Midwest corn in spring of 2017 is starting the season favoring seedling disease symptoms. It is difficult to sort out the real cause of seed not emerging or emerging much later than adjacent plants. Seeds are planted in environments that vary every few inches for water holding capacity, organic content and microbes. Furthermore, each individual seed varies slightly in its cellular membrane status. With imbibition causing swelling of the membrane bound cell contents, some seed can have problems getting effective metabolism for early cell growth to push out the root and stem structures.
Cell metabolism includes producing the response to attacks by potential pathogens in the soil. These anti-pathogen chemicals (phytoalexins) are usually produced with a complex system of detecting the microbe and concentrating the phytoalexin into the area of the attack. Weakened seed not only are likely to release more carbohydrates and proteins into soil because of membrane injury, but also be less capable of responding to the microbes invading root and mesocotyl tissue.
Diagnosis of seedling disease becomes complicated also. Pathologists can isolate a fungus such as a Fusarium species or an oomycete like a Pythium species, but the actual cause probably involves some interaction between the microbes, metabolic quality for the ‘diseased’ seedling, and a complex environment not only providing potential pathogens but also affecting the seedlings metabolic rate. Soil organisms are affected by the environments as well. Leakage of carbohydrates directs their growth toward the seedling roots but temperatures favor some over others. Pythium’s swimming spores do well in cool wet environments but can be inhibited by certain seed treatments that have very little effect on fungi such as Fusarium species. Other seed treatments can inhibit the latter group of microbes but are less effective against Pythium. Corn seed genetics and seed quality can be greater factors than either group of chemicals. Cold wet heavy soils for a prolonged time can overcome all methods of defense.
After the stress on the seedlings is reduced, remaining plants that emerge can give normal production especially if they are uniform in growth with adjacent corn plants. The metabolism of these plants will promote the recovery and normal root growth. Those plants that survive but emerge later than adjacent plants will have difficulty competing for light and mineral uptake which will be reflected in grain productivity.
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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.