Those first few weeks in the spring when the corn seed germinates and emerges can cause grower anxiety as the hypocotyl pushes upwards. Multiple species of fungi surround the tissue, attempting to enter the fresh growth. Interactions between seed physiological ‘vigor’, infection by fungi such as Fusarium species, environmental pressures including potential damaging organisms and seed treatments are complex.
A low percentage of seed within a seed bag are either dead of having sufficient cellular damage that all embryo cells do not function, perhaps with elongation of seminal root cells but no growth in the mesocotyl cells. Cell membranes damaged during seed maturation or with imbibition can self-repair, but this may result in delay of mesocotyl growth, delaying emergence compared to other seedlings and allowing more time for potential invasion by soil inhabiting fungi. Leakage of nutrients from the seed may also attract the fungi towards the germinating seed.
Fusarium species in the seed are not the only potential pathogens but also others are in nearly all soils. Fusarium verticilloides is one that tends to invade corn tissue after germination, perhaps growing between cells as the seedling extends beyond the soil surface. A few, such as F. graminearum often occupy the shoot base (crown), but it is not always clear if they significantly damage the plant. There is some evidence that presence of fungi in the emerging seedling correlates with reduced photosynthetic rate in leaves of the young plant.
Corn germinates and emerges more uniformly and quicker at 25°C (77°F) but temperate zone growers want to take advantage of the longer growing season by planting when soil temperature are only above 10-15°C. If the temperature remains low after planting, imbibitional damage to membranes is slow to repair and overall physiologic processes are slowed. Although Fusarium species are not favored by the low temperatures, the damaged tissue exudes nutrients to attract the fungi towards the tissue. Low temperatures also slow the production of resistance factors, allowing increased invasion of the tissue. This applies to the nodal roots that emerge after the seedling emerges as well. Soil components also affect the duration of exposure of mesocotyl if it has trouble pushing through the soil surface.
Seed treatments are intended to prevent or inhibit damage from seed-borne fungi and those potential pathogens infecting initial germinating seed. Polymers either added to the chemical fungicide treatments or even if used independent of the treatments can be helpful by slowing down the imbibitional process, potentially reducing the cell membrane damage. Most commercial seed treatments include a mix chemicals aimed at inhibiting fungi within the seed and a few components become somewhat systemic in the young seedlings. Application of seed treatments does require some care to make sure the seed does not absorb too much water and thus overcome the dormancy initiated by drying the seed. An interesting summary of Fusarium control by seed treatments can be found in a thesis at https://lib.dr.iastate.edu/rtd/15394
Among the human accomplishments of developing corn from a tropical grass (Teosinte) to extreme temperate zone environments has been the ability to get successful growth under less than perfect environments. This occurred with efforts of breeders selecting genetics, seed producers developing methods and growers working environments.
About Corn Journal
The purpose of this blog is to share perspectives of the biology of corn, its seed and diseases in a mix of technical and not so technical terms with all who are interested in this major crop. With more technical references to any of the topics easily available on the web with a search of key words, the blog will rarely cite references but will attempt to be accurate. Comments are welcome but will be screened before publishing. Comments and questions directed to the author by emails are encouraged.