Pioneer® brand corn products are rated for stress emergence to help farmers manage early-season risk. Choosing hybrids with higher stress emergence scores can help reduce genetic vulnerability to stand loss due to cold soil temperatures. To generate stress emergence ratings, hybrids are tested over multiple years and environments beginning several years before commercialization. The goal is to generate data from many different types of early-season stress before assigning ratings.
Hybrids are tested in several early-planted field sites, including no-till and continuous corn locations. Testing sites are located in Minnesota, Wisconsin, Iowa, South Dakota, North Dakota, and Michigan and are chosen to reflect the various seedbed and environmental conditions likely to be experienced by farmers. For example, some eastern sites are characterized by extended cold, wet conditions that often persist into late spring and early summer, while northern and Midwestern sites are more likely to provide extreme day/night temperature fluctuations. These testing sites, with their diverse and unique conditions, provide a more thorough understanding of hybrid responses to early season stress. A typical testing site is characterized by large amounts of residue, cold soil (below 50ºF) at planting followed by cold rain or snow and emergence usually requiring two to three weeks.
Pioneer brand corn products are also tested in lab assays that simulate stressful field conditions. These tests, which have been validated by multi-year field trials, provide consistent and reproducible test conditions coupled with the flexibility of year-round testing. These lab assays are used to support hybrid advancement decisions and also to support breeding efforts to improve early season stress tolerance through marker-assisted selection.
In 2018, a wide range of stress emergence conditions and soil temperatures were observed in stress emergence field plots. To demonstrate how stress emergence ratings relate to stand establishment in the field, hybrids were grouped by “low stress emergence” – those with a stress emergence rating of 4, and “high stress emergence” - those with a stress emergence rating of 6.
The trials included 199 low stress emergence hybrids and 159 high stress emergence hybrids. Early stand counts for all hybrids within each group were averaged at each location. As stress level increased, both the low stress emergence and high stress emergence hybrids experienced stand reduction. However, the hybrids with a stress emergence score of 6 were able to maintain higher stands as compared to those with a low stress emergence score (Figure 5).