The toxin fumonisin causing severe disease in horses and other mammals is produced in corn by the fungal species Fusarium verticillioides. This species, once known as Fusarium moniliforme, if a commonly associated with corn worldwide. Whereas other Fusarium species associated with corn are frequent in soil, this species is more dependent on existence is corn debris between crop seasons. The fungus does invade corn seedling roots, especially if root growth is slow due to low temperatures and/or injured by insect feeding.
Fumonisin production by the fungus is linked to a few genes in the fungus leading to some variation among the isolates of F. verticilloidesin production of fumonisin. There is evidence that fumonisin production by the fungus assists in overcoming the plant’s resistance system by causing plant cell death. Fumonisin produced in roots has been shown to be transported to the leaves of the corn plant.
Growth of this fungus in seedling roots is linked to slow growth of the seedling, mostly due to low temperatures. After initial infection, the fungus produces conidia small enough to be carried in the xylem through the complex first node separating the mesocotyl from the coleoptile. It has been noted that low light conditions are associated with more rapid spread from the root to the above ground-portions of the corn plant. This implies that plant physiological condition associated with photosynthesis affects the ability of the fungus to spread within the corn plant.
Fusarium verticilloidesalso infects the kernels through the silk (style). There is evidence that corn genetics associated with the size of the small opening at the tip the corn ovary allowing the pollen entrance is associated with successful early invasion of hyphae of this fungus. Environmental stresses during kernel formation, including insect feeding is also associated with invasion by this fungus.
Corn’s association with this fungus is complex and seemingly ubiquitous. The fungus often appears to be an endophyte, causing no visible harm. Not all variants of the fungus produce fumonisin. Seedlings growing in good environments infected with F. verticilloidesmay express limited damage. Not all kernels infected with this fungus produce fumonisin. It is one of the inhabitants of corn’s environment that can produce a toxin.
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.