uptake.

Our research strategy has been initially to study corn hybrids that differ greatly for NUE and its components. The University of Illinois has been conducting a selection experiment for changes in the relative concentrations of grain protein since 1896, which has resulted in the creation of the Illinois High Protein (IHP) and Illinois Low Protein (ILP) strains. Because protein is how the corn seed stores nitrogen for the next generation’s seedling, selection for differences in grain protein has also resulted in large changes in NUE between IHP and ILP (Table 1).

We have developed hybrids using IHP and ILP as parents and evaluated these hybrids for NUE over the last three years by growing them under different rates of N fertilizer in our nitrogenresponsive nursery. Figure 1 shows the response of the IHP hybrid to increasing rates of N fertilizer, where ears become larger and more filled with kernels at higher N rates.

The results from our 2002 field study are summarized briefly in Table 1. As expected, grain protein is highest for the IHP hybrid and lowest for the ILP hybrid. IHP and ILP differed dramatically in their NUE components. IHP is superior to the commercial hybrid in N uptake efficiency. In contrast, ILP is poor at N uptake, but what little N the plant does acquire is utilized to maintain reasonable grain yields.

We have also collected samples from vegetative tissues and grain of the above three hybrids grown at the different N rates, which we are now using to identify NitroGenes that show strong associations with high N uptake and N utilization. We have discovered some promising NitroGenes that we are now testing for their association with NUE in a diverse set of corn hybrids. We are hopeful that some of these NitroGenes will allow the development of high-yielding corn hybrids under lower rates of applied N fertilizer.

We wish to acknowledge the research support provided to various aspects of this project by C-FAR, Renessen, Pioneer Hi-Bred, BASF Plant Sciences, and Syngenta Seeds.

Table 1. NUE components in IHP compared to ILP hybrids at two different rates of N fertilizer (60 and 180 lbs. per acre).

Genotype	Grain Yield (bu/acre)		Grain Protein %		NUE g grain/g fert N		N Uptake %		N Utilization g grain/g plant N
	60	180	60	180	60	180	60	180	60	180
ILP hybrid	121	148	6.4	7.1	22.9	15.8	86.0	44.1	26.6	35.8
IHP hybrid	97	123	13.3	18.3	14.1	14.1	124.8	108.0	11.7	12.7
Commercial hybrid	182	201	8.2	8.7	42.4	20.0	83.9	73.0	50.5	18.1

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