Cytology

Bgh infected leaves were sampled at 48 hpi by taking 0.5 cm² leaf segments from 10 independent leaves per genotype. A modified 3,3-diaminobenzidine (DAB) uptake was carried out as described by Thordal-Christensen et al.³⁸. Triple staining with Evans blue, aniline blue and calcofluor white was performed following the protocol developed by Felix Mauch’s Group at the University of Fribourg³⁹. Trypan blue retention on 0.3 mm wide mesophyll cross sections was performed as described by van Wees⁴⁰ using Farmer’s fluid (acetic acid: ethanol: chloroform at 1:6:3) rather than chloral hydrate solution to de-stain the tissue. DAB staining of mesophyll cells was performed on epidermal strips as described by Thordal-Christensen et al.³⁸.