Corn seedlings are vulnerable to invasion of the multiple fungi activated by spring temperatures. As the new leaves push out from apical meristem still under the soil surface, the initial 1-4 leaves begin to senesce, weakening their ability to respond to potential invaders such as the fungus Colletotrichum graminicola, cause of anthracnose.
This fungus overwinters of infected leaves and stalks from the previous. This fungus produces very small spores that are carried easily in the wind. Spores landing on the young leaves can produce hyphae that penetrate through the leaf epidermis or through stomata. Vigorous growing leaves in most corn hybrids are mostly resistant to this fungus but weakened first few seedling leaves, as the naturally senesce may lose the ability to fight off the fungus at least in the epidermal cells. The result is a small elongate lesion from which the fungus produces more spores.
These first leaves are not usually damaged enough to hurt development of new leaves and later leaves appear to be mostly resistant. As these initial leaves die, this disease will not be noted until leaf senescence starts occurring late in season after grain fill. In this sense anthracnose is not an aggressive pathogen of corn, mostly being able to attack physiologically weakened plant tissue. The seems to be little correlation between the seedling occurrence of anthracnose and its appearance of corn stalks. I have seen the rare hybrid that would get considerable number of lesions on mid-season leaves and even that hybrid was noted for having superior stalk quality.
Although this fungus will cause long black streaks on outer cells of a corn stalk, there is evidence that it is only successful in rotting the stalk when the plant died from the depletion of the stalk and root from excessive movement of carbohydrates from those tissues to the grain.
Resistance to multiple pathogens, including Colletotrichum graminicola, is a dynamic interaction between the plant physiology and the potential pathogen.
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.