Characterization of a Basidiomycete fungus from stored sugar beet roots

Abstract

Eighteen isolates from sugar beet roots associated with an unknown etiology were characterized based on observations of morphological characters, hyphal growth at 4–28 C, production of phenol oxidases and sequence analysis of internal transcribed spacer (ITS) and large subunit (LSU) regions of the ribosomal DNA (rDNA). The isolates did not produce asexual or sexual spores, had binucleate hyphal cells with clamp connections, grew 4–22 C with estimated optimal growth at 14.5 C and formed a dark brown pigment on potato dextrose or malt extract agar amended with 0.5% tannic acid. Color changes observed when solutions of gum guiac, guiacol and syringaldzine were applied directly to mycelium grown on these media indicated that all isolates produced phenol oxidases. Sequences of ITS and LSU regions on the rDNA gene from 15 isolates were 99.2–100% identical, and analysis of sequence data with maximum likelihood and maximum parsimony suggest that the isolates from sugar beet roots are phylogenetically related to Athelia bombacina, Granulobasidium vellereum and Cyphella digitalis. High statistical support for both loci under different criteria confirmed that Athelia bombacina was consistently the closest known relative to the sugar beet isolates. Additional taxonomic investigations are needed before species can be clarified and designated for these isolates.

• Agaricomycotina
• Basidiomycota
• beet storage
• Beta vulgaris
• root rot

Acknowledgments

We thank Lisa Bukovnik (Duke University, IGSP Sequencing and Genetic Analysis Facility) for her help, Pam Purvear for assistance in literature searches, Julien Crovadore for providing a culture of the apple isolate from Switzerland, and the Snake River Sugar Beet Growers, Beet Sugar Development Foundation and Amalgamated Sugar Co. for assistance and support of this research.

We also thank the USDA CSREES (grants 2007-34500-15893 and 2008-34500-19396 to MAC) for financial support.

These data support the objectives of the United States Department of Agriculture CRIS project 5368-21220-002-00D.