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Applied and Environmental Microbiology, September 2006, p. 6234-6241, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.00744-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Temporal Changes in Microscale Colonization of the Phylloplane by Aureobasidium pullulans

Molly J. McGrath and John H. Andrews^*

Plant Pathology Department, University of Wisconsin, Madison, Wisconsin 53706

Received 30 March 2006/ Accepted 19 June 2006

Colonization of apple leaves by the yeastlike fungus Aureobasidium pullulans was followed quantitatively and spatially at a microscale level throughout two growing seasons. Ten field leaves were sampled on 11 dates in 2003 and 15 dates in 2004. Using an A. pullulans-specific fluorescence in situ hybridization probe and epifluorescence microscopy, we enumerated total cells, swollen-cells and chlamydospores (SCC), and blastospores/mm² on leaf features, including the midvein, other (smaller) veins, and the interveinal regions. By 7 July 2003 and 7 June 2004, the total numbers of A. pullulans cells/mm² were significantly higher (P < 0.05) on the midvein and other veins than in the interveinal regions. This pattern remained consistent thereafter. The primary colonizing morphotype in all regions at all dates was the SCC form, although blastospores always occurred in low numbers. Occupancy was quantified based on the percentage of microscope fields of a particular leaf feature containing 1 A. pullulans cell. In general, as seasons progressed, the percent occupancy of features increased and, for most midvein and veinal features, approximated 100% at the end of both growing seasons. Except for early collections, when A. pullulans cell numbers were low, the percent occupancy of interveinal regions was lower than that of the midvein or other veinal regions. A. pullulans was distributed primarily as single cells throughout the seasons in interveinal regions. On the midvein and other veins, colonies of 4 cells developed over time, and more cells occurred in colonies than as singletons by August. Our results demonstrate that A. pullulans primarily colonizes veins, where populations appear to increase by growth in situ. This pattern is established early in the growing season and persists.

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* Corresponding author. Mailing address: Plant Pathology Department, 1630 Linden Dr., University of Wisconsin, Madison, WI 53706. Phone: (608) 262-9642. Fax: (608) 263-2626. E-mail: jha{at}plantpath.wisc.edu.

Present address: Plant Pathology Department, Michigan State University, East Lansing, MI 48824.

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Applied and Environmental Microbiology, September 2006, p. 6234-6241, Vol. 72, No. 9
0099-2240/06/$08.00+0     doi:10.1128/AEM.00744-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• McGrath, M. J., Andrews, J. H. (2007). Role of Microbial Immigration in the Colonization of Apple Leaves by Aureobasidium pullulans. Appl. Environ. Microbiol. 73: 1277-1286 [Abstract] [Full Text]