Temporal changes in microscale colonization of the phylloplane by Aureobasidium pullulans

Area of Science:

• Plant Pathology
• Microbial Ecology
• Mycology

Background:

• Apple leaf surfaces host diverse microbial communities.
• Understanding fungal colonization patterns is crucial for plant health and disease management.
• Aureobasidium pullulans is a common yeastlike fungus found on plant surfaces.

Purpose of the Study:

• To quantitatively and spatially map the colonization of apple leaves by Aureobasidium pullulans.
• To determine the preferred colonization sites and morphotypes of A. pullulans on apple leaves.
• To track the temporal dynamics of A. pullulans populations throughout two growing seasons.

Main Methods:

• Quantitative and spatial analysis of A. pullulans on field-collected apple leaves over two growing seasons.
• Use of A. pullulans-specific fluorescence in situ hybridization (FISH) probes and epifluorescence microscopy.
• Enumeration of total cells, swollen-cells and chlamydospores (SCC), and blastospores per mm(2) on specific leaf features (midvein, other veins, interveinal regions).

Main Results:

• A. pullulans cell numbers were significantly higher on midveins and other veins compared to interveinal regions throughout both growing seasons.
• The swollen-cell and chlamydospore (SCC) morphotype was dominant, while blastospores were found in low numbers.
• Leaf vein occupancy approached 100% by the end of the growing seasons, with colony formation observed on veins but not in interveinal regions.

Conclusions:

• Aureobasidium pullulans primarily colonizes apple leaf veins, where its populations increase through in situ growth.
• This vein-specific colonization pattern is established early in the growing season and is maintained throughout.
• The findings highlight the importance of leaf venation as a key habitat for A. pullulans on apple leaves.