THE EFFECTIVENESS OF INDUCED RESISTANCE ON YIELD OF MILDEWED BARLEY

In field experiments, the treatment of winter barley with an inducer o f resistance produced by a Bacillus subtilis strain led to an increase d yield after infection with powdery mildew, which could not be accoun ted for the reduction of disease severity alone. Possible reasons for the modified disease-yield-relationship of induced resistant plants we re characterized investigating the formation and translocation of carb ohydrates. The assimilation rates of flag leaves of induced resistant plants increased despite of a remaining infection with powdery mildew which also became obvious in high starch contents of grains. Induced i nfected plants, radiolabelled with (CO2)-C-14, showed an unimpaired tr anslocation of assimilates from the flag leaf into the ear in comparis on to noninfected barley. In order to compare the sink-strength of the fungus quantitatively, leaves from treated and untreated plants with similar infection densities were examined for soluble carbohydrates. R esults of gaschromatographical analysis indicated an increased accumul ation of sucrose in leaf tissue and phloem sap of induced resistant ba rley. Obviously mildew colonies on induced resistant plants were not a ble to accumulate the same amounts of sucrose in their direct environm ents as those on untreated plants. The reduced damaging effect of the fungus on inducer-treated plants is discussed in the context of altere d sink-source relationships between powdery mildew and barley.