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Applied and Environmental Microbiology, February 2008, p. 823-832, Vol. 74, No. 3
0099-2240/08/$08.00+0     doi:10.1128/AEM.01165-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Root Infection and Systemic Colonization of Maize by Colletotrichum graminicola

Serenella A. Sukno,^1,2* Verónica M. García,¹ Brian D. Shaw,¹ and Michael R. Thon^1,2

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843 Centro Hispano-Luso de Investigaciones Agrarias (CIALE), Departamento de Microbiologia y Genética, Universidad de Salamanca, 37007 Salamanca, Spain

Received 24 May 2007/ Accepted 15 November 2007

Colletotrichum graminicola is a filamentous ascomycete that causes anthracnose disease of maize. While the fungus can cause devastating foliar leaf blight and stalk rot diseases, little is known about its ability to infect roots. Previously published reports suggest that C. graminicola may infect maize roots and that root infections may contribute to the colonization of aboveground plant tissues, leading to disease. To determine whether C. graminicola can infect maize roots and whether root infections can result in the colonization of aboveground plant tissues, we developed a green fluorescent protein-tagged strain and used it to study the plant root colonization and infection process in vivo. We observed structures produced by other root pathogenic fungi, including runner hyphae, hyphopodia, and microsclerotia. A mosaic pattern of infection resulted from specific epidermal and cortical cells becoming infected by intercellular hyphae while surrounding cells were uninfected, a pattern that is distinctly different from that described for leaves. Interestingly, falcate conidia, normally restricted to acervuli, were also found filling epidermal cells and root hairs. Twenty-eight percent of plants challenged with soilborne inoculum became infected in aboveground plant parts (stem and/or leaves), indicating that root infection can lead to asymptomatic systemic colonization of the plants. Many of the traits observed for C. graminicola have been previously reported for other root-pathogenic fungi, suggesting that these traits are evolutionally conserved in multiple fungal lineages. These observations suggest that root infection may be an important component of the maize anthracnose disease cycle.

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* Corresponding author. Mailing address: Centro Hispano-Luso de Investigaciones Agrarias (CIALE), Departamento de Microbiología y Genética, Universidad de Salamanca, Avda. Campo Charro s/n, 37007 Salamanca, Spain. Phone: 34 923 294400, ext. 1936. Fax: 34 923 294663. E-mail: ssukno{at}usal.es

Published ahead of print on 7 December 2007.

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Applied and Environmental Microbiology, February 2008, p. 823-832, Vol. 74, No. 3
0099-2240/08/$08.00+0     doi:10.1128/AEM.01165-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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