Back to the root of the problem

The plant that died early actually wilted.  It is frequently a plant that had more kernels than adjacent plants, Kernel numbers influence the distribution of sugars between the living tissue of the roots and the kernels. Water is constantly being lost from the corn plant through the leaves via transpiration. This needs to be replaced by water moving by osmosis into the roots from the soil.  This happens mostly in the young root tissue and then progresses up the xylem tissue in the vascular system because of the cohesion of water molecules.
 
Meanwhile the roots are existing in an environment full of microbes dependent on organic materials for energy.  A few species have the capacity to invade the root cells in a symbiotic relationship in which the root cells benefit from extra mineral uptake, especially phosphorus, while the corn root cell provides carbohydrates to these mycorrhizal fungi. There is some evidence that this relationship actually increases root length and more water uptake.
 
But it is complex down there and the plant cells need to ward off the other fungi that feed on any tissue. Living cells do respond by producing anti-microbe chemicals.  Growing root tips exude proteins but also some anti-fungal agent that wards off invasion.  It is difficult to study the full ecological interaction in roots but it is known that many different fungi eventually invade the roots.  The chemical defense and the growth of new root tips does take energy.  As available sugar supplies wane, the fungi invade.  Eventually fungi destroy young tissue and plug up xylem, causing insufficient water uptake to replace the transpiring water.  Then the plant wilts. Now fungi below and above the soil have free rein to invade the dead cells.  Some fungal species are mostly easily identified, and perhaps are dominant, in the root tissue and/or in the stalk, and consequently we give them the credit.  Gibberella, Diplodia, Anthracnose (Colletotrichum) and Fusarium stalk rots are common names but in actuality these fungi invaded dying and dead plant tissue.