Induced inaccessibility in barley cells exposed to extracellular material released by non-pathogenic powdery mildew conidia

Before germinating, conidia of Blumeria graminis f. sp. hordei ( Bgh) and tritici ( Bgt) and Erysiphe pisi ( Ep) rapidly released extracellular material (ECM) onto barley coleoptile cells. More was released if full rather than partial cell contact was made. Within 5–6.5 h of receiving ECM from Ep or Bgt (non-pathogens) cells showed induced inaccessibility to challenger Bgh. This effect was greater for Ep than Bgt where full contact was required. Abiotic particles and ECM from Bgh did not affect cells' accessibility to subsequent challenger attack by Bgh. This induced inaccessibility must be due to active component(s) within conidial ECM.