Shown are trypan blue-stained Arabidopsis leaves at 6 days after spray-inoculation with Hpa. White (class I), absent or minimal colonisation; light blue (class II),≤50% leaf area colonised by the pathogen; dark blue (class III), ≤75% leaf area colonised by the pathogen, presence of conidiophores; black (class IV), >75% leaf area colonised by the pathogen, conidiophores and abundant sexual spores. Green arrows indicate colonisation by pathogen hyphae; blue arrows indicate hyphae surrounded by trailing necrosis, red arrows indicate conidiophores, black arrows indicate sexual oospores. Insets on the right show higher magnifications of colonisation markers. Scale bar = 50 μm.