Infection and colonization of triticale by Puccinia graminis f. sp. tritici

Histological investigations elucidate infection structure development and the subsequent colonization process of rust pathogens in their cereal hosts. No comprehensive information exists for the infection process of the wheat stem rust fungus, Puccinia graminis f. sp. tritici (Pgt), on triticale, an amphiploid species carrying both the wheat and rye genomes. The adult plant stem rust response of the triticale cultivars 'Kiewiet', 'Coorong' and 'Satu' and the bread wheat control, Line 37-07, was determined under controlled conditions using Pgt pathotypes UVPgt56, UVPgt60 and UVPgt62. Flag leaf sheaths were sampled 24 and 48 h post-inoculation (hpi) for scanning electron microscopy (SEM), 120 hpi for fluorescence microscopy, and 16 days post-inoculation for a fungal biomass assay. Although slight differences were observed between the epidermal morphology of triticale and wheat stem sheaths, SEM results indicated that this did not influence early infection by Pgt. Fluorescence microscopy revealed that colony size was affected by both host genotype and pathotype. Colony size strongly corresponded with fungal biomass accumulation, except in 'Kiewiet', where fungal growth was not restricted to the same degree as in other incompatible interactions. This study shows that methods commonly used for studying histopathology of Pgt in wheat are equally applicable to triticale.