Fusarium in the stalk

​Fusarium species that are often found in dead and live corn plant stalks initially grow between cells, producing enzymes to digest the walls of the pith cells and fibers.  These walls are composed of complex cellulose compounds combined with proteins and basic carbohydrate molecules, formed by biological activity within the living cells and secreted through the cellular membranes.  These compounds protect the cellular contents by structure and some active resistance products as well.  Cell wall components include cellulose, arabinoxylans, hydroxycinnamates, pectins, glycoproteins and lignins.
 
Fungi initially grow between the cells, secreting enzymes to digest the cell wall structures.  Meanwhile living corn cells produce compounds such as Jasmonic acid, abscisic acid and salicylic acid to limit the growth of the Fusarium species.  This battle begins with the first incursion of the fungus, perhaps with injury to the seedlings or perhaps with corn borer.  Artificially infecting the stalk with any of the fungi associated with corn stalk rot shortly after pollination usually shows infection limited to area near to point of inoculation.  As the tissue matures the fungi seem to more rapidly spread, digesting more cell walls.  Breaking down the complex compounds allows the fungus to utilize more simple carbohydrates for their own metabolism.
 
Digestion of the cell wall components weakens the strength of the stalk beyond the sudden decrease of strength that occurred with the plant wilted after root rot.  The wilting caused the pith cells to withdraw from the rind, effectively changing the structure from a rod to a tube.  This alone is believed to reduced strength by one-third.   Corn hybrids that tend to construct more and stronger cells in the rind can have less lodging but the physical change from a rod to tube is difficult to match by cell wall strength alone.
 
Maintaining sturdy stalks until harvest is a balance among producing sufficient carbohydrates for filling all kernels, avoiding wilt by delaying death of root cells and maintaining stalk cells alive to fend off potential pathogens such as Fusarium species.  Acceptable grain yields and standability occurs when the potential stresses from low light, leaf diseases, mineral deficiencies and insect damage are matched by the hybrid producing sufficient photosynthesis to balance these three needs within the plants.