Stalk rot cause is not simple
There is a tendency to give the identity of the most obvious fungus in a rotting stalk as the cause when significant lodging occurs in a corn field. It is Diplodia, or Anthracnose or Fusarium or Gibberella because these are the most easily identified fungi on the rotting material. In fact, multiple other fungi are probably in the same stalk rotting the dead stalk tissue. Most importantly, these fungi did not cause the stalk tissue to die but entered after the stalk tissue died. Living corn tissue fends off these and the many other potential saprophytes in and on soil debris. Any of these fungi successfully invade the stalk tissue when the plant tissue no longer produces the metabolites to fend off these potential saprophytes.
When analyzing the cause of significant stalk rot in a field, one needs to look for the reason the plant lost its ability to fend off the fungus and lost its strength to stay upright. A third of that strength is due to the lower stalk tissue that has pith tissue connected to the outer rind cells, essentially forming a rod. These pith cells are large parenchyma cells filled with liquid and stored, soluble carbohydrates. These carbohydrates are available to the roots for their metabolism and, when called upon by the hormones directing flow, also to the newly forming kernels. If previous and continuing photosynthesis in the plant produces enough carbohydrate to meet the demand of the kernels and the roots the plant maintains succulent, living pith tissue throughout the stalk and thereby maintaining the stalk strength. Potential invaders are warded off by the metabolism of those living cells.
Discerning the cause of why one plant died and lodged and not all plants require a more diligent search than simply naming the most obvious fungus. Pith tissue died prematurely and shrunk away from the stalk rind, changing the structure from a solid rod to a hollow tube. Furthermore, those multiple saprophytes easily invaded the dead tissue, further weakening the stalk.
The analysis of why has to include reasons why was there not enough carbohydrate in the pith tissue of the rotted stalk to maintain living pith cells. It is not as simple as naming the dominant fungus in the dead stalk
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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.