Seedling disease dynamics
Upon planting seed is exposed to an environment with many factors affecting the success of germinating and successfully producing a growing plant. When corn seed, with its own biological potential problems, is placed in soil populated by multiple micro-organisms ready to feed on organic matter, multiple battles begin. As the seed imbibes water, internal membranes swell, causing some leakage of stored sugars and proteins into the soil. Many soil organisms grow towards the damaged seedlings, attracted by the leaked substances. First tissue exposed to the potential invaders are the primary root and mesocotyl, two tissues that are later disposed when the secondary roots take over for the main root functions. Invaders are detected chemically by the corn cells near the invasion, turning on local production of resistance antibiotics. Success in suppression of the invaders is affected by aggression and intensity of the potential pathogens, environmental effect on pathogens and seedling and the biological vigor of the seedling.
Several fungal species are associated with seedling root rots. Fusarium, Penicillium, Pythium and Rhizoctonia species are among the most prominent fungi found in diseased corn seedlings. Fusarium species are common in nearly all soils with any organic matter. Every corn seedling is exposed to this fungus and yet only a few show symptoms. The actual cause of the seedling disease is usually more complex than simply identifying the fungus present in the corn tissue. Analysis of the cause should include consideration of environmental factors such as water concentration and temperature, and seed germination quality. Vigorous seedling growth can quickly dispose of primary root and mesocotyl dependency as secondary roots develop and new leaf tissue produces the quantity of resistance factors needed to control potential invaders such as these fungi.
Seed treatments can give the seedling some temporary relief from fungal invasion pressures. Genetic variability within the pathogen population can weaken its affect in some circumstances. Vigorous early growth due to corn hybrid genetics and seed quality favor escape from seedling disease pathogens even when environments are not optimum for early corn growth. Corn genetics and seed viability tests are strong deterrents to seedling diseases. Favorable environments also contribute.
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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.