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Applied and Environmental Microbiology, February 2007, p. 1277-1286, Vol. 73, No. 4
0099-2240/07/$08.00+0     doi:10.1128/AEM.01620-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Role of Microbial Immigration in the Colonization of Apple Leaves by Aureobasidium pullulans{triangledown}

Molly J. McGrath{dagger} and John H. Andrews*

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

Received 12 July 2006/ Accepted 20 November 2006

The role of microbial immigration in the veinal colonization pattern of Aureobasidium pullulans on the adaxial surface of apple leaves was investigated in two experiments at two periods (early and late seasons) in 2004 by applying green fluorescent protein (GFP)-tagged blastospores to the foliage of orchard trees. Individual leaves were resampled by a semidestructive method immediately after inoculation (t0) and about 1 (t1), 2 (t2), and 3 (t3) weeks later. At t0, there were no significant (P ≤ 0.05) differences in densities (cells/mm2) on veinal (excluding midvein) sites and those on interveinal sites, but at all points thereafter, densities were significantly higher on veins. GFP-tagged A. pullulans cells remained primarily as singletons on interveinal regions (≥90% at all points), while ≥20% of cells over veins at t3 were in colonies of ≥4 cells. The colonies that developed from single cells placed on midveins and other veins were significantly larger than those that developed on interveinal regions of detached field and seedling leaves incubated under controlled conditions. Colonies primarily developed linearly along veins, reaching average colony sizes (72 h) of 24.4 ± 12.7 (mean ± standard deviation) cells. In contrast, colonies on interveinal regions tended to average only 2.9 ± 1.3 cells, with less linearity. To examine the potential role of A. pullulans growth-inhibiting factors associated with interveinal features, single GFP-tagged A. pullulans cells in droplets previously incubated on interveinal sites were placed on midveins and compared to midvein colonies derived from cells in a water-only suspension. No differences in colony size resulted. Our results indicate that immigration limitation and growth-inhibiting factors are not the primary factors responsible for A. pullulans veinal colonization patterns in the field. Rather, indirect evidence suggests that growth-promoting substances occur locally in the veinal areas.

* 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.

{triangledown} Published ahead of print on 1 December 2006.

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

Applied and Environmental Microbiology, February 2007, p. 1277-1286, Vol. 73, No. 4
0099-2240/07/$08.00+0     doi:10.1128/AEM.01620-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Slepecky, R. A., Starmer, W. T. (2009). Phenotypic plasticity in fungi: a review with observations on Aureobasidium pullulans. Mycologia 101: 823-832 [Abstract] [Full Text]  


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