Submitted to: Mycological Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/7/2004
Publication Date: 6/14/2005
Citation: Wicklow, D.T., Roth, S., Deyrup, S.T., Gloer, J.B. 2005. A protective endophyte of maize: Acremonium zeae antibiotics inhibitory to Aspergillus flavus and Fusarium verticillioides. Mycological Research. 109(5):610-618. Interpretive Summary: Acremonium zeae is a type of fungus called an endophyte that is commonly isolated from healthy corn plants or corn kernels showing no visible symptoms of disease. Cultural tests have shown that this endophyte is antagonistic to Aspergillus flavus and Fusarium verticillioides, both species of toxin-producing molds that cause substantial annual losses to the U.S. corn crop. Chemical studies revealed that the metabolites accounting for this activity were two newly reported antibiotics pyrrocidines A and B. Pyrrocidine B was detected in grain from ears of a commercial hybrid that were inoculated in the 'milk stage' of kernel maturity with pyrrocidine producing cultures of Acremonium zeae. This is the first report of natural products from Acremonium zeae. These results invite further studies to reveal those environmental conditions under which this protective endophyte becomes the dominant fungus in corn, as well as the potential use of antagonistic cultures of Acremonium zeae as biocontrol agents to eliminate aflatoxin and fumonisin contamination in corn at harvest. The corn seed industry will benefit from the knowledge that Acremonium zeae may be a confounding variable impacting the results of resistance trials for aflatoxin/fumonisin as well as other fungal or bacterial pathogens.
Technical Abstract: The maize endophyte Acremonium zeae Gams and Sumner is antagonistic to kernel rotting and mycotoxin producing fungi Aspergillus flavus and Fusarium verticillioides in cultural tests for antagonism and interferes with A. flavus infection and aflatoxin contamination of preharvest maize kernels. Chemical studies of an organic extract from maize kernel fermentations of A. zeae NRRL 13540, which displayed significant antifungal activity against A. flavus and F. verticillioides, revealed that the metabolites accounting for this activity were two newly reported antibiotics pyrrocidines A and B. Pyrrocidines were detected in fermentation extracts for twelve NRRL cultures of A. zeae isolated from maize kernels harvested in Illinois (4/4 cultures), North Carolina (5/5), Georgia (1/2) and "USA" (2/2). Pyrrocidine B was detected by LCMSMS in whole symptomatic maize kernels removed at harvest from ears of a commercial hybrid that were wound-inoculated in the milk stage with A. zeae NRRL 13540 or NRRL 13541. In an evaluation of cultural antagonism between 13 isolates of A. zeae in pairings with A. flavus NRRL 6541 and F. verticillioides NRRL 25457, A. zeae NRRL 6415 and NRRL 34556 produced the strongest reaction, inhibiting both organisms at a distance while continuing to grow through the resulting clear zone at an unchanged rate. Potential interactions between A. zeae and other maize endophytes are considered and the significance of these interactions relative to the aflatoxin and fumonisin contamination of preharvest maize is presented. This is the first report of natural products from Acremonium zeae.