Assessing the Agronomic Value of Novel Transgenic Traits in Corn.

Novel transgenic events in corn, including drought tolerance and improved nitrogen use efficiency, are currently under development, and may be nearing commercial release. Frequency and severity of drought vary widely within the United States, and thus the value of a trait for drought tolerance is expected to vary among regions. Using corn yields over the period of 1990 to 2009 for the US and for states in the US Corn Belt, I calculated adjusted trendlines by assuming that all below-trend yields would have been on the trendline had genotypes carried traits for drought tolerance. This was done as a single iteration. The value of this “trait” was then taken as the difference between actual and adjusted trendlines. Due to low frequency of drought in the second decade of this period, the value of drought tolerance decreased for US corn, from 0.32 Mg ha^-1 in 1990 to 0.07 Mg ha^-1 in 2009; the average over the twenty years was 0.19 Mg ha^-1. Seven Corn Belt states showed declines in value over this period, two states showed little change, and three states showed increasing value. The value of drought tolerance at the end of the period ranged from 0.06 Mg ha^-1 in Iowa to 0.60 Mg ha^-1 in non-irrigated corn in Nebraska, and was inversely correlated with yield levels. We do not have similar methods to assess the value of N efficiency in corn, but data from recent work indicates that top-yielding hybrids tend to maximize return to N and profitability, even if they are not the most N-efficient. Regardless of what traits become available, high yields and good agronomic performance will continue to be primary criteria by which corn hybrids are valued.