Abstract
Viewing of Phytophthora cinnamomi by microscopic examination in planta is often difficult as structures such as hyphae, chlamydospores and oospores are often indistinguishable from those of other fungi with histological stains not enabling species differentiation. This lack of staining specificity makes the localisation of P. cinnamomi hyphae and reproductive structures within plant tissue difficult, especially in woody tissues. This study demonstrates that utilising a species-specific fluorescently labelled DNA probe allowed P. cinnamomi to be specifically detected and visualised using fluorescent in situ hybridisation (FISH) without damage to plant or pathogen cell integrity. This approach provides a new application of FISH with potential use in the study of plant-pathogen interactions in planta.