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Figure 1. The mesocotyl extends, pushing the coleoptile through the soil surface. With light and the pressure from the expanding leaves, the coleoptile ruptures allowing the plumule and other leaves to grow and develop.
The processes of germination and emergence are highly dependent upon several types of plant hormones. One type thought to be instrumental in geotropism is auxins. Auxins are similar to the synthetic plant hormones in herbicides, such as 2,4-D, and cause cell elongation. Hormones can be greatly affected by temperature and other environmental conditions.
Figure 2. Under conditions such as prolonged exposure to cool soil temperatures, the mesocotyl can grow abnormally resulting in premature rupture of the coleoptile and leafing out below the soil surface.
Symptoms of chilling injury can also be caused by other factors and may be compounded by additional stresses during germination. These stresses may include herbicide injury, disease, or soil crusting. Since symptoms are not unique to chilling injury, they can be hard to decipher.
Other Causes of Leafing Out Soil Compaction and Sidewall Compaction Physical resistance from compaction, including sidewall compaction, can result in coleoptile damage or inadequate elongation of the mesocotyl.
As wet soils dry, a crust layer can form on the soil surface, potentially delaying or preventing seedling emergence. Crusting may be more common in fields with fine textured soils, low organic matter, and little surface residue, especially where excessive tillage has taken place. A rotary hoe can break up the crust and aid seedling emergence. Timing is essential and breaking the crust as soon as possible is most beneficial. If seeds are not infected with disease, cooler soils will allow seedlings to survive longer when trying to break through the crust.
Cool and stressful conditions can increase the risk for herbicide injury, particularly from herbicides such as 2,4-D. Risk of leafing out from herbicide injury would likely be more evident in overlapped areas.
If the coleoptile senses light the mesocotyl is signaled to stop elongating. This normally occurs when the mesocotyl is approximately 3/4 inch below the soil surface. Cloddy or sandy soils can allow light to hit the coleoptile when the mesocotyl is more than ¾ inch below the soil surface. The leaves continue to expand below the coleoptile causing it to rupture. The exposed leaves then struggle to penetrate through the soil for successful emergence (Figure 3).
Figure 3. Cloddy soils can allow light to reach the coleoptile, hindering elongation of the mesocotyl, resulting in premature rupture of the coleoptile and leafing out below the soil surface.
Warm Germination Test. A standardized Warm Germination Test was established by the Association of Official Seed Analysts (AOSA). The Federal Seed Act requires seed companies to report these Warm Germination Scores for all seed lots. Since all seed is tested using the same standardized testing procedures, a 95% Warm Germination Score means the same thing, regardless of which company, lab, or seed regulatory agency conducted the test.
Contrastingly, Cold Germination or “Vigor” tests are not required for compliance with state and federal seed law, nor is there a standardized test across the seed industry. Many companies, universities, and independent seed testing labs have developed and implemented various forms of Cold Germination tests to help establish and differentiate the quality of their seed beyond the legal testing requirements. Monsanto has developed and deployed a proprietary, internal vigor (Cold Germination) test in an effort to better predict emergence potential across environments. The results of this test are used internally as an integral part of the quality management system to help provide only the highest quality seed to our customers. This information is not shared outside of the quality review team, as the scores generated by the test are ultimately irrelevant in the context of other tests. For example, an 85% test result from the proprietary test Monsanto utilizes may be an equivalent or better indication of stress emergence compared to a 90% test result from a different, less rigorous test. Unfortunately, even if all of the variables were fully understood for each testing procedure, making a comparison of results across the tests could be misleading since it would be based on making various assumptions. The bottom line - there is no way to know the actual difference between Cold Germination scores from various testing sources in the absence of an industry standard.
Similar to a Cold Germination test, there is not a procedure standardized across the industry for “Saturated Cold Germination” tests. Therefore, testing procedures and test results are likely to vary by lab.
Monsanto has a great deal of confidence in the Cold Germination test utilized internally. The validity of this test has been proven across millions of acres for numerous seasons. That being said, germination scores are only indicators of potential and not absolute measures of performance. They are the best indicators available to predict the experience a grower will ultimately have when seed is planted; however, they are not perfect and there will always be exceptions. Monsanto takes seed quality very seriously and strives to deliver the most consistent, highest quality seed a farmer can buy.
Sources: 1 Elmore, R. and L. Abendroth. April 8, 2005. Do corn kernel size and shape really matter? Crop Watch Newsletter. University of Nebraska-Lincoln. 2 Abendroth, L.J. et. al. 2011. Corn growth and development. Iowa State University Extension. PMR 1009. 3 Nielsen, R.L. 2010. The emergence process in corn. Purdue University Extension. http://www.agry.purdue.edu (verified 4/29/2012) 4 Nielsen, R.L. 2008 Early planted corn feeling :under the weather”. Purdue University Extension. http://www.agry.purdue.edu/ (verified 4/29/2012) Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Leaf Design℠ is a servicemark of Monsanto Company. ©2012 Monsanto Company. 05022012EJP