Submitted to: Canadian Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 8, 1996
Publication Date: N/A
Interpretive Summary: Corn is parasitized by the mold Fusarium moniliforme, and it produces several compounds that are toxic to horses and swine. Corn contaminated with this mold is correlated with human esophageal cancer. The mold is very common and it or its toxins are found on almost every kernel of corn and in corn byproducts. It is not known exactly how all corn is contaminated with this mold and its toxin, so scientists at RRC examined the nature of the association of the mold during the growth of corn plants using light and electron microscopy. The results indicate that corn plants can be 100% infected with the fungus and never show any signs of infection throughout the growth of corn, and very seldom is there a disease produced by the fungus. Further, we showed that the mold has infected plants internally two days after germination. This type of infection is referred to as symptomless and, since the mold is found inside the plant, it is endophytic. It is this symptomless endophytic association with corn that should be considered the manner by which the production of toxins is accomplished, and it offers an explanation of how food grade corn may contain toxins and yet go unnoticed, i.e., non-moldy.
Technical Abstract: Fusarium moniliforme Sheldon is a nonobligate parasite of maize that produces several mycotoxins. This fungus causes systemic infections of maize kernels, which then serve as dissemination vehicles and inoculum sources. Infected plants may or may not show disease symptoms. Symptomless infection was studied in maize plants, and was compared with plants that eventually showed symptoms of seedling disease. Three isolates of F. moniliforme, a hygromycin mutant of two of these isolates, and F. fujikuroi were used to infect surface and internally sterilized maize kernels, and symptomatic and symptomless infections were observed for 8 weeks. The results indicated that in symptomless infected plants, hyphae were intercellular only and distributed throughout the plant, whereas in plants showing disease symptoms, the fungus was both intercellular and intracellular. Symptomless plants remained symptomless throughout the observation period, and at the ultrastructural level there was no evidence of an antagonistic relationship. This indicates that the symptomless state persists beyond the seedling stage and could contribute, without visual signs, to the total mycotoxin contaminants of maize both before and during kernel development.