Induced inaccessibility and accessibility in the oat powdery mildew system: insights gained from use of metabolic inhibitors and silicon nutrition

Fungal-induced inaccessibility in oat to Blumeria graminis requires active cell processes. These are reiterative de novo cell processes involved in inherent penetration resistance. Therefore, induced inaccessibility may well involve cellular memory of the initial attack. Phenylpropanoid biosynthesis inhibitors (AOPP and OH-PAS) and phosphate scavengers (DDG and d-mannose) strongly suppressed induced inaccessibility, but silicon nutrition had no effect. Induced accessibility was modulated by the presence of fungal haustoria inside cells. Haustoria actively suppress or reprogram infected plant cells toward a constant state of penetration susceptibility. Neither inhibitor treatments nor silicon nutrition affected fungal-induced accessibility.