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Estimation of Conidia Production by Individual Pustules of Erysiphe graminis f. sp. tritici. Gregory Shaner, Assistant Professor, Department of Botany and Plant Pathology, Purdue University, West Lafayette, Indiana 47907; Phytopathology 63:847-850. Accepted for publication 10 January 1973. DOI: 10.1094/Phyto-63-847.

Considerable variation was found in pustule area and density of conidial chains of Erysiphe graminis f. sp. tritici on individual leaves of mature wheat. Descriptive scales were devised to estimate these two characters independently. Pustule area was estimated on an A to C scale (class C having the largest pustules). Conidial chain density was estimated on a 0-3 scale (class 3 having the greatest number of conidial chains per unit area). Inoculum potentials associated with the various scale values were determined by measuring pustule area and harvesting spores from representative pustules of each area class and conidial chain density class. Class 3 pustules produced 4.5 and 13 times as many conidia as class 2 and class 1 pusutles, respectively. Class 0 pustules produced no conidia. Class C pustules produced 3.4 and 9.8 times as many conidia as class B and class A pustules, respectively. Class 3 pustules were generally larger than class 2 pustules which in turn were generally larger than class 1 pustules. Since pustule area and conidial chain density are related, only one of these need be estimated as a measure of inoculum potential. This potential may be used as one criterion for selecting or evaluating wheat for “slow mildewing” resistance.

Additional keywords: epidemiology, powdery mildew.