EFFECT OF POWDERY MILDEW (ERYSIPHE-GRAMINIS F-SP HORDEI) ON PHOTOSYNTHESIS AND GRAIN-YIELD OF PARTIALLY RESISTANT GENOTYPES OF SPRING BARLEY (HORDEUM-VULGARE L)

The effect of powdery mildew on the photosynthesis and grain yield of partially resistant spring barley was investigated. The effect of powdery mildew on the CO2 exchange rate (CER) of inoculated and non-inoculated leaves was measured in several glasshouse experiments. Grain yield reduction by powdery mildew was determined in three field experiments. The CER of the inoculated leaves was reduced by infection but that of the non-inoculated leaves was not significantly different from that of the corresponding leaves of the control plants. The reduction in CER of the different genotypes was closely related to the percentage leaf area infected with powdery mildew. The correlation between degree of mildew infection and grain yield reduction varied between r = 0.84 (significant at P = 0.01) and r = 0.41 (not significant). Differences in greenness of the crop were correlated better with grain yield reduction (r = 0.66. P = 0.01) than powdery-mildew infection itself. Low percentages of powdery-mildew infection did not lead to significant reduction in grain yield. Partial resistance to powdery mildew could thus be a valuable attribute of future barley varieties.