Alternaria brassicae interactions with the model Brassicaceae member Arabidopsis thaliana closely resembles those with Mustard (Brassica juncea)

Progression of Alternaria brassicae infection on B. juncea cv. Varuna and A. thaliana accession Gre-0. Comparative analysis of macroscopic infection phenotypes 7 dpi on Varuna leaf upon artificial inoculation (a), under field conditions (b), and upon artificial inoculation on Gre-0 leaf surface (c). Initiation of spore germination at 6 hpi from terminal and intercalary cells of conidiophores on Varuna (d) and Gre-0 (e). Conidia with multiple branched hyphae were observed at 24 hpi on the surface of Varuna (f). Hyphae forming ALS near the stomatal opening on Varuna leaf surface (g). Penetration via stomata on Varuna leaf surface (h, i), Gre-0 (k) at 48 hpi. SEM image showing hyphal growth on the Varuna leaf surface at 72 hpi (j). Direct fungal penetration through epidermal cell junctions on Gre-0 leaf surface at 48 hpi (l). Fungal invasion into the healthy mesophyll cells at 96 hpi (m) and darkly stained dead cells at the site of inoculation at 96 hpi (m′). Ramified hyphal growth between the two mesophyll cells at 96 hpi (n). Re-emergence of young fungal hyphae through the stomata of Varuna 6 dpi (o