Identification of Differential Agronomic Traits in EARLY STAGE Teosinte, Flint, Dent, and Sugar (SWEET) Corn Varieties in Competition with Weeds.

Today’s monocultural corn practices rely heavily on herbicide inputs for weed control. Herbicide resistant weeds have become a persistent mainstream problem and organic markets have expanded, creating needs for other weed management techniques. Weed tolerance (WT), the ability of a crop plant to withstand weed presence, has had limited examination.  Some corn varieties demonstrate more WT than others, with leaf width and canopy architecture often cited as the WT mechanism.  However, the genetic response(s) that underpin WT traits are unknown.  Modern corn varieties were derived from teosintes that are weedy species adapted to wild conditions and competitive by nature. Our hypothesis is that the teosinte genome has traits that can be developed to increase the competitive advantages of corn over weeds. Introductions of teosinte and varieties of corn (including dent, heritage, and sweet corn types) were cultivated with and without weed pressure during the 2013 and 2014 growing seasons. Early and end of season growth characteristics including leaf area, plant height, stem diameter, biomass, and yield, when possible, indicated a wide range of weed tolerance.  Differences between weedy and weed-free treatments within a type ranged from 1-10% in corn height, 3-20% in leaf area, 1-27% in corn biomass (July), 0.4-28% in top collar height  (September), and 2-17% in grain yield on a per cob basis at harvest (October). Varieties demonstrating the greatest and least deviations in these characteristics measured between treatments have been selected for preliminary molecular analysis (data not available at this time). Identifying early season growth characteristics and gene expression associated with maintaining high yield under weed stress conditions can, in the long term, lead to better understanding the mechanisms of WT, its heritability, and the reduction of weed control inputs.