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The infection processes of Sclerotinia sclerotiorum in cotyledon tissue of a resistant and a susceptible genotype of Brassica napus
Background and Aims Sclerotinia sclerotiorum can attack .400 plant species worldwide. Very few studies
have investigated host–pathogen interactions at the plant surface and cellular level in resistant genotypes of oilseed rape/canola (Brassica napus).
Methods Infection processes of S. sclerotiorum were examined on two B. napus genotypes, one resistant cultivar ‘Charlton’ and one susceptible ‘RQ001-02M2’ by light and scanning electron microscopy from 2 h to 8 d post-inoculation (dpi).
Key Results The resistant ‘Charlton’ impeded fungal growth at 1, 2 and 3 dpi, suppressed formation of appresoria and infection cushions, caused extrusion of protoplast from hyphal cells and produced a hypersensitive reaction.
At 8 dpi, whilst in ‘Charlton’ pathogen invasion was mainly confined to the upper epidermis, in the
susceptible ‘RQ001-02M2’, colonization up to the spongy mesophyll cells was evident. Calcium oxalate crystals were found in the upper epidermis and in palisade cells in susceptible ‘RQ001-02M2’ at 6 dpi, and throughout leaf tissues at 8 dpi. In resistant ‘Charlton’, crystals were not observed at 6 dpi, whereas at 8 dpi they were mainly confined to the upper epidermis. Starch deposits were also more prevalent in ‘RQ001-02M2’.
Conclusions This study demonstrates for the first time at the cellular level that resistance to S. sclerotiorum in B. napus is a result of retardation of pathogen development, both on the plant surface and within host tissues. The resistance mechanisms identified in this study will be useful for engineering disease-resistant genotypes and for developing markers for screening for resistance against this pathogen.
Key words: Canola, oilseed rape, white mould, stem rot, plant-pathogen interaction, incompatible interaction, protoplast extrusion, calcium oxalate, starch grains.
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