Description:
AbstractShot holes on oriental cherry (Prunus serrulata var. spontanea) leaves were investigated to evaluate their role in the elimination of pathogens using analytical electron microscopy. Small brown spots caused by Mycosphaerella cerasella appeared on the leaf surface and developed into shot holes that were approximately 1–5 mm in diameter. Field emission scanning electron microscopy revealed clusters of fungal conidiophores and hyphal growth on the leaf surface around the shot holes. The fungal structures were mostly located within a radius of 500 μm from the shot holes and confined to the epidermal sector separated by veins. X‐ray microanalysis revealed distinct calcium ring patterns encircling the shot holes. The abscised surfaces consisted of suberized plant cells colonized with filamentous fungi and yeasts. Embedded in the mesophyll tissue, druse crystals were co‐localized with calcium and oxygen. Despite the fungal presence around the shot holes, no further expansion of the shot holes was observed on the leaf surface. These results suggest that shot holes may represent an incomplete but neutral abscission of infection loci in the presence of necrotrophic fungal pathogens. This microscopy study provides insight into the formation and roles of calcium oxalate in plants under pathological conditions.