Effects of Induced Resistance on Disease Severity/Yield Relations in Mildewed Barley

Field experiments showed that the treatment of winter barley with microbial metabolites produced by a Bacillus subtilis strain led to increased yields in spite of a remaining mildew infection. Disease severity/yield relations obtained on a single tiller basis for either mildew infection at EC 75 or area under disease progress curve (AUDPC) were negatively correlated for untreated plants (R²= 89%, 94%) while this relation did not exist for inducer-treated ones (R²= 10%, 13%). Despite an increasing infection density. yields of main tillers of inducertreated plants were not decreased. On the other hand area under green leaf area curve (AUGLAC) showed a higher correlation with grain yield (R²= 89%) of inducer-treated plants. Possible explanations for the mitigated damaging effect of powdery mildew were expected in carbohydrate metabolism. especially carbohydrate formation and translocation. Assimilation rates of flag leaves of inducer-treated barley with similar infection densities to those of untreated plants were increased over a prolonged period and even exceeded those of non infected ones. In inducer-treated plants the export of ¹⁴CO₂ from flag leaves into ears remained unimpaired by mildew infection and the allocation of assimilates to grains was highest at late stages of grain filling. Obviously plants were stimulated by inducer treatments to compensate for the damaging effect of powdery mildew and to tolerate mildew infection without yield loss.