Isolation of Powdery Mildew Haustoria from Infected Barley

Blumeria graminis is a fungus that causes powdery mildews on grasses, such as barley. Investigations of this pathogen present many challenges due to its obligate biotrophic nature. This means that the fungus can only grow in the presence of a living host plant. B. graminis forms epiphytic mycelia on the plant surface and feeding organs (haustoria) inside the epidermal cells of the host plant. Therefore, it is difficult to separate the fungus from plant tissues. This protocol shows how to obtain different fungal structures from powdery mildew infected barley leaves. The epiphytic mycelia including conidia and conidiophores can be separated after immersing the infected leaves into 5% cellulose acetate dissolved in acetone, and peeling off the cellulose acetate membrane. Then, the haustoria are isolated from dissected epidermis after cellulase degradation of plant cell walls. The isolated haustoria remain intact with few plant impurities. The haustoria may be visualized by epifluorescence microscopy after staining with the chitin-specific dye WGA-Alexa Fluor 488. Finally, dissected material can be either processed immediately or kept at -80 °C for long-term storage for studies on gene expression and protein identification, for example by mass spectrometry.