Signal Molecules Inducing Systemic Resistance and Susceptibility in Barley Seedlings

Exudate collected from the cut end of barley seedlings exhibited both activities that induced systemic resistance and susceptibility against Erysiphe graminis f. sp. hordei race Hh4 depending on the time after pruning. Exudates collected between 3–6 h after pruning showed maximum activity that induced systemic resistance, whereas those during 9–12 h conversely induced susceptibility in barley seedlings. The accumulation of antifungal substances in barley leaves correlates to the timing, of induced resistance. The antifuntingal substances were watersoluble and severely affected the infection of E. graminis f. sp. hordei.