Written by Juniper Kiss.
Powdery mildews are common obligate biotrophic fungal pathogens of many crops and wild plants worldwide. Their colonies are often attacked in the field by mycoparasitic fungi belonging to the genus Ampelomyces.
The mycoparasites penetrate the hyphae of powdery mildews on the host plant surfaces, and continue their development intracellularly, i.e. inside the powdery mildew hyphae. The asexual and the sexual sporulation of the parasitized powdery mildew colonies is reduced, or completely stopped, and a part of the colonies are killed by Ampelomyces. Since the 1980s, some Ampelomyces strains have been commercialized as biocontrol agents of crop pathogenic powdery mildews. The tritrophic interactions between host plants, powdery mildews and Ampelomyces mycoparasites have been recognized first in the 19th century by Heinrich Anton De Bary, the ‘Founding Father of Plant Pathology’.
Nemeth et al. (2019) genetically modified two strains of Ampelomyces to express the Green Fluorescent Protein (GFP) in their hyphae and spores. These transformants emit green light when examined with fluorescence microscopy, even when they are growing inside the cells of the powdery mildews. Thus, the detection of Ampelomyces structures was greatly enhanced with this technique when diverse powdery mildews, as well as leaf and soil samples containing GFP-expressing Ampelomyces transformants, were examined with fluorescence microscopy compared to other microscopic methods.
The authors showed for the first time that Ampelomyces can persist up to 21 days on mildew-free host plant surfaces, where it can attack powdery mildew structures as soon as these appear after this period. They have also revealed that these mycoparasites cannot sporulate in decomposing, powdery mildew-infected leaves on the ground, or in sterile soil samples. These results indicate that Ampelomyces cannot spread extensively as a saprobe in the environment; instead, it acts primarily as a mycoparasite of powdery mildews on host plant surfaces.
The publication is the Editor’s Pick from the August issue of Phytopathology and it is open access: https://apsjournals.apsnet.org/doi/full/10.1094/PHYTO-01-19-0013-R