Prominent ear rotting fungi such as Aspergillus flavus, Stenocarpella maydis (Diplodia), Fusarium verticilloides and Fusarium graminearum (Gibberella zeae) have multiple ways of attacking the developing ear. One of the means of attack is through the silk. Fusarium species have been shown to travel through the silk channel and through the micropyle into the pollinated ovule. Others have been shown to move on the surface of the silks to infect the developing kernel pericarp. If the pericarp and seed coat of the developing kernel is wounded by insects such as ear worm, the fungus gains entry into the kernel. Stenocarpella maydis can enter through silk, but often infects the base of the ear and surrounding husk tissue. From stem tissue at the base of ear it grows in the young developing ear. Aspergillus flavus, producer of aflatoxin, grows on the surface of silk and then on the surface of kernels, entering the kernels only with injury.
All of these fungi persist in soils but differ how they are favored with environments. Timing of rain seems to greatly affect the occurrence of the infection. There are varietal differences in resistance to each of them that can be measured in controlled conditions. Field evaluations based upon natural infection carries risks of faulty conclusions because stresses that cause delays in silking because of soil drainage differences, or maturity differences in relation to time of rain can be confusing. There are times when a variety may appear to be susceptible in one variety display plot but the same hybrid with different planting date would be judged as resistant in another plot. Caution is advised in drawing conclusions concerning resistance among corn hybrids.
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.