Another Fusarium species, Fusarium graminearum, forms a sexual stage of the fungus when its mating types combine. That sexual stage is identified by the name of Gibberella zeae. This fungus is associated with Gibberella stalk rot and wheat scab. The fungus is common in corn debris, producing huge numbers of Fusarium spores during much of the corn-growing season. Spores germinate on the silks, with the fungal filaments growing down the silk channel towards the ovule. Generally, if pollen tube growth reaches the ovule first, the following collapsing, dry silk tissue effectively stops the fungus. Silks are most vulnerable during cool, wet weather as pollen spread is poor but fungal spore production is high. This results with a prolonged period of silk exposure. Later infection of the kernels appears to be related to kernels physically injured by hail or insects. Husk leaves tightly wrapped around the ear also appears to be related to spread of this mold within the ear.
Early infected kernels will fail to develop completely, will be light in weight and often will not germinate if planted as seed. Later infection can spread to cover much of the ear with a mold as the fungus spreads from the initial infection area. This mold produces mycotoxins including deoxynivalenol (DON). This toxin is associated with severe health problems in swine. The fungal spores produced among the grain also can be detected by swine and cows, causing them to reject the grain. I recall a personal situation in which I was a sent a corn sample from seed dealer who claimed that newly harvested grain was rejected by pigs and calves. Observation of the grain in my lab showed lots of Fusarium spores- so much that I asked to see the storage bin where the grain was stored. A single hand full of the grain from the bin revealed a cloud of spores. The grain was dried in the bin by air being blown from the bottom up through the bin. This air, however was moved over an accumulation of previous year’s debris below the grain. A sampling of that debris revealed that it was heavily infected with Fusarium. The new crop was being inoculated with the fungus as it was being dried.
DON has been shown to accumulate in grain stored at moisture higher than 20.5%. One should assume that the fungus is ubiquitous and that monitoring the grain drying and storage is important to avoiding this toxin problem.
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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.