Analysis of the Effects of Erysiphe graminis DC. on the Growth of Barley

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Abstract
Three barley varieties, Plumage Archer, Proctor, and Haisa II, inoculated soon after emergence with Erysiphe graminis, the cause of powdery mildew, grew and yielded less than barley repeatedly sprayed with lime sulphur. Size of roots was affected more than tops, so the dry-weight ratio of root/total plant was decreased. The smaller tops reflected fewer shoots which, later, were also smaller than on sprayed plants. Decreases in leaf area paralleled decreases in dry weight of tops. Powdery mildew affected the balance between the absorbing system and the assimilating and transpiring system by decreasing the average dry weight of roots per unit leaf area from 0.92 to 0.63 mg./cm2. Disease also decreased the efficiency of unit leaf area; from 12 to 68 days after inoculation, the mean net assimilation rate was 226.6 in sprayed controls and 166.0±8.6 m.g./dm.2/week in the inoculated series. Powdery mildew retarded stem elongation and possibly caused stunting. Fewer and smaller ears were produced by inoculated than by sprayed plants.