The isolation and characterization of Taphrina betulina and other yeasts residing in the Betula pendula phylloplane.

The phylloplane is an important microbial habitat and a reservoir of organisms that affect plant health, both positively and negatively. Taphrina betulina is the causative agent of birch witches′ broom disease. Taphrina are dimorphic, invading theirs hosts in a filamentous form and residing in the host phyllosphere in their non-infectious yeast form. As such, they are widely accepted to be found a resident yeasts on their hosts, even on healthy tissues; however, there is little experimental data to support this. With the aim of exploring the local infection ecology of T. betulina, we have isolated yeasts from the phylloplane of birch, using three classes of samples; from infected symptom bearing leaves inside brooms, healthy leaves from branches away from brooms on broom bearing trees, and symptom-free leaves from symptom-free trees. Isolations yielded 224 yeast strains, representing 11 taxa, including T. betulina, which was the most common isolate and was found in all sample classes, including asymptomatic leaves. Genotyping with two genetic markers revealed genetic diversity among these T. betulina isolates, with seven distinct genotype differentiated by the markers used. Of the 57 T. betulina strains, 22 representative strains were selected for further studies and preliminarily characterized, revealing differences in size and the ability to produced compounds with activity to activate the signalling pathway for the plant hormone auxin.