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Applied and Environmental Microbiology, January 2008, p. 136-142, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01538-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Host-Synthesized Secondary Compounds Influence the In Vitro Interactions between Fungal Endophytes of Maize{triangledown}

Megan Saunders* and Linda M. Kohn

Department of Ecology and Evolutionary Biology, University of Toronto, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6

Received 6 July 2007/ Accepted 19 October 2007

Maize produces a suite of allelopathic secondary metabolites, the benzoxazinoids. 2,4-Dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one and 2,4-dihydroxy-2H-1,4-benzoxazin-3-one reside as glucosides in plant tissue and spontaneously degrade to 6-methoxy-2-benzoxazolinone (MBOA) and 2-benzoxazolinone (BOA) upon plant cell disruption. Several maize-associated fungi in the genus Fusarium can metabolize MBOA and BOA. BOA tolerance levels in 10 species of Fusarium and in the maize endophytes Nigrospora oryzae, Acremonium zeae, and Periconia macrospinosa were characterized. BOA tolerance ranged from 0.25 to 1.10 mg/ml among species. The influence of substrate alteration by one species on the subsequent growth of another species was assessed in the presence and absence of BOA. The colony area of the secondary colonizer in heterospecific interactions was compared to that in autospecific interactions (one isolate follows itself). In the presence of BOA, four of six secondary colonizers had greater growth (facilitation) when primary colonizers had higher BOA tolerance than the secondary colonizer. When the primary colonizer had lower tolerance than the secondary, three of six secondary colonizers were inhibited (competition) and three not significantly affected. In BOA-free medium, the number of isolates that were facilitated or inhibited was the same regardless of the tolerance level of the primary colonizer. Two of six secondary colonizers were facilitated, two inhibited, and two not significantly affected. This study provides some support for facilitation in stressful conditions under the Menge-Sutherland model. The results are not consistent with the corresponding prediction of competition in the absence of stress. The hypothesis drawn from these data is that in the presence of a toxin, fungal species that detoxify their substrate can enhance the colonization rate of less tolerant fungi.

* Corresponding author. Mailing address: Department of Ecology and Evolutionary Biology, University of Toronto, 3359 Mississauga Road North, Mississauga, Ontario, Canada L5L 1C6. Phone: (905) 828-5338. Fax: (905) 828-3792. E-mail: msaunder{at}utm.utoronto.ca

{triangledown} Published ahead of print on 9 November 2007.

Applied and Environmental Microbiology, January 2008, p. 136-142, Vol. 74, No. 1
0099-2240/08/$08.00+0     doi:10.1128/AEM.01538-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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